liu.seSearch for publications in DiVA
Change search
Refine search result
45678910 301 - 350 of 2080
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • oxford
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 301.
    Colibaba, G. V
    et al.
    Moldova State Univ, Moldova.
    Avdonin, A.
    Polish Acad Sci, Poland.
    Shtepliuk, Ivan
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. Frantsevich Inst Problems Mat Sci NASU, Ukraine.
    Caraman, M.
    Moldova State Univ, Moldova.
    Domagala, J.
    Polish Acad Sci, Poland.
    Inculet, I.
    Moldova State Univ, Moldova.
    Effects of impurity band in heavily doped ZnO:HCl2019In: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 553, p. 174-181Article in journal (Refereed)
    Abstract [en]

    A comparative study of properties of ZnO:HCl single crystals obtained by various methods is presented. Characterization by photoluminescence, optical and electrical measurements in the wide temperature range has allowed to analyze the energy spectra of Cl-containing stable defects in ZnO. Presence of shallow Cl donors, deeper donor complexes, incorporating several Cl atoms or stable H-Cl pairs and presence of compensating deep acceptors, attributed to VznClo centers, are demonstrated. The presence of shallow donor impurity band, as well as strong dependence of its activation energy on the doping level is shown. The controversy of various models for estimation of this dependence is discussed. It is demonstrated, that 90% of this dependence is caused by feature of temperature dependence of Hall coefficient related to conductive impurity band, and a more correct equation for activation energy is suggested. An abnormally low efficiency of neutral impurity scattering of charge carriers and strong optical absorption in the near-IR spectral range are demonstrated and attributed to upper conductive impurity band of negatively charged donors with an extra electron.

    The full text will be freely available from 2020-10-25 12:55
  • 302.
    Cubarovs, Mihails
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Pedersen, Henrik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Högberg, Hans
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Darakchieva, Vanya
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Jens, Jensen
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Persson, Per
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Henry, Anne
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Epitaxial CVD growthof sp2-hybridized boron nitrideusing aluminum nitride as buffer layer2011In: Physica Status Solidi. Rapid Research Letters, ISSN 1862-6254, E-ISSN 1862-6270, Vol. 5, no 10-11, p. 397-399Article in journal (Refereed)
    Abstract [en]

    Epitaxial growth of sp2-hybridized boron nitride (BN) using chemical vapour deposition, with ammonia and triethyl boron as precursors, is enabled on sapphire by introducing an aluminium nitride (AlN) buffer layer. This buffer layer is formed by initial nitridation of the substrate. Epitaxial growth is verified by X-ray diffraction measurements in Bragg–Brentano configuration, pole figure measurements and transmission electron microscopy. The in-plane stretching vibration of sp2-hybridized BN is observed at 1366 cm–1 from Raman spectroscopy. Time-of-flight elastic recoil detection analysis confirms almost perfect stoichiometric BN with low concentration of carbon, oxygen and hydrogen contaminations.

  • 303.
    Dagnelund, Daniel
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Buyanova, Irina
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Chen, Weimin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Murayama, A.
    Furuta, T.
    Hyomi, K.
    Souma, I.
    Oka, Y.
    Exciton spin injection from a ZnCdMnSe diluted magnetic quantum well to self-assembled CdSe quantum dots2007In: Fourth International School and Conference on Spintronics and Quantum Information Technology Spintech IV,2007, 2007, p. 156-Conference paper (Other academic)
  • 304.
    Dagnelund, Daniel
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Buyanova, Irina
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Mchedlidze, T.
    Chen, Weimin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Utsumi, A.
    Furukawa, Y.
    Moon, S.
    Wakahara, A.
    Yonezu, H.
    Effect of nitrogen ion bombardment on defect formation and luminescence efficiency of GaNP epilayers grown by molecular-beam epitaxy2006In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 88, no 10, p. 101904-Article in journal (Refereed)
    Abstract [en]

    Radiative efficiency of GaNP epilayers grown on GaP substrates by solid-source molecular beam epitaxy is significantly improved by reduced nitrogen ion bombardment during the growth. Based on the results of temperature-dependent photoluminescence (PL) and optically detected magnetic resonance studies (ODMR), the observed improvements are attributed to reduced formation of defects, such as a Ga interstitial related defect and an unidentified defect revealed by ODMR. We demonstrate that these defects act as competing recombination centers, which promote thermal quenching of the PL intensity and result in a substantial (34×) decrease in room-temperature PL intensity. © 2006 American Institute of Physics.

  • 305.
    Dagnelund, Daniel
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Vorona, Igor
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Wang, X
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Buyanova, Irina
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Chen, Weimin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Geelhaar, L.
    Infineon Technologies, Corporate Research, Munich, Germany .
    Riechert, H.
    Infineon Technologies, Corporate Research, Munich, Germany .
    Optically detected cyclotron resonance studies of InGaNAs/GaAs structures2007In: Physics of semiconductors : 28th International Conference on the Physics of Semiconductors, ICPS 2006, Vienna, Austria, 24-28 July 2006, American Institute of Physics (AIP), 2007, p. 383-384Conference paper (Other academic)
    Abstract [en]

    We report on our recent results from a systematic study of layered structures containing an InGaNAs/GaAs quantum well (QW), by the optically detected cyclotron resonance (ODCR) technique. By monitoring photoluminescence (PL) emissions from various layers the predominant ODCR peak is shown to be related to carriers with a 2D character and an effective mass of 0.51 me. The responsible carriers are ascribed to be electrons in GaAs/AlAs superlattices (SL) that are employed in the laser structures to prevent carrier leak by sandwiching the InGaNAs/GaAs QW. This conclusion is based on the following observations: (a) the ODCR peak is only observed in the structures containing the SL; (b) the effective mass value determined by the ODCR peak is independent of In and N compositions; (c) the same ODCR peak is also observed by monitoring PL from the SL. Unfortunately no ODCR signal related to InGaNAs was observed

  • 306.
    Danielsson, E.
    et al.
    KTH, Dept. Microelectron./Info. Technol., P.O. Box Electrum 229, S-164 40 Kista, Sweden.
    Zetterling, C.-M.
    KTH, Dept. Microelectron./Info. Technol., P.O. Box Electrum 229, S-164 40 Kista, Sweden.
    Domeij, M.
    KTH, Dept. Microelectron./Info. Technol., P.O. Box Electrum 229, S-164 40 Kista, Sweden.
    Ostling, M.
    Östling, M., KTH, Dept. Microelectron./Info. Technol., P.O. Box Electrum 229, S-164 40 Kista, Sweden.
    Forsberg, Urban
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Janzén, Erik
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Investigation of thermal properties in fabricated 4H-SiC high power bipolar transistors2003In: Solid-State Electronics, ISSN 0038-1101, E-ISSN 1879-2405, Vol. 47, no 4, p. 639-644Article in journal (Refereed)
    Abstract [en]

    Silicon carbide bipolar junction transistors have been fabricated and investigated. The transistors had a maximum current gain of approximately 10 times, and a breakdown voltage of 450 V. When operated at high power densities the device showed a clear self-heating effect, decreasing the current gain. The junction temperature was extracted during self-heating to approximately 150 °C, using the assumption that the current gain only depends on temperature. Thermal images of a device under operation were also recorded using an infrared camera, showing a significant temperature increase in the vicinity of the device. The device was also tested in a switched setup, showing fast turn on and turn off at 1 MHz and 300 V supply voltage. Device simulations have been used to analyze the measured data. The thermal conductivity is fitted against the self-heating, and the lifetime in the base is fitted against the measurement of the current gain. © 2003 Elsevier Science Ltd. All rights reserved.

  • 307.
    Danielsson, E.
    et al.
    KTH.
    Zetterling, C.M.
    KTH.
    Domeij, M.
    KTH.
    Östling, M.
    Forsberg, Urban
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Switching Peformance for Fabricated and Simulated 4H-SiC High Power Bipolar Transistors2003In: Solid State Electronics, Vol. 47, 2003, p. 639-Conference paper (Refereed)
  • 308. Danielsson, E
    et al.
    Zetterling, CM
    KTH, Dept Microelect & Informat Technol, SE-16440 Kista, Sweden Linkoping Univ, Dept Phys & Measurement Technol, SE-58183 Linkoping, Sweden.
    Ostling, M
    KTH, Dept Microelect & Informat Technol, SE-16440 Kista, Sweden Linkoping Univ, Dept Phys & Measurement Technol, SE-58183 Linkoping, Sweden.
    Forsberg, Urban
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Janzén, Erik
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Investigation of thermal properties in fabricated 4H-SiC high-power bipolar transistors2002In: Materials Science Forum, Vols. 389-393, 2002, Vol. 389-3, p. 1337-1340Conference paper (Refereed)
    Abstract [en]

    Silicon Carbide bipolar junction transistors have been fabricated and investigated. The transistors had a maximum current gain of approximately 10 times, and a breakdown voltage of up to 600 V. When operated at high power densities the device showed a clear self-heating effect, decreasing the current gain. The junction temperature was extracted during self-heating to approximately 150 degreesC, using the assumption that the current gain only depends on temperature. Thermal images of a device under operation were also recorded using an infrared camera, showing a significant temperature increase in the vicinity of the device. Physical device simulations have been used to analyze the measured data. The thermal conductivity is fitted to model the measured self-heating, and the lifetime in the base is fitted against the measurement of the current gain.

  • 309. Danielsson, O
    et al.
    Jonsson, S
    Henry, Anne
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Janzén, Erik
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Predicting growth rates of SiC epitaxial layers grown by hot-wall chemical vapor deposition2002In: Materials Science Forum, Vols. 389-393, 2002, Vol. 389-3, p. 219-222Conference paper (Refereed)
    Abstract [en]

    The growth of device quality epitaxial layers requires precise control of the thickness and doping uniformity. By using simulations a better understanding of the growth process can be achieved and process optimization may be possible. The present work uses an extensive chemistry model, to accurately predict growth rates of epitaxial layers grown by chemical vapor deposition. Simulations are made in three dimensions to accurately model the horizontal reactor used in the experiments. Experimental results show four main growth zones, which are characterized by different morphological defects. Certain defects can be attributed to either silicon rich or carbon rich deposition, which is confirmed by X-ray photospectroscopy measurements. Different cases are studied, changing the total pressure in the growth chamber.

  • 310.
    Danielsson, Olof
    et al.
    Linköping University, Faculty of Health Sciences. Linköping University, Department of Neuroscience and Locomotion.
    Forsberg, Urban
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Janzén, Erik
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Predictions of nitrogen doping in SiC epitaxial layers2003In: Materials Science Forum, Vols. 433-436, 2003, Vol. 433-4, p. 137-140Conference paper (Refereed)
    Abstract [en]

    Growth of device quality epitaxial layers requires precise control of thickness and doping uniformities. Computer simulations can provide growers with the necessary knowledge for improving and optimizing the growth process. In this work, the CVD process is simulated in three dimensions, using a reaction-mass transport model. A simplified quantitative model for the nitrogen incorporation in intentionally doped 4H-SiC samples has been developed and applied to a wide range of process parameters. Different reaction schemes are necessary for the two faces of SiC to account for the different doping incorporation behavior. The simulations are validated by experimental data measured by SIMS with good agreement.

  • 311. Danielsson, Ö
    et al.
    Forsberg, Urban
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Henry, Anne
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Janzén, Erik
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Enlarging the usable growth area in a hot-wall silicon carbide CVD reader by using simulation2001In: Materials Science Forum, Vols. 353-356, 2001, Vol. 353-3, p. 99-102Conference paper (Refereed)
    Abstract [en]

    The chemical vapor deposition (CVD) growth of large area silicon car-bide epitaxial layers with homogeneous properties requires a large area with homogeneous temperature in the CVD reactor. In the present work we show that by changing the design of the CVD reactor, but keeping the overall dimension the same, this area can be enlarged by at least a factor of three.. By using a simulation tool new designs can be tried out and optimized in the computer before testing them in practice. The simulation is set up as a 2D axisymmetric problem and validation is made in a 2D horizontal hot-wall CVD reactor. Very good agreements between simulated and measured results are obtained. The zone with a temperature variation of less than 5 degrees at an operating temperature of 1650 degreesC increased to 64% of the whale susceptor length. In addition, the power input needed to reach the operating temperature decreased by 15%.

  • 312.
    Danielsson, Örjan
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Simulations of Silicon Carbide Chemical Vapor Deposition2002Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Most of the modern electronics technology is based on the semiconducting material silicon. The increasing demands for smaller electronic devices with improved performance at lower costs drive the conventional silicon technology to its limits. To meet the requirements from the industry and to explore new application areas, other materials and fabrication methods must be used. For devices operating at high powers, high temperatures and high frequencies, the so-called wide bandgap semiconductors can be used with great success. Silicon carbide (SiC) and III-nitrides are wide bandgap materials that have gained increased interest in recent years. One important technique in manufacturing of electronic devices is chemical vapor deposition (CVD), by which thin layers can be deposited. These layers may have different electrical properties, depending on the choice of material and doping. Generally in CVD, a reactive gas mixture flows through a heated reactor chamber, where the substrates are placed. Complex chemical reactions take place in the gas and on the substrate surface, leading to many intermediate species and by-products, and eventually to the desired deposition. For the growth of device quality material it is important to be able to control the properties of the grown layers. These properties generally depend on the growth conditions in the reaction chamber, and on the chemistry of the deposition process. So far, empirical trial-and-error methods have been employed in the development of growth processes. Due to the lack of basic understanding of the governing physical processes, progress is costly and time consuming. Improving and optimizing the CVD process, as well as improving the fundamental understanding of the whole process is of great importance when good quality material should be produced. For this, computer simulations of the relevant physical and chemical phenomena can provide the necessary tools. This thesis focuses on computer simulations of the CVD process, in particular CVD of SiC. Simulations can be used not only as a tool for optimizing growth processes and reactor designs, they can also give information about physical phenomena that are difficult to measure, such as the gas-phase composition or the flow paths inside the reactor.

    Heating of the CVD susceptor is a central part of the process. For the growth of high quality SiC a relatively high temperature must be used. A convenient method for heating to high temperatures is by induction. A low resistive material, such as graphite, is placed inside a coil, which is given an alternating current. The graphite is then heated by the induced currents due to ohmic resistance. In this thesis the temperature distribution inside a CVD reactor, and how it is influenced by changes in coil frequency, power input to the coil and graphite thickness, is investigated. It is shown that by changing the placement and shape of the coil and by using insulation material correctly, a more uniform temperature distribution can be obtained.

    A model for the growth of SiC is used to predict growth rates at various process parameters. A number of possible factors influencing the growth rate are investigated using this model. The importance of including thermal diffusion and the effect of etching by hydrogen is shown, and the effect of parasitic growth investigated. Simulations show a mass transport limited growth, as seen from experiments.

    An improved susceptor design with an up-lifted substrate holder plate is investigated and compared to a conventional hot-wall reactor and to a cold-wall reactor. It is shown that stress induced by thermal gradients through the substrate is significantly reduced in the hot-wall reactor, and that stress due to backside growth can be diminished using the new design. Positive side effects are that slightly higher growth rates can be achieved, and that the growth temperature can be slightly lowered in the new susceptor.

    The doping incorporation behavior is thoroughly investigated experimentally for intentional doping with nitrogen and aluminum. The doping incorporation on both faces of SiC, as well as on two different polytypes is investigated. Equilibrium calculations are preformed, giving possible candidates for species responsible for the doping incorporation. To predict nitrogen doping concentrations, a simplified quantitative model is developed and applied to a large number of process parameters. It is seen that the same species as predicted by equilibrium calculations are produced, but the reactions producing these species are relatively slow, so that the highest concentrations are at the outlet of the reactor. It is thus concluded that N2 must be the major specie responsible for the nitrogen incorporation in SiC.

    For the growth of III-nitrides, ammonia is often used to give the nitrogen needed. It is well known that ammonia forms a solid adduct with the metalorganic gas, which is used as the source for the group III elements. It would thus be beneficial to use some other gas instead of ammonia. Since purity is of great importance, N2 gas would be the preferred choice. However, N2 is a very stable molecule and difficult to crack, even at high temperatures. It is shown that hydrogen can help in cracking nitrogen, and that growth of III-nitrides can be performed using N2 as the nitrogen-bearing gas, by only small changes to a conventional hot-wall CVD reactor.

    List of papers
    1. Investigation of the temperature profile in a hot-wall SiC chemical vapour deposition reactor
    Open this publication in new window or tab >>Investigation of the temperature profile in a hot-wall SiC chemical vapour deposition reactor
    2002 (English)In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 235, no 1-4, p. 352-364Article in journal (Refereed) Published
    Abstract [en]

    The chemical vapor deposition (CVD) technique is widely used to grow epitaxial layers of silicon carbide. To meet the demands for high quality epitaxial layers, which have good morphology and a minimum variation of the doping and thickness, a good knowledge of the CVD process is essential. The present work uses a simulation tool to investigate several parameters influencing the heating of <!--[if !vml]--><!--[endif]-->a hot-wall CVD reactor. The simulations are set up as 2D axisymmetric problems and validation is made in a 2D horizontal hot-wall CVD reactor. By applying the knowledge achieved from the simulations, the temperature profile is optimized to give as large area as possible with homogeneous temperature. New susceptor and coil designs are tested. A very good agreement between the simulated and the measured results is obtained. The new design has a temperature variation of less than 0.5% over more than 70% of the total susceptor length at an operating temperature of 1650°C. In addition, the power input needed to reach the operating temperature is decreased by 15% compared to the original design. 3D simulations are performed to show that the changes made in the 2D case give similar results for the real 3D case.

    Place, publisher, year, edition, pages
    ScienceDirect, 2002
    Keywords
    A1. Computer simulation, A1. Heat transfer, A3. Chemical, vapor deposition, A3. Hot-wall epitaxy, B2. Semiconducting silicon carbide
    National Category
    Other Engineering and Technologies not elsewhere specified
    Identifiers
    urn:nbn:se:liu:diva-15064 (URN)10.1016/S0022-0248(01)01831-0 (DOI)
    Available from: 2008-10-13 Created: 2008-10-13 Last updated: 2017-12-11Bibliographically approved
    2.
    The record could not be found. The reason may be that the record is no longer available or you may have typed in a wrong id in the address field.
    3. Predicted nitrogen doping concentrations in silicon carbide epitaxial layers grown by hot-wall chemical vapor deposition
    Open this publication in new window or tab >>Predicted nitrogen doping concentrations in silicon carbide epitaxial layers grown by hot-wall chemical vapor deposition
    2003 (English)In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 250, no 3-4, p. 471-478Article in journal (Refereed) Published
    Abstract [en]

    A simple quantitative model for the surface adsorption of nitrogen has been developed to simulate the doping incorporation in intentionally doped 4H-SiC samples during epitaxial growth. Different reaction schemes are necessary for the two faces of SiC. The differences are discussed, and implications to the necessary model adjustments are stressed. The simulations are validated by experimental values for a large number of different process parameters with good agreement.

    Keywords
    A1. Doping, A1. Growth models, A3. Chemical vapor deposition, A3. Hot wall epitaxy, B2. Semiconducting silicon carbide
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-46680 (URN)10.1016/S0022-0248(02)02513-7 (DOI)
    Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-12-13
    4. Reducing stress in silicon carbide epitaxial layers
    Open this publication in new window or tab >>Reducing stress in silicon carbide epitaxial layers
    2003 (English)In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 252, no 1-3, p. 289-296Article in journal (Refereed) Published
    Abstract [en]

    A susceptor for the epitaxial growth of silicon carbide, with an up-lifted substrate holder, is investigated and compared to other susceptor designs both experimentally and by the use of computational fluid dynamics simulations. It is shown that the wafer bending due to temperature gradients is diminished in a hot-wall reactor compared to growth in a cold-wall reactor. The substrate backside growth is diminished using the up-lifted substrate holder, limiting the substrate bending due to the backside growth. Thereby the stress built into the epitaxial layers during growth is significantly reduced. Simulations indicate a lower effective C/Si ratio over the wafer, and a lower preferable growth temperature, as compared to the original susceptor design. In addition a slightly higher growth rate is achieved

    Place, publisher, year, edition, pages
    Elsevier, 2003
    Keywords
    A1. Computer simulation; A3. Chemical vapor deposition; A3. Hot wall epitaxy; B2. Semiconducting silicon carbide
    National Category
    Condensed Matter Physics Other Physics Topics
    Identifiers
    urn:nbn:se:liu:diva-104590 (URN)10.1016/S0022-0248(03)00938-2 (DOI)
    Available from: 2014-02-19 Created: 2014-02-19 Last updated: 2017-12-06Bibliographically approved
    5. Using N2 as precursor gas in III-nitride CVD growth
    Open this publication in new window or tab >>Using N2 as precursor gas in III-nitride CVD growth
    2003 (English)In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 253, no 1-4, p. 26-37Article in journal (Refereed) Published
    Abstract [en]

    Computational fluid dynamics simulations have been performed to explore the possibility of using nitrogen gas as a precursor to III-nitride growth. A chemical model for the gas-phase decomposition of N2 has been used to show that large enough amounts of reactive species can be formed under conditions not far from those used in normal metalorganic chemical vapor deposition. Simulations were performed in 2D for various concentrations of N2, and comparisons with the use of NH3 were made. A modified reactor design needed to achieve high enough concentrations of reactive species is suggested. The possibility to increase the growth rate and material quality in III-nitride growth is discussed.

    Place, publisher, year, edition, pages
    Elsevier, 2003
    Keywords
    A1. Computer simulation; A1. Growth models; A3. Hot wall epitaxy; A3. Metalorganic chemical vapor deposition; B2. Semiconducting III–V materials
    National Category
    Materials Chemistry
    Identifiers
    urn:nbn:se:liu:diva-104589 (URN)10.1016/S0022-0248(03)00971-0 (DOI)
    Available from: 2014-02-19 Created: 2014-02-19 Last updated: 2017-12-06Bibliographically approved
    6. Nitrogen doping of epitaxial Silicon Carbide
    Open this publication in new window or tab >>Nitrogen doping of epitaxial Silicon Carbide
    Show others...
    2002 (English)In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 236, no 1-3, p. 101-112Article in journal (Refereed) Published
    Abstract [en]

    Intentional doping with nitrogen of 4H- and 6H-SiC has been performed using a hot-wall CVD reactor. The nitrogen doping dependence on the temperature, pressure, C/Si ratio, growth rate and nitrogen flow has been investigated. The nitrogen incorporation for C-face material showed to be C/Si ratio independent, whereas the doping decreased with increasing C/Si ratio for the Si-face material in accordance with the “site-competition” model. The nitrogen incorporation was constant in a temperature “window” of 75°C on Si-face material indicating a mass transport limited incorporation. Increasing the growth rate resulted in a decrease of nitrogen incorporation on Si-face but an increase on C-face material. Finally, a comparison between previously published results on cold-wall CVD-grown material and the present hot-wall-grown material is presented.

    Place, publisher, year, edition, pages
    ScienceDirect, 2002
    Keywords
    A1. Doping, A3. Hot wall epitaxy, B2. Superconducting materials
    National Category
    Other Engineering and Technologies not elsewhere specified
    Identifiers
    urn:nbn:se:liu:diva-15068 (URN)10.1016/S0022-0248(01)02198-4 (DOI)
    Note
    The status of this article on the day of the defence was: Submitted and the title of the article was "Nitrogen doping of Silicon Carbide: Effect of Process Parameters"Available from: 2008-10-13 Created: 2008-10-13 Last updated: 2017-12-11Bibliographically approved
    7. Aluminum doping of epitaxial Silicon Carbide
    Open this publication in new window or tab >>Aluminum doping of epitaxial Silicon Carbide
    Show others...
    2003 (English)In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 253, no 1-4, p. 340-350Article in journal (Refereed) Published
    Abstract [en]

    Intentional doping of aluminum in 4H and 6H SiC has been performed using a hot-wall CVD reactor. The dependence of aluminum incorporation on temperature, pressure, C/Si ratio, growth rate, and TMA flow has been investigated. The aluminum incorporation showed to be polarity dependent. The high aluminum incorporation on the Si-face is closely related to the carbon coverage on the SiC surface. Changes in process parameters changes the effective C/Si ratio close to the SiC surface. Increased growth rate and C/Si ratio increases the aluminum incorporation on the Si-face. Diffusion limited incorporation occurs at high growth rate. Reduced pressure increases the effective C/Si ratio, and at low growth rate, the aluminum incorporation increases initially, levels off at a critical pressure, and continues to decrease below the critical pressure. The aluminum incorporation showed to be constant in a temperature range of 50°C. The highest atomic concentration of aluminum observed in this study was 3×1017 and 8×1018 cm−3 in Si and C-face, respectively.

    Place, publisher, year, edition, pages
    ScienceDirect, 2003
    Keywords
    A1. Doping; A1. Growth models; A3. Chemical vapor deposition processes; A3. Hot wall epitaxy; B2. Semiconducting silicon carbide
    National Category
    Other Engineering and Technologies not elsewhere specified
    Identifiers
    urn:nbn:se:liu:diva-15055 (URN)10.1016/S0022-0248(03)01045-5 (DOI)
    Note
    The status of the article on the defence day was: Submitted and the original title was "Aluminum doping of Silicon Carbide: Effect of Process Parameters".Available from: 2008-10-13 Created: 2008-10-13 Last updated: 2017-12-11Bibliographically approved
  • 313.
    Danielsson, Örjan
    et al.
    Linköping University, Department of Physics, Chemistry and Biology.
    Forsberg, Urban
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    Henry , Anne
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    Investigation of the temperature profile in a hot-wall SiC chemical vapour deposition reactor2002In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 235, no 1-4, p. 352-364Article in journal (Refereed)
    Abstract [en]

    The chemical vapor deposition (CVD) technique is widely used to grow epitaxial layers of silicon carbide. To meet the demands for high quality epitaxial layers, which have good morphology and a minimum variation of the doping and thickness, a good knowledge of the CVD process is essential. The present work uses a simulation tool to investigate several parameters influencing the heating of <!--[if !vml]--><!--[endif]-->a hot-wall CVD reactor. The simulations are set up as 2D axisymmetric problems and validation is made in a 2D horizontal hot-wall CVD reactor. By applying the knowledge achieved from the simulations, the temperature profile is optimized to give as large area as possible with homogeneous temperature. New susceptor and coil designs are tested. A very good agreement between the simulated and the measured results is obtained. The new design has a temperature variation of less than 0.5% over more than 70% of the total susceptor length at an operating temperature of 1650°C. In addition, the power input needed to reach the operating temperature is decreased by 15% compared to the original design. 3D simulations are performed to show that the changes made in the 2D case give similar results for the real 3D case.

  • 314.
    Danielsson, Örjan
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Forsberg, Urban
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials . Linköping University, The Institute of Technology.
    Janzén, Erik
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Predicted nitrogen doping concentrations in silicon carbide epitaxial layers grown by hot-wall chemical vapor deposition2003In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 250, no 3-4, p. 471-478Article in journal (Refereed)
    Abstract [en]

    A simple quantitative model for the surface adsorption of nitrogen has been developed to simulate the doping incorporation in intentionally doped 4H-SiC samples during epitaxial growth. Different reaction schemes are necessary for the two faces of SiC. The differences are discussed, and implications to the necessary model adjustments are stressed. The simulations are validated by experimental values for a large number of different process parameters with good agreement.

  • 315.
    Danielsson, Örjan
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Hallin, Christer
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Reducing stress in silicon carbide epitaxial layers2003In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 252, no 1-3, p. 289-296Article in journal (Refereed)
    Abstract [en]

    A susceptor for the epitaxial growth of silicon carbide, with an up-lifted substrate holder, is investigated and compared to other susceptor designs both experimentally and by the use of computational fluid dynamics simulations. It is shown that the wafer bending due to temperature gradients is diminished in a hot-wall reactor compared to growth in a cold-wall reactor. The substrate backside growth is diminished using the up-lifted substrate holder, limiting the substrate bending due to the backside growth. Thereby the stress built into the epitaxial layers during growth is significantly reduced. Simulations indicate a lower effective C/Si ratio over the wafer, and a lower preferable growth temperature, as compared to the original susceptor design. In addition a slightly higher growth rate is achieved

  • 316.
    Danielsson, Örjan
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Using N2 as precursor gas in III-nitride CVD growth2003In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 253, no 1-4, p. 26-37Article in journal (Refereed)
    Abstract [en]

    Computational fluid dynamics simulations have been performed to explore the possibility of using nitrogen gas as a precursor to III-nitride growth. A chemical model for the gas-phase decomposition of N2 has been used to show that large enough amounts of reactive species can be formed under conditions not far from those used in normal metalorganic chemical vapor deposition. Simulations were performed in 2D for various concentrations of N2, and comparisons with the use of NH3 were made. A modified reactor design needed to achieve high enough concentrations of reactive species is suggested. The possibility to increase the growth rate and material quality in III-nitride growth is discussed.

  • 317.
    Danielsson, Örjan
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Kordina, Olle
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Simulations of SiC CVD - Perspectives on the need for surface reaction model improvements2014In: SILICON CARBIDE AND RELATED MATERIALS 2013, PTS 1 AND 2, Trans Tech Publications , 2014, Vol. 778-780, p. 218-221Conference paper (Refereed)
    Abstract [en]

    Simulations of SiC chemical vapor deposition is an excellent tool for understanding, improving and optimizing this complex process. However, models used up to date have often been validated for one particular set of process parameters, often in the silicon limited growth regime, in one particular growth equipment. With chlorinated precursors optimal growth condition is often found to take place at the border between carbon limited and silicon limited regimes. At those conditions the previous models fail to predict deposition rates properly. In this study we argue that molecules like C2H2, C2H4 and CH4, actually might react with the surface with much higher rates than suggested before. Comparisons are made between the previous model and our new model, as well as experiments. It is shown that higher reactivities of the hydrocarbon molecules will improve simulation results as compared to experimental findings, and help to better explain some of the trends for varying C/Si ratios.

  • 318.
    Danielsson, Örjan
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Li, Xun
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Ojamäe, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Chemistry. Linköping University, Faculty of Science & Engineering.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Pedersen, Henrik
    Linköping University, Department of Physics, Chemistry and Biology, Chemistry. Linköping University, The Institute of Technology.
    Forsberg, Urban
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    A model for carbon incorporation from trimethyl gallium in chemical vapor deposition of gallium nitride2016In: Journal of Materials Chemistry, ISSN 0959-9428, E-ISSN 1364-5501, Vol. 4, no 4, p. 863-871Article in journal (Refereed)
    Abstract [en]

    Gallium nitride (GaN) semiconductor material can become semi-insulating when doping with carbon. Semi-insulating buffer layers are utilized to prevent leakage currents in GaN high power devices. Carbon is inherently present during chemical vapor deposition (CVD) of GaN from the use of trimethyl gallium (TMGa) as precursor. TMGa decomposes in the gas phase, releasing its methyl groups, which could act as carbon source for doping. It is previously known that the carbon doping levels can be controlled by tuning the CVD process parameters, such as temperature, pressure and precursor flow rates. However, the mechanism for carbon incorporation from TMGa is not yet understood. In this paper, a model for predicting carbon incorporation from TMGa in GaN layers grown by CVD is proposed. The model is based on ab initio quantum chemical calculations of molecular adsorption and reaction energies. Using Computational Fluid Dynamics, with a chemical kinetic model for decomposition of the precursors and reactions in the gas phase, to calculate gas phase compositions at realistic process conditions, together with the proposed model, we obtain good correlations with measurements, for both carbon doping concentrations and growth rates, when varying the inlet NH3/TMGa ratio. When varying temperature (800 – 1050°C), the model overpredicts carbon doping concentrations at the lower temperatures, but predicts growth rates well, and the agreement with measured carbon doping concentrations is good above 1000°C.

  • 319.
    Danielsson, Örjan
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Sukkaew, Pitsiri
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Ojamäe, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Physical Chemistry. Linköping University, The Institute of Technology.
    Kordina, Olof
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Shortcomings of CVD modeling of SiC today2013In: Theoretical Chemistry accounts, ISSN 1432-881X, E-ISSN 1432-2234, Vol. 132, no 11, p. 1398-Article in journal (Refereed)
    Abstract [en]

    The active, epitaxial layers of silicon carbide (SiC) devices are grown by chemical vapor deposition (CVD), at temperatures above 1,600 °C, using silane and light hydrocarbons as precursors, diluted in hydrogen. A better understanding of the epitaxial growth process of SiC by CVD is crucial to improve CVD tools and optimize growth conditions. Through computational fluid dynamic (CFD) simulations, the process may be studied in great detail, giving insight to both flow characteristics, temperature gradients and distributions, and gas mixture composition and species concentrations throughout the whole CVD reactor. In this paper, some of the important parts where improvements are very much needed for accurate CFD simulations of the SiC CVD process to be accomplished are pointed out. First, the thermochemical properties of 30 species that are thought to be part of the gas-phase chemistry in the SiC CVD process are calculated by means of quantum-chemical computations based on ab initio theory and density functional theory. It is shown that completely different results are obtained in the CFD simulations, depending on which data are used for some molecules, and that this may lead to erroneous conclusions of the importance of certain species. Second, three different models for the gas-phase chemistry are compared, using three different hydrocarbon precursors. It is shown that the predicted gas-phase composition varies largely, depending on which model is used. Third, the surface reactions leading to the actual deposition are discussed. We suggest that hydrocarbon molecules in fact have a much higher surface reactivity with the SiC surface than previously accepted values.

  • 320.
    Danielsson, Örjan
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Sukkaew, Pitsiri
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Yazdanfar, Milan
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Kordina, Olle
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Simulation of Gas-Phase Chemistry for Selected Carbon Precursors in Epitaxial Growth of SiC2013In: Materials Science Forum, ISSN 0255-5476, E-ISSN 1662-9752, Vol. 740-742, p. 213-216Article in journal (Refereed)
    Abstract [en]

    Numerical simulations are one way to obtain a better and more detailed understanding of the chemical vapor deposition process of silicon carbide. Although several attempts have been made in this area during the past ten years, there is still no general model valid for any range of process parameters and choice of precursors, that can be used to control the growth process, and to optimize growth equipment design. In this paper a first step towards such a model is taken. Here, mainly the hydrocarbon chemistry is studied by a detailed gas-phase reaction model, and comparison is made between C3H8 and CH4 as carbon precursor. The results indicate that experimental differences, which previous models have been unable to predict, may be explained by the new model.

  • 321. Dannefaer, S.
    et al.
    Avalos, V.
    Syväjärvi, Mikael
    Linköping University, Department of Physics, Chemistry and Biology.
    Yakimova, Rositsa
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    The role of nitrogen in the annealing of vacancies in 4H-SiC2005In: Materials Science Forum, Vols. 483-485, 2005, Vol. 483-485, p. 481-484Conference paper (Refereed)
  • 322. Dannefaer, S
    et al.
    Avalos, V
    Syväjärvi, Mikael
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Yakimova, Rositsa
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Vacancies in As-grown and electron-irradiated 4H-SiC epilayers investigated by positron annihilation2003In: Materials Science Forum, Vols. 433-436, 2003, Vol. 433-4, p. 173-176Conference paper (Refereed)
    Abstract [en]

    Epilayers of 4H-SiC were investigated by positron annihilation spectroscopies: four epilayers and their substrates were investigated. The epilayers (47 to 220 mum thick) contained significantly lower grown-in vacancy concentration than did their substrates, and there was no dependency on layer thickness. Upon electron irradiation silicon vacancies were introduced at the same rate in epilayer and in substrate.

  • 323.
    Darakchieva, V.
    et al.
    IFM Linköpings universitet.
    Paskov, Plamen
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Schubert, Mattias
    Fakultät für Physik und Geowissenshaften Universität Leipzig.
    Paskova, Tanja
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Arwin, Hans
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Applied Optics .
    Monemar, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Amano, H.
    Dept of Electrical and Electronic Engineering Meijo University, Japan.
    Akasaki, I.
    Dept. of Electrical and Electronic Engineering Meijo University, Japan.
    Strain evolution and phonons in AlN/GaN superlattices2003Article in journal (Refereed)
    Abstract [en]

    AlN/GaN superlattices (SLs) with different periods grown on GaN buffer layers were studied by infrared spectroscopic ellipsometry (IRSE), Raman scattering (RS) and high-resolution reciprocal space mapping (RSM). The lattice parameters and the degree of strain in the GaN buffer and the SL constituents were determined. Phonon modes originating from the buffer layer and the SL sublayers were identified and their frequency shifts were correlated with the strain state of the films.

  • 324.
    Darakchieva, Vanya
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Infrared generalized ellipsometry on non-polar and superlattice group-III nitride films: Strain and phonon anisotropy2008In: Physica Status Solidi (A) Applications and Materials, ISSN 1862-6300, Vol. 205, no 4, p. 905-913Article in journal (Refereed)
    Abstract [en]

    This contribution reviews the application of generalized infrared spectroscopic ellipsometry (GIRSE) to studies of optical phonons in heteroepitaxial wurtzite GaN films with a-plane orientation and c-plane Al(Ga)N/GaN superlattices. We demonstrate the capability of GIRSE to detect spectrally narrow dichroism, caused by anisotropic strain in non-polar oriented films thereby allowing a precise location of the phonon mode resonances for different polarizations. A distinct correlation between anisotropic strain components, which have been independently asessed by high-resolution X-ray diffraction, and phonon frequencies reveal the phonon deformation potentials. Further, GIRSF is shown to be a valuable tool in identification of superlattice phonon modes and their character. The frequency shifts of the superlattice modes with respect to the strain-free positions are analyzed versus strain and composition in order to assess the mode suitability for estimation of strain, polarization doping, and composition for the individual layers in complex device heterostructures. © 2008 WILEY-VCH Verlag GmbH & Co. KGaA.

  • 325.
    Darakchieva, Vanya
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Unraveling the free electron behavior in InN2008In: International Conference on electronic Materials 2008, IUMRS-ICEM 2008,2008, 2008, p. 34-Conference paper (Refereed)
    Abstract [en]

      

  • 326.
    Darakchieva, Vanya
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Barradas, N P
    Institute Tecnol and Nucl, P-2686953 Sacavem, Portugal CFNUL, P-1649003 Lisbon, Portugal .
    Xie, Mengyao
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Lorenz, K
    Institute Tecnol and Nucl, P-2686953 Sacavem, Portugal CFNUL, P-1649003 Lisbon, Portugal .
    Alves, E
    Institute Tecnol and Nucl, P-2686953 Sacavem, Portugal CFNUL, P-1649003 Lisbon, Portugal .
    Schubert, M
    University Nebraska, Department Elect Engn, Lincoln, NE 68588 USA .
    Persson, Per
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Giuliani, Finn
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Munnik, F
    Forschungszentrum Dresden Rossendorf, D-01314 Dresden, Germany .
    Hsiao, Ching-Lien
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Tu, L W
    Natl Sun Yat Sen University, Department Phys, Kaohsiung 80424, Taiwan Natl Sun Yat Sen University, Centre Nanosci and Nanotechnol, Kaohsiung 80424, Taiwan .
    Schaff, W J
    Cornell University, Department Elect and Comp Engn, Ithaca, NY 14853 USA .
    Role of impurities and dislocations for the unintentional n-type conductivity in InN2009In: PHYSICA B-CONDENSED MATTER, ISSN 0921-4526, Vol. 404, no 22, p. 4476-4481Article in journal (Refereed)
    Abstract [en]

    We present a study on the role of dislocations and impurities for the unintentional n-type conductivity in high-quality InN grown by molecular beam epitaxy. The dislocation densities and H profiles in films with free electron concentrations in the low 10(17) cm(-1) and mid 10(18) cm(-3) range are measured, and analyzed in a comparative manner. It is shown that dislocations alone could not account for the free electron behavior in the InN films. On the other hand, large concentrations of H sufficient to explain, but exceeding substantially, the observed free electron densities are found. Furthermore, enhanced concentrations of H are revealed at the film surfaces, resembling the free electron behavior with surface electron accumulation. The low-conductive film was found to contain C and it is suggested that C passivates the H donors or acts as an acceptor, producing compensated material in this case. Therefore, it is concluded that the unintentional impurities play an important role for the unintentional n-type conductivity in InN. We suggest a scenario of H incorporation in InN that may reconcile the previously reported observations for the different role of impurities and dislocations for the unintentional n-type conductivity in InN.

  • 327.
    Darakchieva, Vanya
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Beckers, Manfred
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics.
    Hultman, Lars
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics.
    Xie, Mengyao
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Monemar, Bo
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Carlin, J.-F
    Grandjean, N.
    Strain and compositional analyzes of Al-rich Al1-xInxN alloys grown by MOVPE: impact on the applicability of Vegard's rule2008In: Physica Status Solidi (C) Current Topics in Solid State Physics, 2008, p. 1859-1862Conference paper (Refereed)
    Abstract [en]

    We have studied composition and strain in Al1–xInxN films with 0.128 x 0.22 grown on GaN-buffered sapphire substrates by metalorganic vapor phase epitaxy. A good agreement between the In contents determined by Rutherford backscattering spectrometry (RBS) and Xray diffraction (XRD) is found for x 18, suggesting applicability of Vegard's rule in the narrow compositional range around the lattice matching to GaN. The increase of the In content up to x = 0.22 leads to a formation of sub-layers with a higher composition, accompanied by deviations from Vegard's rule. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

  • 328.
    Darakchieva, Vanya
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Beckers, Manfred
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics.
    Xie, Mengyao
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Hultman, Lars
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics.
    Monemar, Bo
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Carlin, J-. F.
    Feltin, E.
    Gonschorek, M.
    Grandjean, N.
    Effects of strain and composition on the lattice parameters and applicability of Vegard's rule in Al-rich Al1-x Inx N films grown on sapphire2008In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 103, no 10, p. 103513-Article in journal (Refereed)
    Abstract [en]

    The lattice parameters and strain evolution in Al1-x In x N films with 0.07≤x≤0.22 grown on GaN-buffered sapphire substrates by metal organic vapor phase epitaxy have been studied by reciprocal space mapping. Decoupling of compositional effects on the strain determination was accomplished by measuring the In contents in the films both by Rutherford backscattering spectrometry (RBS) and x-ray diffraction (XRD). Differences between XRD and RBS In contents are discussed in terms of compositions and biaxial strain in the films. It is suggested that strain plays an important role for the observed deviation from Vegard's rule in the case of pseudomorphic films. On the other hand, a good agreement between the In contents determined by XRD and RBS is found for Al1-x Inx N films with low degree of strain or partially relaxed, suggesting applicability of Vegard's rule in the narrow compositional range around the lattice matching to GaN. © 2008 American Institute of Physics.

  • 329.
    Darakchieva, Vanya
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Birch, Jens
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics.
    Paskov, Plamen
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Tungasmita, Sukkaneste
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Paskova, Tanja
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Monemar, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Strain evolution in high temperature AlN buffer layers for HVPE-GaN growth2002In: Physica status solidi. A, Applied research, ISSN 0031-8965, E-ISSN 1521-396X, Vol. 190, no 1, p. 59-64Article in journal (Refereed)
    Abstract [en]

    High temperature AlN buffer layers are deposited on a-plane sapphire by reactive magnetron sputtering. The effect of the buffer thickness on the AlN structural properties and surface morphology are studied in correlation with the subsequent hydride vapour phase epitaxy of GaN. A minimum degree of mosaicity and screw dislocation density is determined for a 50 nm thick AlN buffer. With increasing the AlN thickness, a strain relaxation occurs as a result of misfit dislocation generation and higher degree of mosaicity. A blue shift of the E-1(TO) frequency evaluated by means of infrared reflection spectroscopy is linearly correlated with an increase in biaxial compressive stress in the films through the IR stress factor k(E1)(b) = 2.57 +/- 0.26 cm(-1) GPa(-1).

  • 330.
    Darakchieva, Vanya
    et al.
    Linköping University, Department of Physics, Chemistry and Biology.
    Birch, Jens
    Linköping University, Department of Physics, Chemistry and Biology.
    Schubert, M
    Paskova, Tanja
    Linköping University, Department of Physics, Chemistry and Biology.
    Tungasmita, S
    Wagner, G
    Kasic, A
    Monemar, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Strain-related structural and vibrational properties of thin epitaxial AIN layers2004In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 70, no 4, p. 045411-Article in journal (Refereed)
    Abstract [en]

    The effect of film thickness on the strain and structural properties of thin epitaxial AIN films has been investigated by high resolution x-ray diffraction techniques and transmission electron microscopy. As a result a sublayer model of the degree of strain and related defects for all films is proposed. A sublayer with low defect density and a strain gradient is found to be present in all films and it reaches a maximum thickness of 65 nm. The films are compressively strained and the strain relaxation after a thickness of 65 nm is shown to be accompanied by misfit dislocation generation and increase of the mosaic tilt. The vibrational properties of the films have been studied by generalized infrared spectroscopic ellipsometry. The proposed sublayer model has been successfully applied to the analysis of the ellipsometry data through model calculations of the infrared dielectric function which confirm the sublayer model. It is found that the strain gradient results in a gradient of the phonon mode frequencies and broadening parameter. The initial strain relaxation in the films leads to narrowing of the observable infrared modes, while further strain relaxation broadens the modes when substantial defect generation occurs.

  • 331.
    Darakchieva, Vanya
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Boosalis, A.
    Department of Engineering, University of Nebraska-Lincoln, Lincoln, Nebraska, USA.
    Zakharov, A. A.
    Lund University, Maxlab, Lund, Sweden.
    Hofmann, T.
    Department of Engineering, University of Nebraska-Lincoln, Lincoln, Nebraska, USA.
    Schubert, M.
    Department of Engineering, University of Nebraska-Lincoln, Lincoln, Nebraska, USA.
    Tiwald, T. E.
    J. A. Woollam Co., Lincoln, Nebraska, USA.
    Iakimov, Tihomir
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Vasiliauskas, Remigijus
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Yakimova, Rositsa
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Large-area microfocal spectroscopic ellipsometry mapping of thickness and electronic properties of epitaxial graphene on Si- and C-face of 3C-SiC(111)2013In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 102, no 21, p. 213116-Article in journal (Refereed)
    Abstract [en]

    Microfocal spectroscopic ellipsometry mapping of the electronic properties and thickness of epitaxial graphene grown by high-temperature sublimation on 3C-SiC (111) substrates is reported. Growth of one monolayer graphene is demonstrated on both Si- and C-polarity of the 3C-SiC substrates and it is shown that large area homogeneous single monolayer graphene can be achieved on the Si-face substrates. Correlations between the number of graphene monolayers on one hand and the main transition associated with an exciton enhanced van Hove singularity at ∼4.5 eV and the free-charge carrier scattering time, on the other are established. It is shown that the interface structure on the Si- and C-polarity of the 3C-SiC(111) differs and has a determining role for the thickness and electronic properties homogeneity of the epitaxial graphene.

  • 332.
    Darakchieva, Vanya
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Hofmann, T.
    Schubert, M.
    Lu, H.
    Schaff, W.J.
    Monemar, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Conduction band effective mass anisotropy and nonparabolicity of InN2006In: 3rd Workshop on Indium Nitride,2006, 2006Conference paper (Refereed)
    Abstract [en]

    Invited talk

  • 333.
    Darakchieva, Vanya
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Hofmann, T.
    Schubert, M.
    Monemar, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Lu, H.
    Schaff, W.J.
    Hsiao, C.-L.
    Liu, T.-W.
    Chen, L.-C.
    Muto, D.
    Nanishi, Y.
    New insight into the free carrier properties of InN2008In: International workshop on Nitride semiconductors IWN2008,2008, 2008Conference paper (Refereed)
    Abstract [en]

      

  • 334.
    Darakchieva, Vanya
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Hofmann, T.
    University of Nebraska-Lincoln, USA.
    Schubert, M.
    University of Nebraska-Lincoln, USA.
    Sernelius, Bo
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Giuliani, Finn
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Xie, Mengyao
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Persson, Per O. A.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Monemar, Bo
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Schaff, W. J.
    Cornell University, Ithaca, NY, USA.
    Hsiao, C.-L.
    National Taiwan University, Taipei, Taiwan.
    Chen, L.-C.
    National Taiwan University, Taipei, Taiwan.
    Nanishi, Y
    Ritsumeikan University, Shiga, Japan.
    Unravelling the free electron behavior in InN2008In: Optoelectronic and Microelectronic Materials and Devices, 2008, IEEE , 2008, p. 90-97Conference paper (Refereed)
    Abstract [en]

    Precise measurement of the optical Hall effect in InN using magneto-optical generalized ellipsometry at IR and THz wavelengths, allows us to decouple the surface accumulation and bulk electron densities in InN films by non-contact optical means and further to precisely measure the effective mass and mobilities for polarizations parallel and perpendicular to the optical axis. Studies of InN films with different thicknesses, free electron densities and surface orientations enable an intricate picture of InN free electron properties to emerge. Striking findings on the scaling factors of the bulk electron densities with film thickness further supported by transmission electron microscopy point to an additional thickness dependent doping mechanism unrelated to dislocations. Surface electron accumulation is observed to occur not only at polar but also at non-polar and semi-polar wurtzite InN, and zinc blende InN surfaces. The persistent surface electron density shows a complex behavior with bulk density and surface orientation. This behavior might be exploited for tuning the surface charge in InN.

  • 335.
    Darakchieva, Vanya
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    Hofmann, T
    University of Nebraska.
    Schubert, M
    University of Nebraska.
    Sernelius, Bo
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics . Linköping University, The Institute of Technology.
    Monemar, Bo
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    Persson, Per
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Giuliani, Finn
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Alves, E
    Sacavem, Portugal.
    Lu, H
    Cornell University.
    Schaff, W J
    Cornell University.
    Free electron behavior in InN: On the role of dislocations and surface electron accumulation2009In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 94, no 2, p. 022109-Article in journal (Refereed)
    Abstract [en]

    The free electron behavior in InN is studied on the basis of decoupled bulk and surface accumulation electron densities in InN films measured by contactless optical Hall effect. It is shown that the variation in the bulk electron density with film thickness does not follow the models of free electrons generated by dislocation-associated nitrogen vacancies. This finding, further supported by transmission electron microscopy results, indicates the existence of a different thickness-dependent doping mechanism. Furthermore, we observe a noticeable dependence of the surface electron density on the bulk density, which can be exploited for tuning the surface charge in future InN based devices.

  • 336.
    Darakchieva, Vanya
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Lorenz, K
    Institute of Tecnology and Nucl, Portugal .
    Barradas, N P
    Institute of Tecnology and Nucl, Portugal .
    Alves, E
    Institute of Tecnology and Nucl, Portugal .
    Monemar, Bo
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Schubert, M
    University of Nebraska.
    Franco, N
    Institute of Tecnology and Nucl, Portugal .
    L Hsiao, C
    National Taiwan University.
    Chen, L C
    National Taiwan University.
    Schaff, W J
    Cornell University.
    Tu, L W
    National Sun Yat Sen University.
    Yamaguchi, T
    Ritsumeikan University.
    Nanishi, Y
    Ritsumeikan University.
    Hydrogen in InN: A ubiquitous phenomenon in molecular beam epitaxy grown material2010In: APPLIED PHYSICS LETTERS, ISSN 0003-6951, Vol. 96, no 8, p. 081907-Article in journal (Refereed)
    Abstract [en]

    We study the unintentional H impurities in relation to the free electron properties of state-of-the-art InN films grown by molecular beam epitaxy (MBE). Enhanced concentrations of H are revealed in the near surface regions of the films, indicating postgrowth surface contamination by H. The near surface hydrogen could not be removed upon thermal annealing and may have significant implications for the surface and bulk free electron properties of InN. The bulk free electron concentrations were found to scale with the bulk H concentrations while no distinct correlation with dislocation density could be inferred, indicating a major role of hydrogen for the unintentional conductivity in MBE InN.

  • 337.
    Darakchieva, Vanya
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Lorenz, K
    CFNUL.
    Xie, Mengyao
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Alves, E
    CFNUL.
    Hsiao, C L
    National Taiwan University.
    Chen, L C
    National Taiwan University.
    Tu, L W
    National Sun Yat Sen University.
    Schaff, W J
    Cornell University.
    Yamaguchi, T
    Ritsumeikan University.
    Nanishi, Y
    Ritsumeikan University.
    Unintentional incorporation of hydrogen in wurtzite InN with different surface orientations2011In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 110, no 6, p. 063535-Article in journal (Refereed)
    Abstract [en]

    We have studied hydrogen impurities and related structural properties in state-of-the-art wurtzite InN films with polar, nonpolar, and semipolar surface orientations. The effects of thermal annealing and chemical treatment on the incorporation and stability of H are also discussed. The near-surface and bulk hydrogen concentrations in the as-grown films increase when changing the surface orientation from (0001) to (000 (1) over bar) to (1 (1) over bar 01) and to (11 (2) over bar0), which may be associated with a decrease in the grain size and change of the growth mode from 2D to 3D. Thermal annealing at 350 degrees C in N(2) leads to a reduction of H concentrations and the intrinsic levels of bulk H are found to correlate with the structural quality and defects in the annealed films.

  • 338.
    Darakchieva, Vanya
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Lorenz, K
    Institute Tecnol and Nucl, Portugal .
    Xie, Mengyao
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Alves, E
    Institute Tecnol and Nucl, Portugal .
    Schaff, W J
    Cornell University.
    Yamaguchi, T
    Ritsumeikan University.
    Nanishi, Y
    Ritsumeikan University.
    Ruffenach, S
    University of Montpellier 2.
    Moret, M
    University of Montpellier 2.
    Briot, O
    University of Montpellier 2.
    Unintentional incorporation of H and related structural and free-electron properties of c- and a-plane InN2012In: PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE, ISSN 1862-6300, Vol. 209, no 1, p. 91-94Article in journal (Refereed)
    Abstract [en]

    In this work, we present a comprehensive study on the hydrogen impurity depth profiles in InN films with polar c-plane and nonpolar a-plane surface orientations in relation to their structural and free-electron properties. We find that the as-grown nonpolar films exhibit generally higher bulk and near-surface H concentrations compared to the polar InN counter-parts. The latter may be partly associated with a change in the growth mode from 2D to 3D and a decrease in the grain size. Thermal annealing leads to a reduction of H concentrations and the intrinsic H levels are influenced by the structural characteristics of the films. The factors allowing reduction of bulk H and free electron concentrations in a-plane films are discussed.

  • 339.
    Darakchieva, Vanya
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Monemar, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Paskova, Tanja
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Einfeldt, S.
    Hommel, D
    Lourdudoss, S.
    Phonons in strained AlGaN/GaN superlattices2007In: 6th International Symposium on Blue Laser and Light Emitting Diodes,2006, Physica Status Solidi, vol C4: WILEYVCH Verlag GmbH & Co. KGaA , 2007, p. 170-Conference paper (Refereed)
  • 340.
    Darakchieva, Vanya
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Monemar, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Usui, A.
    On the lattice parameters of GaN2007In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 91, no 3, p. 031911-Article in journal (Refereed)
    Abstract [en]

    The lattice parameters of low-defect density, undoped bulk GaN fabricated by hydride vapor phase epitaxy (HVPE) on (0001) sapphire and subsequent substrate removal, are precisely determined using high-resolution x-ray diffraction. The obtained values, c=5.18523 Å and a=3.18926 Å, are compared with the lattice parameters of freestanding HVPE GaN from different sources and found to be representative for state-of-the-art undoped HVPE bulk GaN material. A comparison with bulk GaN fabricated by the high-pressure technique and homoepitaxial GaN is made, and significant differences in the lattice parameters are found. The observed differences are discussed and a possible explanation is suggested. © 2007 American Institute of Physics.

  • 341.
    Darakchieva, Vanya
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Monemar, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Usui, A.
    R and D Division, Furukawa Co. Ltd., Tsukuba, Ibaraki, 305-0865, Japan.
    Saenger, M.
    Department of Electrical Engineering, University of Nebraska, Lincoln, NE 68588, United States.
    Schubert, M.
    Department of Electrical Engineering, University of Nebraska, Lincoln, NE 68588, United States.
    Lattice parameters of bulk GaN fabricated by halide vapor phase epitaxy2008In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 310, no 5, p. 959-965Article in journal (Refereed)
    Abstract [en]

    The lattice parameters of low-defect density undoped bulk GaN fabricated by halide vapor phase epitaxy (HVPE) and removal of the substrate are precisely determined using high-resolution X-ray diffraction. The obtained values, c = 5.18523 over(A, °) and a = 3.18926 over(A, °) are compared with the lattice parameters of free-standing HVPE-GaN from different sources and found to be representative for state-of-the-art undoped HVPE bulk GaN material. A comparison with bulk GaN fabricated by the high pressure technique and homoepitaxial GaN layer is made, and the observed differences are discussed in terms of their free-electron concentrations, point and structural defects. © 2007 Elsevier B.V. All rights reserved.

  • 342.
    Darakchieva, Vanya
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Paskov, Plamen
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Paskova, Tanja
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Birch, Jens
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics.
    Tungasmita, Sukkaneste
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Monemar, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Deformation potentials of the E-1(TO) mode in AlN2002In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 80, no 13, p. 2302-2304Article in journal (Refereed)
    Abstract [en]

    The deformation potentials of the E-1(TO) mode in AlN are experimentally determined by combining infrared reflection spectroscopy and x-ray diffraction measurements and using a reported value of the Raman-stress factor for hydrostatically stressed bulk AlN. The deformation potentials are found to strongly depend on published stiffness constants of AlN. A comparison with earlier theoretically calculated values of the deformation potentials is made. (C) 2002 American Institute of Physics.

  • 343.
    Darakchieva, Vanya
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Paskov, Plamen
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Paskova, Tanja
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Valcheva, E.
    Monemar, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Heuken, M.
    Aixtron AG, D-52072 Aachen, Germany.
    Lattice parameters of GaN layers grown on a-plane sapphire: Effect of in-plane strain anisotropy2003In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 82, no 5, p. 703-705Article in journal (Refereed)
    Abstract [en]

    The lattice parameters of GaN layers grown on a-plane sapphire were investigated. The hydride vapor phase epitaxy and metalorganic vapor phase epitaxy were used for the determination of parameters. The strain anisotropy was found to have different values in the films and obtained values of parameters were grouped around two values.

  • 344.
    Darakchieva, Vanya
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Paskov, Plamen
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Valcheva, E.
    Paskova, Tanja
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Schubert, M.
    Fak. F. Physik and Geowissenschaften, Universität Leipzig, 04103 Leipzig, Germany.
    Bundesmann, C.
    Fak. F. Physik and Geowissenschaften, Universität Leipzig, 04103 Leipzig, Germany.
    Lu, H.
    Department of Electrical Engineering, Cornell University, Ithaca, NY 14853, United States.
    Schaff, W.J.
    Department of Electrical Engineering, Cornell University, Ithaca, NY 14853, United States.
    Monemar, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Infrared ellipsometry and Raman studies of hexagonal InN films: Correlation between strain and vibrational properties2004In: Superlattices and Microstructures, ISSN 0749-6036, E-ISSN 1096-3677, Vol. 36, no 4-6, p. 573-580Article in journal (Refereed)
    Abstract [en]

    The vibrational properties of InN films with different strain have been studied using Infrared ellipsometry and Raman scattering spectroscopy. We have established a correlation between the phonon mode parameters and the strain, which allows the determination of the deformation potentials and the strain-free frequencies of the InN E1(TO) and E2 modes. The LO phonons and their coupling to the free-carrier plasmon excitations are also discussed in relation to the carrier concentration in the films. © 2004 Elsevier Ltd. All rights reserved.

  • 345.
    Darakchieva, Vanya
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Paskova, T.
    Institute of Solid State Physics, University of Bremen, 28359 Bremen, Germany.
    Schubert, M.
    Department of Electrical Engineering, University of Nebraska, Lincoln, NE 68588, United States.
    Paskov, Plamen
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Arwin, Hans
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Applied Optics .
    Monemar, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Hommel, D.
    Institute of Solid State Physics, University of Bremen, 28359 Bremen, Germany.
    Heuken, M.
    Aixtron AG, D-52072 Aachen, Germany.
    Off, J.
    Institute of Physics 4, University of Stuttgart, 70569 Stuttgart, Germany.
    Haskell, B.A.
    Materials Department, University of California, Santa Barbara, CA 93106, United States.
    Fini, P.T.
    Materials Department, University of California, Santa Barbara, CA 93106, United States.
    Speck, J.S.
    Materials Department, University of California, Santa Barbara, CA 93106, United States.
    Nakamura, S.
    Materials Department, University of California, Santa Barbara, CA 93106, United States.
    Effect of anisotropic strain on phonons in a-plane and c-plane GaN layers2007In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 300, no 1, p. 233-238Article in journal (Refereed)
    Abstract [en]

    We have studied phonons in two types of anisotropically strained GaN films: c-plane GaN films grown on a-plane sapphire and a-plane GaN films grown on r-plane sapphire. The anisotropic strain in the films is determined by high-resolution X-ray diffraction (HRXRD) in different measuring geometries and the phonon parameters have been assessed by generalized infrared spectroscopic ellipsometry (GIRSE). The effect of strain anisotropy on GaN phonon frequencies is presented and the phonon deformation potentials aA1 (TO), bA1 (TO), cE1 (TO) and cE1 (LO) are determined. © 2006 Elsevier B.V. All rights reserved.

  • 346.
    Darakchieva, Vanya
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Paskova, Tanja
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Paskov, Plamen
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Arwin, Hans
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Applied Optics .
    Schubert, M
    Monemar, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Figge, S
    Hommel, D
    Haskell, BA
    Fini, PT
    Nakamura, S
    Assessment of phonon mode characteristics via infrared spectroscopic ellipsometry on a-plane GaN2006In: Physica status solidi. B, Basic research, ISSN 0370-1972, E-ISSN 1521-3951, Vol. 243, no 7, p. 1594-1598Article in journal (Refereed)
    Abstract [en]

    Generalized infrared spectroscopic ellipsometry was applied to study the vibrational properties of anisotropically strained a-plane GaN films with different thicknesses. We have established a correlation between the phonon mode parameters and the strain, which allows the determination of the deformation potentials and strain-free frequency of the GaN A,(TO) mode. These results are compared with previous theoretical and experimental findings and discussed.

  • 347.
    Darakchieva, Vanya
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Paskova, Tanja
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Paskov, Plamen
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Monemar, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Ashkenov, N.
    Fak. fur Phy. and Geowissenschaften, Universität Leipzig, 04103 Leipzig, Germany.
    Schubert, M.
    Fak. fur Phy. and Geowissenschaften, Universität Leipzig, 04103 Leipzig, Germany.
    Residual strain in HVPE GaN free-standing and re-grown homoepitaxial layers2003In: Physica status solidi. A, Applied research, ISSN 0031-8965, E-ISSN 1521-396X, Vol. 195, no 3, p. 516-522Article in journal (Refereed)
    Abstract [en]

    The lattice parameters of as-grown hydride vapor phase epitaxy GaN layers on sapphire, free-standing layers after the substrate lift-off, and homoepitaxial layers grown on the free-standing layers are measured. The in-plane and out-of-plane strains are calculated. It is found that the substrate removal leads to strain relaxation in the crack-free GaN free-standing layers to a certain extent. A small increase of the strain in the GaN homoepitaxial layers compared to the free-standing layers is observed. Cathodoluminescence (CL) spectroscopy and imaging, photoluminescence (PL) and Raman measurements are used as complementary tools in the residual strain analysis.

  • 348.
    Darakchieva, Vanya
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Paskova, Tanja
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Paskov, Plamen
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Monemar, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Ashkenov, N.
    Schubert, M.
    Structural characteristics and lattice parameters of hydride vapor phase epitaxial GaN free-standing quasisubstrates2005In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 97, no 1, p. 013517-Article in journal (Refereed)
    Abstract [en]

    We have studied the lattice parameters of hydride vapor phase epitaxy (HVPE)-GaN quasisubstrates in relation to their structural properties. Layers grown on single-layer metalorganic vapor phase epitaxy (MOVPE) templates and on epitaxial lateral overgrown MOVPE templates are characterized by Raman scattering, high-resolution x-ray diffraction, and reciprocal space mapping. The strain relaxation in the films versus their thickness was found to proceed similarly in the GaN samples grown using the two types of templates but the strain saturates at different nonzero levels. The lattice parameters of relatively thin HVPE-GaN free-standing quasisubstrates indicate that no total strain relaxation is achieved after the sapphire removal. The lattice parameters of the thick quasisubstrates grown on different templates are not affected by the separation process and are found to have values very close to the reference strain-free lattice parameters of GaN powder. © 2005 American Institute of Physics.

  • 349.
    Darakchieva, Vanya
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Paskova, Tanja
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Schubert, M.
    Optical phonons in a-plane GaN under anisotropic strain2008In: Group-III nitrides with nonpolar surfaces: growth, properties and devices / [ed] Tanya Paskova, Wiley , 2008, 1, p. 219-253Chapter in book (Other academic)
    Abstract [en]

    This is the first monograph to discuss in detail the current stage of development of nonpolar nitrides, with specific emphasis on the three main topics of crystal growth, properties and device studies. World–class researchers summarize their own recent achievements in their respective fields of expertise, covering both nonpolar and semipolar nitride materials. The bulk of the discussion in each chapter is related to the physical properties of the material obtained by the respective technique, in particular, defect density and properties of the defects in nonpolar nitrides. In addiiton, the optical and vibrational properties are also addressed in several chapters, as is progress in heterostructures, quantum wells and dots based on the AlGaN/GaN and the InGaN/GaN systems. Finally, an outlook of the application areas of the differently grown materials is presented in most chapters, together with the capabilities and limitations of the respective growth approaches used.

  • 350.
    Darakchieva, Vanya
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Paskova, Tanja
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Schubert, M.
    Arwin, Hans
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Applied Optics .
    Paskov, Plamen
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Monemar, Bo
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Hommel, D.
    Off, J.
    Scholz, F.
    Heuken, M.
    Haskell, B.A.
    Fini, P.T.
    Speck, S.J.
    Nakamura, S.
    Anisotropic strain and phonon deformation potentials in GaN2007In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 75, no 19, p. 195217-Article in journal (Refereed)
    Abstract [en]

    We report optical phonon frequency studies in anisotropically strained c -plane- and a -plane-oriented GaN films by generalized infrared spectroscopic ellipsometry and Raman scattering spectroscopy. The anisotropic strain in the films is obtained from high-resolution x-ray diffraction measurements. Experimental evidence for splitting of the GaN E1 (TO), E1 (LO), and E2 phonons under anisotropic strain in the basal plane is presented, and their phonon deformation potentials c E1 (TO), c E1 (LO), and c E2 are determined. A distinct correlation between anisotropic strain and the A1 (TO) and E1 (LO) frequencies of a -plane GaN films reveals the a A1 (TO), b A1 (TO), a E1 (LO), and b E1 (LO) phonon deformation potentials. The a A1 (TO) and b A1 (TO) are found to be in very good agreement with previous results from Raman experiments. Our a A1 (TO) and a E1 (LO) phonon deformation potentials agree well with recently reported theoretical estimations, while b A1 (TO) and b E1 (LO) are found to be significantly larger than the theoretical values. A discussion of the observed differences is presented. © 2007 The American Physical Society.

45678910 301 - 350 of 2080
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • oxford
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf