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Hansson, Göran
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Publications (10 of 57) Show all publications
Adnane, B., Karlsson, F., Hansson, G., Holtz, P.-O. & Ni, W.-X. (2010). Spatially direct and indirect transitions of self-assembled SiGe/Si quantum dots studied by photoluminescence excitation spectroscopy. Applied Physics Letters, 96(18), 181107
Open this publication in new window or tab >>Spatially direct and indirect transitions of self-assembled SiGe/Si quantum dots studied by photoluminescence excitation spectroscopy
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2010 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 96, no 18, p. 181107-Article in journal (Refereed) Published
Abstract [en]

Well-resolved photoluminescence excitation (PLE) spectra are reported for selfassembled SiGe dots grown on Si(100) by molecular beam epitaxy. The observation of two excitation resonance peaks is attributed to two different excitation/de-excitation routes of interband optical transitions connected to the spatially direct and indirect recombination processes. It is concluded that two dot populations are addressed by each monitored luminescence energy for the PLE acquisition.

Keywords
Ge-Si alloys, luminescence, molecular beam epitaxial growth, self-assembly, semiconductor quantum dots
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-53204 (URN)10.1063/1.3424789 (DOI)000277422000007 ()
Note
Original Publication: Bouchaib Adnane, Fredrik Karlsson, Göran Hansson, Per-Olof Holtz and Wei-Xin Ni, Spatially direct and indirect transitions of self-assembled SiGe/Si quantum dots studied by photoluminescence excitation spectroscopy, 2010, Applied Physics Letters, (96), 18, 181107. http://dx.doi.org/10.1063/1.3424789 Copyright: American Institute of Physics http://www.aip.org/ Available from: 2010-01-19 Created: 2010-01-19 Last updated: 2017-12-12
Razado, I., He, J., Zhang, H., Hansson, G. & Uhrberg, R. (2009). Electronic structure of Ge(111)c(2x8): STM, angle-resolved photoemission, and theory. PHYSICAL REVIEW B, 79(20), 205410
Open this publication in new window or tab >>Electronic structure of Ge(111)c(2x8): STM, angle-resolved photoemission, and theory
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2009 (English)In: PHYSICAL REVIEW B, ISSN 1098-0121, Vol. 79, no 20, p. 205410-Article in journal (Refereed) Published
Abstract [en]

The surface electronic structure of Ge(111)c(2x8) was studied by experimental techniques [low-energy electron diffraction, scanning tunneling microscopy (STM), and angle-resolved photoelectron spectroscopy (ARPES)] and theoretical band-structure calculations. Bias-dependent STM images exhibit two different types of adatoms (A(T),A(R)) and rest atoms (R-T,R-R) confirming the presence of asymmetries within the c(2x8) cell. The ARPES study resulted in a more detailed picture of the surface electronic structure of the Ge(111)c(2x8) surface compared to earlier studies. The energy dispersion curves showed the presence of seven surface bands labeled A1, A2, A2(), A3, A4, A4(), and A5. The experimental surface bands were compared to the calculated band structure of the full c(2x8) unit cell. The most important results are (i) we have identified a split surface-state band in the photoemission data that matches a split between R-T and R-R derived rest atom bands in the calculated surface band structure. This allows us to identify the upper A2 band with the R-R and the lower A2() band with the R-T rest atoms. (ii) The uppermost highly dispersive band (A1) originates from states below the adatom and rest atom layers and should not be confused with rest atom bands A2 and A2(). (iii) The bias-dependent changes in the adatom/rest atom contrast in the experimental STM images were closely reproduced by simulated STM images generated from the calculated electronic structure. (iv) A split was observed in the back-bond derived surface band at higher emission angles (A4 and A4()).

Keywords
band theory, elemental semiconductors, germanium, low energy electron diffraction, photoelectron spectra, scanning tunnelling microscopy, surface states
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-19417 (URN)10.1103/PhysRevB.79.205410 (DOI)
Note
Original Publication: Ivy Razado, Jiangping He, Hanmin Zhang, Göran Hansson and Roger Uhrberg, Electronic structure of Ge(111)c(2x8): STM, angle-resolved photoemission, and theory, 2009, PHYSICAL REVIEW B, (79), 20, 205410. http://dx.doi.org/10.1103/PhysRevB.79.205410 Copyright: American Physical Society http://www.aps.org/ Available from: 2009-08-17 Created: 2009-06-22 Last updated: 2012-02-06Bibliographically approved
Adnane, B., Karlsson, F., Zhao, M., Hansson, G., Holtz, P.-O. & Ni, W.-X. (2009). Origin of photoresponse at 8-14 μm in stacks of self-assembled SiGe/Si quantum dots. Physical Review B. Condensed Matter and Materials Physics
Open this publication in new window or tab >>Origin of photoresponse at 8-14 μm in stacks of self-assembled SiGe/Si quantum dots
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2009 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235XArticle in journal (Other academic) Submitted
Abstract [en]

A normal incidence photodetector operating at 8-14 μm is demonstrated using p-type δ-doped SiGe dot multilayer structures grown by molecular beam epitaxy on Si(001) substrates. Based on the experimental results of photoluminescence and photoluminescence excitation spectroscopies together with numerical analysis, the origin of the measured photocurrent was attributed to intersubband optical transitions between the heavy hole and light hole states of the valence band of the self-assembled SiGe dots and subsequent lateral transport of photo-excited carriers in the conduction channels formed by Ge wetting layers.

National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-53203 (URN)
Available from: 2010-01-19 Created: 2010-01-19 Last updated: 2017-12-12
Adnane, B., Karlsson, F., Hansson, G., Holtz, P.-O. & Ni, W.-X. (2009). Photoluminescence excitation spectroscopy of self-assembled SiGe/Si quantum dots.
Open this publication in new window or tab >>Photoluminescence excitation spectroscopy of self-assembled SiGe/Si quantum dots
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2009 (English)Manuscript (preprint) (Other academic)
Abstract [en]

Photoluminescence excitation (PLE) experiments are reported for various self-assembled SiGe/Si dot samples grown on Si(001) by molecular beam epitaxy at substrate temperatures ranging from 430 to 580 C. Two excitation peaks were observed, and the characteristics of the involved optical transitions were studied in detail by PLE (in one case implemented together with selective photoluminescence, SPL) on different samples containing either only one SiGe dot layer or multiple SiGe-dot/Si stacks. The temperature- and power-dependence of the excitation properties together with the results of six-band k.p calculations support the assignment of the observed PLE peaks to spatially direct and indirect transitions collected from two different SiGe dot populations.

National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-53205 (URN)
Available from: 2010-01-19 Created: 2010-01-19 Last updated: 2015-01-23
Zhao, M., Hansson, G. & Ni , W.-X. (2009). Strain relaxation of thin Si0.6Ge0.4 grown with low-temperature buffers by molecular beam epitaxy. JOURNAL OF APPLIED PHYSICS, 105(6), 063502-
Open this publication in new window or tab >>Strain relaxation of thin Si0.6Ge0.4 grown with low-temperature buffers by molecular beam epitaxy
2009 (English)In: JOURNAL OF APPLIED PHYSICS, ISSN 0021-8979 , Vol. 105, no 6, p. 063502-Article in journal (Refereed) Published
Abstract [en]

A double-low-temperature-buffer variable-temperature growth scheme was studied for fabrication of strain-relaxed thin Si0.6Ge0.4 layer on Si(001) by using molecular beam epitaxy (MBE), with particular focuses on the influence of growth temperature of individual low-temperature-buffer layers on the relaxation process and final structural qualities. The low-temperature buffers consisted of a 40 nm Si layer grown at an optimized temperature of similar to 400 degrees C, followed by a 20 nm Si0.6Ge0.4 layer grown at temperatures ranging from 50 to 550 degrees C. A significant relaxation increase together with a surface roughness decrease both by a factor of similar to 2, accompanied with the cross-hatch/cross-hatch-free surface morphology transition, took place for the sample containing a low-temperature Si0.6Ge0.4 layer that was grown at similar to 200 degrees C. This dramatic change was explained by the association with a certain onset stage of the ordered/disordered growth transition during the low-temperature MBE, where the high density of misfit dislocation segments generated near surface cusps largely facilitated the strain relaxation of the top Si0.6Ge0.4 layer.

Keywords
buffer layers, dislocations, Ge-Si alloys, molecular beam epitaxial growth, order-disorder transformations, semiconductor growth, semiconductor materials, semiconductor thin films, surface morphology, surface roughness
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-17893 (URN)10.1063/1.3091266 (DOI)
Note
Original Publication: Ming Zhao, Göran Hansson and Wei-Xin Ni, Strain relaxation of thin Si0.6Ge0.4 grown with low-temperature buffers by molecular beam epitaxy, 2009, JOURNAL OF APPLIED PHYSICS, (105), 6, 063502. http://dx.doi.org/10.1063/1.3091266 Copyright: American Institute of Physics http://www.aip.org/ Available from: 2009-05-05 Created: 2009-04-24 Last updated: 2009-05-05Bibliographically approved
Zhang, H., Sakamoto, K., Hansson, G. & Uhrberg, R. (2008). High-temperature annealing and surface photovoltage shifts on Si(111)7×7. Physical Review B. Condensed Matter and Materials Physics, 78(3), 035318
Open this publication in new window or tab >>High-temperature annealing and surface photovoltage shifts on Si(111)7×7
2008 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 78, no 3, p. 035318-Article in journal (Refereed) Published
Abstract [en]

The relation between annealing temperature and surface photovoltage (SPV) shifts on the Si(111)7×7 surface of lightly n-doped substrates has been studied by core-level and valence-band photoelectron spectroscopies at 100 K. The SPV shift was found to depend strongly on the annealing temperature and the photon flux. Between 900 and 1150 °C the magnitude of the SPV shift shows a general decrease with annealing temperature. After a narrow plateau, the SPV shift becomes positive for annealings at 1250 and 1270 °C. As a consequence, the adatom surface state of the 7×7 surface appears above the Fermi level. The unexpected SPV shift can be explained by the formation of a p-type layer during high-temperature annealing of the Si sample. The role of boron and carbon contaminations has been discussed in this context in the literature. By correlating the SPV shifts with the C 1s and B 1s core-level signals, we conclude that carbon, but not boron, is involved in the formation of the p-type layer. Further, our results show that the annealing temperature plays a crucial role when binding energies are determined from photoemission spectra at low temperature. The effect is of particular importance in the study of surface band-gap openings related to phase transitions at low temperature.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-46988 (URN)10.1103/PhysRevB.78.035318 (DOI)000258190300094 ()
Available from: 2013-03-26 Created: 2009-10-11 Last updated: 2017-12-13Bibliographically approved
Karim, A., Hansson, G. V. & Linnarsson, M. K. (2008). Influence of Er and O concentrations on the microstructure and luminescence of Si:Er/O LEDs. Journal of Physics, Conference Series, 100(042010)
Open this publication in new window or tab >>Influence of Er and O concentrations on the microstructure and luminescence of Si:Er/O LEDs
2008 (English)In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 100, no 042010Article in journal (Refereed) Published
Abstract [en]

Erbium(Er)/Oxygen(O) doped Silicon (Si) layers grown by molecular beam epitaxy (MBE), can be used for fabricating Si-based light emitting diodes. The electroluminescence intensity from these layers depends sensitively on the formation of specific types of Er/O precipitates inside the Si host. We have performed a detailed microstructure analysis of MBE-grown Er/O doped Si layers using electron microscopy and combined it with secondary ion mass spectrometry (SIMS) measurements as well as electroluminescence studies. Two types of microstructures are observed in different samples with specific Er and O concentrations and grown using Er and Si co-evaporation in O ambient. The first type of microstructure consists of planar precipitates along (311) planes mostly initiated at the onset of the growth of the Si:Er/O layer. The second characteristic type of microstructure observed contain round precipitates of Er/O. Using analytical microscopy techniques it was revealed that the round precipitates contain a higher ratio of Er to O as compared to the planar precipitates of the first type. The planar precipitates normally result in structures with high electroluminescence intensity while the structures with round precipitates have low intensity.

National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-12569 (URN)10.1088/1742-6596/100/4/042010 (DOI)
Available from: 2008-09-15 Created: 2008-09-15 Last updated: 2017-12-14
Karim, A., Du, C.-X. & Hansson , G. (2008). Influence of exposure to 980 nm laser radiation on the luminescence of Si: Er/O light-emitting diodes. JOURNAL OF APPLIED PHYSICS, 104(12), 123110-
Open this publication in new window or tab >>Influence of exposure to 980 nm laser radiation on the luminescence of Si: Er/O light-emitting diodes
2008 (English)In: JOURNAL OF APPLIED PHYSICS, ISSN 0021-8979 , Vol. 104, no 12, p. 123110-Article in journal (Refereed) Published
Abstract [en]

Erbium (Er) codoping with oxygen (O) in Si is a well-known method for producing electroluminescent material radiating at 1.54 mu m through a 4f shell transition of Er3+ ions. In this work the influence of exposure to 980 nm radiation on the electroluminescence (EL) of reverse biased Si:Er/O light-emitting diodes (LEDs), which give a strong room temperature 1.54 mu m intensity, is presented and discussed. All the device layers, including Er/O doped Si sandwiched between two Si0.82Ge0.18 layers, have been grown on silicon on insulator substrates using molecular beam epitaxy and processed to fabricate edge emitting Si:Er/O waveguide LEDs. Electromagnetic mode confinement simulations have been performed to optimize the layer parameters for waveguiding. The temperature dependence of the 1.54 mu m EL intensity exhibits an abnormal temperature quenching with a peak near -30 degrees C, and at -160 degrees C it has decreased by a factor of 5. However, irradiating the devices with a 980 nm laser gives an enhancement of the 1.54 mu m EL intensity, which is more dramatic at low temperatures (e.g., -200 degrees C) where the quenched EL signal is increased up to almost the same level as at room temperature. The enhancement of the EL intensity is attributed to the photocurrent generated by the 980 nm laser, reducing the detrimental avalanche current.

Keywords
electroluminescence, electroluminescent devices, elemental semiconductors, erbium, Ge-Si alloys, laser beam effects, light emitting diodes, optical waveguide components, oxygen, photoconductivity, radiation quenching, semiconductor doping, semiconductor epitaxial layers, silicon, silicon-on-insulator
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-16512 (URN)10.1063/1.3050316 (DOI)
Note
Original Publication: Amir Karim, Chun-Xia Du and Göran Hansson, Influence of exposure to 980 nm laser radiation on the luminescence of Si: Er/O light-emitting diodes, 2008, JOURNAL OF APPLIED PHYSICS, (104), 12, 123110. http://dx.doi.org/10.1063/1.3050316 Copyright: American Institute of Physics http://www.aip.org/ Available from: 2009-02-02 Created: 2009-01-30 Last updated: 2009-02-02Bibliographically approved
Gomes, P. F., Cerdeira, F., Larsson, M., Elfving, A., Hansson, G., Ni, W.-X., . . . García-Cristóbal, A. (2008). Large optical emission blue shift in Ge/Si quantum dots under external biaxial strain. In: ICPS 29th International Conference on the Physics of Semiconductors,2008.
Open this publication in new window or tab >>Large optical emission blue shift in Ge/Si quantum dots under external biaxial strain
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2008 (English)In: ICPS 29th International Conference on the Physics of Semiconductors,2008, 2008Conference paper, Published paper (Refereed)
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-44291 (URN)76182 (Local ID)76182 (Archive number)76182 (OAI)
Available from: 2009-10-10 Created: 2009-10-10
Zhao, M., Karim, A., Hansson, G., Ni, W.-X., Townsend, P., Lynch, S. A. & Paul , D. J. (2008). Molecular beam epitaxy growth of Si/SiGe bound-to-continuum quantum cascade structures for THz emission. Thin Solid Films, 517(1), 34-37
Open this publication in new window or tab >>Molecular beam epitaxy growth of Si/SiGe bound-to-continuum quantum cascade structures for THz emission
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2008 (English)In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 517, no 1, p. 34-37Article in journal (Refereed) Published
Abstract [en]

A Si/SiGe bound-to-continuum quantum cascade design for THz emission was grown using solid-source molecular beam epitaxy on Si0.8Ge0.2 virtual substrates. The growth parameters were carefully studied and several samples with different boron doping concentrations were grown at optimized conditions. Extensive material characterizations revealed a high crystalline quality of the grown structures with an excellent growth control. Layer undulations resulting from a nonuniform strain field, introduced by high doping concentration, were observed. The device characterizations suggested that a modification on the design was needed in order to enhance the THz emission.

Keywords
Molecular beam epitaxy (MBE), Si/SiGe, Quantum cascade, X-ray diffraction, Transmission electron microscopy (TEM)
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-16177 (URN)10.1016/j.tsf.2008.08.091 (DOI)
Available from: 2009-01-09 Created: 2009-01-09 Last updated: 2017-12-14
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