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Ciechonski, Rafal
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Publications (10 of 22) Show all publications
Kakanakova-Georgieva, A., Ciechonski, R., Forsberg, U., Lundskog, A. & Janzén, E. (2009). Hot-Wall MOCVD for Highly Efficient and Uniform Growth of AIN. Crystal Growth & Design, 9(2), 880-884
Open this publication in new window or tab >>Hot-Wall MOCVD for Highly Efficient and Uniform Growth of AIN
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2009 (English)In: Crystal Growth & Design, ISSN 1528-7483, Vol. 9, no 2, p. 880-884Article in journal (Refereed) Published
Abstract [en]

We demonstrated successful growth of AIN at a temperature of 1200 degrees C in a set of hot-wall MOCVD systems with the possibility of straightforward scaling up the process on larger wafer areas to meet the demand of device technologies. We outlined several aspects of the carefully optimized design and process parameters with relevance to achievement of a high overall growth rate (1 and up to 2 mu m/h), efficiency, and uniformity, which to a great extent depends on how consumption of growth-limiting species by gas-phase adduct formation can actively be prevented. Mixing of the precursors upstream from the deposition area facilitates uniform epitaxial growth, while the greater uniformity of substrate temperature inherent to the hot-wall reactor and rotation of the wafer are of fundamental importance for layer-growth uniformity. The AIN layer thickness can be controlled with an accuracy of +/- 1.3% on 2 in. wafers. The low-temperature cathodoluminescence spectrum of the AIN epitaxial material is strongly dominated by the intense near band-gap deep UV emission at about 208 nm.

National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-16875 (URN)10.1021/cg8005663 (DOI)
Available from: 2009-02-22 Created: 2009-02-20 Last updated: 2014-09-15
Forsberg, U., Lundskog, A., Kakanakova-Georgieva, A., Ciechonski, R. & Janzén, E. (2009). Improved hot-wall MOCVD growth of highly uniform AlGaN/GaN/HEMT structures. Journal of Crystal Growth, 311(10), 3007-3010
Open this publication in new window or tab >>Improved hot-wall MOCVD growth of highly uniform AlGaN/GaN/HEMT structures
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2009 (English)In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 311, no 10, p. 3007-3010Article in journal (Refereed) Published
Abstract [en]

The inherent advantages of the hot-wall metal organic chemical vapor deposition (MOCVD) reactor (low temperature gradients, less bowing of the wafer during growth, efficient precursor cracking) compared to a cold-wall reactor make it easier to obtain uniform growth. However, arcing may occur in the growth chamber during growth, which deteriorates the properties of the grown material. By inserting insulating pyrolytic BN (PBN) stripes in the growth chamber we have completely eliminated this problem. Using this novel approach we have grown highly uniform, advanced high electron mobility transistor (HEMT) structures on 4 semi-insulating (SI) SiC substrates with gas-foil rotation of the substrate. The nonuniformities of sheet resistance and epilayer thickness are typically less than 3% over the wafer. The room temperature hall mobility of the 2DEG is well above 2000 cm(2)/V s and the sheet resistance about 270 Omega/sqr.

Keywords
Metalorganic chemical vapor deposition, Nitrides, High electron mobility transistors
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-19663 (URN)10.1016/j.jcrysgro.2009.01.045 (DOI)
Note
Original Publication: Urban Forsberg, Anders Lundskog, A Kakanakova-Georgieva, Rafal Ciechonski and Erik Janzén, Improved hot-wall MOCVD growth of highly uniform AlGaN/GaN/HEMT structures, 2009, JOURNAL OF CRYSTAL GROWTH, (311), 10, 3007-3010. http://dx.doi.org/10.1016/j.jcrysgro.2009.01.045 Copyright: Elsevier Science B.V., Amsterdam. http://www.elsevier.com/Available from: 2009-08-17 Created: 2009-07-10 Last updated: 2017-12-13Bibliographically approved
Ciechonski, R. (2007). Growth and characterization of SiC and GaN. (Doctoral dissertation). Linköping: Linköping University Electronic Press
Open this publication in new window or tab >>Growth and characterization of SiC and GaN
2007 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

At present, focus of the SiC crystal growth development is on improving the crystalline quality without polytype inclusions, micropipes and the occurrence of extended defects. The purity of the grown material, as well as intentional doping must be well controlled and the processes understood. High-quality substrates will significantly improve device performance and yield. One of the aims of the thesis is further understanding of polytype inclusion formation as well as impurity control in SiC bulk crystals grown using PVT method also termed seeded sublimation method. Carbonization of the source was identified as a major reason behind the polytype inclusion occurrence during the growth. The aim of this work was further understanding of sublimation growth process of 4H-SiC bulk crystals in vacuum, in absence of an inert gas. For comparison growth in argon atmosphere (at 5 mbar) was performed. The effect of the ambient on the impurity incorporation was studied for different growth temperatures. For better control of the process in vacuum, tantalum as a carbon getter was utilized.

The focus of the SiC part of the thesis was put on further understanding of the PVT epitaxy with an emphasis on the high growth rate and purity of grown layers.

High resistivity 4H-SiC samples grown by sublimation with high growth rate were studied. The measurements show resistivity values up to high 104 cm. By correlation between the growth conditions and SIMS results, a model was applied in which it is proposed that an isolated carbon vacancy donor-like level is a possible candidate responsible for compensation of the shallow acceptors in p-type 4H-SiC. A relation between cathodoluminescence (CL) and DLTS data is taken into account to support the model.

To meet the requirements for high voltage blocking devices such as high voltage Schottky diodes and MOSFETs, 4H-SiC epitaxial layers have to exhibit low doping concentration in order to block reverse voltages up to few keV and at the same time have a low on-state resistance (Ron). High Ron leads to enhanced power consumption in the operation mode of the devices. In growth of thick layers for high voltage blocking devices, the conditions to achieve good on-state characteristics become more challenging due to the low doping and pronounced thicknesses needed, preferably in short growth periods. In case of high-speed epitaxy such as the sublimation, the need to apply higher growth temperature to yield the high growth rate, results in an increased concentration of background impurities in the layers as well as an influence on the intrinsic defects.

On-state resistance Ron estimated from current density-voltage characteristics of Schottky diodes on thick sublimation layers exhibits variations from tens of mΩ.cm2 to tens of Ω.cm2 for different doping levels. In order to understand the occurrence of high on-state resistance, Schottky barrier heights were first estimated for both forward and reverse bias with the application of thermionic emission theory and were in agreement with literature reported values. Decrease in mobility with increasing temperature was observed and its dependencies of T–1.3 and T–2.0 for moderately doped and low doped samples, respectively, were estimated. From deep level measurements by Minority Carrier Transient Spectroscopy (MCTS), an influence of shallow boron related levels and D-center on the on-state resistance was observed, being more pronounced in low doped samples. Similar tendency was observed in depth profiling of Ron. This suggests a major role of boron in a compensation mechanism.

In the second part of the thesis growth and characterization of GaN is presented. Excellent electron transport properties with high electron saturate drift velocity make GaN an excellent candidate for electronic devices. Especially, AlGaN/GaN based high electron mobility transistors (HEMT) have received an increased attention in last years due to their attractive properties. The presence of strong spontaneous and piezoelectric polarization due to the lattice mismatch between AlGaN and GaN is responsible for high free electrons concentrations present in the vicinity of the interface. Due to the spatial separation of electrons and ionized donors or surface states, 2DEG electron gas formed near the interface of the heterostructure exhibits high sheet carrier density and high mobility of electrons. Al0.23Ga0.77N/GaN based HEMT structures with an AlN exclusion layer on 100 mm semiinsulating 4H-SiC substrates have been grown by hot-wall MOCVD. The electrical properties of the two-dimensional electron gas (2DEG) such as electron mobility, sheet carrier density and sheet resistance were obtained from Hall measurements, capacitance-voltage and contact-less eddy-current techniques. The effect of different scattering mechanisms on the mobility have been taken into account and compared to the experimental data. Hall measurements were performed in the range of 80 to 600 K. Hall electron mobility is equal to 17140 cm2(Vs)-1 at 80 K, 2310 cm2(Vs)-1 at room temperature, and as high as 800 cm2(Vs)-1 at 450 K, while the sheet carrier density is 1.04x1013 cm-2 at room temperature and does not vary very much with temperature. Estimation of different electron scattering mechanisms reveals that at temperatures higher than room temperature, experimental mobility data is mainly limited by optical phonon scattering. At relevant high power device temperature (450 K) there is still an increase of mobility due to the AlN exclusion layer.

We have studied the behaviour of Ga-face GaN epilayers after in-situ thermal treatment in different gas mixtures in a hot-wall MOCVD reactor. Influence of N2, N2+NH3 and N2+NH3+H2 ambient on the morphology was investigated in this work. The most stable thermal treatment conditions were obtained in the case of N2+NH3 gas ambients. We have also studied the effect of the increased molar ratio of hydrogen in order to establish proper etching conditions for hot-wall MOCVD growth.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2007. p. 50
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1151
Keywords
SiC, GaN, Deep level transient spectroscopy, Minority Carrier Transient Spectroscopy, Hall effect, Cathodoluminescence, Scanning electron microscopy, Atomic Force microscopy, sublimation growth, MOCVD, heterostructures, High Electron Mobility transistor, point defects
National Category
Other Engineering and Technologies not elsewhere specified
Identifiers
urn:nbn:se:liu:diva-10314 (URN)978-91-85895-26-7 (ISBN)
Public defence
2007-12-18, Planck, Fysikhuset, Campus Valla, Linköpings Universitet, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2007-12-04 Created: 2007-12-04 Last updated: 2009-04-24Bibliographically approved
Ciechonski, R., Lundskog, A., Forsberg, U., Kakanakova-Georgieva, A., Pedersen, H. & Janzén, E. (2007). High 2DEG mobility of HEMT structures grown on 100 mm SI 4H-SiC substrates by hot-wall MOCVD. Journal of Applied Physics
Open this publication in new window or tab >>High 2DEG mobility of HEMT structures grown on 100 mm SI 4H-SiC substrates by hot-wall MOCVD
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2007 (English)In: Journal of Applied PhysicsArticle in journal (Refereed) Submitted
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-12787 (URN)
Available from: 2007-12-04 Created: 2007-12-04 Last updated: 2015-03-11
Lundskog, A., Forsberg, U., Kakanakova-Georgieva, A., Ciechonski, R., Ivanov, I. G., Darakchieva, V., . . . Rorsman, N. (2007). Highly Uniform Hot-Wall MOCVD Growth of High-Quality AlGaN/GaN HEMT-Structures on 100 mm Semi-Insulating 4H-SiC Substrates. In: ICNS-7,2007.
Open this publication in new window or tab >>Highly Uniform Hot-Wall MOCVD Growth of High-Quality AlGaN/GaN HEMT-Structures on 100 mm Semi-Insulating 4H-SiC Substrates
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2007 (English)In: ICNS-7,2007, 2007Conference paper, Published paper (Other academic)
Abstract [en]

   

National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-39806 (URN)51333 (Local ID)51333 (Archive number)51333 (OAI)
Available from: 2009-10-10 Created: 2009-10-10 Last updated: 2011-12-29
Ewing, D., Porter, L., Wahab, Q. U., Ciechonski, R., Syväjärvi, M. & Yakimova, R. (2007). Inhomogeneous electrical characteristics in 4H-SiC Schottky diodes. Semiconductor Science and Technology, 22(12), 1287-1291
Open this publication in new window or tab >>Inhomogeneous electrical characteristics in 4H-SiC Schottky diodes
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2007 (English)In: Semiconductor Science and Technology, ISSN 0268-1242, E-ISSN 1361-6641, Vol. 22, no 12, p. 1287-1291Article in journal (Refereed) Published
Abstract [en]

Hundreds of current-voltage (I-V) measurements of Ni, Pt and Ti Schottky diodes on 4H-SiC were conducted at low applied voltages. The SiC substrates contained homoepitaxial layers grown by either chemical vapor deposition or sublimation. While near-ideal contacts were fabricated on all samples, a significant percentage of diodes (∼7%-50% depending on the epitaxial growth method and the diode size) displayed a non-ideal, or inhomogeneous, barrier height. These 'non-ideal' diodes occurred regardless of growth technique, pre-deposition cleaning method, or contact metal. In concurrence with our earlier reports in which the non-ideal diodes were modeled as two Schottky barriers in parallel, the lower of the two Schottky barriers, when present, was predominantly centered at one of the three values: ∼0.60, 0.85 or 1.05 eV. The sources of these non-idealities were investigated using electron-beam- induced current (EBIC) and deep-level transient spectroscopy (DLTS) to determine the nature and energy levels of the defects. DLTS revealed a defect level that corresponds with the low- (non-ideal) barrier height, at ∼0.60 eV. It was also observed that the I-V characteristics tended to degrade with increasing deep-level concentration and that inhomogeneous diodes tended to contain defect clusters. Based on the results, it is proposed that inhomogeneities, in the form of one or more low-barrier height regions within a high-barrier height diode, are caused by defect clusters that locally pin the Fermi level. © 2007 IOP Publishing Ltd.

National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-39593 (URN)10.1088/0268-1242/22/12/008 (DOI)50007 (Local ID)50007 (Archive number)50007 (OAI)
Available from: 2009-10-10 Created: 2009-10-10 Last updated: 2017-12-13
Paskaleva, A., Ciechonski, R., Syväjärvi, M., Atanassova, E. & Yakimova, R. (2005). Characterization of 4H-SiC MOS structures with Al2O3 as gate dielectric. In: Materials Science Forum, Vols. 483-485. Paper presented at ECSCRM2004 (pp. 709-712). , 483
Open this publication in new window or tab >>Characterization of 4H-SiC MOS structures with Al2O3 as gate dielectric
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2005 (English)In: Materials Science Forum, Vols. 483-485, 2005, Vol. 483, p. 709-712Conference paper, Published paper (Refereed)
Abstract [en]

The electrical properties of Al2O3 as a gate dielectric in MOS structures based on n- and p-type 4H-SiC grown by sublimation method have been investigated and compared to the properties of similar structures utilizing SiO2. The electrically active defects in the structures are studied by CV method. The results show that the type as well as spatial and energy distribution of defects in Al2O3/SiC and SiO2/SiC samples are different. The structures with Al2O3 on p-type 4H-SiC demonstrate much better C-V characteristics than the p-type 4H-SiC/SiO2 structures.

Keywords
high-k dielectrics on SiC, Al(2)O3, MOS structures
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-48231 (URN)
Conference
ECSCRM2004
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2010-12-08
Ciechonski, R. (2005). Device characteristics of sublimation grown 4H-SiC layers. (Licentiate dissertation). Linköping: Linköpings universitet
Open this publication in new window or tab >>Device characteristics of sublimation grown 4H-SiC layers
2005 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

At present, focus of the SiC crystal growth development is on improving the crystalline quality without polytype inclusions, micropipes and the occurrence of extended defects. The purity of the grown material, as well as intentional doping must be well controlled and the processes understood. High-quality substrates will significantly improve device performance and yield. One of the aims of the licentiate thesis is further understanding of polytype inclusion formation as well as impurity control in SiC bulk crystals grown using PVT method also termed seeded sublimation method. We have identified a carbonization of the source as a major reason behind the polytype inclusion occurrence during the growth. The aim of this work was further understanding of sublimation growth process of 4H-SiC bulk crystals in vacuum, in absence of an inert gas. For comparison growth in argon atmosphere (at 5 mbar) was performed. The effect of the ambient on the impurity incorporation was studied for different growth temperatures. For better control of the process in vacuum, tantalum as a carbon getter was utilized.

The major focus of the thesis was put on further understanding of the PVT epitaxy with an emphasis on the high growth rate and the purity of grown layers.

High resistivity 4H-SiC samples grown by sublimation with high growth rate were studied. The measurements show resistivity values up to high 104 Ωcm. By correlation between the growth conditions and SIMS results, we apply a model in which it is proposed that an isolated carbon vacancy donor-like level is a possible candidate responsible for compensation of the shallow acceptors in p-type 4H-SiC. A relation between cathodoluminescence (CL) and DL TS data is taken into account to support the model.

To meet the requirements for high voltage blocking devices such as high voltage Schottky diodes and MOSFETs, 4H-SiC epitaxial layers have to exhibit low doping concentration in order to block reverse voltages up to few keV and at the same time have a low on-state resistance (Ron). High Ron leads to enhanced power consumption in the operation mode of the devices. In growth of thick layers for high voltage blocking devices, the conditions to achieve good on-state characteristics become more challenging due to the low doping and pronounced thicknesses needed, preferably in short growth periods. In case of high-speed epitaxy such as the sublimation, the need to apply higher growth temperature to yield the high growth rate, results in an increased concentration of background impurities in the layers as well as an influence on the intrinsic defects.

On-state resistance Ron estimated from current density-voltage characteristics of Schottky diodes on thick sublimation layers exhibits variations from tens of mΩ.cm2 to tens of Ω.cm2 for different doping levels. In order to understand the occurrence of high on-state resistance, Schottky barrier heights were first estimated for both forward and reverse bias with the application of thermionic emission theory and were in agreement with a literature reported values. Decrease in mobility with increasing temperature was observed and its dependencies of T-1.3 and T-2.0 for moderately doped and low doped samples, respectively, were estimated. From deep level measurements by Minority Carrier Transient Spectroscopy, an influence of shallow boron related levels and D-center on the on-state resistance was observed, being more pronounced in low doped samples. Similar tendency was observed in depth profiling of Ron. This suggests a major role of boron in a compensation mechanism.

Metal-Oxide-Semiconductor (MOS) capacitors were fabricated and characterized on 4H-SiC epilayers grown by PVT (sublimation) epitaxy and compared to the properties of similar structures on CVD grown layers. Detailed investigations of the PVT structures indicate a stable behaviour of the interface traps from roomtemperature up to 475 K. The amount of positive oxide charges Qo is 6.83x109 cm-2 at room temperature and decreases with temperature increase which suggests temperature stability of processed devices. The density of interface states Dit obtained by AC conductance method is lower in the case of PVT sample.

AI203 as an alternative gate dielectric was studied. The implementation of this high-k dielectric is required in the case of high electric fields at which the usage of SiO2 may result in the reliability problems. The electrical properties of AI2O3 as a gate dielectric in MOS structures based on n- and p-type 4H-SiC grown by sublimation method were investigated and compared to the properties of similar structures utilizing SiO2.

Place, publisher, year, edition, pages
Linköping: Linköpings universitet, 2005. p. 50
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1150
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-31210 (URN)16958 (Local ID)91-85297-50-X (ISBN)16958 (Archive number)16958 (OAI)
Available from: 2009-10-09 Created: 2009-10-09 Last updated: 2013-11-07
Porro, S., Ciechonski, R., Syväjärvi, M. & Yakimova, R. (2005). Electrical Analysis and Interface States Evaluation of of Ni Schottky diodes on 4H-SiC thick epilayers. Physica Status Solidi (a) applications and materials science, 202(13), 2508-2514
Open this publication in new window or tab >>Electrical Analysis and Interface States Evaluation of of Ni Schottky diodes on 4H-SiC thick epilayers
2005 (English)In: Physica Status Solidi (a) applications and materials science, ISSN 1862-6300, E-ISSN 1862-6319, Vol. 202, no 13, p. 2508-2514Article in journal (Refereed) Published
Abstract [en]

This work has been focused on characterization of thick 4H-SiC layers produced by sublimation epitaxy. Nickel Schottky contacts have been fabricated in order to characterize the grown material and evaluate the interfacial layer between metal and semiconductor. The characterization study includes current-voltage and capacitance-voltage high temperature measurements, from which Schottky barrier, net donor concentration and on-state resistance values have been extracted. The diodes show a typical behavior of J-V and C-V curves with temperature, with Schottky barrier heights of 1.3 eV ÷ 1.4 eV and net donor concentration of 4 × 1015 cm-3 ÷ 1 × 1016 cm-3. From the Bardeen's model on reverse J-V, the density of states of the interfacial layer has been estimated to 7 × 1011 eV-1 cm-2 ÷ 8 × 1011 eV-1 cm-2, a value that is similar to the density of states of oxide layers in deliberated MOS structures realized on the same epilayers.

Place, publisher, year, edition, pages
John Wiley & Sons, 2005
Keywords
73.20.Hb, 73.30.+y, 73.40.Ns, 73.61.Le
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-12786 (URN)10.1002/pssa.200521147 (DOI)
Available from: 2007-12-04 Created: 2007-12-04 Last updated: 2017-05-11Bibliographically approved
Paskaleva, A., Ciechonski, R., Syväjärvi, M., Atanassova, E. & Yakimova, R. (2005). Electrical behavior of 4H-SiC metal-oxide-semiconductor structures with Al2O3 as gate dielectric. Journal of Applied Physics, 97(12), 124507
Open this publication in new window or tab >>Electrical behavior of 4H-SiC metal-oxide-semiconductor structures with Al2O3 as gate dielectric
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2005 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 97, no 12, p. 124507-Article in journal (Refereed) Published
Abstract [en]

The electrical properties of Al2O3 as a gate dielectric in metal-oxide-semiconductorstructures based on n- and p-type 4H-SiC grown by sublimation method have been investigated and compared to the properties of similar structures utilizing SiO2. The electrically active defects in the structures are studied by capacitance–voltage (C–V) and current–voltage (I–V) methods. The results show that the type as well as spatial and energy distributions of defects in Al2O3/SiC and SiO2/SiC samples are different. The structures with Al2O3 on p-type 4H-SiC demonstrate much better electrical characteristics than the p-type 4H-SiC/SiO2 structures. It is demonstrated that the conduction process in the former is governed by Fowler–Nordheim electron tunneling from the Al gate whereas in the latter the hole tunneling from SiC is the more probable process. This difference combined with the higher defect density in p-type SiC/SiO2 structures defines the higher leakage currents compared to the structures utilizing Al2O3.

National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-30684 (URN)10.1063/1.1938267 (DOI)16289 (Local ID)16289 (Archive number)16289 (OAI)
Available from: 2009-10-09 Created: 2009-10-09 Last updated: 2017-12-13
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