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Device characteristics of sublimation grown 4H-SiC layers
Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
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. , 50 p.
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1150
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:liu:diva-31210Local ID: 16958ISBN: 91-85297-50-X (print)OAI: oai:DiVA.org:liu-31210DiVA: diva2:252033
Available from: 2009-10-09 Created: 2009-10-09 Last updated: 2013-11-07
List of papers
1. Effect of Ambient on 4H-SiC Bulk Crystals grown by Sublimation
Open this publication in new window or tab >>Effect of Ambient on 4H-SiC Bulk Crystals grown by Sublimation
2003 (English)In: Materials Science Forum, Vols. 433-436 / [ed] Peder Bergman and Erik Janzén, 2003, Vol. 433-436, 75-78 p.Conference paper, Published paper (Refereed)
Abstract [en]

Sublimation bulk growth in vacuum using graphite crucibles and such with tantalum shielding of the crucible walls has been studied. Residual nitrogen, aluminum and boron doping in the material grown in vacuum is presented. Activation energies of growth rate in respect to growth temperature in vacuum are deduced. The estimated values are 21 kcallmole for growth temperatures below 2075°C and 128 kcal/mole in the range of growth temperatures between 2075°C and 2275°C. Cathodoluminescence spectra taken from samples grown in the graphite crucible in absence of tantalum under different pressures show nitrogen-alurninum DAP transition and strong luminescence from deep boron. This is not the case for samples grown in the tantalum environment.

Keyword
Bulk Growth, Doping, Boron, Tantalum, Cathodoluminescence
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-12782 (URN)10.4028/www.scientific.net/MSF.433-436.75 (DOI)
Conference
ECSCRM 2002. Linköping, Sweden, September 1-5, 2002
Available from: 2007-12-04 Created: 2007-12-04 Last updated: 2013-11-07
2. Structural instabilities in growth of SiC crystals
Open this publication in new window or tab >>Structural instabilities in growth of SiC crystals
2005 (English)In: Journal of Crystal Growth, ISSN 0022-0248, Vol. 275, no 1-2, e461-e466 p.Article in journal (Refereed) Published
Abstract [en]

Misoriented grains, which may occur on the growth front of 6H–SiC boules have been studied in relation to their appearance during sublimation growth. The effect was obtained by applying growth conditions at which the source powder was gradually approaching graphitisation and the vapour becoming C-rich. The high off-orientation of the grains is demonstrated through etching in molten KOH and transmission light optical microscopy. Micropipes propagating in the single crystal area and facing the misoriented grain have been studied, and it is shown that they may either be terminated at the grain or their propagation is altered to be parallel with the grain boundary. It has been found that the polytype of the grains may switch from 6H to 4H, which is explained by the change of the Si/C ratio in the vapour.

Keyword
Crystal morphology; Volume defects; Growth from vapor; Single crystal growth; Semiconductor silicon compounds
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-12783 (URN)10.1016/j.jcrysgro.2004.11.020 (DOI)
Available from: 2007-12-04 Created: 2007-12-04 Last updated: 2013-11-07
3. Growth of device quality 4H-SiC by high velocity epitaxy
Open this publication in new window or tab >>Growth of device quality 4H-SiC by high velocity epitaxy
2004 (English)In: Materials Science Forum, Vols. 457-460, 2004, Vol. 457-460, 201-204 p.Conference paper, Published paper (Refereed)
Abstract [en]

Thick (>20 μm) 4H-SiC layers in doping range of low 1015-1016 cm-3 were grown by sublimation epitaxy at a growth rate of similar to50 mum/hour. Two inch 25 μm thick layers were fabricated with standard thickness deviation of 3.77%. Effect of important process parameters on the material grade has been discussed. The Schottky diodes processed on this material sustained 900V reverse voltage at a current of 1.7 x 10-8 A, while measured on MOS capacitors the interface state density was as low as similar to6-9 x 1010 cm-2.

Keyword
fast growth, sublimation epitaxy, 4H-SiC, device quality, schottky diode, MOS capacitor, interface state density
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-48297 (URN)10.4028/www.scientific.net/MSF.457-460.201 (DOI)
Conference
ICSCRM 2003, Lyon, Fance, October 5-10, 2003
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2013-11-07
4. Effect of boron on the resistivity of compensated 4H-SiC
Open this publication in new window or tab >>Effect of boron on the resistivity of compensated 4H-SiC
2003 (English)In: Journal of electronic materials, ISSN 0361-5235, Vol. 32, no 5, 452-457 p.Article in journal (Refereed) Published
Abstract [en]

High-resistivity 4H-SiC samples grown by sublimation with a high growth rate are studied. The measurements show resistivity values up to a high of 104 Ωcm. The secondary ion mass spectroscopy (SIMS) results revealed a presence of only common trace impurities such as nitrogen, aluminum, and boron. To understand the compensation mechanism in these samples, capacitance deep-level transient spectroscopy (DLTS) on the p-type epilayers has been performed. By correlation between the growth conditions and SIMS results, we apply a model in which it is proposed that an isolated carbon vacancy donorlike 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.

Keyword
SiC sublimation epitaxy, DLTS, compensation, deep levels, carbon vacancy, high resistivity, semi-insulating
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-12784 (URN)10.1007/s11664-003-0177-0 (DOI)
Available from: 2007-12-04 Created: 2007-12-04 Last updated: 2013-11-07
5. Evaluation of On-state Resistance and Boron-related Levels in n-type 4H-SiC
Open this publication in new window or tab >>Evaluation of On-state Resistance and Boron-related Levels in n-type 4H-SiC
2005 (English)In: Materials Science Forum, Vols. 483-485, 2005, Vol. 483-485, 425-428 p.Conference paper, Published paper (Refereed)
Abstract [en]

Specific on-resistance Ron estimated from current density-voltage characteristics of Schottky diodes on thick 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 the 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 dependence of 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 thus resulting in high Ron.

Keyword
On-state resistance, I-V, C-V, MCTS, Sublimation, High-speed epitaxy, Deep
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-12785 (URN)
Conference
ECSCRM2004
Available from: 2007-12-04 Created: 2007-12-04 Last updated: 2013-11-07
6. Electrical Analysis and Interface States Evaluation of of Ni Schottky diodes on 4H-SiC thick epilayers
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, 2508-2514 p.Article 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
Keyword
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
7. Evaluation of MOS structures processed on 4H–SiC layers grown by PVT epitaxy
Open this publication in new window or tab >>Evaluation of MOS structures processed on 4H–SiC layers grown by PVT epitaxy
2005 (English)In: Solid-State Electronics, ISSN 0038-1101, E-ISSN 1879-2405, Vol. 49, no 12, 1917-1920 p.Article in journal (Refereed) Published
Abstract [en]

MOS capacitors have been fabricated on 4H–SiC epilayers grown by physical vapor transport (PVT) epitaxy. The properties were compared with those on similar structures based on chemical vapor deposition (CVD) layers. Capacitance–voltage (CV) and conductance measurements (GV) were performed in the frequency range of 1 kHz to 1 MHz and also at temperatures up to 475 K. Detailed investigations of the PVT structures indicate a stable behaviour of the interface traps from room temperature up to 475 K. The amount of positive oxide charge QO is 6.83 × 109 cm−2 at room temperature and decreases with temperature increase. This suggests that the processed devices are temperature stable. The density of interface states Dit obtained by Nicollian–Brews conductance method is lower in the structure based on the PVT grown sample.

National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-30706 (URN)10.1016/j.sse.2005.08.008 (DOI)16318 (Local ID)16318 (Archive number)16318 (OAI)
Available from: 2009-10-09 Created: 2009-10-09 Last updated: 2017-12-13
8. Electrical behavior of 4H-SiC metal-oxide-semiconductor structures with Al2O3 as gate dielectric
Open this publication in new window or tab >>Electrical behavior of 4H-SiC metal-oxide-semiconductor structures with Al2O3 as gate dielectric
Show others...
2005 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 97, no 12, 124507- p.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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