Silicon carbide grown by liquid phase epitaxy in microgravity
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Silicon carbide grown by liquid phase epitaxy in microgravity R. Yakimova and M. Syv¨aj¨arvi Department of Physics and Measurement Technology, Link¨oping University, S-581 83 Link¨oping, Sweden
C. Lockowandt Swedish Space Corporation, PO Box 4207, S-171 04 Solna, Sweden
M. K. Linnarsson Solid State Electronics, Royal Institute of Technology, S-164 40 Kista-Stockholm, Sweden
H. H. Radamson and E. Janz´en Department of Physics and Measurement Technology, Link¨oping University, S-581 83 Link¨oping, Sweden (Received 11 April 1997; accepted 21 July 1997)
6H and 4H polytype silicon carbide (SiC) layers have been grown on ground and under microgravity conditions by liquid phase epitaxy (LPE) from a solution of SiC in Si-Sc solvent at 1750 ±C. The effects of gravity on the growth parameters and material characteristiques have been studied. The growth rate, Sc incorporation, and the structural defects are modified in reduced gravity conditions, while the polytype reproduction of the substrate is not affected. The results obtained are intriguing as to further experiments providing objects for carrier lifetime measurements. I. INTRODUCTION
Silicon carbide has in comparison with Si superior properties regarding power electronics.1 However, the quality of the material needs to be improved considerably before it can become useful. The substrate crystals contain small inherent channels oriented along the c-axis and mostly propagating into the subsequently grown epitaxial layers. These defects, called micropipes, are disastrous for large area devices. Moreover, for highvoltage bipolar devices a long lifetime of the injected carriers is required. There is not sufficient knowledge of the origin of carrier lifetime limiting defects in SiC, but most commonly it is ascribed to vacancies and vacancy complexes associated with deep level impurities like vanadium and titanium. Liquid phase epitaxy (LPE) is a suitable method to produce high quality material and to provide information about crystal growth and defect formation mechanism.2 Growth from solution may give rise to an impurity microsegregation and growth instabilities due to the gravitation-induced convection, resulting in an alteration of the point defect density. In this respect, LPE growth under microgravity enables the elimination of the growth parameter which is not possible to control under normal conditions. The aim of the present study was to compare SiC growth from liquid phase under microgravity and onground conditions as to main impurity incorporation and growth-related defects. II. EXPERIMENT AND CHARACTERIZATION
The LPE module was launched on the Swedish microgravity rocket MASER 7 at Esrange in May 1996. 1812
http://journals.cambridge.org
J. Mater. Res., Vol. 13, No. 7, Jul 1998
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The total time of microgravity was about 6–7 min, and the residual acceleration after burnout stage was less than 1024 g. The SiC growth furnace was developed by the Swedish Space Corporation and was capable of proc
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