Growth of Large Diameter Semi-Insulating 6H-SiC Crystals by Physical Vapor Transport
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Growth of Large Diameter Semi-Insulating 6H-SiC Crystals by Physical Vapor Transport M. Yoganathan1, A. Gupta1, E. Semenas1, E. Emorhokpor1, C. Martin1, T. Kerr1, I. Zwieback1, A. E. Souzis1, T.A. Anderson1, C.D. Tanner2, J. Chen2, D.L. Barrett1,2, R.H. Hopkins2, C.J. Johnson2, Fei Yan3, W.J. Choyke3, and R.P. Devaty3. 1 II-VI, Inc., 20 Chapin Rd, Suite 1005, Pine Brook, NJ 07058. 2 II-VI, Inc., 375 Saxonburg Blvd., Saxonburg, PA 16056. 3 University of Pittsburgh, Department of Physics and Astronomy, Pittsburgh, PA 15260. ABSTRACT Semi-insulating (SI) 6H-SiC boules up to 110mm in diameter have been grown by Physical Vapor Transport (PVT). SI properties have been achieved by vanadium compensation, which resulted in the room temperature electrical resistivity exceeding 2x1011Ω·cm. Low temperature photoluminescence (LTPL) data shows the presence of the deep intrinsic defect level UD-1 in addition to V4+. The nitrogen-bound exciton (NBE) luminescence is weak in heavily vanadium compensated 6H-SiC. INTRODUCTION SiC finds its application in semiconductor devices operating at high temperature, high power, high frequencies, and in harsh conditions. The availability of affordable, high quality and large diameter SI SiC substrates is critical to the successful development of new generations of SiC-based high power and high frequency devices. In this paper we report on the progress achieved at II-VI, Inc., in PVT growth of large diameter V-doped SI 6H-SiC crystals. EXPERIMENTAL DETAILS Large 6H-SiC single crystals, up to 110mm in diameter, have been grown using a scaled-up PVT [1] growth process. Growth has been carried out at temperatures between 2000°C and 2300°C in inert atmosphere at pressures ranging from 5 to 50 mm Hg. The crystals have been in-situ doped with V [2, 3], which leads to deep compensation of shallow donors or acceptors and results in a very high electrical resistivity. DISCUSSION In order to maintain crystal quality in the scaled-up process, we optimized several elements of PVT growth, including seed bonding and the expansion of crystal diameter. Achieving good thermal contact (bond) between the seed and graphite seed-holder, with
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a b c Figure 1. Cross-sections of seed bond regions. a - seed bond with small voids causing appearance of individual TDC’s. b - a large void leading to a cluster of defects. c - void-free bond leads to defect-free growth. The seed is bright green in color. the bonding layer free of voids and cracks, represents one of the major challenges in growing high quality SiC boules. The situation worsens for large diameter crystals because seed bonding becomes more difficult with increase in the seed diameter. It is known that voids in the bond layer provide escape routes for the gaseous species subliming from the seed backside and result in thermal decomposition cavities (TDC’s) propagating into the crystal bulk [4]. Figure 1 shows microphotographs of boule cross-sections with a small void, large void, and without any voids. The photographs show that in the absence of voi
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