On the preparation of vanadium doped PVT grown SiC boules with high semi-insulating yield

Different approaches to prepare SiC crystals with high semi-insulating yield and homogeneous electrical properties by adding a vanadium source in PVT SiC bulk growth are investigated. Up to four different compensation regimes are formed during SiC bulk growth depending on the concentration of other incorporated impurities. Vanadium doping leads to semi-insulating SiC regimes with thermal activation energies of either about 900meV or about 1.7meV as measured with temperature-dependent Hall effect. A yield of semi-insulating material of 80% of the boule has been achieved by a doping technique utilizing an inner container placed inside the crucible. The yield was limited only by the high initial nitrogen incorporation which exceeds the solubility limit of vanadium in SiC of 4 x 10(17) cm(-3) especially in the early stages of growth. Using vanadium/boron co-doping, thermal activation energies of about 1.7eV are found. But in this case the yield is restricted to 40% maximum due to the time-dependent incorporation of vanadium, boron, and nitrogen. Finally, measurement techniques to observe the V3+ and V5+ concentration in the crystal are presented which allow direct determination of the compensation regime at different stages of growth. (C) 2003 Elsevier Science B.V. All rights reserved.