VANADIUM RELATED NEAR-BAND-EDGE ABSORPTION-BANDS IN 3 SIC POLYTYPES

Low-temperature optical absorption experiments have been performed on a variety of n-type, p-type, and high-resistivity silicon carbide samp les, including the polytypes: 4H, 6H, and 15R. These experiments revea l a set of absorption band close to the band edge with a fine structur e depending upon the polytype. Each sample exhibits a spectrum with th e number of lines corresponding to the number of inequivalent substitu tional lattice sites contained in the polytype. A correlation of these lines with the neutral vanadium (2)E-->T-2(2) intracenter transition indicates that the initial state for the near-band-gap absorption line s is the (2)E State of the 3d(1) configuration of vanadium. The near-b and-edge absorption Tines were interpreted as due to an exciton bound to a vanadium donor with an electron occupying an atomic-like d state. The position of the vanadium acceptor level was estimated to be, at m ost, 250 meV from the conduction band for the cubic site in 6H SiC. (C ) 1995 American Institute of Physics.