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We report on the identification of molybdenum trace impurities in commercial 6H-SiC substrates by conventional and optically detected electron spin resonance (ESR, ODESR) and magnetic circular dichroism (MCD) absorption techniques. The two impurity charge states Mo(exp4+) (4d(exp 2)) and Mo(exp 3+) (4d( exp 3) are identified. Consequently, this impurity is electrically active as a deep level acceptor state. In addition we observe the 3.A2 -> 3.T2 crystal field absorptions of Mo(exp 4+) (4d(exp 2)) in the spectral range 1.1-1.25 eV. The consequences of the present findings, for the use of Mo as an electrical contact material, are pointed out.

Nominally undoped zinc-blende polytype 3C-SiC single crystals have been studied by conventional electron-spin resonance (ESR), by the magnetic circular dichroism (MCD) absorption technique, and by optically detected ESR via the MCD (MCD-ESR). Apart from the dominant ESR signal ascribed to residual boron acceptors, an anisotropic spectrum with many fines is observed near liquid-He temperatures. It collapses into a hyperfine octet for H (111). This spectrum is identified as the anisotropic 2E ground-state resonance of V high4plus (3d high1) on the cubic Si site in 3C-SiC. Above 15 K this spectrum disappears and an isotropic hyperfine octet appears. It is interpreted as the motionally averaged spectrum of the anisotropic V high4plus spectrum. The data are analyzed in terms of Ham's theory of the dynamic Jahn-Teller effect for a high2 E state. A sharp optical line at 6681 cm high-1 has been found in MCD absorption. On this line the MCD-ESR of V high4plus is observed, which identifies the l ine as being related to V high4plus. It is interpreted as the zero-phonon line of the V high4plus high2 E about high2 T sub2 crystal-field transition.

Electron spin resonance (ESR) of silicon-substitutional vanadium in its neutral V (exp 4+)(ind Si) (3d (exp 1)) state has been observed in cubic bulk 3C-SiC single crystals. By photo-ESR the position of the (0/+) deep donor level of vanadium could be located at E (ind V)+1.7eV. Using this level as common reference in 3C-SiC and 6H-SiC, the valence-band discontinuity in the 3C-SiC/6H-SiC interface is predicted as Delta E (ind V)=0.l eV, with the valence-band of 3C-SiC lying lower in energy. We also offer an explanation for the absence of intra-3d-shell infrared luminescence of V (exp 4+) (3d (exp 1)) in 3C-SiC.