Trace impurities of vanadium in Lely-grown silicon carbide single crystals have been detected by their strong, polytype-specific photoluminescence in the 1.3-1.5 mym near-infrared spectral rang, as well as by infrared absorption. A high 0/A high-, and possibly also as a deep donor. The role of vanadium as minority-carrier lifetime killer in SiC-based optoelectronic devices is suggested from these data

Hall-effect and infrared-absorption measurements are performed on n-type 4H-SiC samples to investigate the energy positions of the ground state and the excited states of the nitrogen donor in the 4H polytype of silicon carbide. Two electrically active levels (Hall effect) and three series of absorption lines (infrared spectra) are assigned to two nitrogen donor species which substitute on the two inequivalent lattice sites (h,k) in 4H-SiC. Valley-orbit splitting of the ground-state level of the nitrogen donors on hexagonal sites (h) is found to be equal to ΔEvo(h)=7.6 meV. It is shown that the energy position of excited states of both nitrogen donors can be calculated by the effective-mass approximation by assuming anisotropic effective masses m⊥=0.18m0 and m∥=0.22m0. The influence of the two inequivalent lattice sites on the values of ionization energy and valley orbit splitting of the nitrogen donor ground-state levels is discussed.

Hall effect and infrared absorption measurements of n-type silicon carbide of the 6H polytype are employed to investigate the energy position of the ground state and excited states of the nitrogen donor. A donor model is proposed that assigns four series of absorption lines to electronic transitions of three donor species residing at three inequivalent lattice sites (h,k1,k2). A valley-orbit splitting of 12.6 meV is determined for donors on the hexagonal site h. For 2p0, 2p±, 3p0, and 3p± excited states, the effective-mass approximation is found to hold within experimental errors assuming a transverse and longitudinal effective electron mass of m⊥=(0.24±0.01) m0 and m∥=(0.34±0.02) m0, respectively.

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