NITROGEN DONORS IN 4H-SILICON CARBIDE

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 DELTA(E(vo) (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 perpendicular-to = 0.18 m0 and m parallel-to = 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.