Abstract
Discrete series of lines have been observed for many years in donor-acceptor pair (DAP) spectra in 3C-SiC. In this work, the splitting of both type-I (N-B, P-Al) and type-II (N-Al, N-Ga) DAP spectra in 3C-SiC has been systematically investigated by considering the multipole terms. For type-I spectra, in which either N or B substitutes on C sites or P and Al replace Si, the splitting energy of the substructure for a given shell is almost the same for both pairs. For type-II spectra, in which N is on the C site while Al and Ga acceptors replace Si, we find that, when compared with literature data, the splitting energy for a given shell is almost independent of the identity of the acceptor. For both type-I and type-II spectra, this splitting energy can be successfully explained by the octupole term V-3 alone with k(3)=-2x10(5) angstrom(4) meV. Comparing the experimental donor and acceptor binding energies with the values calculated by the effective-mass model, this suggests that the shallow donor (N, P) ions can be treated as point charges while the charge distribution of the acceptor ions (Al, Ga, B) is distorted in accord with the T-d point group symmetry, resulting in a considerable value for k(3). This gives a reasonable explanation for the observed splitting energies for both type-I and type-II DAP spectra.