Site-dependent donor and acceptor levels in 6 H-SiC

Abstract

The photoluminescence of N- and Al- or Ga-doped 6 H-SiC has been studied. Radiative transitions between free electrons and holes bound to acceptors in cubic-like and hexagonal-like sites are assigned. Donor-acceptor pair transitions between donor and acceptor impurities in cubic-like and hexagonal-like sites are analyzed. From studies on these transitions, the ionization energies of impurities in cubic-like and hexagonal-like sites in 6 H-SiC are estimated to be 248.5 and 239 meV for Al acceptors, 333 and 317 meV for Ga acceptors, and 155 and 100 meV for N donors, respectively. The ratios of the ionization energies of acceptors in the cubic-like sites to the hexagonal-like sites are almost constant, ≈1.04-1.05. The origin of the difference of the ionization energies of impurities in the different sites is discussed on the basis of the quantum defect model. For acceptors this is mainly caused by differences in the local dielectric constants.