Identification and activation energies of shallow donors in cubic SiC

Abstract

Silicon carbide grown by the chemical vapor deposition process on silicon often contains high concentrations of nitrogen donors with a binding energy of 54 meV as determined from photoluminescence studies. In contrast, the conductivity in the same samples is dominated by a heavily compensated shallow donor with a binding energy below 20 meV. The conventional view is that these two donors are the same. The 54 meV donors usually are assumed to be isolated substitutional nitrogen in regions of low concentration while the <20 meV donors are believed to be nitrogen in regions of high concentration. The most convincing evidence for this identification is the continuum of binding energies from 50 to 15 meV for SiC as a function of donor concentration compiled from published results. Evidence for reassessing the conventional view is given in this article and several experiments supporting the conventional view are reconsidered. As a result of this reconsideration, we propose that the donors below 20 meV which dominate the conductivity are not neutral, substitutional nitrogen in high concentration but some other center. D− centers and donor complexes are possible origins of this donor. The D− center appears to have many of the characteristics required for satisfactory modeling of this material.