IDENTIFICATION AND ACTIVATION-ENERGIES OF SHALLOW DONORS IN CUBIC SIC

Silicon carbide grown by the chemical vapor deposition process on sili con often contains high concentrations of nitrogen donors with a bindi ng energy of 54 meV as determined from photoluminescence studies. In c ontrast, the conductivity in the same samples is dominated by a heavil y compensated shallow donor with a binding energy below 20 meV. The co nventional view is that these two donors are the same. The 54 meV dono rs usually are assumed to be isolated substitutional nitrogen in regio ns of low concentration while the < 20 meV donors are believed to be n itrogen 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 p ublished results. Evidence for reassessing the conventional view is gi ven in this article and several experiments supporting the conventiona l view are reconsidered. As a result of this reconsideration, we propo se that the donors below 20 meV which dominate the conductivity are no t neutral, substitutional nitrogen in high concentration but some othe r center. D- centers and donor complexes are possible origins of this donor. The D- center appears to have many of the characteristics requi red for satisfactory modeling of this material.