First-Principles Study of Defects in GaN, AlN and Their Alloys

摘要

We employed first principles calculations with supercell approach to study various defects in AlN, GaN, InN, related wide gap semiconductors, and their alloys. For the exchange and correlation functions, we used both the standard local density approximations (or generalized gradient approximations) and time consuming HSE hybrid functional which can provide electronic band gaps that are much closer to the experimental values. The later is being used when more accurate determination of defect levels is needed. In this program, we also employed the FEFF codes, which is the software specially designed for the simulation of the x-ray absorption spectrum, to allow a direct comparison between our crystal structure models and actual measurements. We have accomplished several important results. (a) We reconfirm our earlier calculations that Mg and Be are deep acceptors in AlN by using HSE hybrid functional which does not suffer from band gap underestimation problems. (b) We calculated Al Frenkel pairs (interstitial Al and Al vacancy pairs) in AlN. Both the stability and the structure are very similar to the case of Ga Frenkel pairs in GaN that we have studied last year. We also found that the barrier for the pair to recombine is approximately 0.2 eV which is very small (similar to the case of GaN), making the pairs unlikely to be stable at room temperature. c) We studied the x-ray absorption spectrum of InN and In2O3 alloys. Special attentions have been paid to understand the source of the features in the calculated XANES.