Amphoteric properties of substitutional carbon impurity in GaN and AlN

Electronic structure and formation energies of substitutional carbon impurities in hexagonal GaN and AlN were studied by quantum molecular dynamics. Substitutions on both cation and anion sites were considered. C-cation is a shallow donor, while C-N is a shallow acceptor. A DX-like configuration is metastable for C-Ga and C-Al(0), and stable for C-Al(-). The solubility of carbon is excellent, but it is accompanied by efficient self-compensation of carbon accepters by carbon donors. This is due to two factors: (i) the large energy gain induced by electron transfer from C-cation to C-N, which is close to the band gap energy, and (ii) the large binding energy (similar to 1 eV) of nearest neighbor C-cation(+)-C-N(-) pairs. (C) 1996 American Institute of Physics.