The transition from shallow to deep centers, as a function of pressure or alloying, was investigated for O and Si donors on the basis of first-principles total-energy calculations. The stability of the localized deep state (DX center) was found to depend upon interactions between the impurity, and third-nearest neighbor atoms, which occurred at different positions in the zincblende and wurtzite phases. Such DX-center formation was suppressed in the zincblende phase, as well as that of Si donors. The results supported the identification of O as being the unintentional dopant in n-type GaN, and cast new light on the driving force for DX formation.

C.G.Van de Walle: Physical Review B, 1998, 57[4], R2033-6