Poster abstract

Semiconductor alloys with varying compositions have attracted considerable interest in the last years due to their applications in microelectronic and optoelectronic devices. The electrical and optical properties of these materials are to a great extent determined by native defects such as antisites and vacancies. We present calculations of the electronic and atomic structures of neutral and charged nitrogen vacancies in Al_xGa_(1-x)N alloys using a combination of first-principles methods which enables us to treat point defects in ternary alloys on the same level as they are treated in binary compounds. The treatment of the alloys is based on the generalized quasichemical approach [1] to disorder and composition effects and a cluster expansion to account for the various configurations [2]. The point defects are modelled by supercells which are multiples of the alloy clusters. The total energy and electronic structure calculations are performed within the density functional theory and the local spin density approximation. Explicitly a pseudopotential-plane-wave code is used. We study the atomic geometry, the energetics, and the charge-dependent vacancy states for the clusters and the alloys versus cation numbers or composition x.

[1] A. Sher, M. van Schilfgaarde, A. B. Chen, and W. Chen, Phys. Rev. B 36, 4279 (1987) [2] J. W. D. Connolly and A. R. Williams, Phys. Rev. B 27, 5169 (1983)