Session M18 - III-IV Nitride Semiconductors V: Theory (DMP Focused Session).
MIXED session, Wednesday morning, March 18, 1998
409A, Los Angeles Convention Center

M18.01
Electronic Structure of Nitride Alloys
Laurent Bellaiche (National Renewable Energy Laboratory)

GaN-based III-V alloys have recently attracted considerable attention due to their prospects in light-emitting device applications. Here, using large (512-1024 atom) empirical pseudopotential supercell calculations, we have investigated their optical and electronic properties. We find that the III-V nitride alloys, and especially the anion-mixed nitride alloys (GaAsN and GaPN), are different from most isovalent alloys in that: (1) they exhibit anomalous optical properties: the band-gap bowing coefficient is composition-dependent and large, and the interband transition probability is composition-dependent and weak. (2) Local clustering of atoms in these alloys leads to significant changes in the optical properties. (3) Long-range CuPt ordering leads to a very large decrease of the band gap making the anion-mixed alloys semimetallic. All of these anomalies reflect wavefunction localization and isovalent impurity levels, and are induced by large atomic relaxation. This shows that simple and often used approximations (e.g., the virtual crystal approximation) are inadequate to describe the electronic structure of the III-V nitride alloys. Our calculation reproduces very well the experimental band gaps of nitride alloys films.