Electronic Structure of Heavily and Randomly Nitrogen Doped GaAs near the Fundamental Band Gap

Abstract

On increasing the nitrogen doping concentration in GaAs, states associated with isolated, paired and clustered (i.e., more complex configurations) nitrogen atoms sequentially appear, with their energy levels being resonant for the isolated center and most of the pairs and becoming bound for a couple of pairs and clusters. At a nitrogen mole concentration of x ∼ 0.1%, the shallow nitrogen bound states have merged with the GaAs band edge, which effectively gives rise to a band gap reduction, but the deeper nitrogen bound states persist as discrete levels. We study the behavior of nitrogen at this transition concentration, using various techniques (photoluminescence under selective excitation, electroreflectance, and Raman scattering), in order to gain insight into the large band gap reduction observed at all nitrogen concentrations. The validity of a few existing models proposed for explaining the large band gap reduction will be briefly discussed.