Electronic Structure Evolution of Dilute III–V Nitride Alloys

This chapter gives an overview of the modern empirical pseudopotential method (EPM) and its application to the dilute III-V nitrides. Detailed analysis of super cell models of the nitrides supports the theory of alloy formation involving the interactions between nitrogen-induced localized cluster states (CS) with many Perturbed Host States (PHS). Super cell calculations of small nitrogen clusters show that comparatively few nitrogen's can introduce very deep, below band gap states, and thus details of nitride alloy nano structure are fundamental to determining nitride alloy properties. Pseudo potential modeling has also provided several predictions to be checked by experiment. The EPM distinguished itself from the phenomenological Band Anti-Crossing (BAC) model which ignores CS beyond the isolated nitrogen and uses a single host state, thus failing to explain the phenomena associated with the existence of numerous local environments in the alloy. The existence of CS is most strongly evident in photoluminescence (PL), where these states appear pinned in energy as a function of nitrogen concentration, and in pressure dependent measurements, where their distinct non-host-like (or “deep level”) nature is immediately apparent.