Electronic structure of point defects in semiconductor alloys

Abstract

A simplified tight-binding approach based on the coherent potential approximation (CPA) formalism is presented for the host electronic structure of semiconductor alloys (e.g. Ga_1-xAl_xAs). Several schemes to locate the gap level due to point defects are discussed. In particular, a novel scheme is introduced: the deep level approximation (DLA). It is pointed out that the vacancy results in the CPA are identical to the simpler virtual crystal approximation (VCA). In addition, the electronic band structure of SixGe_1-x alloys is presented using a non-orthogonal tight-binding approach, namely the extended Hückel theory (EHT). Preliminary calculations of the dependence of the band gap on concentration are also presented.