Effects of disorder on the electronic density of states of III-V compounds

We investigate the effects of two types of disorder on the electronic density of states of III-V semiconductors using simple tight-binding models and the empirical pseudopotential method. For the first type of disorder we consider a stoichiometric system with fourfold coordination, all bonds satisfied, variations in the bond lengths and angles, and only unlike-atom bonds. The second type of disorder includes the properties of the first with the addition of like-atom bonds. These two types of disorder are studied explicitly by taking GaAs as a prototype and making various GaAs structures using the atomic positions of certain crystal structures with short-range disorder. These structures are crystals; however, they have atoms in the primitive cells arranged in varying fashions. A comparison of the trends observed in the densities of states with the inclusion of different types of disorder reveals valuable information concerning the relationship of the structural nature of an amorphous system to its density of states. We present a model of the density of states of our amorphous prototype GaAs, for each type of disorder, which we believe would be consistent with some of the present experimental radial-distribution-function data. The effects of these types of disorder are discussed in general, and hopefully they will be useful in identifying specific types of disorder in amorphous samples.