Electronic properties and microhardness of semiconductor alloys
Ekpenuma, Sylvester Nwabuzor
The results of theoretical investigations of the properties of semiconductor alloys are presented. First, the effects of alloy disorder on the electronic properties of four III-V quaternary alloys are investigated using an extension of the bonding-antibonding coherent potential approximation (CPA) formalism. The alloys considered have two disordered sublattices so that their chemical formulae have the general form AxBi_a;CyDi_y. Some alloys of this type are used in optoelectronic devices. Results are presented for the densities of states, the self energies, and the band gap bowing for the alloys Ala.Gai_a.AsyPi_y, AliGai_xAsySbi_y, Gaa:Ini_a:AsyPi_y, and Gaa.Ini_a:AsySbi_y. Comparisons of these CPA results are made with Virtual Crystal Approximation (VGA) results, and with experimental data where available. Second, the electronic properties of the II-VI alloy Hgi_a._yCda.ZnyTe are calculated. To do this, an extension is made of a previously developed CPA formalism for quaternary alloys of the form Ai_a._yBa;CyD to include spin-orbit coupling in the input bandstructures. This study is motivated by recent results that indicate improvement in the structural properties of the widely used infrared material Hgi_a.Cda.Te on the addition of few per cent zinc. Results for the effective masses and band gap variations with compositions are presented. Lastly, a formalism for the calculation of the alloy microstructural hardness is developed. This formalism combines a solid-solution hardening model, an analysis of the composition dependence of critical stress, and an empirical relation for the alloy hardness. Results for the hardness variations with composition for the II-VI alloys Cdi_a;Zna:Te, Hgi_a.Cda.Te, Hgi_a;ZnxTe, and Hgi_a;_yCda;ZnyTe are presented and compared with available data. The results for Hgi_a:-yCda;ZnyTe verify improved structural properties of Hgi_a:Cda.Te on the addition of zinc. Results for the composition dependence of hardness are also presented for the III-V alloys InxGai_a;As, Gaa;Ini_a.Sb, Ala.Ini_a:Sb, Gaa;Ini_a;P, and Ala;Ini_a.As and compared with experimental data where available.