Electronic properties and microhardness of semiconductor alloys
Ekpenuma, Sylvester Nwabuzor
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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.