ELSEVIER Computational Materials Science 3 (1995) 393-401 COMPUTATIONAL MATERIALS SCIENCE Band structure calculations of Ga, _,A1,As, GaAs, _-x P, and AlAs under pressure H. Aourag, M. Ferhat ‘, B. Bouhafs, N. Bouarissa, A. Zaoui, N. Amrane, B. Khelifa ’ zyxwvutsr Computational Materials Science Laboratory, Physics Department, Vrkersity of Sidi-Bel-Abbes, Sidi-Bel-Abbes 22000, Algeria Received 2 May 1994; revised 5 August 1994; accepted 10 September 1994 zyxwvutsrqponmlkjihgfedcbaZYX Abstract The band structure of Ga,_,Al,As and GaAs_,P, cation and anion alloys respectively are calculated within the virtual crystal approximation using an adjusted empirical pseudopotential scheme, which incorporates compositional disorder as an effective potential. It is shown that the present theory, which is free from any additional parameter, satisfactorily produces the band-gap bowings. The effect of alloying was correlated to the effect of positive and negative pressure in AlAs. We have also calculated the variation of the ionicity of these alloys under pressure, the results are linked to the high pressure phase transitions. 1. Introduction Semiconductor alloys provide a natural means of tuning the magnitude of the forbidden gap and other material parameters so as to optimize and widen the applications of semiconductor devices. With the advent of small-structure systems, such as quantum wells and superlattices, the effects of alloy compositions, size, device geometry, doping and controlled lattice strain can be combined to achieved maximum tunability. Although a theory capable of interpolating al- loy band structure between those of the pure constituent compounds is desirable, no suffi- ciently detailed method to accomplish this end currently exists. Many prior theories [l-13] have 1 Present address: Laboratoire d’optique, Institut de Physique, Universitk d’Oran Es-stnia, 31100, Algeria. been designed to predict only trends of specific band quantities, such as the band gaps [l-12] and the effective masses [13] at band edges. The virtual-crystal approximation (VCA) is es- sentially the only method that has been used for detailed alloy band-structure calculations. VCA treats an alloy as a perfectly periodic crystal with an average potential at each sublattice site and does not include in lowest order the effects of aperiodic fluctuations in the crystal potentials. When aperiodic part of the potential is suffi- ciently small, perturbation theory can be applied to the VCA results to account for some disorder- induced effects [12,14]. Even in the few cases in which attempts were made to treat realistic sys- tems, the results were not completely satisfactory [12]. There is no satisfactory theory that is based on a well defined set of potentials and predicts a wide range of phenomena, such as the alloy con- centration variation of band energies, effective 0927-0256/95/$09.50 0 1995 Elsevier Science B.V. All rights reserved XSDI 0927-0256(94)00080-8