Materials Chemistry and Physics 77 (2002) 507–510 Band structure of III–V ternary semiconductor alloys beyond the VCA A. Bechiri a , F. Benmakhlouf a , N. Bouarissa b,∗ a Physics Department, University of Tebessa, 12002 Tebessa, Algeria b Physics Department, University of M’sila, 28000 M’sila, Algeria Received 4 September 2001; received in revised form 9 October 2001; accepted 20 January 2002 Abstract The band structures of some zincblende III–V semiconductor alloys are calculated beyond the virtual crystal approximation (VCA) using the empirical pseudopotential method (EPM). Our results show that the calculated optical bandgap bowing parameter agree with the experiment only when going beyond the VCA. We also found that the direct bandgap (Ŵ → Ŵ) bowing factor becomes generally larger on going from alloys with small lattice mismatches to those with larger ones. © 2002 Elsevier Science B.V. All rights reserved. Keywords: Zincblende; Virtual crystal approximation; Empirical pseudopotential method Semiconductor alloys provide a natural means of tuning the magnitude of the forbidden gap so as to optimize and widen the applications of semiconductor devices. The III–V semiconductor alloys have opened up new generations of device applications during the last few decades [1] by dra- matically increasing the possibilities for engineering the material properties. Recently, there has been an increasing interest in the electronic properties of the III–V semiconductor alloys and consequently in their electro-optical applications as high- efficiency light-emitting diodes and high-speed switching devices [1–6]. The bandgap energy is known to be one of the most impor- tant device parameters because it is strongly connected with the operating wavelength of the opto-electronic devices. To this purpose the dependence of the fundamental energy gap on the alloy composition assumes particular importance. In the treatment of alloy problems, the material parame- ters are normally derived from those of the endpoint com- pounds in terms of a simple interpolation procedure. The simplest approximation for the electronic structure of alloys is the virtual crystal approximation (VCA) in which the alloy potential is replaced by the concentration weighted av- erage of the constituent potentials while neglecting compo- sitional disorder effects. However, recent experimental and theoretical studies on several semiconductor alloys indicate that the VCA breaks down whenever the mismatch between ∗ Corresponding author E-mail address: n bouarissa@yahoo.fr (N. Bouarissa). the electronic properties of the constituent atoms exceeds a certain critical value [5–8]. Generally, this discrepancy is attributed to the compositional disorder effect not taken into account in the VCA [5,8]. This has provoked an interest in understanding bowing factors, i.e. account for the deviation from VCA in terms of the properties of the constituent compounds. In the present study, we have carried out the bandgap calculations on various III–V semiconductor alloys using the empirical pseudopotential method (EPM) within the VCA where the effects of compositional disorder are in- cluded in the calculations. Our objective is to see how the compositional disorder affects the electronic band structure of III–V semiconductor alloys when going from small to large lattice mismatches and to show the dependence of the optical bandgap bowing factor on the lattice mismatch. In the EPM, the crystal potential is represented by a lin- ear superposition of atomic potentials, which are modified to obtain good fits to the experimental direct and indirect bandgaps. Further details are presented by Cohen and Che- likowsky [9]. The method of optimization of the empirical pseudopotential parameters used in the present study is the non-linear least squares method [10]. The experimental en- ergy bandgaps along the principal symmetry lines used in the fitting procedure are listed in Table 1, whereas the ad- justed local pseudopotential form factors (in Ry) together with the lattice constants (in atomic units) of binary semi- conductors of interest are presented in Table 2. For the ternary semiconductor alloys of the form A 1-x B x C, the symmetric and antisymmetric form factors 0254-0584/02/$ – see front matter © 2002 Elsevier Science B.V. All rights reserved. PII:S0254-0584(02)00124-4