Composition dependence of theΓ8-Γ6transition in mercury cadmium telluride: A reexamination

The composition dependence of the ${\Gamma }_8$-${\Gamma }_6$ transition in mercury cadmium telluride (MCT) has long been classified apart among all disordered alloy systems. The nonconstant bowing parameter reported in this case could only be accounted for in terms of a finite departure from the virtual-crystal approximation but was not clearly reflected in the properties of carriers and/or the characteristics of the alloys. Moreover this nonconstant bowing appears to be a unique feature of MCT. First, it departs from all reports concerning standard II-VI and III-V materials which, even for structurally disordered systems like In-Ga-As, still exhibit a constant bowing and a parabolic dependence of the fundamental absorption edge on alloy composition. Second, it is not easily reflected in many band-structure calculations. Most of the time, even if they have been performed in the light of the coherent-potential approximation (CPA), they fail to reproduce such a complicated scheme.