Effect of high intrinsic ion concentrations on electron energies in solid solutions of III–V and II–VI semiconductors

Abstract

In solid solutions of III–V and II–VI semiconductors, the energy gap is observed to show a quadratic “bowing” behavior in its dependence on solution concentration, and this bowing is large (1–3 eV) for most of the systems which have been observed. The most detailed studies have been of the (GaP)1−x(ZnSe)x system. In this system and for fairly dilute solutions (x or (1 − x) ⩽ 0.12), the energy gap deviates from quadratic behavior, the deviation (a further shrinking of the gap) varying as the square root of the concentration for x and 1 − x ⩽ 0.05. As the concentration fraction is increased above 0.06, the deviation decreases and eventually vanishes for values of x and 1 − x ≳ 0.12. Qualitatively similar behavior is also seen in the GaP-ZnS and GaAs-ZnSe systems. This behavior is discussed in terms of available theoretical treatments of the effects of high ion concentrations on the electron energies. High ion concentrations are expected to lead to decreased electron energies for a given electron state as well as to tailing of the densities of states into the gap, in qualitative agreement with observation.