Electronic density of states and optical spectrum of tetrahedrally bonded amorphous III-V semiconductors

Abstract

The disorder in an amorphous III-V semiconductor is described in terms of spatial variation in local density. The electronic density of states for the amorphous semiconductors are then simulated by a weighted sum of the crystalline electronic density of states (EDS) with a variation in local density. It is shown that the amorphous electronic density thus obtained is equivalent to its crystalline counterpart with the energy of each electronic state broadened by an individual broadening parameter, which is related to the degree of disorder of the amorphous semiconductor considered and the "sensitivity" of the energy of the particular state to variations in local density. The result of our phenomenological model is similar to that of Kramer's complex-band-structure calculation based on Green's-function formalism. The optical spectra for the corresponding materials are also calculated using the theoretical EDS, along with the nondirect transition model with an energy-dependent matrix element. The results are compared with available experimental data.