ELECTRONIC STRUCTURE AND OPTICAL ABSORPTION IN NONCRYSTALLINE SEMICONDUCTORS

A procedure is proposed for calculating the continuum spectrum of amorphous semiconductors and is applied to the case of disordered germanium. By use of the observation that the short-range order characteristic of crystalline Ge is present in the amorphous phase, a band structure is constructed. The lack of long-range order is introduced through an electron-lattice coupling parameter. The spectral-weight method is then used to compute ε2(ω), and the result compares quite favorably with experiment. The calculations suggest that the observed band gap may be a sensitive test of the true atomic volume after correction for pinhole effects. It also appears that crystal momentum is a weakly conserved quantity. © 1969 The American Physical Society.