Bandwidth narrowing in N type many-valley semiconductors

The density of states is calculated for a random distribution of shallow donors in many-valley semiconductors, as well as the inverse participation ratio in the near vicinity of the Fermi energy. The N random impurities were simulated with a computer, within a diamond lattice as a host. Kohn-Luttinger donor wave function was associated with each impurity. It was found that the left energy side (or the high energy side when the effect of nonorthogonality is taken into account) of the density of states is strongly reduced to a small tail when compared to the case of neglecting many-valley effects. At the Fermi energy, the density of stares is considerably enhanced in relation to the latter case; this leads to an enhancement of the extrinsic specific heat. The inverse participation ratio varies with the impurity concentration, presenting different states which are responsible for different physical properties. An analytical calculation taking into account these effects was carried out for the sake of comparison.