Hopping transport in a-Ge and a-Si

Abstract

An unreasonably large pre-exponential factor for conductivity is an old problem with interpretations of hopping transport data on a-Si and a-Ge. It is shown that an appropriate concave density of states eliminates this problem, and explains some other experimental features. Results of a percolation theory for exponential densities of states are presented. Comparison with experiments on high-density Si and Ge gives Bohr radii of 6 and 13 Å and values for N(E _F) of 7 × 10²⁰ and 2 × 10¹⁸ eV⁻¹ cm⁻³, respectively.