The statistical shift of the chemical potential causing anomalous conductivity in hydrogenated microcrystalline silicon

Abstract

The behavior of the electrical conductivity in hydrogenated microcrystalline silicon (μ c-Si:H) that is frequently observed is explained by considering the statistical shift in the chemical potential as a function of the crystalline fraction (Xc), the dangling bond density (N db), and the doping density (Nd). Our model shows that temperature dependent dc conductivity measurements above room temperature can be very well explained by (unintentional) micro doping of μ c-Si:H. It is shown that the statistical shift in the chemical potential (μ) is influenced mostly by the ratio between Nd and Ndb. It is concluded that the anomalous dependence of the apparent activation energy (Ea) and the apparent exponential prefactor (σ0) on Xc can be explained by behavior of μ, that can be induced by a change in this ratio between Nd and Ndb. We used an effective medium approximation for the electron density of states (DOS) of μc-Si:H. The DOS is calculated as a weighted sum of the DOS of c-Si and the DOS of a-Si:H, parameterized by Xc, Ndb, and Nd. The conductivity is deduced assuming a single dominant conduction path above the conduction edge of a-Si:H