Thickness dependent conductivity of n-type hydrogenated amorphous silicon

We report a thickness dependent conductivity for nominally homogenous films grown from glow discharges of 0.05% phosphine in silane. Measurements are presented for conductance parallel and perpendicular to the film plane for thicknesses from 0.1 to 3.8 μm. Our results are successfully modeled by two parallel layers: 1) a low conductivity surface or interface layer about 0.2 μm thick with an activation energy of 0.4 eV near room temperature, and 2) a bulk layer with a higher conductivity and a 0.2 eV activation energy. If we interpret the 0.2 μm thickness as a Debye screening length, we deduce a density of states of about 1016 cm-3eV-1 near the fermi level. © 1980.