The Meyer-Neldel rule in conductivity of microcrystalline silicon

The dark conductivity (σ_d) has been measured from 300 to 440K on undoped hydrogenated microcrystalline silicon (μc-Si:H) films having different thicknesses. The carrier transport is found to be thermally activated with single activation energy (E_a) in all the samples. The E_a increases as the film thickness decreases. At the same time logarithmic of dark conductivity prefactor (σ_o) is found to follow a linear relation with activation energy, known as the Meyer-Neldel rule (MNR). Results are explained in terms of increased degree of disorder in thinner samples. Thus change in E_a with the film thickness is directly related to the density of localized states at the Fermi level in grain boundary (GB). Therefore varying the film thickness and, hence, the exponential density of states induces a statistical shift of Fermi level which gives rise to the observed MNR.