Electrical conductivity and Meyer–Neldel rule: The role of localized states in hydrogenated amorphous silicon

The Meyer–Neldel rule (MNR) has been observed in recent calculations of the electrical conductivity of hydrogenated amorphous silicon. To elucidate the origin of this effect, we have performed comparative studies on crystalline Si and non-hydrogenated a-Si. We find that the MNR is not present in the crystal, and is present in a-Si. This suggests that the existence of localized states and the energy dependence of the electron-lattice coupling for these states is an essential feature of the MNR for amorphous phases of silicon.