ELECTRONIC CONDUCTIVITY OF HYDROGENATED NANOCRYSTALLINE SILICON FILMS

A heteroquantum-dots (HQD) model for hydrogenated nanocrystalline silicon films (nc-Si:H) is proposed. The main features of our model are as follows. (i) the nanocrystalline grains and the amorphous counterparts in which they are embedded have very different band gap and band structures. As a result, they form heterojunctionlike structures in the interface regions, where the band offset effects dramatically reduce the activation energy and the grains act like quantum dots. (ii) In the presence of an external field, the activated electrons in the quantum dots conduct via quantum tunneling through the interface barriers. By means of the HQD model, we have identified the conduction of nc-Si:H as a thermal-assisted tunneling process. Our results show that there are two distinct regimes for the conductivity of nc-Si:H: (i) the low-temperature regime, where there is a simple activation energy Delta E; (ii) the high-temperature regime, where Delta E is effectively enhanced by the temperature effect of the electronic tunneling in the nanoscale particles. The theory is in good agreement with the experiments. (C) 1995 American Institute of Physics.