An exploratory study of the conduction mechanism of hydrogenated nanocrystalline silicon films

By using the ultrahigh vacuum plasma enhanced chemical vapor deposition system to prepare nc-Si:H films with high conductivity, the experimental results show that the conductivity of nc-Si:H films increases with decreasing the mean grain size of films. Hence, there exists a small size effect on the conduction process. Based on the experimental data, we used the effective-medium theory to calculate the partial conductivity sigma(c) of crystallites and sigma(i) of the interface conductivity, respectively. Otherwise, we found that there existed two structure phase change point results from the effective-medium theory calculated for the materials of silicon films. The results suggest that the high conductivity of nc-Si:H films results mainly from the crystallites, and moreover, the interface region may serve as insulator layers. Thus, we may consider that the crystallites in nc-Si:H films act as quantum dots. In this paper, we present a heteroquantum dot tunneling model to discuss the transport process for the nc-Si:H films. Our calculated results agree very well with the experimental conductivity data for nc-Si:H films. (C) 1997 American Institute of Physics.