AN EXPLORATORY-STUDY OF THE CONDUCTION MECHANISM OF HYDROGENATED NANOCRYSTALLINE SILICON FILMS

By using the ultrahigh vacuum plasma enhanced chemical vapor depositio n system to prepare nc-Si:H films with high conductivity, the experime ntal results show that the conductivity of nc-Si:H films increases wit h 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 conduct ivity sigma(c) of crystallites and sigma(i) of the interface conductiv ity, respectively. Otherwise, we found that there existed two structur e phase change point results from the effective-medium theory calculat ed for the materials of silicon films. The results suggest that the hi gh conductivity of nc-Si:H films results mainly from the crystallites, and moreover, the interface region may serve as insulator layers. Thu s, we may consider that the crystallites in nc-Si:H films act as quant um dots. In this paper, we present a heteroquantum dot tunneling model to discuss the transport process for the nc-Si:H films. Our calculate d results agree very well with the experimental conductivity data for nc-Si:H films. (C) 1997 American Institute of Physics.