Bandtails and defects in microcrystalline silicon (mu c-Si : H)

The transport and recombination mechanism of microcrystalline silicon films , mu c-Si:H is determined by specific defects, Si dangling bonds, and local ized bandtail states. In spite of the complex heterogeneous structure, many properties of these films can be described in terms of models that have be en developed for hydrogenated amorphous silicon, a-Si:H: (1) In the high-te mperature regime (T>200 K), the conductivity obeys a Meyer-Neldel relations hip which suggests a statistical shift of the Fermi level due to bandtail s tates. (2) At low temperature (T<50 K), the photoconductivity appears to be due to hopping transport in bandtail states and the recombination occurs b y distant pair recombination. The discussion addresses the question of the assignment of the defect and bandtail states to different regions in the he terogeneous structure of the films. (C) 2000 American Vacuum Society.