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

The transport and recombination mechanism of microcrystalline silicon films, $\mathrm{\mu c-}\mathrm{Si:H}$ is determined by specific defects, Si dangling bonds, and localized bandtail states. In spite of the complex heterogeneous structure, many properties of these films can be described in terms of models that have been developed for hydrogenated amorphous silicon, $\mathrm{a-}\mathrm{Si:H}:$ (1) In the high-temperature regime $\text{(T>200\hspace{0.05em}}\mathrm{K}\mathrm{),}$ the conductivity obeys a Meyer–Neldel relationship which suggests a statistical shift of the Fermi level due to bandtail states. (2) At low temperature $\text{(T<50\hspace{0.05em}}\mathrm{K}\mathrm{),}$ the photoconductivity appears to be due to hopping transport in bandtail states and the recombination occurs by distant pair recombination. The discussion addresses the question of the assignment of the defect and bandtail states to different regions in the heterogeneous structure of the films.