Evidence for narrow mid-gap defect band in amorphous selenium from low-temperature anomalous electrical properties

摘要

Electrical properties of amorphous selenium films (similar to 2.1 mu m thick) were investigated at different temperatures between 225 K and room temperature. The samples were prepared using thermal evaporation method. The capacitance and conductance were measured and analyzed to study their changes with temperature and voltage. An anomalous peak is found in the conductance- and capacitance-temperature curves at similar to 245 K. The phenomenon can be linked to the distribution of defect states near the mid-gap and the change in 'effective transport energy' at which the transport takes place.