Impact ionization process in amorphous selenium

Abstract Temperature and electric field dependences of impact ionization rates α (for electron) and β (for hole) in a-Se have been determined by photo-multiplication measurements on sandwich type photo-cells. It has been found that both α and β decrease with decreasing temperature, in contrast to those of crystalline semiconductors. The results obtained at room temperature have been fitted to those calculated by Baraff's theory taking the geminate recombination process into account. The observed temperature dependences suggest characteristic mechanisms of the impact ionization process in this material.