One‐dimensional lucky‐drift model with scattering and movement asymmetries for impact ionization in amorphous semiconductors

A lucky-drift (LD) model for impact ionization has been recently successfully used to account for avalanche phenomenon in amorphous semiconductors. This model however leads to the dependence of the impact ionization coefficient on the sample thickness. However such dependence has not been confirmed experimentally. Recently LD model has been improved taking into account the scattering and movement asymmetry of charge carriers in the applied electric field. As a result, the impact ionization coefficient was obtained independent on the sample thickness. We apply the improved LD model to study the field dependence of the impact ionization coefficient in a-Se, a-Si:H and Ge2Sb2Te5. We show that even in one-dimensional formulation of the improved LD model the agreement between theoretical results and experimental data evidenced in a-Se is better than that in the formulation with scattering and movement symmetry. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)