Light-induced metastable defects or light-induced metastable H atoms in a-Si:H films?

摘要

In hydrogenated amorphous silicon (a-Si:H) films,the increase of the metastable defect density under high-intensity illumination is usually described by an empirical two-parameter stretched-exponential time dependence (characteristic time tau )_SE and dispersion parameter beta ).In this study,a clearly different (one-parameter) analytic function is obtained from a microscopic model based on the formation of metastable H (MSH) atoms in a-Si:H films.Assuming that MSH atoms are the only mobile species,only three chemical reactions are significant: MSH are produced from doubly hydrogenated (SiH HSi) configurations and trapped either at broken bounds or Si-H creation (LIC) of defects.Competition between trapping sites results in a saturation of N(t) at a steady-state value N_SS.A one-parameter fit of this analytical function to experimental data is generally good,indicating that the use of a statistical distribution of trap energies is not necessary.