The Staebler–Wronski effect and the thermal equilibration of defect and free carrier concentrations

Abstract

Light-induced changes in the photo-, σph, and dark, σd, conductivities of undoped hydrogenated amorphous silicon (a-Si:H) and amorphous silicon–carbon are investigated as functions of deposition and measurement temperature. Previous work described the temperature dependence of the annealed state σph and σd of a series of intrinsic a-Si:H materials deposited over a range of substrate temperatures, 200 °C<Ts<380 °C, and a thermal equilibrium framework for the high temperature behavior of the relationship between concentrations of dangling bond defects (DBs) and free carriers. The annealed-state results are extended to the light-degraded state where elevated temperatures ensure equilibration of the free carrier and DB concentrations as suggested by the thermal equilibrium framework. Both σd and σph in the light-degraded-equilibrium state decrease compared to the annealed state while the ratio, σd/σph, remains unchanged. From this result, relationships between the Fermi level and the ratio of positively and negatively charged DBs are derived in terms of the thermal equilibrium framework equations.