Spatial and energetic profiling of defects in thin-film silicon

Abstract

The calibration of the density of states (DOS) obtained from transient photocurrent (TPC) measurements on PECVD hydrogenated amorphous silicon (a-Si : H) over a wide temperature range is investigated. It is shown that by including a lumped empirical correction to the temperature dependence of parameters such as the free-carrier mobility and capture coefficient, somewhat improved consistency in the DOS calculations may be achieved. The onset of trap saturation is considered as a possible reference point for calibration. Significant differences in the TPC DOS in a-Si : H when using either red or green laser pulse excitations are reported, and are attributed to spatial variations in the defect distribution through the film. Metastable defects produced by exposure of one side of the film to strongly absorbed light are correlated with an increased DOS when probed with the green laser from the same side.