Post-transit photocurrent analysis of the distribution of localized states in a-Si:H and its alloys

The sandwich-cell sample geometry that is used for measuring the transient photocurrents in traditional time-of-flight (TOF) experiments in amorphous semiconductors, can also be used well beyond the TOF transit time to measure the emission of charge carriers from deep traps. A density-of-states profile can then be calculated from the emission current, provided deep retrapping or random energy fluctuations do not dominate the response. Hydrogenated amorphous silicon and its alloys provide a full rang of examples for; the possibilities and problems of the technique.