Determination of the gap state density differences in hydrogenated amorphous silicon and Si/Ge

Time resolved photo- and thermoelectric effects (TTE) were used to simultaneously determine the thermal diffusivity, carrier lifetimes, carrier mobilities, trap levels and trap level densities in crystalline and amorphous Si (a-Si:H) and Si/Ge (a-Si/Ge:H) samples. In particular, gap density of state differences can be obtained from the decay of the ambipolar charge distribution, i.e. stage II of the TTE transients. This type of spectroscopy has been applied in particular to dark and light soaked a-Si:H samples and indeed large differences are observed.