Limitations of the thermally stimulated conductivity as a technique for studying the density of states ofa-Si:H

The thermally stimulated conductivity (TSC) in hydrogenated amorphous silicon has been measured for photoexcitations at various temperatures. It has been clearly demonstrated that a low-temperature (LT) peak exists in the TSC independent of photoexcitation temperature ${\mathit{T}}_{\mathit{e}}$ when ${\mathit{T}}_{\mathit{e}}$ is sufficiently low. This result indicates that recent interpretations of the LT peak in the TSC are probably incorrect, and throws strong doubt upon the validity of the recent analyses of the TSC and, thus, upon the usefulness of the density of states deduced based on such an analysis. It is shown that the structure in the TSC is correlated with that in the temperature dependence of the steady-state photoconductivity and, therefore, the TSC is probably controlled by recombination.