Drift mobility in hydrogenated amorphous silicon from photoconductivity decay

Abstract

We present the results of a study of the steady‐state photoconductivity and its decay after the termination of illumination, as a function of temperature and intensity, in a‐Si:H samples produced by rf sputtering and the plasma‐enhanced chemical vapor deposition (PECVD) of silane. The electron drift mobility, deduced from the initial rate of decay of the photocurrent, appears activated, with activation energies in the range of 0.20–0.24 eV for the sputtered films and ∼0.1 eV less for the PECVD films. The activated behavior results from the interaction of photoconducting electrons with potential fluctuations, or a shoulder in the density of states below the extended state transport level. Inconsistencies in the interpretation of the drift mobility magnitudes are resolved by the proposition that a substantial fraction (>90%) of the photogenerated carries recombine very quickly only in films with a high hole μτ. In such films, only a small fraction of the photogenerated electrons contribute significantly to the steady‐state photoconductivity measured in a coplanar gap configuration.