TCS study of n- and p-channel amorphous silicon thin-film transistors

Abstract

We apply a transient current spectroscopy (TCS) to n-channel and, for the first time, also to p-channel TFTs made with a-Si:H and a-SiN x :H. The data are analysed in terms of an effective density of interface states, N i (E). We find that N i (E) has a maximum near midgap and a minimum in each half of the band gap, the lower one being less pronounced than the upper one. The TFT properties are modified by exposing the nitride to an oxygen plasma prior to the deposition of the a-Si:H film. Short exposures (t e 2 as a gate insulator. We also study the effect of bias-temperature stress (BTS) on the properties of our TFTs. Positive (negative) BTS causes a metastable increase of N i (E) predominantly in the lower (upper) half of the band gap. Our results suggest that the metastable defects but not the stable ones are caused by chemical equilibration within a defect pool.