Anisotropic excess noise within a-Si:H

Anisotropic excess noise is reported for hydrogenated amorphous silicon. The simple act of reversing the bias on small samples of a-Si:H leads to startling changes in the noise. These large variations are observed for samples where the excess noise features a random telegraph switching (RTS) noise component in addition to 1/f noise. These samples display non-ohmic characteristics. Other samples which display no observable RTS noise, however, show little change in the 1/f noise following a reverse in bias. These results show that the substantial RTS within a-Si:H is associated with anisotropic effects, such as a graded band gap. This behaviour is observed in a-Si:H material grown by both the plasma enhanced chemical vapour deposition and the rf sputtered deposition methods.