Anisotropic excess noise is reported for hydrogenated amorphous silico
n. The simple act of reversing the bias on small samples of a-Si:H lea
ds to startling changes in the noise. These large variations are obser
ved for samples where the excess noise features a random telegraph swi
tching (RTS) noise component in addition to 1/f noise. These samples d
isplay non-ohmic characteristics. Other samples which display no obser
vable RTS noise, however, show little change in the 1/f noise followin
g a reverse in bias. These results show that the substantial RTS withi
n 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 deposi
tion methods.