1/f Noise in doped and undoped amorphous silicon

We measured the spectrum of conductance fluctuations in n-type, p-type, and undoped hydrogenated amorphous silicon (a-Si:H) as a function of temperature. In general, the spectra can be fit to a power law, 1/f(alpha), although in the p-type and undoped samples deviations from a strict power law occur. For n-type and p-type samples, the noise magnitude increases with temperature by approximately a factor of 5 from 295 to 450 K. The slope parameter, alpha, also increases with temperature in the p-type samples from near unity to 1.4 but not in the n-type sample where it remains near 1.05 independent of temperature. The undoped sample could be measured only over a limited range of elevated temperatures, but alpha does trend larger. The undoped and lightly doped material have similar noise levels but larger p-type doping reduces the noise by two orders of magnitude. Correlation measurements indicate the 1/f noise is Gaussian for all samples. However, intermittent random-telegraph noise is observed in n-type material. (C) 2000 Elsevier Science B.V. All rights reserved.