Effect of light exposure on 1/f noise in a-Si:H

We measure the changes induced in the 1/f(alpha) conductance fluctuation power spectrum of n-type alpha-Si:H in the dark after illumination by band-gap light of intensity 0.17 W/cm(2). Initially the relative noise power decreases by a factor of 5 over the first 100 min of exposure. For longer exposures, the noise recovers but preferentially at higher frequencies causing alpha to decrease from 1.1 in the annealed state to between 0.8 and 0.9 after 60 h of illumination. Also after long exposures, the spectrum does not fit a simple power law but has additional weight at higher frequencies. Other aspects are typical of 1/f noise, a linear dependence on applied current and Gaussian statistics, in both the annealed and light soaked states, which are in disagreement with other reports on similar material. Some of the increase in noise beyond the 100 min exposure is attributed to carriers interacting with localized states that become emptied as the Fermi level drops. (C) 1999 American Vacuum Society. [S0734-211X(99)01201-9].