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

We measure the changes induced in the 1/f(alpha) conductance fluctuation po wer spectrum of n-type alpha-Si:H in the dark after illumination by band-ga p light of intensity 0.17 W/cm(2). Initially the relative noise power decre ases by a factor of 5 over the first 100 min of exposure. For longer exposu res, the noise recovers but preferentially at higher frequencies causing al pha 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 an d Gaussian statistics, in both the annealed and light soaked states, which are in disagreement with other reports on similar material. Some of the inc rease in noise beyond the 100 min exposure is attributed to carriers intera cting with localized states that become emptied as the Fermi level drops. ( C) 1999 American Vacuum Society. [S0734-211X(99)01201-9].