Light-induced changes of the non-gaussian 1/f noise statistics in doped hydrogenated amorphous silicon

The influence of metastable photo-induced conductance changes (the Staebler- Wronski effect) on the l/f noise power spectra of co-planar current fluctuations in n- type doped hydrogenated amorphous silicon (a-Si:H) is studied. The average magnitude and spectral slope of the 1/f noise are not altered significantly due to illumination, when measured with identical d.c. currents passing through the film before and after light exposure. The conductance noise in the annealed state is strongly non-Gaussian, which is reflected in large noise power correlation coefficients between different octaves, a noise power distribution which is much broader than the expected x² distribution and a l/f-like second spectrum. Following light exposure, the correlation coefficients decrease, the noise power distribution is well described by a x² distribution and the second spectrum becomes frequency independent. Annealing the a-Si:H film to 450 K restores the non-Gaussian statistics of the 1/f noise. The non-Gaussian noise statistics in a-Si: H are interpreted as indicating the presence of strong correlations between the inhomogeneous current filaments believed to be responsible for the current noise. The reduction in the non-Gaussian statistics upon illumination could result from an increase in the disorder at the mobility edge, decreasing the correlations between neighbouring current filaments.