Investigating Hydrogen Glass Dynamics in Amorphous Germanium and Amorphous Silicon-Germanium Alloys*

A hydrogen glass model has successfully accounted for stretched exponential relaxation (SER) of the conductivity and non-Gaussian 1/f noise in hydrogenated amorphous silicon (a-Si:H) thin films, in agreement with hydrogen diffusion studies. We have recently reported non-Gaussian 1/f noise in hydrogenated amorphous germanium (a-Ge:H) consistent with hierarchically constrained kinetics, reflected in log-normal noise power distributions, strong correlations between noise power octave bins and scaling of the second spectra. The similarities in the 1/f noise of a-Ge:H and a-Si:H motivated our study of current relaxation in a-Ge:H. However, unlike the a-Si:H SER decay of the conductivity, in a-Ge:H we find a time-dependent increase of the conductivity at constant temperature. For a-Ge:H, the stretched exponential power-law exponent and time constant are similar to that observed in a-Si:H, but only for temperatures above 390K. A set of hydrogenated amorphous silicon-germanium alloys are studied to investigate the transition in the noise statistics and conductivity relaxation as the alloy fraction changes.