In this paper we find that the stretched-exponential relaxation commonly observed in disordered systems is explained by time-dependent atomic diffusion. The relaxation is observed in the electronic properties of hydrogenated amorphous silicon (a-Si:H), a ‘‘hydrogen glass’’ material, and reflects the equlibration of localized electronic states. The relaxation is attributed to the motion of bonded hydrogen which exhibits dispersive diffusion with a characteristic power-law time dependence. A quantitative relation between the relaxation and the diffusion is established.

• Received 1 April 1987

DOI:https://doi.org/10.1103/PhysRevLett.59.1037