A model was proposed for the behavior of H at moderate temperatures. It was assumed that H had both a donor and an acceptor level in the band gap, and could thus exist in 3 charge states: Ho, H+, H-. Its motion was slowed by the formation of H2 molecules as well as by interactions with dopant atoms. Good simulations were obtained for both n-type and p-type material with various dopant levels. The diffusivity of neutral H was in agreement with extrapolations of high-temperature data.

D.Mathiot: Physical Review B, 1989, 40[8], 5867-70