Kinetic model for desorption of hydrogen from amorphous hydrogenated silicon

Abstract

We have previously shown experimentally that the addition of dopants causes large changes in the hydrogen desorption from a-Si:H. A new kinetic many-body semiphenomenological model for this desorption process is proposed. It takes into account the atomic and electronic properties of the material. The model is based on the kinetic many-body theory of thermally activated rate processes in solids. The model considers atomic and electronic phenomena occurring in the submicronic vicinity of a ${\mathrm{H}}_2$ molecule desorbed from hydrogenated amorphous silicon (a-Si:H). The phenomena are synchronized with the desorption event of duration ${\mathrm{\tau }}_1$=${10}^{\mathrm{-}13}$–${10}^{\mathrm{-}12}$ s. The following main results are obtained. (i) The Arrhenius-like equation for the rate coefficient K of hydrogen desorption is derived from the kinetic consideration of the desorption event without invoking the equilibrium rate theory. (ii) The Arrhenius activation energy ΔE and prefactor ${\mathit{K}}_0$ are expressed in terms of local parameters that characterize atomic and electronic processes induced by short-lived large energy fluctuations of surface atoms. These processes occur in the vicinity of a desorbed ${\mathrm{H}}_2$ molecule during the desorption event. (iii) The ‘‘abnormally’’ large range of observed variations in the prefactor ${\mathit{K}}_0$ (about 14 orders of magnitude) and in the activation energy ΔE (a factor of 7), caused by dopant variations, are explained for the first time. (iv) A linear dependence between variations ln${\mathit{K}}_0$ and ΔE found in hydrogen desorption from a-Si:H is explained. The dependence is associated with the kinetic compensation effect (CEF). (v) Coefficients in the CEF equation and other kinetic parameters are calculated and expressed in terms of material characteristics, in good agreement with experimental data.