Hydrogen and deuterium incorporation and release processes in r.f.-sputtered hydrogenated or deuterated amorphous germanium films

Abstract

In this work the out-diffusion mechanisms of H and D in r.f.-sputtered amorphous Ge films are presented. The H (D) profiles, concentrations and bonding characteristics have been studied in samples annealed at different temperatures and for various annealing times. For this purpose, elastic recoil detection analysis, scanning electron microscopy, infrared transmission spectroscopy and H (D) thermal effusion techniques were used. The main result of the present work is that two kinds of H (D) motion process coexist in r.f.-sputtered hydrogenated (deuterated) amorphous Ge films: a fast process, most probably due to the presence of voids and pinholes in the film, and a slow process due to the dispersive-like diffusion of atomie H (D) in the amorphous network. It has also been found that thermal annealing of the samples above the deposition temperature (210°C) induces structural changes. The diffusion coefficient D _H of H is found to be time dependent (dispersive), as expected with a dispersion parameter α = 0.95 at 280°C. D _H at constant diffusion length (L≈ 60 nm) is temperature activated, with an activation energy of 0.44 ± 0.09 eV. Finally, the possible correlation between H (D) diffusion and light-induced metastable defect creation and relaxation in r.f.-sputtered hydrogenated a-Ge is discussed.