Hydrogen diffusion in single crystal and polycrystalline zinc oxide was investigated by deuterium diffusion and H effusion experiments. Deuterium concentration depth profiles were measured as a function of the passivation temperature, while in H effusion experiments the molecular H flux was measured as a function of the heating rate. The diffusion coefficient exhibits thermally activated behavior and varied between EA = 0.17 and 0.37eV. The change of EA was accompanied by a change of the diffusion pre-factor by eight orders of magnitude. This indicated that EA was not related to the energetic position of H transport sites or the barrier height between such sites. Using the microscopic diffusion pre-factor, the position of the H chemical potential, µH, was estimated. With increasing temperature, µH decreased with a rate of ≈0.0013eV/K. At H concentrations of less than 1017/cm3µH was pinned. The H density of states was derived from H effusion data, which was consistent with a diffusion activation of about 1.0eV as was originally reported by Mollwo and Thomas and Lander. Clear evidence for H deep traps was found in single crystal and polycrystalline ZnO.

Hydrogen Migration in Single Crystal and Polycrystalline Zinc Oxide. N.H.Nickel: Physical Review B, 2006, 73[19], 195204 (9pp)