On the temperature dependence of mobility in hydrogenated indium-doped ZnO thin films

Abstract DC reactively sputtered indium-doped ZnO (IZO) thin films were studied after incorporating hydrogen by depositing them in the presence of hydrogen in the plasma as well as by post-annealing IZO films in hydrogen. The effect of hydrogen incorporation is investigated quantitatively by fitting the temperature-dependent mobility data, employing a scattering model in terms of acceptors and donors present in these degenerate semiconducting films. The study establishes that hydrogen in these films causes the passivation of zinc vacancies (VZn), and results in the enhancement of carrier concentration. The photoluminescence spectroscopy provides additional experimental support for passivation of VZn by hydrogen. In the case of hydrogen post-annealed films, a sharper decrease in the ratio of acceptor to donor concentration from 0.35 to 0.18 and an associated larger increase in mobility from 12.8 to 29.4 cm2 V−1 s−1 are observed. The room temperature deposited degenerate films possess a high donor concentration of 8.65 × 1020 cm−3 and conductivity of 2.6 × 103 Ω−1 cm−1. It is clearly evident that the major contribution to mobility in the entire temperature range of 20–300 K is due to the interaction of charge carriers with the ionized impurities. However, in the higher temperature regime of 100–300 K, the acoustical contribution progressively lowers the carrier mobility by ∼10–15%. Based on this analysis, a mobility value approaching 80 cm2 V−1 s−1 is predicted for acceptor free films.