Hydrogen Centers in Semiconductor Oxides In2O3 and Ga2O3 Studied by FTIR Spectroscopy

Hydrogen is found to be an n-type dopant in In2O3 that gives rise to unintentional conductivity. An infrared (IR) absorption line observed at 3306 cm−1 is assigned to the Hi+ center. We have performed two types of experiments to determine the diffusivity of Hi+ in In2O3 from its IR absorption spectra. (i) At temperatures near 700 K, the O-H line at 3306 cm−1 is used to determine the diffusivity of Hi+ from its in-diffusion and out-diffusion behaviors. (ii) At temperatures near 160 K, stress has been used to produce a preferential alignment of the Hi+ center that has been detected in IR absorption experiments made with polarized light [1]. With the help of theory, the kinetics with which a stress-induced alignment can be produced yield the time constant for a single jump of the Hi+ center and also the diffusivity of Hi+ near 160 K. The combination of the diffusivity of Hi+ found near 700 K by mass-transport measurements and that found near 160 K from the time constant for a single Hi+ jump determines the diffusivity for Hi+ over eleven decades!Hydrogen has a strong influence on the electrical properties of transparent con- ducting oxides where it can give rise to shallow donors and can passivate deep compensating defects. Vibrational spectroscopy has shown that the introduction of H into Ga2O3 produces a dominant hydrogen center with a strongly polarized vibrational line at 3437.0 cm−1. Theory assigns the 3437.0 cm−1 line to a defect with two equivalent H atoms trapped at a relaxed Ga vacancy. We also produced a reservoir of additional hydrogen defects in Ga2O3 by annealing treatments in an H2 ambient followed by rapid cooling. These additional defects are not as thermally stable as the VGa-2H center and have different polarization properties. Some of these defects appear to be shallow donors and others appear to be VGa-H complexes1with structures different than the 3437.0 cm−1 center. These additional defects can be converted into the VGa-2H defect by annealing in an inert ambient