Chemical and electrical measurements of Ti/(010) beta-Ga2O3 and Ti/(001) beta-Ga2O3 interfaces were conducted as a function of annealing temperature using x-ray photoelectron spectroscopy (XPS), current density-voltage (J-V), and capacitance-voltage (C-V) measurements. XPS revealed partial Ti oxidation at both interfaces in the as-deposited condition, with more Ti oxidation on the (001) beta-Ga2O3 epilayer surface than the (010) beta-Ga2O3 substrate surface. The amount of oxidized Ti increased with annealing temperature. The Schottky barrier heights for as-deposited (unannealed) Au/Ti/(010) beta-Ga2O3 and Au/Ti/(001) beta-Ga2O3 contacts as determined from J-V and C-V measurements were between 0.64 and 0.83 eV. Shifts in XPS core level peaks for Ti/(010) beta-Ga2O3 suggest that the Schottky barrier height decreases with temperature up to 350 degrees C for 10-min anneals and increases for 10-min anneals >= 460 degrees C. Taken together, the results suggest a strong dependence of Ti reactivity on the beta-Ga2O3 surface, which can affect the electrical performance and stability of Ti/beta-Ga2O3 ohmic contacts at elevated temperatures.
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