UV Photoelectron Spectroscopy of Band Alignment at Ohmic ITO/β-Ga2O3 Interfaces Grown by Pulsed Laser Deposition*

We report the determination of the band offset between ohmic indium tin oxide (ITO) contacts and epitaxial β-Ga2O3 grown by pulsed laser deposition (PLD) and characterized using ultraviolet photoelectron spectroscopy (UPS) and optical measurements. The bandgaps of the materials were 4.1 eV for β-Ga2O3 and 3.64 eV for ITO. Changes in the Fermi level position with respect to the band edges with annealing in N2 at 550°C for 1 minute were measured and correlated with contact resistivity using TLM, and electrical properties using Hall characterization. Annealing decreased specific contact resistivity from 1.5x10^-1 Ω.cm² to 1.9x10^-2 Ω.cm². The Type II conduction band offset was 0.31 eV and 0.47 eV for as-deposited and annealed heterojunctions, respectively. Based on the bandgap, work function, and Fermi level position measurements, schematic band diagrams of the staggered heterojunction are reported. The results demonstrate the potential of ITO as an ohmic electrode to β-Ga2O3 for sensors and transparent electronics.