Impacts of device processing on contact interfaces to (010) β-Ga2O3

Metal-semiconductor interfaces to Ga2O3 have been demonstrated to be highly sensitive to device processing conditions. Liftoff processing leads to inconsistency in ohmic contact formation and quality due to apparent chemical modification of the surface layer, which is not affected by most traditional surface cleanings but can be removed by Ga-flux polishing. Metal-first processing on as-grown material, which avoids exposure of the Ga2O3 surface to photoresist prior to metal deposition, has been shown to form reliable, low-resistance ohmic contacts. Investigation of the chemical composition of contacts to material that has been modified by liftoff and cleaned by Ga-flux polishing by x-ray photoelectron spectroscopy (XPS) reveals slight variations in the oxidation states of the Ti and Ga in the contacts that indicate the nature of the surface chemistry modification.