Study of Plasma Treatment Effects on β-Gallium Oxide Metal Contacts

Gallium Oxide (Ga₂O₃) has been considered a promising material for next-generation power electronics due to its ultra-wide bandgap of 4.6-4.9 eV. With its remarkable properties, including an 8 MV/cm high breakdown electric field, tremendous Baliga’s figure of merit (BFOM), and excellent chemical and thermal stability, it is a potential material for high-power and high-frequency applications. Nevertheless, the formation of reliable and thermally stable ohmic contacts to this material is still a daunting task, derived from its peculiar material properties that result in difficulties in lowering the contact resistance and enhancing the thermal stability at metal/Ga_{<span style="font-size:10.8333px">2</span>}O_{<span style="font-size:10.8333px">3</span>} interfaces.
Here, we study the effects of plasma processing of β-Ga₂O₃ surfaces on Ti/Ga₂O₃ interfacial properties with the aim of improving the ohmic contact performance. The surface of a commercially available β-Ga₂O₃ crystal substrate was plasma treated in varied conditions, and Ti thin films of nanometer thickness were e-beam deposited on samples both with and without the plasma treatments. These samples were characterized with x-ray photoelectron spectroscopy (XPS) to understand the metal-Ga₂O₃ interactions at the interface. The XPS features, such as the binding energy position and peak intensity of each chemical state component for three major elements, including Ga, O, and Ti, were found to be different between the samples with and without the plasma treatments. A detailed analysis of the XPS data suggests a Fermi level shift in the plasma-treated samples, possibly related to the plasma effects on carrier density and defect passivation at the Ti/Ga₂O_{<span style="font-size:10.8333px">3</span>} interface. In addition, transmission line model (TLM) measurements were performed to determine the contact resistance to determine the plasma effects on metal-semiconductor barrier height. The electrical properties and thermal stability of Ti/Ga₂O₃ contacts are correlated with the structural information at the interface. These findings provide valuable insights to develop effective surface-engineering approaches for optimizing the electronic performance of β-Ga₂O₃-based devices