Contacting mechanically exfoliated β-Ga₂O₃ nanobelts for (opto)electronic device applications

We systematically investigated the properties of metal contacts deposited on exfoliated β-Ga₂O₃ nanobelts. Unintentionally doped β-Ga₂O₃ was mechanically exfoliated from bulk β-Ga₂O₃ crystal and transferred onto SiO2/Si substrate having a back gate configuration. Electrodes were formed by depositing Ti/Au or Ni/Au onto the transferred β-Ga₂O₃ nanobelts, followed by rapid thermal annealing (RTA) with different ambient gases and temperatures. Using scanning transmission electron microscopy (STEM) and energy-dispersive X-ray spectroscopy (EDS), it was shown that titanium reacts with oxygen to form titanium oxide, which has ohmic behavior. In contrast, nickel does not form an ohmic contact despite 600°C thermal treatment. The lower oxygen partial pressure in a nitrogen atmosphere as compared to air results in more oxygen vacancies within the Ga₂O₃ nanobelts during RTA and a negative threshold voltage shift. A decreased current level after high temperature annealing can be ascribed to significant outward diffusion of oxygen and gallium atoms and to oxidation of the metal electrode. Our results can pave a route to demonstrating high performance β-Ga₂O₃ nanobelt-based (opto)electronic devices.