We systematically investigated the properties of metal contacts deposited on exfoliated β-Ga 2 O 3 nanobelts. Unintentionally doped β-Ga 2 O 3 was mechanically exfoliated from bulk β-Ga 2 O 3 crystal and transferred onto SiO 2 /Si substrate having a back gate configuration. Electrodes were formed by depositing Ti/Au or Ni/Au onto the transferred β-Ga 2 O 3 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 Ga 2 O 3 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-Ga 2 O 3 nanobelt-based (opto)electronic devices.
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Bae et al. (2016) studied this question.
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