Accelerated Aging Stability of β-Ga₂O₃-Titanium/Gold Ohmic Interfaces

Stable ohmic contacts are critical to enable efficient operation of high-voltage electronic devices using ultrawide bandgap semiconductors. Here we perform, for the first time, thermally accelerated aging of Ti/Au ohmic interfaces to (010) β-Ga₂O₃. We find that a heavily doped semiconductor, doped n-type by Si-ion implantation, treated with reactive ion etch (RIE), results in a low specific contact resistance of ∼10^-5 Ω cm² that is stable upon accelerated thermal aging at 300 °C for 108 h. The low resistance interface is due to thermionic field emission of electrons over an inhomogeneous barrier. Scanning/transmission electron microscopy indicates that the multi-layered structure and elemental distribution across the contact interface, formed during a 1 min 470 °C post-metallization anneal, do not change noticeably over the aging period. A ∼1 nm interfacial layer is observed by high-resolution microscopy at the Ti-TiO/Ga₂O₃ interface on all samples exposed to RIE, which may contribute to their excellent stability. In addition, longer-range facet-like interfacial features are observed, which may contribute to the inhomogeneous barrier. In contrast, Ti/Au junctions to moderately doped (010) Ga₂O₃ made with no RIE treatment exhibit a high contact resistance that increases upon accelerated aging, along with a partially lattice-matched interface. The methods used here to understand the process, structure, and electrical property relationships for Ti/Au contact interfaces to β-Ga₂O₃ can be applied to assess and tune the stability of a variety of other oxide-semiconductor interfaces.