Ultrathin Stable Ohmic Contacts for High-Temperature Operation of ..beta..-Ga2O3 Devices: Article No. 043211

Beta gallium oxide (beta-Ga2O3) shows significant promise in the high-temperature, high-power, and sensing electronics applications. However, long-term stable metallization layers for Ohmic contacts at high temperature present unique thermodynamic challenges. The current most common Ohmic contact design based on 20 nm of Ti has been repeatedly demonstrated to fail at even moderately elevated temperatures (300-400 degrees) due to a combination of non-stoichiometric Ti/Ga2O3 interfacial reactions and kinetically favored Ti diffusion processes. Here we demonstrate stable Ohmic contacts for Ga2O3 devices operating up to 500-600 degrees using ultrathin Ti layers with a self-limiting interfacial reaction. The ultrathin Ti layer in the 5nm Ti / 100nm Au contact stack is designed to fully oxidize while forming an Ohmic contact, thereby limiting both thermodynamic and kinetic instability. This novel contact design strategy results in an epitaxial conductive anatase titanium oxide interface layer that enables low-resistance Ohmic contacts that are stable both under long-term continuous operation (>500 hours) at 600 degrees in vacuum (= 10-4 Torr), as well as after repeated thermal cycling (15 times) between room temperature and 550 degrees in flowing N2. This stable Ohmic contact design will accelerate the development of high-temperature devices by enabling research focus to shift towards rectifying contacts and other interfacial layers.