Low-Resistive Ohmic Contacts in High-Electron-Mobility AlN/GaN Heterostructures by Suppressing the Oxygen Incorporation

AlN/GaN heterostructures are pursued for high-speed and high-power devices due to the superiority of their high-mobility and high-density two-dimensional electron gas. However, the Ohmic contacts for high-mobility AlN/GaN heterostructures are difficult to realize, while the reason remains unrevealed. In this article, we reported a low-resistive Ohmic contact in AlN/GaN heterostructures with a high electron mobility of 1510 cm2 V–1 s–1 by simply using rapid thermal annealing. Transmission electron microscopy analysis confirms that the incorporation of oxygen is the main impediment for Ohmic contacts, which forms Al2O3 and voids in the interlayers and induces a near-open-circuit contact. By suppressing the incorporation of oxygen, a complete polycrystalline alloy without oxides is achieved, with a low contact resistance of ∼0.33 Ω·mm as an optimized result. Furthermore, the restrictions for Ohmic contacts in a high-mobility AlN/GaN heterostructure are also clarified, which are ascribed to the lack of an adequate Ti + AlN reaction. Giving a physical model of the contact formation as well as providing improved contact resistance via simplified techniques, this study is indicative of the enhanced functioning of versatile devices.