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

Abstract

AlN/GaN heterostructures are pursued for high-speed and high-power devices due to the superiority of their highmobility 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 cm 2 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 Al 2 O 3 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.

AlN/GaN HEMTs with fmax Exceeding 300 GHz by Using Ge-Doped n++GaN Ohmic Contacts

“…Due to the possession of high-mobility and high-density two-dimensional electron gas (2DEG), AlGaN/GaN high electron mobility transistors (HEMTs) are believed as promising candidates in the field of radio frequency (RF) devices. – Nonetheless, the optimized AlGaN barrier thickness is around 20–40 nm, which makes a reduced gate control capability, and the short channel effects occur during device scaling. , Recently, the AlN/GaN heterostructure with ultrathin barrier thickness provides a solution to the short channel effects, with excellent gate response. – It also has a rather high 2DEG density exceeding 2 × 10 13 cm –2 , ensuring a high current density for HEMTs toward RF applications. , …”

“…1−4 Nonetheless, the optimized AlGaN barrier thickness is around 20−40 nm, which makes a reduced gate control capability, and the short channel effects occur during device scaling. 5,6 Recently, the AlN/GaN heterostructure with ultrathin barrier thickness provides a solution to the short channel effects, with excellent gate response. 7−9 It also has a rather high 2DEG density exceeding 2 × 10 13 cm −2 , ensuring a high current density for HEMTs toward RF applications.…”