Demonstration of AlGaN/GaN HEMTs on vicinal sapphire substrates with large misoriented angles

In this work, the electrical characteristics of AlGaN/GaN high-electron-mobility transistors (HEMTs) on vicinal c-plane sapphire substrates with different misoriented angles are investigated. As the angle increases from 0.2°, 1.0° to 4.0°, an enlarged width and height of surface step bunching as well as significantly enhanced electron mobility from 957, 1123 to 1246 cm2/V s were measured. As a result, a large boost in the maximum output current (IDmax) from ∼300 mA/mm (on a 0.2° substrate) to ∼650 mA/mm (on a 4.0° substrate) can be observed. Importantly, HEMTs on 1.0° and 4.0° substrates exhibit an obvious anisotropic electrical behavior: the IDmax along the [11-20] orientation is larger than that along the [10-10] orientation. Such a difference becomes more distinct as the misoriented angle increases, attributing to the lifted step height that would introduce a potential barrier for the electron transport along the [10-10] orientation. In short, this work demonstrates an effective approach toward the realization of high-performance HEMTs with anisotropic electrical behavior on a single device platform.