The high-frequency characteristics of high electron mobility transistors applying AlGaN for a channel layer (AlGaN channel HEMTs) with greater impacts of alloy disorder scattering than those in conventional HEMTs with a GaN channel layer (GaN channel HEMTs) are investigated. The obtained electron saturation velocity was 4.7 × 10 6 cm/s and the cutoff frequency was 7 GHz in the AlGaN channel HEMTs with a gate length of 1 μm. These results are promising for several gigahertz band operations of AlGaN channel HEMTs.

AlGaN/GaN high-electron-mobility transistors (HEMTs) with Schottky gate contacts are strong candidates for high-power applications with high-frequency operation. The existence of interfacial traps between Schottky gate contacts and an AlGaN surface is one of the issues causing relatively high gate leakage current in these HEMTs. High-temperature gate annealing, which reduces the density of traps owing to the interfacial reaction between Schottky gate contacts and an AlGaN surface, was investigated using a single-Ni-layer gate structure to prevent the alloying of conventional stacked metal layers such as Ni/Au and Pt/Au. As a result, a strong gate annealing temperature dependence of Schottky characteristics was observed and this dependence also caused drain current collapse. In addition, it was confirmed that 700 °C is the optimal gate annealing temperature for improving both the Schottky characteristics and drain current collapse. These results are attributed to the change in the density of interfacial trap states.