High-frequency characterization of AlGaN/GaN MIS-HEMTs and HEMTs at cryogenic temperatures

The high-frequency characteristics of AlGaN/GaN metal-insulator-semiconductor high-electron-mobility transistors (MIS-HEMTs) and HEMTs are thoroughly investigated for cryogenic applications. Compared with HEMT, MIS-HEMT has an additional SiN passivation upon the AlGaN layer, which also serves as the gate dielectric. The experimental results show that the DC characteristics of MIS-HEMT exhibit more pronounced improvements than that of HEMT when the temperature decreases from 300 K to 4 K. However, the high-frequency parameters of HEMT, such as cutoff frequency and maximum oscillation frequency, perform more significantly than MIS-HEMT at low temperatures. These phenomena are attributed to the different gate structures between MIS-HEMT and HEMT and the fact that the surface-related charge trapping in HEMT is suppressed at low temperatures. Therefore, optimizing the AlGaN/GaN structure under the gate and reducing traps in the device is crucial for achieving good high-frequency performance under extreme temperature conditions.