The degradation phenomenon and mechanism of AlGaN / GaN heterojunction field-effect transistors (HFETs) working at cryogenic temperature have been rarely reported. In this paper, the off-state capacitance of AlGaN / GaN HFETs at low temperature and the room temperature was investigated. The negative differential capacitance at 77 K and 300 K are 11.26 F and 0.69 F, respectively. The capacitance was tested at different temperatures, which showed that the negative differential capacitance came from low-temperature conditions. At room temperature, the resistance was increased sharply under the gate of the device off-state. At this time, the current leakage channel was turned on, the phenomenon of negative differential capacitance was caused by an accumulation of electrons. Through the C-V test at different frequencies at low temperature, it reflects the relationship between the trap level, the off-state leakage current, and the negative differential capacitance. This investigation would provide a reference for the application and reliability analysis of RF GaN devices in a low-temperature environment.

HFET,low-temperature,negative differential capacitance