DC Characteristics of Wide-bandgap Semiconductor Field-effect Transistors at Cryogenic Temperatures

We investigated the characteristics of AlGaN/GaN heterostructure field-effect transistors (HFETs) and 4H-SiC metal semiconductor field-effect transistors (MESFETs) at cryogenic temperatures to evaluate potential for extreme environmental applications. AlGaN/GaN HFETs demonstrated increased output currents and a negative shift of channel pinch-off voltage as the temperature decreased from 300 K to 50 K. 4H-SiC MESFETs demonstrated dependence on temperature opposite to that of the AlGaN/GaN HFETs. The negative temperature coefficient of the output current in AlGaN/GaN HFETs is attributed to a mobility enhancement accompanying a channel resistance reduction at cryogenic temperatures. AlGaN/GaN HFETs benefit from a heterostructure without intentional doping, showing no degradation in the channel carrier density. In 4H-SiC MESFETs, the reduction in the channel carrier density due to the deactivation of channel dopants results in a positive shift of the threshold voltage, and thereby a significant degradation of the output current. Our results confirm AlGaN/GaN HFETs to be strong candidates for cryogenic applications compared to 4H-SiC MESFETs.