2.3 kV GaN Super-Heterojunction FET for Cryogenic Power Switching

Power switches capable of cryogenic temperature operation are desired for cryogenic systems, such as rocket propulsion systems and superconducting machines. Si and SiC MOSFETs are potential candidates for cryogenic power switching. They are vertical devices with a doped drift region. While the carrier mobility may increase with decreasing temperature, carrier freezeout at low temperature causes degradation of on-resistance (R_ON). GaN lateral HEMT, where 2DEG is free from carrier freezeout, is another strong candidate for cryogenic power switching. GaN HEMTs show 5X reduction in R_ON at cryogenic temperature, due to increase in mobility resulting from reduced electron-phonon scattering. However, the maximum operating voltage of GaN HEMT at cryogenic temperature is limited to 650 V [1] , insufficient for high power systems. GaN super-heterojunction (SHJ) FET offers a path to scale the operating voltage to over 10 kV [2] , by leveraging charge-balance in the SHJ structure. This paper provides the 1 st report of characteristics of GaN SHJ FET at cryogenic temperature.