Gate-length scaling of AlGaN/GaN HEMTs for cryogenic low-noise operation

This work investigates gate-length (LG) scaling of AlGaN/GaN high electron mobility transistors (HEMTs) for cryogenic low-noise radio frequency (RF) operation at 4 K, targeting applications in radio astronomy receivers and quantum readout front ends. Devices with LG ranging from 1 down to 0.15 μm are characterized and analyzed using a delay-time framework to connect transport dynamics to RF and noise performance. The shortest gate tested device achieves a minimum noise temperature (Tmin) of 6 K at 5 GHz at 4 K, representing approximately an order of magnitude improvement compared to room temperature operation (300 K). The analysis indicates that enhanced effective electron velocity and reduced access resistances drive the observed improvements in RF and noise performance with both LG downscaling and cryogenic cooling while also revealing a growing influence of short-channel effects and parasitics at cryogenic temperatures. These results provide practical design guidelines for pushing GaN HEMTs toward lower noise through continued scaling and targeted optimization of access and contact resistances.