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Characterization and Modeling of Cryogenic Ultralow-Noise InP HEMTs

Detailed S-parameter and noise characterization and modeling of ultralow-noise InP/InAlAs/InGaAs high-electron mobility transistors (InP HEMTs) optimized for operation at 10 K are presented. At the optimum low-noise bias at 10 K, the InP HEMT exhibited a 60% improvement in cutoff frequency fT and a 100% improvement in dc transconductance gm compared with 300 K. A small-signal noise model was evaluated at different bias conditions at 10 and 300 K. The bias dependence of the minimum noise temperature at low-noise operation was modeled at 10 K. The temperature dependence of the threshold voltage VT, gm, and gate-source and gate-drain capacitances Cgs and Cgd indicated that the excellent cryogenic noise performance of optimized InP HEMTs is due to a higher degree of confinement in the carrier concentration closest to the gate at 10 K compared with 300 K. As a result, a fast depletion of the HEMT channel with respect to drain current Id occurs under cryogenic operation.