Characteristics of GaAs/AlGaAs-doped channel MISFET's at cryogenic temperatures

High-frequency measurements at cryogenic temperatures to 125 K of 0.3- mu m gate length GaAs-Al/sub 0.3/Ga/sub 0.7/As metal-insulator-semiconductor field-effect transistors (MISFETs) with a doped channel are discussed. Experimental results demonstrate significant improvement in performance including an increase in the maximum frequency of oscillation from 70 to 81 GHz and an increase in the unity current gain cutoff frequency from 46 to 57 GHz. Independently determined decreases in electron mobility and increases in electron velocity under similar conditions lead to the conclusion that carrier velocity and not mobility controls transport in these devices. These results show the high-speed potential of doped channel MISFETs at both room temperature and cryogenic temperatures.>