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

The authors present high-frequency measurements at cryogenic temperatures to 125 K of 0.3-μm gate length GaAs/Al0.3Ga0.7 As metal insulator semiconductor field-effect transistors (MISFET's) with a doped channel. Experimental results demonstrate significant improvement in performance including an increase in the maximum frequency of oscillation fmax from 70 to 81 GHz and an increase in the unity current gain cutoff frequency fT 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 MISFET's at both room temperature and cryogenic temperatures