Short pulse transfer characteristics of Al/sub x/Ga/sub 1-x/As/GaAs and Al/sub x/Ga/sub 1-x/As/In/sub y/Ga/sub 1-y/As modulation-doped heterojunction FET's

Short-pulse drain current versus gate voltage transfer characteristics measured for modulation-doped HFETs (MODFETs) with four donor-layer-channel-layer combinations-(1) Al/sub 0.3/Ga/sub 0.7/As-GaAs, (2) Al/sub 0.2/Ga/sub 0.8/As-GaAs, (3) Al/sub 0.3/Ga/sub 0.7/As-In/sub 0.2/Ga/sub 0.8/As, and (4) Al/sub 0.2/Ga/sub 0.8/As-In/sub 0.2/ a/sub 0.8/As-are compared with the DC transfer characteristics. The measurements are relevant to high-speed switching in HFET circuits. Significant shifts in threshold voltage are observed between the DC and short-pulse characteristics for the structures with n/sup +/-Al/sub 0.3/Ga/sub 0.7/As donor layers, while the corresponding shifts for structures with n/sup +/-Al/sub 0.2/Ga/sub 0.8/As donor layers are relatively small or virtually nonexistent.<
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