An In/sub 0.52/Al/sub 0.48/As/n/sup +/-In/sub 0.53/Ga/sub 0.47/As MISFET with a modulation-doped channel

A heterostructure metal-insulator-semiconductor field-effect transistor (MISFET) with a modulation-doped channel is proposed. In this device, a very thin undoped subchannel is located between the undoped wide-bandgap insulator and a thin heavily doped channel. In the depletion mode of operation, electron transport takes place along the heavily doped channel. When the device enters the accumulation mode of operation, electrons pile up against the heterointerface in the high-mobility undoped subchannel. This results in markedly improved transport characteristics at the onset of accumulation. The concept is demonstrated in the In/sub 0.52/Al/sub 0.48/As/In/sub 0.53/Ga/sub 0.47/As system on InP. A 1.5- mu m-gate-length MISFET shows a unity current-gain cutoff frequency of 37 GHz.<
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