An In/sub 0.52/Al/sub 0.48/As/n/sup +/-In/sub x/Ga/sub 1-x/As heterostructure field-effect transistor with an In-enriched channel

In/sub 0.52/Al/sub 0.48/As/n/sup +/-In/sub x/Ga/sub 1-x/As HFETs have been fabricated with InAs fractions between 0.53 and 0.7 in the channel. These HFETs, also called MIDFETs (metal-insulator doped-channel FETs), have a doped channel and an undoped wide-bandgap insulator. The enhancement of InAs in the channel results in a marked improvement in transconductance and peak drain current. Devices with L/sub g/=1 mu m and x=0.7 display an unprecedented I/sub d/ of 656 mA/mm and g/sub m/ of 296 mS/mm. As x is increased, however, there is an increase in the gate current, a dramatic decrease in the breakdown voltage, and a degradation of pinch-off. Leakage at the gate-mesa edge overlap is found to be partially responsible for these effects. To achieve the substantial gains in transport that higher InAs fractions offer, better isolation technology is required.<>