Strained-insulator In/sub x/Al/sub 1-x/As/n/sup +/-In/sub 0.53/Ga/sub 0.47/As heterostructure field-effect transistors

In an effort to enhance the conduction band discontinuity between channel and insulator, In/sub x/Al/sub 1-x/As/n/sup +/-In/sub 0.53/Ga/sub 0.47/As heterostructure field-effect transistors (HFETs) were fabricated with InAs mole fractions in the In/sub x/Al/sub 1-x/As gate insulator of x=0.52 (lattice matching), 0.48, 0.40, and 0.30. Decreasing the InAs mole fraction in the insulator results in reduced forward- and reverse-bias gate currents, increased reverse gate breakdown voltage, and reduced real-space transfer of hot electrons from channel to gate. Down to x=0.40, these improvements trade off with a slightly reduced transconductance, but the gain in gate bias swing results in an increase in maximum current drivability. From x=0.40 to x=0.30, there is a drastic decrease in transconductance, coincident with a high density of misfit dislocations.>