Highly lattice-mismatched In/sub 0.26/Ga/sub 0.74/As/GaAs MESFET's: impact of critical thickness on device performance

Fabrication of 0.25- mu m-gate MESFETs directly on In/sub 0.26/Ga/sub 0.74/As epitaxial layers which are much thicker than the pseudomorphic critical thickness is described. The InAs mole fraction is increased in the MESFET channel to 26%. Whether the device performance can be further improved without detrimental dislocation effects as the channel thickness exceeds the critical thickness considerably is investigated. Despite large lattice mismatch and high defect density, these devices show excellent microwave performance with an extrinsic f/sub t/ of 120 GHz. Bias-dependent S-parameters indicate that the In/sub 0.26/Ga/sub 0.74/As MESFET maintains excellent device performance down to very low drain current without showing any performance degradation due to misfit or threading dislocations.<>