FETs on lattice-mismatched substrates: GaAs/InP and GaAs-AlGaAs/Si

High-performance 0.9- mu m-gate-length GaAs MESFETs on InP substrates and 1- mu m-gate-length GaAs-AlGaAs SDHTs on Si substrates are reported. The GaAs-on-InP MESFET structures exhibited extrinsic transconductances of 377 mS/mm at a gate bias of 0.6 V. The drain I-V characteristic showed excellent saturation, and the devices exhibited no light sensitivity of the DC characteristics. A unity current gain cutoff frequency of 22 GHz and a maximum frequency of oscillation of 30 GHz were measured. For the SDHTs on Si, the maximum transconductance was 220 mS/mm at 300 K and 364 mS/mm at 77 K. A minimum propagation delay of 28 ps/stage at room temperature was obtained for a 19-stage direct coupled FET logic ring oscillator with a power dissipation of 1.1 mW/stage. Microwave performance (f/sub T/=15 GHz, f/sub max/=22 GHz) comparable to that of homoepitaxial devices was obtained.<>