PROCESS FOR ENHANCEMENT/DEPLETION-MODE GAAS/INGAAS/ALGAAS PSEUDOMORPHIC MODFETS USING SELECTIVE WET GATE RECESSING

A process for enhancement/depletion (E/D)-mode GaAs/InGaAs/AlGaAs pseudomorphic modulation-doped field-effect transistors (MODFETs) using citric acid: H2O2 solutions for selective wet gate recessing has been developed. Extrinsic DC transconductances g(m) as high as 450 and 600 mS/mm, and unity cur-rent-gain cutoff frequencies f(t) of 75 and 66 GHz at room temperature have been achieved for 0.3-mu-m gate-length depletion-mode MODFET (DFET) and enhancement-mode MODFET (EFET), respectively. Standard deviations for threshold voltage and transconductance of less than 16 mV and 25 mS/mm, respectively, have been achieved for both the DFETs and EFETs. Ring oscillators fabricated in direct-coupled FET logic technology have exhibited a propagation delay of 13 ps at room temperature.