Process for en hancem ent/depletion-mode GaAs/InGaAs/AIGaAs 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 600mS/mm, and unity current-gain cutoff frequencies f_t of 75 and 66 GHz at room temperature have been achieved for 0·3 μm 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 25mS/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 13ps at room temperature.