This study examines the effect of gate recess depth on the electrical and RF performance of AlGaN/GaN high electron mobility transistors (HEMTs) before and after die-attach. Devices with greater recess depths exhibited more significant changes in transconductance, pinch-off voltage, and RF metrics, such as cut-off frequency (ft) and maximum frequency (fmax), compared to non-recessed devices. However, recessed devices also showed substantial increases in gate and drain leakage currents, indicating adverse effects of packaging-induced stresses.

We propose criteria for recess etching to fabricate T-gate used in InGaAs HEMTs. By patterning additional rectangular pads on the source and drain metals in the e-beam lithography step, it is possible to measure the drain-to-source resistance (Rds) and current (Ids). the ratio (Γ) of before and after etching for each Rds and Ids can be used as criteria to determine the point in time to stop etching. By performing recess etching with Γ= 1.97 for Rds and Γ= 0.38 for Ids on an epiwafer having cap doping concentration of 2= 1019 cm−3 and channel indium content of 0.7, we have fabricated InGaAs mHEMT device showing gm,max= 1603 mS/mm and ft= 290 GHz at Lg= 124 nm. The criteria presented can be applied to InGaAs HEMTs with various epitaxial structures.