Optimized recess etching criteria for T‐gate fabrication achieving f t = 290 GHz at L g = 124 nm in metamorphic high electron mobility transistor with In 0.7 Ga 0.3 As channel

The authors propose criteria for recess etching to fabricate T‐gate used in InGaAs high electron mobility transistors (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 ( R ds ) and current ( I ds ). The ratio (Γ) of before and after etching for each R ds and I ds can be used as criteria to determine the point in time to stop etching. By performing recess etching with Γ= 1.97 for R ds and Γ= 0.38 for I ds on an epiwafer having cap doping concentration of 2 × 10 19 cm −3 and channel indium content of 0.7, the authors have fabricated InGaAs metamorphic high electron mobility transistor (mHEMT) device showing g m,max = 1603 mS/mm and f t = 290 GHz at L g = 124 nm. The criteria presented can be applied to InGaAs HEMTs with various epitaxial structures.