Abstract
In this paper, we report a highly selective wet gate recess process using a succinic-based solution for fabricating InGaAs/InAlAs/GaAs metamorphic HEMTs (MHEMT). We developed the wet gate recess process using a solution of succinic acid and $H_2O_2$ to selectively etch the heavily doped-InGaAs ohmic layer over an InAlAs Schottky layer. The etch rate of the InGaAs layer was about 120 nm/min, and an etch selectivity of the InGaAs to the InAlAs layer higher than 100 was obtained. The 0.2-${\mu}$m GaAs-based MHEMT devices were fabricated using the wet gate recess process. The wet-recessed, 0.2${\times}$100 ${\mu}$m MHEMT devices showed DC output characteristics having a high gate-to-drain breakdown voltage of -7.6 V, an extrinsic transconductance ($g_{m.max}$) of 700 mS/mm, and a threshold voltage ($V_{th}$) of -0.95 V. The wet recessed MHEMT showed good pinch-off characteristics and exhibited good DC uniformities across a 4-inch GaAs wafer having a $V_{th}$ uniformity of 7.4 % and an extrinsic transconductance of 4.6 %. The $f_T$ and $f_{max}$ obtained for a PHEMT device were 115 GHz and 230 GHz, respectively.