Monolithic integration of InAlAs/InGaAs/InP enhancement- and depletion-mode high electron mobility transistors

A process for the monolithic integration of enhancement- and depletion-mode high electron mobility transistors (E/D-HEMTs) in the lattice-matched InAlAs/InGaAs/InP material system is reported for gate lengths ranging from 0.3 μm to 1.0 μm. The E-HEMTs with a 0.3 μm gate length exhibit a threshold voltage of +187 m V and a maximum DC extrinsic transconductance of 625 mS/mm, while a threshold voltage of -443 mV and a transconductance of 462 mS/mm are measured for D-HEMTs of the same gate length. Variations of threshold voltage for all devices under study was minimal, with the 0.3 μm gate length devices showing a standard deviation of 12 mV for the D-HEMTs and only 7 mV for the E-HEMTs. The devices demonstrate excellent RF performance, with the 0.3 μm E-HEMTs exhibiting a unity current gain cutoff frequency (f_t) of 95 GHz, and the 0.3 μm D-HEMTs yielding a nearly identical f_t of 102 GHz. To the best of the authors' knowledge, this is the first report of high speed monolithically integrated E/D HEMTs on lattice-matched InP-based materials.