Enhanced characteristics in gate-recessed and sidewall-recessed AlGaAs/InGaAs PHEMTs by citric-based selective wet etching

Abstract

Improveddevice performance in Al 0.2 Ga 0.8 As/In 0.15 Ga 0.85 As gaterecessed enhancement-mode pseudomorphic high electron mobility transistors (E-PHEMTs) and sidewall-recessed depletion-mode PHEMTs (D-PHEMTs) using a newly developed citric buffer etchant are reported. The innovated etchant near room temperature (23 C) possesses a high GaAs/Al 0.2 Ga 0.8 As or In 0.15 Ga 0.85 As/Al 0.2 Ga 0.8 As etching selectivity (>250) applied to an etched stop surface. For E-PHEMTs, the transconductance (G m ) of 315 mS/mm and high linearity of 0.46 V-wide gate voltage swing (drop of 10% peak G m ), corresponding to 143 mA/mm-wide I DS , even at a gate length of 1 mm is obtained. For microwave operation, this 1 mm-gate E-PHEMT shows the f max (maximum operation frequency) of 29.2 GHz and the f T (cut-off frequency) of 11.2 GHz, respectively. The measured minimum noise figure (NF min ), under V DS ¼ 3 V and I DS ¼ 7.5 mA, is 0.56 dB at 1 GHz with the associated gain of 10.86 dB. The NF min is less than 1.5 dB in the frequency range from 1 to 4 GHz. In addition, an effective and simple method of selective gate sidewall recess is utilized to etch the low barrier in In 0.15 Ga 0.85 As channel at mesa sidewalls for D-PHEMTs. For D-PHEMTs with 1 Â 100 mm 2 exhibit a very low gate leakage current of 2.4 mA/mm even at V GD ¼ À10 V and high gate breakdown voltage over 25 V. As compared to that of no sidewall recess, nearly two orders of reduction in magnitude of gate leakage current and 100% improvement in gate breakdown voltage are achieved.

On the Pseudomorphic High Electron Mobility Transistors (PHEMTs) With a Low-Temperature Gate Approach

“…The conventional AlAs etch stop layer also provides a DX-center source and a high oxidation rate in highhumidity conditions for PHEMTs [7]. In addition, for gaterecessed conditions, the high selectivity for GaAs or InGaAs over Al x Ga 1−x As is ordinarily achieved by increasing Al mole fraction (x > 0.3) [8]. On the other hand, the Schottky contact metallization is generally achieved using either the conventional thermal evaporation (TE) or sputtering technique.…”