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

摘要

Improved device performance in Al0.2Ga0.8As/In0.15Ga0.85As gate-recessed 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 degrees C) possesses a high GaAs/Al0.2Ga0.8As or In0.15Ga0.85As/Al0.2Ga0.8As 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 mu m is obtained. For microwave operation, this 1 mu m-gate E-PHEMT shows the f(max) (maximum operation frequency) of 29.2GHz and the f(T) (cut-off frequency) of 11.2 GHz, respectively. The measured minimum noise. gure (NFmin), under V-DS = 3V and I-DS 7.5 mA, is 0.56 dB at 1GHz with the associated gain of 10.86 dB. The NFmin 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 In0.15Ga0.85As channel at mesa sidewalls for D-PHEMTs. For D-PHEMTs with 1 x 100 mu m(2) exhibit a very low gate leakage current of 2.4 mA/ mm even at V-GD = -10V 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.