Gate-recessed delta-doping enhancement-mode Al0.2Ga0.8As/In0.15Ga0.85As PHEMTs using a new citric buffer etchant

Gate-recessed delta-doping Al0.2Ga0.8As/In0.15Ga0.85As enhancement-mode pseudomorphic HEMTs (E-PHEMTs) using a newly developed citric buffer etchant are reported for the first time. The innovated etchant near room temperature (23 °C) possesses a high GaAs/Al0.2Ga0.8As etching selectivity (>250) applied to an etched stop surface with a root-mean-square (rms) roughness of only 0.197 nm. This device has the transconductance (Gm) of 315 mS/mm and high linearity of 0.46 V-wide swing (drop of 10% peak Gm) in gate bias, corresponding to 143 mA/mm-wide IDS, even at a gate length of l μm. For microwave operation, this l μm-gate E-PHEMT shows the MSG (maximum stable gain) of 16.2 dB at 6.6 GHz and the ft (cutoff frequency) of 11.2 GHz. The measured minimum noise figure (NFmin), under VDS=3V and IDS=7.5mA, is 0.56 dB at 1 GHz 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.