Highly Selective GaAs/Al0.2Ga0.8As Wet Etch Process for the Gate Recess of Low-Voltage-Power Pseudomorphic High-Electron-Mobility Transistor

A selective wet etch process for the gate recess of the GaAs power pseudomorphic high-electron-mobility transistors (pHEMT's) was developed. The power pHEMT's used in this study were epitaxially grown power Al 0.2 Ga 0.8 As/In 0.2 Ga 0.8 As pHEMT's with a 250 Å GaAs cap layer and a 300 Å Al 0.2 Ga 0.8 As electron-donating layer. The electron-donating layer was used as the etch-stop layer for the gate recess. A selectivity of 3400:1 was achieved for GaAs/Al 0.2 Ga 0.8 As layers using citric acid/tripotassium citrate/hydrogen peroxide etching solutions in this study. This is the highest selectivity for GaAs/Al x Ga 1- x As selective etching reported so far. The pHEMT's processed using this selective etching demonstrated good device power performance, and the wet recess process did not cause any contamination or damage to the device. The test data indicates that this selective etch process can be of practical use for forming the gate recess of the power pHEMT's with good device performance and excellent electrical uniformity.