Highly selective etching of GaAs on Al_0.2Ga_0.8

Highly selective etching (>150) of GaAs over Al_0.2Ga _0.8As with low GaAs etch rates (<50 Å/s) can be performed using a newly developed CA/H₂O₂/H₂O etchant (CA = citric acid: H₂O of 1:1 by weight). Modulating the H ₂O₂ content in this etching system can overcome the weakness of previously nonselective etching inference using CA/H ₂O₂ + H₂O, and solve the problem of excessive GaAs etch rates (>100 Å/s) associated with using traditional CA/H ₂O₂ solutions. When applied to pseudomorphic high electron mobility transistors (PHEMTs), high etching uniformity and a smooth surface (rms roughness of only 2.01 Å) are observed during gate recessing; the gate leakage currents are then suppressed, suggesting the applicability of the CA/H₂O₂ /H₂O system to fabricating PHEMTs.