Very high selective etching of GaAs/Al0.2Ga0.8As for gate recess process to pseudomorphic high electron mobility transistors (PHEMT) applications using citric buffer solution

Highly selective wet etching of GaAs on Al0.2Ga0.8As can be realized using citric buffer (citric acid/H2O2/H2O) solutions. The selectivity can be up to 256, which is distinct from the previous non-selectivity inference, due to consulting the role of H2O2 in this etching system. The etch stop mechanism is demonstrated by X-ray photoelectron spectroscopy (XPS) and indicates the formation of dense oxide Al2O3 on Al0.2Ga0.8As to stop etching. The applications to pseudomorphic high electron mobility transistors (PHEMT) gate recess processes, no obvious drain current decrease can be perceived even after 8 min overetching. The etched surface is very smooth with the roughness of only 1.97 Angstrom. The devices also show excellent etched uniformity with a small threshold voltage deviation of 28 mV and good electrical performance, which is useful to the heterostructure device fabrications.