Selective wet etching of GaAs on Al0.24Ga0.76As for GaAs/Al0.24Ga0.76As/In0.22Ga0.78As PHEMT

A selective etching solution of GaAs over Al0.24Ga0.76As, composed of acid- buffer solution (citric acid monohydrate + potassium citrate) and H2O2. has been developed for GaAs/Al0.24Ga0.76As/In0.22Ga0.78As PHEMT applications. The best selectivity of 776 was achieved using the mixed solution (citric a cid-buffer solution:H2O2 = 5:1). The etch rate of GaAs in the solution is a s low as 46.6 Angstrom /s. Both the low etch rate of GaAs and the high sele ctivity exhibit the standard deviation of pinch-off voltage of 1.0 mum-gate PHEMTs as low as +/-0.029V across a 3 in wafer. This demonstrates the appl icability of this solution to the gate recess process.