Selective wet etching of GaAs on Al sub( 0.24)Ga sub( 0.76)As for GaAs/Al sub( 0.24)Ga sub( 0.76)As/In sub( 0.22)Ga sub( 0.78)As 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 acid-buffer solution:H2O2 = 5:1). The etch rate of GaAs in the solution is as low as 46.6 Aa/s. Both the low etch rate of GaAs and the high selectivity exhibit the standard deviation of pinch-off voltage of 1.0 m m-gate PHEMTs as low as plus or minus 0.029 V across a 3 in wafer. This demonstrates the applicability of this solution to the gate recess process.