The Development of a Highly Selective KI/I 2 /H 2 O/H 2 SO 4 Etchant for the Selective Etching of Al 0.3 Ga 0.7 As over GaAs

The selective etching of n-Al 0.3 Ga 0.7 As with respect to p + -GaAs is useful for the fabrication of AlGaAs/GaAs heterojunction bipolar transistors (HBTs). The KI/I 2 /H 2 O/H 2 SO 4 etching solution was found to be superior to the KI/I 2 /H 2 O solution in terms of selectivity. The selectivity could be furthered improved by aging the etching solution for 3 days and by lowering the temperature from room temperature to the ice point. The best selectivity achieved was 330 with etch rates of 0.165 µ m/min and 0.0005 µ m/min for Al 0.3 Ga 0.7 As and GaAs respectively for a stabilized KI/I 2 /H 2 O/H 2 SO 4 at an etching temperature of 3° C.