Selective etching of GaAs and Al0.30Ga0.70As with citric acid/hydrogen peroxide solutions

A volumetric 10:1 ratio of citric acid (50% by weight) and hydrogen peroxide (30%) is shown to be a better selective etchant of GaAs/Al0.30Ga0.70As systems than the more commonly used ammonium-hydroxide/hydrogen peroxide solutions in terms of the selectivity of the etching rate, the smoothness of the etched surface, and the abruptness of the etch-defined edge. In addition, the citric acid/hydrogen peroxide solution does not attack Shipley 1400 series positive photoresists. This simple and reproducible selective etching process has been applied to prepare GaAs optical devices for transmission measurements (‘‘doughnut’’ samples).