INCREASED MODULATION DEPTH OF SUBMICRON GRATINGS PRODUCED BY PHOTOELECTROCHEMICAL ETCHING OF GAAS

Submicron optical diffraction gratings with improved modulation depth were photoelectrochemically etched on n-GaAs. This etching technique uses an elevated etchant temperature to exceed the spatial resolution limits imposed by etching at room temperature, and provides a method of photoelectrochemical etching of gratings whose period is shorter than those of previously reported photoelectrochemically etched gratings. The improved grating modulation depth, the result of an increase in electrolyte temperature, was experimentally measured by etching 0.28-mu-m period gratings at five different temperatures. These results are compared with theoretical predictions based on analytical expressions for the reaction rate at the etched surface. Experimentally, a 25-degrees-C increase in the etching temperature improved the grating amplitude by a factor of 1.7, which is in agreement with the theoretical predictions.