Non-Holographic Periodic Structures

The crystaiiographic orientationai effects on the photoanodic etching profiies are particulariy usefui in fabricating Echeiie-type diffraction gratings 

n is the electron stoichiometry (equivalents/mole) of the photoanodic dissolution reaction, W is the width (cm) of each groove, a is the angle of the groove face with respect to the (100) surface, p is the angle of the crystal slice with respect to the (100) surface, and N is the number of grooves/cm. 

An example from this laboratory demonstrates the photoelectrochernical etching of blazed structures. Crystals of n-GaAs (Nq = 5x1 O Vcm ) were cut and polished with (100), (100)-8° and (100)-18° orientations. The other parameters in Eq. 5 were n = 6, N = 500 and W = 2x1 O cm. The electrolyte composition was 0.1 M KCI, adjusted to pH 3, and the light intensity was 30 mW/cm . The potential was held at the onset of the photon limited region, 0.4 volt vs. SCE. Initial structures were etched under the assumption that the interior angles were 70.54°, as defined by the (ill) Ga surfaces. However, we found under closer examination that this angle was dependent on the etching conditions and on the electrolyte, and was closer to 90° under the present conditions. This would correspond most closely to the (223)Ga-rich surface. With a 

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