The Way to Uniformity in Porous III–V Compounds via Self-Organization and Lithography Patterning

Electrochemical etching techniques offer wide possibilities for modifying the surface morphology of semiconductors. Depending on the substrate type, electrolyte, illumination, etc., anodic etchingmay lead to both the electropolishing and the formation of pores. The factors determining the morphology of electrochemically etched III–V compounds have been reviewed by Gomes and Goossens as well as by Notten et al. [1,2]. Under anodic conditions the pand n-type materials were found to behave quite differently. For instance, in the case of p-GaAs substrates in acidic solutions, the current in the anodic direction rises rapidly to very high values causing electropolishing of the material [3]. At the same time the n-GaAs/aqueous electrolyte interface shows diode characteristics. Under forward bias a cathodic current is observed, while under reverse bias the current measured in the dark is very low. In the case of n-type materials under anodic bias, the current limiting factor seems to be the space-charge layer at the semiconductor surface, i.e., the electron transfer at the interface is limited by tunnelling through the depletion