Effects of electrochemical attack on GaAs(100) surfaces

The search for porous and/or nanostructured semiconductors is a continuing one, which is also the case for HI-V materials. In this work the surface of GaAs bulk and epitaxial structures was investigated by electrochemical treatment. Anodic oxidation in a water solution of tiron was applied. Dark, +/-1.5 V bias voltages, various current densities and various integrated charge values were applied. Microscopic investigation of the treated surfaces indicated the indispensable role of surface and crystallographic defects in the starting phases of the electrochemical etching. Three basic and general types of shapes of etch pits, connected with dislocations, were distinguished. Possible porosity was suspected in bulk samples, in highly doped n(++) substrate material. The epitaxial structures showed a very new effect: selective etching of the substrate, the formation of cavities in the substrate material below the epitaxial film.