Recent advances in defect-selective etching of GaN

Abstract

In this communication two defect-selective etching methods for GaN are evaluated and critically compared: (i) orthodox etching in molten bases (KOH–NaOH eutectic denoted E) and in hot H 2SO 4/H 3PO 4 acids (denoted HH etching) and (ii) photoelectrochemical (PEC) etching in aqueous KOH solutions. The parameters of etching are given for different type of materials, i.e. bulk crystals and epitaxial layers, for both Ga- and N-polar {0 0 0 1} surfaces. It is shown that molten bases are effective in revealing nano-pipes, inversion domains (IDs) and some dislocations, but the optimal etching parameters depend on the type of material, type and density of defects and polarity. Both orthodox etchants that result in the formation of pits on dislocations are also suitable for revealing micro-defects in heavily Mg-doped GaN single crystals but instead of pits, protruding etch features are formed. The reliability and limitations of these etching methods in revealing defects are demonstrated by means of transmission electron microscopy (TEM) calibration and by the selective formation of etch pits on dislocations introduced by indentation. Comparison with PEC etching, newly developed for GaN, is briefly discussed.