Defect sensitive etching of nitrides: appraisal of methods

Abstract

AbstractDefect selective etching methods used for structural characterization of nitrides (GaN, AlGaN, InGaN and AlN) single crystals and epitaxial layers are summarized. The mechanism of surface reactions during orthodox chemical etching and photoetching is briefly described. Examples of defects which can be revealed mainly in bulk and epitaxial GaN using different etching systems are shown together with schematic models of defects. Special attention is given to selective etching and analysis of complex electrically active non‐homogeneities in bulk and HVPE‐grown GaN, which show up as areas of different etch rate, i.e. different carrier concentration. These defects are clearly visible after photo‐etching on both Ga‐polar surface and on any non‐polar cleavage plane. Ultra high selectivity of electroless photoetching on electrically active defects is explained by separation of photocurrent‐potential plots of areas with different carrier concentration. Formation of nano‐pillars on dislocations during photoetching is explained by recombinative properties of linear defects for photo‐generated carriers. Special applications of defect‐selective etching methods for (i) nano‐patterning of GaN surface for preparing highly efficient platforms for surface enhanced Raman spectroscopy (SERS) measurements and (ii) overgrowth of deep etch pits for reduction of dislocation density during HVPE growth of thick GaN crystals is also demonstrated. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)