Complementary study of defects in GaN by photo-etching and TEM

Photoelectrochemical (PEC) etching in KOH aqueous solutions has been used to study defects in N-polar hetero-epitaxial GaN layers. Detailed cross-sectional TEM study of PEC-etched material revealed that apart from dislocations, also inversion domains (IDs) give rise to the formation of etch features. When the diameter of IDs remains in the tens of nanometer range, the defects are entirely resistant to the etching medium. However, IDs with diameters above the critical value (∼80 nm) are preferentially etched in their centers, resulting in the formation of pronounced crater-like etch features. This indicates that photo-etching of GaN takes place via the ‘electroless’ mechanism, with the critical role of holes for surface reactions and points at the recombinative property of inversion domain boundaries (IDBs).