Changes in Surface Morphology and Photoluminescence Spectrum during Photoelectrochemical Etching of (0001) n-GaN on Sapphire

Surface morphological and 10K photoluminescence (PL) spectral changes during photoelectrochemical (PEC) etching for (0001) face of n-GaN on sapphire are reported. The etching is initiated from the step edges and the etch pit density increases to 5× 1010 cm-2 which is larger than the total dislocation density of GaN sample. Subsequently, the neighboring etch pits are connected to form triangular hillocks which are surrounded by {11-20} facets. Then the whisker structure is formed by way of mesh morphology. The whisker density is nearly equal to the dislocation density including edge dislocation (2× 109 cm-2). The donor-bound exciton peak of as-grown n-GaN redshifts 24 meV by the whisker formation, indicating the relaxation of compressive strain and the contribution of deeper impurity bound excitons. The broad peaks of lower energies than 3.35 eV are enhanced by the whisker formation. [DOI: 10.1380/ejssnt.2010.392]