In-plane bandgap control in porous GaN through electroless wet chemical etching

Nanoporous GaN structures were formed from crystalline GaN on conducting SiC substrate using metal-assisted electroless etching in HF/H₂O ₂. Morphology varies as a function of etch time and solution parameters. The resulting porous GaN (PGaN) displays cathodoluminescence (CL) with two bands blue-shifted from the bulk bandgap energy by 103 meV and 352 meV, respectively. Appearance of the blueshifted emission is correlated with the development of highly anisotropic wire-like structures in the morphology, with the higher energy CL band arising from the portion of the structure with the smallest feature sizes. These observations suggest that the blueshifted emission arises from quantum confinement effects. CL imaging indicates that the blueshifted emission is spatially segregated from the band gap emission. Variations in morphology and light emission properties apparent between Pt-coated and uncoated areas likely arise from hole transport and access of solution reagents to the GaN interface.