Correlation between Structural and Photoelectrochemical Properties of GaN Porous Nanostructures Formed by Photo-Assisted Electrochemical Etching

Abstract

We investigated the correlation between structural and photoelectrochemical properties of GaN porous nanostructures formed by photo-assisted electrochemical etching. The porous nanostructures were formed during light irradiation of the top-surface of homo-epitaxial layers grown on freestanding GaN substrates. The pore depth, wall thickness, and surface morphology of porous nanostructures were strongly influenced by the way holes generated by the light irradiation were supplied. Such structural features influenced the optical properties of GaN porous nanostructures. The photoluminescence peaks measured on GaN porous nanostructures were shifted to higher energies because of the quantum confinement in the thin GaN walls between pores. Formation of porous nanostructure decreased the photoreflectance of the GaN surface, and the smallest reflectance was obtained from the porous sample having large pores on its surface after the ultrathin layer with small pores had been removed by surface-etching. The photoelectrochemical response measured on GaN porous nanostructures in a NaCl electrolyte were drastically enhanced by the unique features of those structures, such as low photoreflectance and large surface area. The largest photocurrents were obtained from the sample from which H3PO4 treatment had removed the ultrathin layer without thinning the pore walls.