The morphologies and optical properties of three-dimensional GaN nano-cone arrays

Abstract

Three-dimensional (3D) GaN nanostructures with well-aligned nano-cones have been prepared via a laser interference lithography + inductively coupled plasma (ICP) etching method. The effect of radio-frequency (RF) power and KOH solution etching on morphologies and optical properties of the GaN nano-cones has been studied by scanning electron microscopy, energy dispersive spectroscopy, room-temperature and low-temperature photoluminescence (PL) measurements. Our results show that the sidewall obliquity of GaN nano-cones increases from 63° to 80° with the increase of RF power from 60 W to 120 W, while their height and PL intensity peak at the RF power of 80 W. At 10 K, the excitonic interband Γ^V₉–Γ^C₇ and Γ^V₇ (upper band)–Γ^C₇ transitions were clearly observed for the GaN nano-cones, which were found to be 3.487 eV and 3.493 eV, respectively. After etching with KOH solution the nano-cones' surface was obviously roughened and their PL intensity increased by around 60%, although their internal quantum efficiency determined by low-temperature PL measurement was only increased by 6%. The enhanced PL intensity could be mainly ascribed to the improved light extraction efficiency and/or light absorption efficiency. It is expected that the 3D GaN nanostructures prepared in the work can offer a new growth template candidate for the fabrication of GaN based nanoLEDs.