Fabrication of an InGaN/GaN-based LED nanorod array by nanosphere lithography and its optical properties

Abstract

In order to reduce the residual strain in multiple quantum wells (MQWs) with an InGaN/GaN heterostructure and enhance the light extraction efficiency of a gallium-nitride-based LED simultaneously, we fabricated a highly periodic multiple quantum well (MQW) nanorod array with an InGaN/GaN heterostructure capable of reducing the residual strain inside the GaN lattice and acting as a two-dimensional (2D) photonic crystal (PC) using polystyrene (PS) nanosphere lithography (NSL) followed by a reactive ion etching (RIE) process and an inductively coupled plasma-reactive ion etching (ICP-RIE) process. Each individual InGaN/GaN nanorod has a tapered shape from bottom to top with dimensions of 2 ∼ 2.5 µm (length) and 400 ∼ 600nm (diameter). Structural and morphological measurements were undertaken using a field-emission scanning electron microscope (FE-SEM), and the optical properties were measured by scanning-electron-microscope cathodoluminescence (SEM-CL) and photoluminescence (PL) instruments. The proposed InGaN/GaN MQW nanorod array demonstrated higher MQW intensity levels compared to non-processed bare GaN wafer in both the PL and the CL spectra due to the relaxation of residual strain and the increment of the extraction efficiency through the highly periodic 2D photonic crystal structure.