Structural and optical properties of near-UV LEDs grown on V-grooved sapphire substrates fabricated by wet etching

Abstract

V-grooved sapphire substrates (VGSS) were fabricated by a simple wet etching process with SiO2 stripe masks along < 1 (1) over bar 20 > orientation of the sapphire substrate and a mixed solution of H2SO4 and H3PO4. The growth of low-defect GaN template was optimized by two-step growth technique of metalorganic vapor deposition (MOCVD), resulting in the threading dislocation (TD) density of 2-4 x 10(7) cm(-2) in the entire region of the GaN template. The epitaxial structure of near-UV light emitting diode (LED) was grown on the GaN templates on both the VGSS and the flat sapphire substrate (FSS) in order to compare the characteristics of their structural and optical properties. The internal quantum efficiency and the extraction efficiency of the LED structure grown on the VGSS were remarkably increased when compared to the conventional LED structure grown on the FSS. It seems to be attributed to the reduction in the TD density of the GaN template on the VGSS and the decrease in the number of times of total internal reflections of the light flux due to the V-grooved pattern, respectively. The increase in optical output power of the LED grown on the VGSS agreed well with the expected value based on the simulation of the commercial Light Tool program and temperature-dependent photoluminescence (PL) intensities. (c) 2006 Elsevier B.V. All rights reserved.