Improvement in Extraction Efficiency of GaN-Based Light-Emitting Diodes with Textured Surface Layer by Natural Lithography

Abstract

In this study, p-side-up GaN-based light-emitting diodes (LEDs) with textured indium-tin oxide (ITO) or silicon dioxide (SiO 2 ) surface layers were investigated by natural lithography using polystyrene spheres (PSs) as an etching mask. It was found that the ITO top layer provides better roughness than SiO 2 . Under the optimum surface treatment parameter, the roughnesses of textured ITO and SiO 2 surface layers are 140 nm and 15 nm, respectively. The diameter of PSs in the textured ITO surface is still maintained at about 250-300 nm. Correspondingly, the size of PSs in the SiO 2 surface is reduced to about 100 nm. The output powers of LEDs with textured ITO and SiO 2 surfaces and conventional LEDs are 10.9, 9.5, and 8.5 mW at 20 mA, respectively. LEDs fabricated using the textured ITO surface produced an output power that exceeded that of planarsurface LEDs by about 28% at 20 mA dc current.

Fabrication of GaN-based LEDs with 22° undercut sidewalls by inductively coupled plasma reactive ion etching

“…[5][6][7][8][9] It has been shown that one could construct the GaN surface so that photons can escape easily thus enhancing the LED out-put intensity. [10,11] It is also possible to improve the brightness of the GaN-based LED by fabricating oblique sidewalls. Gao et al [12] reported on the extraction efficiency enhancement by nano-roughened p-GaN surface.…”

Simulation for light power distribution of 3D InGaN/GaN MQW LED with textured surface

“…Textured surface technique became popular in order to avoid the problem that external quantum efficiency is limited by the total internal reflection of emitting light at interface of semiconductor and air due to large difference of refractive index (Yang et al 2005). To form surface texture pattern, several techniques are applied, such as anisotropic photoelectrochemical etching process (Fujii et al 2004), natural lithography (Yang et al 2005).…”

“…Textured surface technique became popular in order to avoid the problem that external quantum efficiency is limited by the total internal reflection of emitting light at interface of semiconductor and air due to large difference of refractive index (Yang et al 2005). To form surface texture pattern, several techniques are applied, such as anisotropic photoelectrochemical etching process (Fujii et al 2004), natural lithography (Yang et al 2005). These techniques make LED surface roughened in shape of trapezia (Han et al 2006), pyramid (Fujii et al 2004) and V-shaped (Tsai et al 2006), Surface roughness is critical and must be controlled by about one-half wavelength according to (Yang et al 2005).…”

“…To form surface texture pattern, several techniques are applied, such as anisotropic photoelectrochemical etching process (Fujii et al 2004), natural lithography (Yang et al 2005). These techniques make LED surface roughened in shape of trapezia (Han et al 2006), pyramid (Fujii et al 2004) and V-shaped (Tsai et al 2006), Surface roughness is critical and must be controlled by about one-half wavelength according to (Yang et al 2005). The dimension of a single texture unit varies near LED peak wavelength (Windisch et al 1999).…”