Improvements in Optical Power and Emission Angle of Blue Light Emitting Diodes Using Patterned Sapphire Substrates with Low Threading Dislocation Densities

Abstract

GaN blue light-emitting diodes (LEDs) with a peak emission wavelength of approximately 461 nm were fabricated on a c-face lens patterned sapphire substrate (PSS) and an unpatterened sapphire substrate (UPSS) by metal organic chemical vapor deposition (MOCVD). The crystal structure of an epitaxial GaN film was improved by using the PSS. The peak wavelengths with electroluminescence intensities of 462 and 464 nm were measured for PSS and UPSS LEDs using a 20 mA injection current. It was found that the electroluminescence intensity of the LEDs grown on the lens PSS was about 61% higher than that of the LEDs prepared on the UPSS. The emission angle of the PSS LED increased by 1.5 times compared with that of the UPSS LED. The luminous intensities of both LEDs increased similarly on both circular and square reflectors. The output power of the PSS LED was 33% greater than that of the LED UPSS. In addition, the reduction in full width at half maximum (FWHM) in the ω-scan rocking curves of GaN on the PSS suggested an improved crystal quality. These significant improvements in output power and emission angle resulted from the enhanced light extraction and the reduced threading dislocation (TD) density using the PSS method.

InGaN-Based Light-Emitting Diodes Fabricated on Nano Patterned Sapphire Substrates with Pillar Height of More than 600 nm by Nanoimprint Lithography

“…In addition, a nano pattern has attracted considerable attention for the further improvement of the light extraction efficiency of InGaN-based lightemitting diodes (LEDs) as an alternative to a conventional micro pattern. [6][7][8][9][10] Nano patterns are fabricated by various methods, such as ball up of metal, 11) electron beam lithography, 12) two-beam holographic lithography, 13) NIP technique, 14) thermal lithography, 15) and a femtosecond laser technique. 16) So far, nano structures, such as a PSS, [17][18][19] a SiO 2 mask on sapphire 20) or in a GaN layer, 21) patterned p-type GaN, 22) patterned ITO, 23) and patented n-type GaN of a thin film LED, 24) have been used for the improvement in light extraction efficiency.…”

Improved External Quantum Efficiency and Controlled Light Distribution for Light-Emitting Diodes with Cone Array Composed of SiO$_{x}$N$_{y}$

“…1,2) The use of a patterned sapphire substrate (PSS) is one means of improving LEE, and various types of PSS have been reported. [3][4][5][6][7] In a previous study, we demonstrated a high EQE using a PSS with a randomly arranged cone array. 8) In recent years, PSSs with structures such as cones and hemispheres have become popular for realizing high-efficiency LEDs, and the effect of PSSs on the LEE has been calculated by many groups.…”