Phosphor-Free Apple-White LEDs with Embedded Indium-Rich Nanostructures Grown on Strain Relaxed Nano-epitaxy GaN

C B Soh,S Tripathy,S Y Chow,R J N Tan,S J Chua,W Liu,A M Yong

doi:10.1007/s11671-010-9712-0

Abstract

Phosphor-free apple-white light emitting diodes have been fabricated using a dual stacked InGaN/GaN multiple quantum wells comprising of a lower set of long wavelength emitting indium-rich nanostructures incorporated in multiple quantum wells with an upper set of cyan-green emitting multiple quantum wells. The light-emitting diodes were grown on nano-epitaxially lateral overgrown GaN template formed by regrowth of GaN over SiO2 film patterned with an anodic aluminum oxide mask with holes of 125 nm diameter and a period of 250 nm. The growth of InGaN/GaN multiple quantum wells on these stress relaxed low defect density templates improves the internal quantum efficiency by 15% for the cyan-green multiple quantum wells. Higher emission intensity with redshift in the PL peak emission wavelength is obtained for the indium-rich nanostructures incorporated in multiple quantum wells. The quantum wells grown on the nano-epitaxially lateral overgrown GaN has a weaker piezoelectric field and hence shows a minimal peak shift with application of higher injection current. An enhancement of external quantum efficiency is achieved for the apple-white light emitting diodes grown on the nano-epitaxially lateral overgrown GaN template based on the light -output power measurement. The improvement in light extraction efficiency, ηextraction, was found to be 34% for the cyan-green emission peak and 15% from the broad long wavelength emission with optimized lattice period.

Highlights

High efficient group-III nitride-based light emitting diodes (LEDs) have been intensively developed in recent years for various applications such as street and traffic lights, back lighting and for headlights of automobiles
We demonstrate the growth of InGaN/GaN LEDs incorporating indium-rich InGaN nanostructures on the nano-epitaxy lateral overgrown GaN template
The use of nano-epitaxially lateral overgrown (ELO) GaN template for growth of LEDs is effective in improving the light output performance of the LEDs through improvement of internal quantum efficiency through the reduction of threading dislocations and stress relaxation

Summary

Introduction

High efficient group-III nitride-based light emitting diodes (LEDs) have been intensively developed in recent years for various applications such as street and traffic lights, back lighting and for headlights of automobiles. At low temperature (4–100 K), the luminescence of the sample arises from the localized quantum like states of the indiumrich InGaN nanostructures, which has a higher efficiency than conventional InGaN/GaN MQWs. Excited carriers from the GaN film tend to relax and recombine at these quantum-dot-like states.

Results

Conclusion