Enhancement of InGaN-Based Light Emitting Diodes Performance Grown on Cone-Shaped Pattern Sapphire Substrates

Huanyou Wang,Yalan Li,Penghua Zhang

doi:10.4236/msce.2014.27006

Abstract

To enhance light extraction effciency, high-quality InGaN-based light emitting diodes (LED) was grown on cone-shaped patterned sapphire (CPSS) by using metal organic chemical vapor deposition (MOCVD). From the transmission electron microscopy (TEM) observation, the CPSS was confirmed to be an efficient way to reduce the threading dislocation density in the GaN epilayer. A sharp and high intensity Photoluminescence (PL) for LED on CPSS at 457 nm compared to LED on unpattern planar sapphire substrates (USS) indicates that the crystalline quality was improved significantly and the internal reflection on the cones of the substrate was enhanced. The output power of the LED on CPSS is higher than that of LED on USS. The achieved improvement of the output power is not only due to the improvement of the internal quantum efficiency upon decreasing the dislocation density, but also due to the enhancement of the extraction efficiency using the CPSS.

Highlights

InGaN-based light-emitting diodes (LEDs) are useful for a wide range of visible light applications [1]-[4]
We describe the fabrication, optical and electrical properties of InGaN LEDs on CPSS by using metal organic chemical vapor deposition (MOCVD)
The surface morphologies of LED wafers grown on CSS and on the CPSS were characterized by atomic force microscope (AFM) as shown in Figure 2(a) and Figure 2(b)

Summary

Introduction

InGaN-based light-emitting diodes (LEDs) are useful for a wide range of visible light applications [1]-[4]. (2014) Enhancement of InGaN-Based Light Emitting Diodes Performance Grown on Cone-Shaped Pattern Sapphire Substrates. Though high brightness InGaN-based LEDs are commercially available, threading dislocations (TDs) with a density of 108 - 109 cm−2 remain in the LED structures due to the large differences of lattice constant and thermal expansion coefficient between the GaN epilayer and the sapphire substrate. How to further reduce the dislocation density is an important issue for fabricating high-performance LEDs. the reflective index of nitride films is higher than that of air and sapphire substrate. The patterned sapphire substrates (PSS) technique as a maskless and growth interruption-free means has proved to be another feasible approach to reducing the TD density and the percentage of total internal light reflection through its geometrical effect [10] [11]. The structural analysis of these LEDs was observed by an atomic force microscope (AFM) and an transmission electron microscopy (TEM)

Experiment

Results and Discussion

Conclusion