Effect of Strains and V-Shaped Pit Structures on the Performance of GaN-Based Light-Emitting Diodes

Shuo-Wei Chen,Chia-Jui Chang,Tien-Chang Lu

doi:10.3390/cryst10040311

Shuo-Wei Chen, Chia-Jui Chang + Show 1 more

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https://doi.org/10.3390/cryst10040311

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Abstract

Strains and V-shaped pits are essential factors for determining the efficiency of GaN-based light-emitting diodes (LEDs). In this study, we systematically analyzed GaN LED structures on patterned sapphire substrates (PSSs) with two types of growth temperature employed for prestrained layers and three different thickness of n-type GaN layers by using cathodoluminescence (CL), microphotoluminescence (PL), and depth-resolved confocal Raman spectroscopy. The results indicated that V-pits formation situation can be analyzed using CL. From the emission peak intensity ratio of prestrained layers and multiple quantum wells (MQWs) in the CL spectrum, information regarding strain relaxation between prestrained layers and MQWs was determined. Furthermore, micro-PL and depth-resolved confocal Raman spectroscopy were employed to validate the results obtained from CL measurements. The growth conditions of prestrained layers played a dominant role in the determination of LED performance. The benefit of the thick layer of n-GaN was the strain reduction, which was counteracted by an increase in light absorption in thick n-type doped layers. Consequently, the most satisfactory LED performance was observed in a structure with relatively lower growth temperature of prestrained layers that exhibited larger V-pits, leading to higher strain relaxation and thinner n-type GaN layers, which prevent light absorption caused by n-type GaN layers.

Highlights

The research on high-brightness laser diodes and light-emitting diodes (LEDs) based onGaN materials and InGaN/GaN multiple quantum wells (MQWs) considerably advanced in the1990s [1,2,3,4]
In sample D, only small V-pits were obtained near the surface region, and threading dislocations (TDs) acted as nonradiative recombination centers when they passed through MQWs
Strain relaxation and V-shaped pit formation in InGaN MQWs were controlled through the growth temperature of prestrained layers

Summary

Introduction

The research on high-brightness laser diodes and light-emitting diodes (LEDs) based onGaN materials and InGaN/GaN multiple quantum wells (MQWs) considerably advanced in the1990s [1,2,3,4]. The research on high-brightness laser diodes and light-emitting diodes (LEDs) based on. GaN materials and InGaN/GaN multiple quantum wells (MQWs) considerably advanced in the. Crystal lattice mismatch constants and differences in thermal expansion coefficients between GaN layers and. Al2 O3 substrates cause high-density threading dislocations (TDs; 108 –1010 /cm2 ) [8,9,10], which are nonradiative recombination centers that reduce the quantum efficiency of light-emitting devices [11,12,13,14,15]. To fulfill the requirements for high-brightness solid-state lighting applications, achieving a high-quality growth of InGaN material is necessary [16,17,18]. The band gap energies of InN and GaN are 0.7 and 3.4 eV, respectively.

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