Highly polarized photoluminescence from c-plane InGaN/GaN multiple quantum wells on stripe-shaped cavity-engineered sapphire substrate

Jongmyeong Kim,Yongjo Park,Seoung-Hwan Park,Jehong Oh,Seungmin Lee,Jungel Ryu,Euijoon Yoon

doi:10.1038/s41598-019-44519-2

Abstract

Highly polarized photoluminescence (PL) from c-plane InGaN/GaN multiple quantum wells (MQWs) grown on stripe-shaped cavity-engineered sapphire substrate (SCES) was realized. The polarization ratio was as high as 0.74 at room temperature. High-resolution X-ray reciprocal space mapping measurements revealed that the InGaN quantum wells on GaN/SCES template were under considerable anisotropic in-plane strain states of −1.178% and −1.921% along the directions perpendicular and parallel to the stripe-pattern, respectively. The anisotropic strain states were attributed to the anisotropic alignment of cavity-incorporated sapphire nano-membranes, which accommodated both anisotropic elastic relaxation in the InGaN quantum well plane as well as the graded elastic relaxation along the vertical direction in the GaN template adjacent to the InGaN/GaN MQWs. The partial strain relaxation in the InGaN wells also contributed to reduction of quantum confined Stark effect, resulting in four times higher PL intensity than InGaN/GaN MQWs on planar sapphire substrate. From theoretical calculations based on k∙p perturbation theory, it was found that fundamental origin of the polarized optical emission was strain-induced modification of valence band structures of the InGaN/GaN MQWs on the SCES. This study will allow us to realize light emitting diodes with highly polarized emission with conventional c-plane sapphire substrates by strain-induced valence band modification.

Highlights

GaN-based light emitting diodes (LEDs) have been widely used in many lighting applications due to their high efficiency and substantial energy savings
We report a realization of the polarized light emission from c-plane InGaN/GaN multiple quantum wells (MQWs) grown on the GaN/SCES template
Structural properties of the reference sample and InGaN/GaN MQWs grown on the GaN/SCES template were analyzed by scanning transmission electron microscopy (STEM), high-resolution X-ray diffraction (XRD) and X’pert Epitaxy Smoothfit software[35], and high-resolution TEM

Summary

Introduction

GaN-based light emitting diodes (LEDs) have been widely used in many lighting applications due to their high efficiency and substantial energy savings. An additional plasma etching process could cause plasma damage and the reduction of active area Other methods such as packaging for side wall emission[21,22] or the integration of metallic nano-gratings have been investigated[23,24]. These methods required complex post-processes for extracting the polarized light emission or resulted in the loss of light due to reflection at the interface between LEDs and the metallic nano-gratings. Strain relaxation in InGaN wells and resultant improvement in optical properties of c-plane InGaN/GaN MQWs have been reported, the structures have been limited to top-down etched nano-structures accompanied by plasma damage and reduction of active area[27,28,29,30]

Methods

Results

Conclusion