Role of hole confinement in the recombination properties of InGaN quantum structures

M Anikeeva,L Lymperakis,J W Tomm,R Calarco,T Schulz,F Mahler,M Albrecht,C Chèze,J Neugebauer

doi:10.1038/s41598-019-45218-8

Abstract

We study the isolated contribution of hole localization for well-known charge carrier recombination properties observed in conventional, polar InGaN quantum wells (QWs). This involves the interplay of charge carrier localization and non-radiative transitions, a non-exponential decay of the emission and a specific temperature dependence of the emission, denoted as “s-shape”. We investigate two dimensional In0.25Ga0.75N QWs of single monolayer (ML) thickness, stacked in a superlattice with GaN barriers of 6, 12, 25 and 50 MLs. Our results are based on scanning and high-resolution transmission electron microscopy (STEM and HR-TEM), continuous-wave (CW) and time-resolved photoluminescence (TRPL) measurements as well as density functional theory (DFT) calculations. We show that the recombination processes in our structures are not affected by polarization fields and electron localization. Nevertheless, we observe all the aforementioned recombination properties typically found in standard polar InGaN quantum wells. Via decreasing the GaN barrier width to 6 MLs and below, the localization of holes in our QWs is strongly reduced. This enhances the influence of non-radiative recombination, resulting in a decreased lifetime of the emission, a weaker spectral dependence of the decay time and a reduced s-shape of the emission peak. These findings suggest that single exponential decay observed in non-polar QWs might be related to an increasing influence of non-radiative transitions.

Highlights

The growth of high quality InGaN quantum wells has been one of the key inventions that paved the way to efficient group III-Nitride based light emitting diodes[1,2,3]
Our system consists of single ML thick InGaN quantum wells separated by GaN barriers ranging from 50 MLs to 6 MLs, so we can control the charge carrier confinement as done for group III-Arsenide semiconductors[17,18,19,20]
quantum wells (QWs) separated by GaN barriers of different thickness were grown by molecular beam epitaxy (MBE) at 550 °C23

Summary

Introduction

The growth of high quality InGaN quantum wells has been one of the key inventions that paved the way to efficient group III-Nitride based light emitting diodes[1,2,3]. Several models have been proposed to explain the observed phenomena based on the: (i) spatial separation of localized, both, electrons and holes[13]; (ii) variation of the local polarization fields due to the compositional fluctuations[14,15]; (iii) charge carrier transfer to lower energy states[16]. All these diverse models were proposed for bulk or few nm thick QW systems, where various localization phenomena interact in a complex and dynamic way.

Methods

Results

Discussion

Conclusion