Cathodoluminescence hyperspectral imaging of trench-like defects in InGaN/GaN quantum well structures

Jochen Bruckbauer,Suman-Lata Sahonta,Colin J Humphreys,Menno J Kappers,Rachel A Oliver,Robert W Martin,Paul R Edwards,Fabien C-P Massabuau

doi:10.1088/0022-3727/47/13/135107

Jochen Bruckbauer, Suman-Lata Sahonta + Show 6 more

Open Access

https://doi.org/10.1088/0022-3727/47/13/135107

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Abstract

Optoelectronic devices based on the III-nitride system exhibit remarkably good optical efficiencies despite suffering from a large density of defects. In this work we use cathodoluminescence (CL) hyperspectral imaging to study InGaN/GaN multiple quantum well (MQW) structures. Different types of trench defects with varying trench width, namely wide or narrow trenches forming closed loops and open loops, are investigated in the same hyperspectral CL measurement. A strong redshift (≈90 meV) and intensity increase of the MQW emission is demonstrated for regions enclosed by wide trenches, whereas those within narrower trenches only exhibit a small redshift (≈10 meV) and a slight reduction of intensity compared with the defect-free surrounding area. Transmission electron microscopy (TEM) showed that some trench defects consist of a raised central area, which is caused by an increase of about 40% in the thickness of the InGaN wells. The causes of the changes in luminescences are also discussed in relation to TEM results identifying the underlying structure of the defect. Understanding these defects and their emission characteristics is important for further enhancement and development of light-emitting diodes.

Highlights

InxGa1−xN/GaN multiple quantum well (MQW) structures are the building blocks of optoelectronic devices such as light-emitting diodes (LEDs) and laser diodes [1, 2]
Secondary electron (SE) imaging revealed the presence of a high density of trench defects besides the commonly occurring V-defect
While the area enclosed by wider trench defects gives luminescence which is redshifted and more intense, the emission from inside loops with narrower trenches is only slightly redshifted and its intensity is lower compared with the surrounding region

Summary

Introduction

InxGa1−xN/GaN multiple quantum well (MQW) structures are the building blocks of optoelectronic devices such as light-emitting diodes (LEDs) and laser diodes [1, 2]. One essential parameter is the growth temperature, as it is used to control the incorporation of InN (which has a low miscibility in GaN). We use cathodoluminescence (CL) spectroscopy to demonstrate that the trench defects can be categorized into several different types and use hyperspectral images encompassing multiple, different trenches to compare their luminescence properties. Cross-section transmission electron microscopy (TEM) allows us to further characterize the structural modifications caused by the trench defect and relate them to their luminescence characteristics

Experimental section

Results and discussion

Conclusion