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Effect of Strains and V-Shaped Pit Structures on the Performance of GaN-Based Light-Emitting Diodes. CRYSTALS 2020. [DOI: 10.3390/cryst10040311] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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.
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Fernando JFS, Zhang C, Firestein KL, Golberg D. Optical and Optoelectronic Property Analysis of Nanomaterials inside Transmission Electron Microscope. SMALL (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2017; 13. [PMID: 28902975 DOI: 10.1002/smll.201701564] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/12/2017] [Revised: 07/11/2017] [Indexed: 05/10/2023]
Abstract
In situ transmission electron microscopy (TEM) allows one to investigate nanostructures at high spatial resolution in response to external stimuli, such as heat, electrical current, mechanical force and light. This review exclusively focuses on the optical, optoelectronic and photocatalytic studies inside TEM. With the development of TEMs and specialized TEM holders that include in situ illumination and light collection optics, it is possible to perform optical spectroscopies and diverse optoelectronic experiments inside TEM with simultaneous high resolution imaging of nanostructures. Optical TEM holders combining the capability of a scanning tunneling microscopy probe have enabled nanomaterial bending/stretching and electrical measurements in tandem with illumination. Hence, deep insights into the optoelectronic property versus true structure and its dynamics could be established at the nanometer-range precision thus evaluating the suitability of a nanostructure for advanced light driven technologies. This report highlights systems for in situ illumination of TEM samples and recent research work based on the relevant methods, including nanomaterial cathodoluminescence, photoluminescence, photocatalysis, photodeposition, photoconductivity and piezophototronics.
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Affiliation(s)
- Joseph F S Fernando
- School of Chemistry, Physics and Mechanical Engineering, Science and Engineering Faculty, Queensland University of Technology (QUT), 2 George Street, Brisbane, QLD, 4000, Australia
| | - Chao Zhang
- School of Chemistry, Physics and Mechanical Engineering, Science and Engineering Faculty, Queensland University of Technology (QUT), 2 George Street, Brisbane, QLD, 4000, Australia
| | - Konstantin L Firestein
- School of Chemistry, Physics and Mechanical Engineering, Science and Engineering Faculty, Queensland University of Technology (QUT), 2 George Street, Brisbane, QLD, 4000, Australia
- National University of Science and Technology "MISIS", Leninsky prospect 4, Moscow, 119049, Russia
| | - Dmitri Golberg
- School of Chemistry, Physics and Mechanical Engineering, Science and Engineering Faculty, Queensland University of Technology (QUT), 2 George Street, Brisbane, QLD, 4000, Australia
- World Premier International Center for Materials Nanoarchitectonics (WPI-MANA), National Institute for Materials Science (NIMS), Namiki 1-1, Tsukuba, Ibaraki, 3050044, Japan
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Chen SW, Li H, Chang CJ, Lu TC. Effects of Nanoscale V-Shaped Pits on GaN-Based Light Emitting Diodes. MATERIALS 2017; 10:ma10020113. [PMID: 28772476 PMCID: PMC5459134 DOI: 10.3390/ma10020113] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/14/2016] [Revised: 01/08/2017] [Accepted: 01/23/2017] [Indexed: 11/25/2022]
Abstract
This paper reviews the formation of nanoscale V-shaped pits on GaN-based light emitting diodes (LEDs) grown by the metal organic chemical vapor deposition (MOCVD) system and studies the effect of V-shaped pits on quantum efficiency. Since V-pits could provide potential barriers around threading dislocations to lessen non-radiative recombinations in such a high defect environment. In our study, multiple InGaN/GaN quantum well samples with different emission wavelengths of 380, 420, 460, and 500 nm were grown, each with different nanoscale V-shaped pits of three diameters for 150, 200, and 250 nm, respectively. It was found that the multiple quantum well (MQW) sample with larger V-pits had a lower pit density, but a relatively larger total V-pits defected area. The optimum diameter of V-pits showing the highest quantum efficiency from the MQW sample depended on the emission wavelength. MQW samples with wavelengths of 380 and 500 nm exhibited the best internal quantum efficiency (IQE) performance at the smallest V-pits area; however, the best performance for MQW samples with wavelength around 420 and 460 nm occurred when large V-pit areas were presented. Photoluminescence (PL) peak shifts and Raman shifts can provide a relationship between quantum-confined Stark effect (QCSE) and IQE, as well as a comparison between strain and IQE. The results obtained in this phenomenological study shall provide a useful guide line in making high-performance GaN-based LEDs with wide emission spectra.
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Affiliation(s)
- Shuo-Wei Chen
- Department of Photonics, National Chiao Tung University, Hsinchu 300, Taiwan.
- Epistar Corporation, Hsinchu 300, Taiwan.
| | - Heng Li
- Department of Photonics, National Chiao Tung University, Hsinchu 300, Taiwan.
| | - Chia-Jui Chang
- Department of Photonics, National Chiao Tung University, Hsinchu 300, Taiwan.
| | - Tien-Chang Lu
- Department of Photonics, National Chiao Tung University, Hsinchu 300, Taiwan.
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Pennycook SJ. Investigating the optical properties of dislocations by scanning transmission electron microscopy. SCANNING 2008; 30:287-298. [PMID: 18613065 DOI: 10.1002/sca.20114] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
The scanning transmission electron microscope (STEM) allows collection of a number of simultaneous signals, such as cathodoluminescence (CL), transmitted electron intensity and spectroscopic information from individual localized defects. This review traces the development of CL and atomic resolution imaging from their early inception through to the possibilities that exist today for achieving a true atomic-scale understanding of the optical properties of individual dislocations cores. This review is dedicated to Professor David Holt, a pioneer in this field.
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Affiliation(s)
- S J Pennycook
- Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA.
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Bourret A, Desseaux J, Renault A. Core structure of the Lomer dislocation in germanium and silicon. ACTA ACUST UNITED AC 2006. [DOI: 10.1080/01418618208243899] [Citation(s) in RCA: 73] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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Myhajlenko S, Batstone JL, Hutchinson HJ, Steeds JW. Luminescence studies of individual dislocations in II-VI (ZnSe) and III-V (InP) semiconductors. ACTA ACUST UNITED AC 2000. [DOI: 10.1088/0022-3719/17/35/017] [Citation(s) in RCA: 84] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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Fitzgerald E. Dislocations in strained-layer epitaxy: theory, experiment, and applications. ACTA ACUST UNITED AC 1991. [DOI: 10.1016/0920-2307(91)90006-9] [Citation(s) in RCA: 354] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
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Cathodoluminescence Characterization of Semiconductors. SEM MICROCHARACTERIZATION OF SEMICONDUCTORS 1989. [DOI: 10.1016/b978-0-12-353855-0.50014-2] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
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