Mechanism of enhanced light output efficiency in InGaN-based microlight emitting diodes

Choi, H. W.; Jeon, Chan‐Wook; Dawson, Martin D.; Edwards, P. R.; Martin, Robert; Tripathy, S.

doi:10.1063/1.1567803

Cited by 130 publications

(85 citation statements)

References 12 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Our measurements also confirmed that the blue-shift in the blue QWs emission is too small to be observed due to the lower lattice mismatch between the active layers and barriers, which is consistent with our previous research. 4 Fig . 3 shows the simulated in-plane compressive strain distribution (i.e., the e xx , a component of the strain tensor) at the edge of a pillar with a diameter of 16 lm.…”

Section: Methodsmentioning

confidence: 99%

“…[3][4][5][6][7][8][9][10][11][12] The fabrication method has typically involved "top-down" patterning by etching an initially planar epitaxial structure containing InGaN/GaN QWs, although studies of directly grown nano-columnar structures have also been reported. 12 Correlations between spectroscopic results and numerical simulations of strain relaxation in the QWs were included in the reports by Yu et al 9 and Kawakami et al 10 The authors of Ref.…”

Section: Introductionmentioning

confidence: 99%

“…Clearly, further improvement of spatial resolution and simulation accuracy will enable a much better understanding of the mechanism of strain relaxation in the micro-GaN pillars, which is critically important to the design of novel micro/nano pixellated LED devices for a wide range of applications. 4,[16][17][18][19] This study focuses on the strain relaxation process in micro-pillars fabricated from an LED wafer optimized for emission at yellow-green wavelengths ($560 nm). These micro-pillars had a fixed height of 1.1 lm, and diameters systematically varied from 2 to 150 lm.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Strain relaxation in InGaN/GaN micro-pillars evidenced by high resolution cathodoluminescence hyperspectral imaging

Xie

Chen

Edwards

et al. 2012

Journal of Applied Physics

Self Cite

View full text Add to dashboard Cite

This version is available at https://strathprints.strath.ac.uk/40400/ Strathprints is designed to allow users to access the research output of the University of Strathclyde. Unless otherwise explicitly stated on the manuscript, Copyright © and Moral Rights for the papers on this site are retained by the individual authors and/or other copyright owners. Please check the manuscript for details of any other licences that may have been applied. You may not engage in further distribution of the material for any profitmaking activities or any commercial gain. You may freely distribute both the url (https://strathprints.strath.ac.uk/) and the content of this paper for research or private study, educational, or not-for-profit purposes without prior permission or charge.Any correspondence concerning this service should be sent to the A size-dependent strain relaxation and its effects on the optical properties of InGaN/GaN multiple quantum wells (QWs) in micro-pillars have been investigated through a combination of high spatial resolution cathodoluminescence (CL) hyperspectral imaging and numerical modeling. The pillars have diameters (d) ranging from 2 to 150 lm and were fabricated from a III-nitride light-emitting diode (LED) structure optimized for yellow-green emission at $560 nm. The CL mapping enables us to investigate strain relaxation in these pillars on a sub-micron scale and to confirm for the first time that a narrow ( 2 lm) edge blue-shift occurs even for the large InGaN/GaN pillars (d > 10 lm). The observed maximum blue-shift at the pillar edge exceeds 7 nm with respect to the pillar centre for the pillars with diameters in the 2-16 lm range. For the smallest pillar (d ¼ 2 lm), the total blue-shift at the edge is 17.5 nm including an 8.2 nm "global" blue-shift at the pillar centre in comparison with the unetched wafer. By using a finite element method with a boundary condition taking account of a strained GaN buffer layer which was neglected in previous simulation works, the strain distribution in the QWs of these pillars was simulated as a function of pillar diameter. The blue-shift in the QWs emission wavelength was then calculated from the strain-dependent changes in piezoelectric field, and the consequent modification of transition energy in the QWs. The simulation and experimental results agree well, confirming the necessity for considering the strained buffer layer in the strain simulation. These results provide not only significant insights into the mechanism of strain relaxation in these micro-pillars but also practical guidance for design of micro/nano LEDs.

show abstract

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Strain relaxation in InGaN/GaN micro-pillars evidenced by high resolution cathodoluminescence hyperspectral imaging

Xie

Chen

Edwards

et al. 2012

Journal of Applied Physics

Self Cite

View full text Add to dashboard Cite

show abstract

“…The blue-shift has been attributed to several different factors, such as band renormalization and band filling [383], and the screening effect of the built-in [371]. Reproduced with permission piezoelectric field [384]. As shown in Fig.…”

Section: Inorganic Heterojunction Ledsmentioning

confidence: 99%

One-dimensional ZnO nanostructures: Solution growth and functional properties

2011

View full text Add to dashboard Cite

One-dimensional (1D) ZnO nanostructures have been studied intensively and extensively over the last decade not only for their remarkable chemical and physical properties, but also for their current and future diverse technological applications. This article gives a comprehensive overview of the progress that has been made within the context of 1D ZnO nanostructures synthesized via wet chemical methods. We will cover the synthetic methodologies and corresponding growth mechanisms, different structures, doping and alloying, positioncontrolled growth on substrates, and finally, their functional properties as catalysts, hydrophobic surfaces, sensors, and in nanoelectronic, optical, optoelectronic, and energy harvesting devices.

show abstract

“…Additionally, periodic resonant modes can be observed in microdisk spectra, with a mode spacing of about 1.1nm, assigned to whispering gallery mode oscillations, as predicted by the relation ∆λ WG = λ 2 /2π Rn. 6 With increasing excitation power, non-linear increases-indicative of stimulated emission-are also observed in the intensities of the 365nm-peak beyond threshold conditions, as depicted in Figure 2(b). To conclude, a micro-cavity structure consisting of microdisks with undercuts fabricated on a GaN/Si substrate can enable optical confinement via whispering gallery modes.…”

mentioning

confidence: 83%

Whispering-gallery mode lasing in GaN microdisks

Choi¹

2007

SPIE Newsroom

View full text Add to dashboard Cite

surface-emitting microdisks overcome mirror fabrication challenges and have a high potential for generating novel microcavity devices.The wide range of wavelengths covered by the Gallium nitride (GaN) group of materials is probably the major reason for its growing use by the semiconductor industry. GaN light emitting diodes are used extensively for illumination and display purposes, 1 while UV emitters have been employed in a wide range of biomedical applications. 2 High-performance GaN transistors have also been demonstrated. The laser diodes emitting at 405nm and found in the latest high-density DVD players are also GaN-based. Shorter wavelengths allow data to be packed more tightly, so it becomes possible to fit more data on a disc even though it is the same size as a CD/DVD.GaN laser diodes are currently fabricated in the conventional edge-emitting geometry, where the laser light propagates parallel to the wafer surface of the semiconductor. However, the newer surface-emitting versions, where the light propagates in the direction perpendicular to the semiconductor surface, offer more advantages. The first is their lower fabrication cost since the chips can be tested on-wafer, unlike edge-emitters that can only be tested at the end of the fabrication process. They also offer beams with lower divergence due to large output apertures, low power consumption, and wavelength tuning.However, the transition from edge to surface emission is not trivial in GaN structures. In principle, a surface-emitting laser requires a vertical cavity with top and bottom mirrors. In practice, high quality GaN materials are grown on sapphire substrates, which makes the insertion of bottom mirrors inherently difficult. One common solution is the deposition of AlGaN/GaN distributed Bragg reflector stacks between the device structure and the sapphire substrate. 3 Alternatively, undercut microdisk lasers that address mirror insertion challenges have also been fabricated using selective photoelectrochemical etching techniques. 4 Recently, we have also developed a microdisk fabrication method based on GaN grown on Si substrates. Pivoted GaN Figure 1. Scanning-electron-microscope images showing (a) the cross section of a single pivoted microdisk and (b) a microdisk array.undercut microdisks were fabricated on GaN/Si templates using a combination of dry and wet etching processes, enabling the exposure of the bottom GaN surface. 5 In our approach, 20µm-microdisks are first defined by photolithography and subsequently transferred to a 1µm-thick GaN layer by inductively coupled plasma etching. The sample is dipped into an isotropic wet etchant which creates the undercut as it removes the Si surrounding the GaN microdisks. The wet-etching process is allowed to proceed until only a tiny Si pedestal remains to support the microdisk while providing a pathway for current injection. This is illustrated in Figure 1(a), showing the cross-sectional SEM image of a microdisk. A microdisk array is also shown in Figure 1(b).The photoluminescence spectra of ...

show abstract

Mechanism of enhanced light output efficiency in InGaN-based microlight emitting diodes

Cited by 130 publications

References 12 publications

Strain relaxation in InGaN/GaN micro-pillars evidenced by high resolution cathodoluminescence hyperspectral imaging

Strain relaxation in InGaN/GaN micro-pillars evidenced by high resolution cathodoluminescence hyperspectral imaging

One-dimensional ZnO nanostructures: Solution growth and functional properties

Whispering-gallery mode lasing in GaN microdisks

Contact Info

Product

Resources

About