Analysis of the stress distribution in the nonuniformly bent GaN thin film grown on a sapphire substrate

Jang, Young‐Il; Kim, Won Rae; Jang, Dong-Hyun; Shim, Jong‐In; Shin, Dong Soo

doi:10.1063/1.3436586

Cited by 12 publications

(5 citation statements)

References 17 publications

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“…Samples A and B were chosen from the edge and center of the wafer and their local dot-like emission densities were approximately 10 4 and 10 2 cm −2 , respectively. It is generally believed that the LED device from the edge of a wafer has relatively poorer performance than the one from the center due to problems related to the wafer bowing during the epitaxial growth [9], [10]. The EQE is obtained by dividing the integrated EL intensity by the injection current.…”

Section: Resultsmentioning

confidence: 99%

Conduction Mechanisms of Leakage Currents in InGaN/GaN-Based Light-Emitting Diodes

Han

Kim

et al. 2015

IEEE Trans. Electron Devices

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Local dot-like emissions in InGaN/GaN-based light-emitting diodes under both forward and reverse biases are investigated by carefully examining their locations and electroluminescence spectra. The effects of dot-like emissions on electrical and optical performances are also discussed. From the properties of the leakage-component dependence on electric field and temperature, the dominant reverse leakage mechanism is investigated as a function of bias from 100 to 400 K. It is concluded that the underlying mechanism of local dot-like emissions are related to threading dislocations under both reverse and forward biases. Index Terms-Dot emission, light-emitting diodes (LEDs), threading dislocations (TDs), variable-range hopping (VRH).

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Section: Resultsmentioning

confidence: 99%

Conduction Mechanisms of Leakage Currents in InGaN/GaN-Based Light-Emitting Diodes

Han

Kim

et al. 2015

IEEE Trans. Electron Devices

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“…1(a) were included in the simulation, although the FEM model did not extend through the full thickness of the sapphire substrate. Detailed analysis of the wafer bowing predicts that a bending-free plane is at a depth of $70 lm; 26 we therefore included 80 lm thick sapphire in order to define a practical boundary condition. Pillar sidewalls were left free from constraints.…”

Section: Methodsmentioning

confidence: 99%

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

Xie

Chen

Edwards

et al. 2012

Journal of Applied Physics

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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.

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“…As a result, ∼170 μm deviation can be caused for 10 μm thickness of GaN on a 4 in. wafer. , Imprinting of nanostructures on such an uneven substrate is quite difficult due to the irregular contact of mold and substrate, and large defects that are comparable with the size of LED chips (as shown in Figure S3a in Supporting Information) influence the chip performance. After dicing the GaN wafer to chips in the follow-up process, these square millimeter-sized LED chips with no PhC structures will have low light extraction efficiency as shown in Figure .…”

Section: Results and Discussionmentioning

confidence: 99%

Step-Controllable Electric-Field-Assisted Nanoimprint Lithography for Uneven Large-Area Substrates

et al. 2016

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Large-area nanostructures are widely used in various fields, but fabrication on large-area uneven substrates poses a significant challenge. This study demonstrates a step-controllable electric-field-assisted nanoimprint lithography (e-NIL) method that can achieve conformal contact with uneven substrates for high fidelity nanostructuring. Experiments are used to demonstrate the method where a substrate coated with liquid resist is brought into contact with a flexible template driven by the applied electric field. Theoretical analysis based on the elasticity theory and electro-hydrodynamic theory is carried out. Effective voltage range and the saturation voltage are also discussed. A step-controllable release of flexible template is proposed and demonstrated to ensure the continuous contact between the template and an uneven substrate. This prevents formation of air traps and allows large area conformal contact to be achieved. A combination of Vacuum-electric field assisted step-controllable e-NIL is implemented in the developed prototype. Finally, photonic crystal nanostructures are successfully fabricated on a 4 in., 158 μm bow gallium nitride light-emitting diode epitaxial wafer using the proposed method, which enhance the light extraction property.

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Analysis of the stress distribution in the nonuniformly bent GaN thin film grown on a sapphire substrate

Cited by 12 publications

References 17 publications

Conduction Mechanisms of Leakage Currents in InGaN/GaN-Based Light-Emitting Diodes

Conduction Mechanisms of Leakage Currents in InGaN/GaN-Based Light-Emitting Diodes

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

Step-Controllable Electric-Field-Assisted Nanoimprint Lithography for Uneven Large-Area Substrates

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