Kun‐Yu Lai

National Central University

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Jr‐Hau He

City University of Hong Kong

Chin-An Lin

King Abdullah University of Science and Technology

Hsin-Ping Wang

King Abdullah University of Science and Technology

Fan‐Ching Chien

National Central University

Thi Anh Nguyet Nguyen

National Central University

Mark A. Johnson

Yale University

Edward A. Preble

RTI International

Chin‐An Lin

Linköping University

Virginia D. Wheeler

United States Naval Research Laboratory

Gong-Cheng Lin

Chunghwa Telecom (Taiwan)

Cooperative Institutions

National Central University

National Taiwan University

National Cheng Kung University

National Yang Ming Chiao Tung University

King Abdullah University of Science and Technology

National Tsing Hua University

National Taiwan University of Science and Technology

Taiwan Semiconductor Manufacturing Company (Taiwan)

Academia Sinica

National Taipei University of Technology

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Packaging efficiency in phosphor-converted white LEDs and its impact to the limit of luminous efficacy

Journal of Solid State Lighting (2014)

Ching-Cherng Sun Yu-Yu Chang Tsung‐Hsun Yang Te-Yuan Chung Cheng-Chien Chen

Abstract In this paper, we start from the study on the packaging efficiency of the phosphor-converted white LED via a new way to measure and calculate the blue light from the blue die to the encapsulation lens. Then we try to estimate the limit of luminous efficacy of a pcW-LED with Type VII structure. In the calculation, with the EQE of 81% of the blue die and Stokes loss, we obtain the optimal limit of luminous efficacy. The largest one reaches 300 lm/W, and occurs for green-white light with CCT from 4000K to 5000K. More practical limit is calculated in considering phosphor quantum loss and geometry loss, and the practical limit of luminous for CRI around 60 is around 210 lm/W, and for CRI larger than 80 is around 175 lm/W. Luminous efficacy will be sacrificed to obtain higher CRI. In order to know the real optical flux on the illuminated target, we introduce the optical utilization factor (OUF). Three application cases are discussed. The OUFs for light bulb, automotive head lamp, and street light are 90%, 60% and 45%, respectively. In considering human factors, it is interesting to find that a light source with lower luminous efficacy can perform higher illumination luminous efficacy (ILE). Therefore it is important to use ILE rather than LE when a light source is practically applied to lighting.

Luminous flux

Luminous efficacy

Color temperature

LED lamp

Luminous intensity

Incandescent light bulb

10.1186/s40539-014-0019-0

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Citations (66)

Excitation current dependent cathodoluminescence study of InGaN/GaN quantum wells grown on m-plane and c-plane GaN substrates

Journal of Applied Physics (2009)

Kun‐Yu Lai T. Paskova Virginia D. Wheeler J. A. Grenko Mark A. Johnson

InGaN/GaN quantum wells (QWs) grown with identical conditions on m-plane and c-plane GaN substrates were studied by cathodoluminescence spectroscopy. At a low current of 10 nA, the emission intensity and wavelength of the m-plane aligned QWs were found to be about two times stronger and 19.5 nm blueshifted with respect to that of the c-plane aligned QWs. An increase in the current over three orders of magnitude was found to result in an increase in the emission intensities, with faster saturation in the m-plane aligned QWs. This was explained by the screening of quantum-confined Stark effect in the emission efficiency of the c-plane aligned QWs.

Cathodoluminescence

Wide-bandgap semiconductor

Saturation (graph theory)

10.1063/1.3264729

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Citations (13)

Catching Single Molecules with Plasmonic Ingan Quantum Dots

SSRN Electronic Journal (2022)

Kun‐Yu Lai Fang Yin Zhao Thi Anh Nguyet Nguyen Chia‐Wei Tsai Che‐Men Chu

Single molecules are elusive, and often produce misleading signals. Surface-enhanced Raman spectroscopy (SERS) is one of the few techniques capable of verifying the presence of single molecules. To achieve the goal, the bianalyte proof is favored by researchers as it relies on the statistical analysis of thousands of spectra, rather than the fluctuating signals observed at limited spots. Since the hotspot of SERS is extremely small (< 10 nm), less than 1 % of the adsorbed molecules can render detectable Raman intensities, making single-molecule capture a rare event. Here, we present the proof with single-molecule signals covering 89.6 % of the scanned spots. This is achieved by plasmonically coupling subsurface InGaN quantum dots (QDs) to every Au nanoparticle on the SERS substrate. The QD-Au complexes extend the plasmonic field far away from the metallic nanojunction, redefining the bianalyte rule for single-molecule detection.

10.2139/ssrn.4251124

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Enhanced light-extraction from hierarchical surfaces consisting of p-GaN microdomes and SiO2 nanorods for GaN-based light-emitting diodes

Applied Physics Letters (2013)

Cheng-Han Ho Yu-Hsuan Hsiao Der‐Hsien Lien Meng‐Lin Tsai Don Chang

We report an efficient light-extraction scheme employing the hierarchical structure, p-GaN microdomes/SiO2 nanorods (NRs), on GaN light-emitting diodes (LEDs). Compared with the flat LED, the LEDs with hierarchical surfaces exhibits a light-output improvement of 36.8%. The considerable enhancement in light-extraction efficiency is attributed to the multiple tilted surfaces of microdomes and the graded refractive indexes provided by the SiO2 NRs, reducing total internal reflection and Fresnel reflection. The enhanced optical performances are supported by the finite-difference time-domain analysis. Advances in light extraction scheme employing hierarchical structures demonstrated here pave the way to solid-state lighting technology.

Nanorod

Wide-bandgap semiconductor

Fresnel equations

Reflection

Solid-State Lighting

10.1063/1.4824848

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Citations (22)

Solar energy harvesting scheme using syringe-like ZnO nanorod arrays for InGaN/GaN multiple quantum well solar cells

Optics Letters (2011)

G. J. Lin Kun‐Yu Lai Chieh-An Lin Jr‐Hau He

Syringe-like ZnO nanorod arrays (NRAs) synthesized by a hydrothermal method were applied as the light-harvesting layer on InGaN-based multiple quantum well (MQW) solar cells. Theoretical calculations show that the NRAs with an abrupt shrinkage of tip diameter can further suppress surface reflectance in comparison with the flat NRAs. InGaN-based MQW solar cells with the syringe-like NRAs exhibit greatly improved conversion efficiencies by 36%. These results are attributed to the improved flatness of the refractive index profile at the air/device interface, which results in enhanced light trapping effect on the device surface.

Nanorod

Flatness (cosmology)

10.1364/ol.37.000061

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Citations (19)

High-voltage thin-film GaN LEDs fabricated on ceramic substrates: the alleviated droop effect at 670 W/cm^2

Optics Express (2013)

Meng-Lun Tsai J.H. Liao Jui-Hung Yeh T. C. Hsu S. J. Hon

High-voltage thin-film GaN LEDs with the emission wavelength of 455 nm were fabricated on ceramic substrates (230 W/m · K). The high-voltage operation was achieved by three cascaded sub-LEDs with dielectric passivation and metal bridges conformally deposited on the side walls. Under the driving power of 670 W/cm(2), the high-voltage LEDs exhibit much alleviated efficiency droop and the operative temperature below 80 °C. The excellent performances were attributed to the improved current spreading within each sub-LED and the superior heat sinking of the ceramic substrate.

Passivation

10.1364/oe.21.027102

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Citations (9)

Nitride-based concentrator solar cells grown on Si substrates

Solar Energy Materials and Solar Cells (2013)

Cheng‐Yi Liu Chien‐Chih Lai J.H. Liao Lung-Chieh Cheng H.H. Liu

Concentrator

Quantum Efficiency

10.1016/j.solmat.2013.05.017

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Citations (16)

A broadband and omnidirectional light-harvesting scheme employing nanospheres on Si solar cells

Nano Energy (2014)

Guan-Jhong Lin Hsin-Ping Wang Der‐Hsien Lien Po-Han Fu Hung-Chih Chang

Reflection

Ray

10.1016/j.nanoen.2014.03.004

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Citations (40)

Simulation and Experiment of Light Trapping Ability of Periodic Si Nanowires

International Photonics and Optoelectronics Meetings (POEM) (2013)

Hsin-Ping Wang Kun-Tong Tsai Kun‐Yu Lai Yi-Ruei Lin Yuh‐Lin Wang

We demonstrate three methods for the fabrication of large scale ordered silicon nanorwires arrays using reactive ion etching (RIE) or metal-assisted chemical etching though colloidal lithography or anodic aluminum oxide (AAO) templates. Si NWAs with desirable diameters could be obtained by shrinking the sizes of colloidal lithography or the pore sizes of AAO templates. The reflection can be eliminated effectively over broadband regions by controlled NWAs; i.e., the wavelength-averaged total reflectance is decreased to 10.0 % at the wavelengths of 200-850 nm. The resulting nanostructures might have great potential applications in photovoltaics.

Template

Nanosphere lithography

Dry etching

10.1364/n3.2013.nsa3a.51

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Catching Single Molecules with Plasmonic InGaN Quantum Dots

Advanced Optical Materials (2023)

Fang Yin Zhao Thi Anh Nguyet Nguyen Chia‐Wei Tsai Che‐Men Chu Wei‐Yen Woon

Abstract Single molecules are elusive and often produce misleading signals. Surface‐enhanced Raman spectroscopy (SERS) is one of the few techniques capable of verifying the presence of single molecules. To achieve the goal, the bianalyte proof is favored by researchers as it relies on the statistical analysis of thousands of spectra, rather than the fluctuating signals observed at limited spots. Since the hotspot of SERS is extremely small (<10 nm), less than 1% of the adsorbed molecules can deliver boosted Raman intensities, making the capture of single molecules a rare event. Here, the proof with single‐molecule signals covering 89.6% of the scanned spots is presented. This is achieved by plasmonically coupling subsurface InGaN quantum dots (QDs) to every Au nanoparticle on the SERS substrate. The QD‐Au complexes extend the plasmonic fields far away from the metallic nanojunction, redefining the bianalyte rule for single‐molecule detection.

Surface-Enhanced Raman Spectroscopy

10.1002/adom.202300431

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Citations (2)