Jinn-Kong Sheu | National Cheng Kung University (original) (raw)

Papers by Jinn-Kong Sheu

The Journal of Physical Chemistry Letters, 2017

Chemical reactions at a solid−liquid interface are of fundamental importance. Interfacial chemica... more Chemical reactions at a solid−liquid interface are of fundamental importance. Interfacial chemical reactions occur not only at the very interface but also in the subsurface area, while existing monitoring techniques either provide limited spatial resolution or are applicable only for the outmost atomic layer. Here, with the aid of the time-domain analysis with femtosecond acoustics, we demonstrate a subatomic-level-resolution technique to longitudinally monitor chemical reactions at solid−water interfaces, capable of in situ monitoring even the subsurface area under atmospheric conditions. Our work was proven by monitoring the already-known anode oxidation process occurring during photoelectrochemical water splitting. Furthermore, whenever the oxide layer thickness equals an integer number of the effective atomic layer thickness, the measured acoustic echo will show higher signal-tonoise ratios with reduced speckle noise, indicating the quantum-like behavior of this coherent-phonon-based technique.

Supporting Information Graphene quantum dot vertical cavity surface emitting lasers Ya-Ju Lee,† *... more Supporting Information Graphene quantum dot vertical cavity surface emitting lasers Ya-Ju Lee,† * Ting-Wei Yeh,† Chen Zou,# Zu-Po Yang,‡ Jia-Wen Chen,† Pei-Lun Hsu,† Ji-Lin Shen, § Chun-Chieh Chang †* , Jinn-Kong Sheu ⊥*, and Lih Y. Lin# † Institute of Electro-Optical Science and Technology, National Taiwan Normal University, No. 88, Sec. 4, Tingchou Road, Taipei 116, Taiwan #Department of Electrical and Computer Engineering, University of Washington, Seattle,

Nanoscale, 2018

We report the first experimental demonstration of curvature-tunable random lasers to control the ... more We report the first experimental demonstration of curvature-tunable random lasers to control the transport mean free path of emitted photons.

Extended Abstracts of the 2009 International Conference on Solid State Devices and Materials, 2009

Scientific Reports, 2016

GaN is a pivotal material for acoustic transducers and acoustic spectroscopy in the THz regime, b... more GaN is a pivotal material for acoustic transducers and acoustic spectroscopy in the THz regime, but its THz phonon properties have not been experimentally and comprehensively studied. In this report, we demonstrate how to use double quantum wells as a THz acoustic transducer for measuring generated acoustic phonons and deriving a broadband acoustic spectrum with continuous frequencies. We experimentally investigated the sub-THz frequency dependence of acoustic attenuation (i.e., phonon mean-free paths) in GaN, in addition to its physical origins such as anharmonic scattering, defect scattering, and boundary scattering. A new upper limit of attenuation caused by anharmonic scattering, which is lower than previously reported values, was obtained. Our results should be noteworthy for THz acoustic spectroscopy and for gaining a fundamental understanding of heat conduction.

Optics express, Jan 6, 2015

A p-i-n structure with near-UV(n-UV) emitting InGaN/GaN multiple quantum well(MQW) structure stac... more A p-i-n structure with near-UV(n-UV) emitting InGaN/GaN multiple quantum well(MQW) structure stacked on a green unipolar InGaN/GaN MQW was epitaxially grown at the same sapphire substrate. Photon recycling green light-emitting diodes(LEDs) with vertical-conduction feature on silicon substrates were then fabricated by wafer bonding and laser lift-off techniques. The green InGaN/GaN QWs were pumped with n-UV light to reemit low-energy photons when the LEDs were electrically driven with a forward current. Efficiency droop is potentially insignificant compared with the direct green LEDs due to the increase of effective volume of active layer in the optically pumped green LEDs, i.e., light emitting no longer limited in the QWs nearest to the p-type region to cause severe Auger recombination and carrier overflow losses.

IEEE Journal of Selected Topics in Quantum Electronics, 2014

ABSTRACT Al0.25Ga0.75N ultraviolet (UV) p-i-n photodiodes (PDs) with top and inverted p-layer str... more ABSTRACT Al0.25Ga0.75N ultraviolet (UV) p-i-n photodiodes (PDs) with top and inverted p-layer structure are created by selective-area growth on a GaN template layer. All PDs exhibit typical zero bias peak responsivity at 310 nm and the UV-to-visible (310/400 nm) spectral rejection ratio is greater than three orders of magnitude. In contrast to conventional AlGaN-based p-i-n photodiodes, the inverted devices with low-resistivity n-type AlGaN top-contact layers exhibit a nearly flat spectral response at the short wavelength regions (210–310 nm). The proposed device structure can achieve solar-blind, AlGaN/GaN-based p-i-n PDs with high-aluminum content and reduced tensile strain due to the lattice mismatch between AlGaN and GaN layers.

Optics Express, 2015

We present a trichromatic GaN-based light-emitting diode (LED) that emits near-ultraviolet (n-UV)... more We present a trichromatic GaN-based light-emitting diode (LED) that emits near-ultraviolet (n-UV) blue and green peaks combined with red phosphor to generate white light with a low correlated color temperature (CCT) and high color rendering index (CRI). The LED structure, blue and green unipolar InGaN/GaN multiple quantum wells (MQWs) stacked with a top p-in structure containing an InGaN/GaN MQW emitting n-UV light, was grown epitaxially on a single substrate. The trichromatic LED chips feature a vertical conduction structure on a silicon substrate fabricated through wafer bonding and laser lift-off techniques. The blue and green InGaN/GaN MQWs were pumped with n-UV light to re-emit low-energy photons when the LEDs were electrically driven with a forward current. The emission spectrum included three peaks at approximately 405, 468, and 537 nm. Furthermore, the trichromatic LED chips were combined with red phosphor to generate white light with a CCT and CRI of approximately 2900 and 92, respectively.

$Research paper thumbnail of Gallium Nitride Diffractive Microlenses Using in Ultraviolet Micro-Optics System$

Optical Review, 2003

In this work, diffractive microlenses were fabricated in GaN usinb' a b'ray-level mask and induct... more In this work, diffractive microlenses were fabricated in GaN usinb' a b'ray-level mask and inductively coupled plasma etching technique. We also propose to insert the GaN/AIN band-pass filter in the microlenses to enhance the ultraviolet/visible rejection ratio. Due to high transparency of GaN and AIN in UV, the microlenses can potentially be used in a UV micro-optics system such ~s for solar-blind detection. In the design example of this work, the structure may enhance the ultaviolet/visible rejection to l02.

2011 37th IEEE Photovoltaic Specialists Conference, 2011

ABSTRACT The GaN/In0.25Ga0.75N double-heterojunction solar cells with rough and nipple arrays Ind... more ABSTRACT The GaN/In0.25Ga0.75N double-heterojunction solar cells with rough and nipple arrays Indium Tin Oxide (ITO) surface texture was fabricated by the inductively coupled plasma reactiveion etching (ICP-RIE) system. The peak of the external quantum efficiency for the samples with rough and nipple arrays ITO surface were each reached 29.17% and 34.25% at 420nm, and the enhancement with nipple arrays achieved highly 40% compared with the flat surface one. The results of the angle dependent current density were shown the outstanding antireflection for wide incident angle from 0° to 60°.

Conference on Lasers and Electro-Optics/International Quantum Electronics Conference and Photonic Applications Systems Technologies, 2004

ABSTRACT

SPIE Newsroom, 2012

LEDs with embedded donut-shaped air voids show great potential as highly efficient sources of nex... more LEDs with embedded donut-shaped air voids show great potential as highly efficient sources of next-generation solid-state lighting.

Solid-State Electronics, 2002

This work investigates dislocation etch pits in epitaxial lateral overgrowth (ELO) GaN by wet etc... more This work investigates dislocation etch pits in epitaxial lateral overgrowth (ELO) GaN by wet etching. A mixture of H 2 SO 4 and H 3 PO 4 was used as an etching solution. SEM and AFM were employed to observe the surface topography. For the as-grown sample, SEM images show the flat, smooth surface without any pits or hillocks. After the chemical etching, hexagonal shaped etch pits were observed at the edge of ELO GaN. AFM observation of etched ELO GaN displayed high densities of etch pits clustered in the ''window'' region and the coalescent line of two growing fronts. In contrast, the overgrowth region was nearly free of etch pits. Moreover, we observed that different sizes of etch pits dominated in ''window'' region and coalescent region. This implied different types dislocations dominated in these regions.

Physical Review B, 2011

The influences of modulated electric fields and modulated magnetic fields on low-energy Landau le... more The influences of modulated electric fields and modulated magnetic fields on low-energy Landau levels (LL's) of monolayer graphene are investigated by the tight-binding model. The ratio of the uniform magnetic-field strength to the modulated field strength is arbitrarily chosen for discussions. Both modulated fields cause the LL's to split into two twofold parabolic subbands; these subbands exhibit periodic oscillations and two kinds of band-edge states. However, the subband dispersions and oscillation amplitudes associated with electric and magnetic modulated fields behave differently. The main features of the electronic structure are reflected in the density of states, which presents pairlike and square-root divergent structures for both modulated field cases. The LL wave functions are strongly affected by both modulated fields, such as the broken symmetry, displacement of the center location, and alteration of the amplitude strength. These changes in the LL wave functions should be reflected in other physical properties, e.g., the optical selection rules. Furthermore, the dependence of the LL properties on the modulation strength and modulation period is also discussed in detail.

physica status solidi c, 2008

We prepared InGaN/GaN multiquantum wells (MQWs) with InGaN/GaN strained layer superlattice (SLS) ... more We prepared InGaN/GaN multiquantum wells (MQWs) with InGaN/GaN strained layer superlattice (SLS) underlayer and with GaN/AlGaN SLS underlayer to create different V‐shaped pits. It was found that pit density became smaller while pit depth and pit diameter both became larger, as compared to the sample without SLS. It was also found that sample surface became rougher with the SLS. Furthermore, it was found that light output intensities observed from the samples with SLS were stronger. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Materials Science and Engineering: B, 2007

The effect of thermal annealing in the range 300-800 °C on the properties of zirconia films prepa... more The effect of thermal annealing in the range 300-800 °C on the properties of zirconia films prepared by ion assisted deposition was studied. It was found that at low temperature the cubic phase is formed. This phase is stable up to 700 °C. All the films exhibit a monophasic monoclinic structure at 800 °C. The stress, estimated from X-ray patterns, shows a transition from tensile to compressive with increasing ion fluence. The refractive index and extinction coefficient do not seem to change appreciably up to 700 °C, showing a marked degradation thereafter. Single step annealing to the highest temperature was found to result in better stability than multistep annealing.

Journal of Lightwave Technology, 2013

This paper investigates GaN-based blue light-emitting diodes (LEDs) grown on sapphire substrates ... more This paper investigates GaN-based blue light-emitting diodes (LEDs) grown on sapphire substrates with selective-area Ar-ion implantation. The GaN-based epitaxial layers grown on the Ar-implanted sapphire substrates (Ar-ISS) exhibited selective growth and subsequent lateral growth because of different lattice constants between the implantation and implantation-free regions. As a result, air voids were formed at the GaN/sapphire interface, above the implanted regions and below the active layers of LEDs. We proposed the GaN layer growth mechanisms on the Ar-ISS, and characterized the LEDs with embedded air voids at the GaN/sapphire interface. Using a 20-mA current injection, the light output of the experimental LEDs was found to be 15% greater than that of conventional LEDs. This enhancement can be attributed to the light scattering at the textured GaN/air void interfaces, which increases the probability of photons escaping from the LEDs. Index Terms-air voids, Ar-implanted sapphire, lateral growth. I. INTRODUCTION T HE output power of a light-emitting diode (LED) depends on its light extraction efficiency (LEE) and on the internal quantum efficiency of the diode's active layer. One of the most significant problems concerning LEE is the occurrence of trapped light in semiconductors as a result of total internal reflection (TIR) [1], [2]. Efforts to improve LEE include attempting to overcome the significant photon loss that results from the TIR inside LEDs. The refractive indexes of sapphire and GaN in GaN-based LEDs grown on sapphire substrate are approximately 1.7 and 2.4, respectively. Therefore, if the GaN/sapphire and GaN/air interfaces are specular, photons emitted from the active layer become virtually trapped within the GaN-based layers. The LEE is enhanced by roughening the semiconductor-air and semiconductor-substrate interfaces. Methods have been developed to create rough Manuscript

Japanese Journal of Applied Physics, 2008

The fabrication of nanopillars containing InGaN/GaN multiple quantum wells has been achieved via ... more The fabrication of nanopillars containing InGaN/GaN multiple quantum wells has been achieved via focused ion beam, using modified beam-shape tuning. Tuning the ion beam astigmatism and/or focusing permits control of the size and shape of IIInitride islands, which makes feasible the fast writing of large-area InGaN/GaN island arrays on epi-layer sample embedded with multiple quantum wells. Interestingly, some islands became high-aspect-ratio nanopillars intermittently under an adequate degree of defocus. Typically, the pillars have diameters of around 100-150 nm and heights of around 600-1500 nm. High-resolution cross-sectional transmission electron microscopy and Z-contrast imaging revealed the preserved perfection of single-crystalline nature and quantum well structure of one single pillar, respectively. The optical characterization on the pillars was also carried out by cathodoluminescence, and the peak position showed a blue shift of 35 meV compared with the original epi-layer wafer.

Japanese Journal of Applied Physics, 2006

Abstract In this study, GaN-based light-emitting diodes (LEDs) were designed with a multi-quantum... more Abstract In this study, GaN-based light-emitting diodes (LEDs) were designed with a multi-quantum-well active region, including a yellow-green and a blue quantum well in each period. Photoluminescence (PL) and electroluminescence (EL) measurements revealed ...