Chang-Hee Cho

Chang-Hee Cho
Daegu Gyeongbuk Institute of Science and Technology | DGIST · Department of Physics and Chemistry

Ph. D.

About

62
Publications
9,125
Reads
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2,006
Citations
Introduction
Chang-Hee Cho currently works at the Department of Physics and Chemistry, Daegu Gyeongbuk Institute of Science and Technology (DGIST). Chang-Hee does research in Optical Physics and Engineering, and Materials Science.
Additional affiliations
March 2017 - present
Daegu Gyeongbuk Institute of Science and Technology
Position
  • Professor (Associate)
September 2012 - February 2017
Daegu Gyeongbuk Institute of Science and Technology
Position
  • Professor (Assistant)
September 2009 - August 2012
University of Pennsylvania
Position
  • PostDoc Position

Publications

Publications (62)
Article
Full-text available
The manipulation of radiative properties of light emitters coupled with surface plasmons is important for engineering new nanoscale optoelectronic devices, including lasers, detectors and single photon emitters. However, so far the radiative rates of excited states in semiconductors and molecular systems have been enhanced only moderately, typicall...
Article
Full-text available
Due to limitations in device speed and performance of silicon-based electronics, silicon optoelectronics has been extensively studied to achieve ultrafast optical-data processing(1-3). However, the biggest challenge has been to develop an efficient silicon-based light source since indirect band-gap of silicon gives rise to extremely low emission ef...
Article
Full-text available
Ultralow-threshold coherent light emitters can be achieved through lasing from exciton-polariton condensates, but this generally requires sophisticated device structures and cryogenic temperatures. Polaritonic nanolasers operating at room temperature lie on the crucial path of related research, not only for the exploration of polariton physics at t...
Article
A conjugated polymer particle in an aqueous phase is covalently networked in 3D by crosslinking with azide groups, leading to significantly enhanced activity—a high photocatalytic H2 evolution rate (11 024 µmol g−1 h−1 (λ > 420 nm)) and a high apparent quantum yield (up to 0.8%). The reaction between the photoactive azide and the alkyl chains of th...
Article
Recently, significant progress has been made in the development of new techniques for the fabrication of mechanically durable, bright, and deformable electroluminescent devices, leading to the emergence of various technologies, such as soft robots, actuators, flexible/stretchable/wearable electronics, and self-healable devices. However, these devic...
Article
Broadband omni-directional anti-reflection characteristics have been an important issue because they can maximize the optical absorption in photovoltaic devices. Here, we investigate the optical properties of ZnO nanoneedle arrays to...
Article
We report on the polarization-controlled amplification of excitonic emission in the monolayer WS2 coupled with ZnO microcavity. From polarization-resolved micro-photoluminescence spectroscopy and numerical modeling, we found that the polarization of WS2 excitonic emission can be tailored by the whispering gallery modes of the birefringent ZnO micro...
Article
All-inorganic materials, mixed halide perovskite (MHP) nanocrystals (NCs), have attracted considerable attention recently because of their excellent luminescent efficiencies and extraordinary physical properties, making them a promising material for next-generation...
Article
Single-atom catalysts are playing a pivotal-role in understanding the atomic-level photocatalytic processes. However, single-atoms are typically non-uniformly distributed on photocatalyst surface, hindering the systematic investigation of structure-property correlation at atomic...
Article
A desire for renewable alternatives to fossil fuels can be achieved by utilizing CO2, H2O, and solar energy to generate solar fuels. A novel N-doped graphene oxide enfolded reduced titania (NGO-RT) composite was demonstrated for photocatalytic CO2 reduction into CH4. Later, a small amount of Pt NPs was deposited on NGO-RT that increases the catalyt...
Article
We prepared MoS2 monolayers on Au nanodot (ND) and nanohole (NH) arrays. Both these sample arrays exhibited enhanced photoluminescence intensity compared with that of a bare SiO2/Si substrate. The reflectance spectra of MoS2/ND and MoS2/NH had clear features originating from excitation of localized surface plasmon and propagating surface plasmon po...
Article
We fabricated plasmonic hybrid nanostructures consisting of MoS2 monolayer flakes and Au nanogratings with a period of 500 nm. The angle-resolved reflectance and photoluminescence spectra of the hybrid nanostructures clearly indicated a coupling between surface plasmon polaritons (SPPs) and incoming photons. The surface photovoltage (SPV) maps coul...
Article
Photocatalytic conversion of CO2 and water vapor to hydrocarbon fuels is a promising approach for storing solar energy while reducing greenhouse gas emissions. However, still certain issues including low product yields, limited photocatalyst stability and relatively high cost have hampered practical implementation of this technology. In the present...
Article
We investigated two-dimensional (2D) exciton diffusion in monolayer WS2 on both SiO2 and hexagonal boron nitride (h−BN) layers to identify the exciton diffusion enhanced by the h−BN bottom layer using spatially resolved photoluminescence imaging combined with time-resolved spectroscopy. The WS2 on the h−BN bottom layer shows an exciton diffusion co...
Cover Page
Consecutively for the second time, my work is selected as the Front Cover for EES. The work is published in the September issue. We investigate a photocatalyst comprised of Blue titania deposited with Cu and Pt nanoparticles for solar light assisted photocatalytic CO2 reduction. The photocatalyst has shown a photoconversion efficiency of 1%, ther...
Article
In the recent remarkable advances in soft electronic systems, light-emitting functions play a prominent role. In particular, polymer composite systems with embedded luminescent particles have attracted considerable attention as a luminescent component owing to their flexibility and simple fabrication. However, most flexible composite-based electrol...
Article
If we wish to sustain our terrestrial ecosphere as we know it, then reducing the concentration of atmospheric CO_2 is of critical importance. An ideal pathway for achieving this would be the use of sunlight to recycle CO_2, in combination with water, into hydrocarbon fuels compatible with our current energy infrastructure. However, while the concep...
Article
Atomically thin transition metal dichalcogenides (TMDs) have recently attracted great attention since the unique and fascinating physical properties have been found in various TMDs, implying potential applications in next-generation devices. The progress towards developing new functional and high-performance devices based on TMDs, however, is limit...
Article
We have performed a variable stripe length method at 5 K to measure the optical gain of CdS nanowires. When the excited carrier density is lower than the Mott density, we found that various inelastic scatterings of excitons and LO-phonons are involved. As a consequence of inelastic exciton-exciton scattering, the excitons scattered down to the low...
Preprint
Full-text available
Atomically thin transition metal dichalcogenides (TMDs) have recently attracted great attention since the unique and fascinating physical properties have been found in various TMDs, implying potential applications in next-generation devices. The progress towards developing new functional and high-performance devices based on TMDs, however, is limit...
Preprint
Controlling light-matter interactions in solid-state systems has motivated intense research to produce bosonic quasi-particles known as exciton-polaritons, which requires strong coupling between excitons and cavity photons. Ultra-low threshold coherent light emitters can be achieved through lasing from exciton-polariton condensates, but this genera...
Article
The intrinsically anisotropic crystallinity of two-dimensional (2D) transition metal dichalcogenides (2D TMDs) layers enables a variety of intriguing material properties which strongly depend on the physical orientation of constituent 2D layers. For instance, 2D TMDs with vertically-aligned layers exhibit numerous dangling bonds on their 2D layer e...
Article
Since semiconducting ZnO has attractive properties such as wide bandgap and large exciton binding energy, it has been motivated to realize efficient ultraviolet (UV) light-emitting diodes (LEDs). Furthermore, facile growth of ZnO nanostructures has triggered numerous researches to examine them as nanoscale building blocks for optoelectronic devices...
Article
Despite their prestigious properties, it is difficult to apply metal-organic frameworks (MOFs) to real field situations owing to their vulnerable structures that are sensitive to moisture. Herein, an O2 plasma technique is introduced as a new method for the activation and protection of HKUST-1 porosity. In an unprecedented manner, O2 plasma-treated...
Article
Here, we report that the tensile strain in silicon nanocrystals embedded in silicon nitride significantly changes the size-dependent evolution of the conduction and valence energy levels, compared with strain-free silicon nanocrystals. Using capacitance spectroscopy, the quantum-confined energy shifts in the conduction and valence levels were ident...
Article
One- to three-dimensional alignments of semiconductors on the micro- or nanoscale have been achieved to tailor their opto-physicochemical properties and improve their photoelectrochemical (PEC) performance. Here, to the best of our knowledge, we report for the first time the fabrication of vertically aligned, well-ordered WO3 microdisc arrays via a...
Article
p-Si wire arrays overlaid with an ultrathin titanium nitride (TiN) film are developed and demonstrated to be an efficient and robust photocathode for hydrogen production. Arrays of vertically aligned 20 μm long p-Si microwires of varying diameters (1.6–14.6 μm) are fabricated via a photolithographic technique, and then the wires are coated with a T...
Article
Full-text available
The atomic-layered semiconducting materials of transition metal dichalcogenides are considered effective light sources with both potential applications in thin and flexible optoelectronics and novel functionalities. In spite of the great interest in optoelectronic properties of two-dimensional transition metal dichalcogenides, the excitonic propert...
Article
Full-text available
In this work, we report a qualitative approach for detecting the adsorption of C-reactive protein on phosphocholine-terminated self-assembled monolayers without the use of any labels. An amplified plasmon of concentration-induced silver nanoparticle aggregates located ~4.0 nm away from the C-reactive protein via the phosphocholineterminated self-as...
Article
Full-text available
We demonstrate the fabrication of a graphene/ZnO nanorod (NR) hybrid structure by mechanical exfoliation of ZnO NRs grown on a graphite substrate. We confirmed the existence of graphene sheets on the hybrid structure by analyzing the Raman spectra and current-voltage (I-V) characteristics. The Raman spectra of the exfoliated graphene/ZnO NR hybrid...
Article
Full-text available
Understanding interactions between light and matter is central to many fields, providing invaluable insights into the nature of matter. In its own right, a greater understanding of light–matter coupling has allowed for the creation of tailored applications, resulting in a variety of devices such as lasers, switches, sensors, modulators, and detecto...
Article
We demonstrate the fabrication of solution based low temperature-processed p-type ZnO NRs doped with phosphorous by using a spin-on-dopant method coupled with a hydrothermal process. We confirmed the incorporation of phosphorous dopants into a ZnO crystal by analyzing SIMS profiles, together with the evolution of the photoluminescence spectra. It i...
Article
By coupling silicon nanowires (~150 nm diameter, 20 micron length) with an {\Omega}-shaped plasmonic nanocavity we are able to generate broadband visible luminescence, which is induced by high-order hybrid nanocavity-surface plasmon modes. The nature of this super-bandgap emission is explored via photoluminescence spectroscopy studies performed wit...
Article
Full-text available
The imminent limitations of electronic integrated circuits are stimulating intense activity in the area of nanophotonics for the development of on-chip optical components, and solutions incorporating direct-bandgap semiconductors are important in achieving this end. Optical processing of data at the nanometre scale is promising for circumventing th...
Article
Core-shell dielectric-metal nanoparticles have demonstrated tunability of their absorption properties due to the size- and shape-dependence of the surface plasmon resonance. Recently, the core-shell semiconductor-insulator-metal nanowire was examined as a platform for manipulating the core emitter lifetimes due to the highly confined and intense el...
Article
Emission from unthermalized (hot) excitons can be observed from high-quality crystals and quantum-well structures due to decreases in the exciton lifetimes but typically with low yields. By employing a plasmonic nanocavity, we observe efficient hot-exciton emission in core-shell CdS-SiO2-Ag nanowires with intensities surpassing those from thermaliz...
Article
Full-text available
Strong coupling of light with excitons in direct bandgap semiconductors leads to the formation of composite photonic-electronic quasi-particles (polaritons), in which energy oscillates coherently between the photonic and excitonic states with the vacuum Rabi frequency. The light-matter coherence is maintained until the oscillator dephases or the ph...
Article
Semiconductor nanowire waveguide cavities hold promise for nanophotonic applications such as lasers, waveguides, switches, and sensors due to the tight optical confinement in these structures. However, to realize their full potential, high quality nanowires, whose emission at low temperatures is dominated by free exciton emission, need to be synthe...
Article
Full-text available
The electronic structure of silicon nanocrystals embedded in a silicon nitride insulating film is identified by using a capacitance spectroscopy. The tunneling capacitor device, which is used in this study, consists of a tunneling silicon nitride, an array of silicon nanocrystals embedded in a silicon nitride film, and a blocking silicon nitride de...
Article
Full-text available
We report the strong size-dependent carrier injection process in quantum-confined silicon nanocrystals embedded in silicon nitride films. As the diameter of silicon nanocrystals increases, the threshold voltage for carrier injection decreases whereas the number of injected carriers increases due to the quantum size effect. The tunneling time for th...
Article
We report the effect of injection current density on the electroluminescence (EL) from silicon quantum dot (QD) light-emitting diodes. The EL spectra as a function of injection current density were blueshifted and broad. These results are attributed to both the increase in the contribution of small Si QDs in the silicon nitride film due to the incr...
Article
Full-text available
We investigated the relationship between the absorption in silicon nanocrystals (Si NCs) and the photocurrent of Si NC solar cells. Here, the absorption of Si NCs in the blue and green light regions was enhanced by up to 14 times compared to bulk Si. In addition, the photocurrent in Si NC solar cells was found to originate from absorption in the Si...
Article
We have investigated the effect of a ZnO doping layer on a silicon quantum dot (Si QD) light-emitting diode (LED). A highly doped ZnO layer was grown on a Si OD layer at room temperature using a radio-frequency sputtering. The power efficiency of Si QD LED containing the ZnO layer were greatly improved by 226% due to an increase in the electron inj...
Article
Full-text available
We report the effect of a nanoroughened Si substrate on silicon quantum dot (Si QD) light-emitting diodes (LEDs). The electroluminescence of Si QD LEDs grown on the nanoroughened Si substrate was remarkably improved by 493% at an injection current of 90 mA compared to those of Si QD LEDs grown on the flat Si substrate. The electrical and optical en...
Article
Full-text available
We report on the photocurrent of silicon nanocrystal (Si NC) photodetectors (PDs) that contain silver (Ag) islands. Here, a larger increase in the photocurrent of Si NC PDs was observed with increasing Ag island size. The maximum increase occurred at the wavelength of the Ag surface plasmon resonance and redshifted as the size of the Ag islands inc...
Article
Full-text available
We report on the effect of nanocrystal size on the photocurrent of silicon nanocrystal (Si NC) photodetectors. The photocurrent onset energy was increased with decreasing the size of Si NCs, which agreed with the blueshift in the absorption onset. The increase in the quantum efficiency with increasing the size of Si NCs was much larger than the inc...
Article
Full-text available
We report the effect of chemical etching of p-GaN using molten KOH:NaOH solution on leakage currents, light output power, and electrostatic discharge (ESD) characteristics of GaN light-emitting diodes (LEDs). Photoluminescence and capacitance-voltage measurement indicated that a deep donor-acceptor pair (DDAP) was densely concentrated near the p-Ga...
Article
Full-text available
A chemical etching using a molten KOH+NaOH solution was developed to improve optical properties and leakage current of GaN light-emitting diodes (LEDs). The Photoluminescence (PL), capacitance-voltage (C-V) and current-voltage (I-V) analysis showed that deep donor-acceptor pair (DDAP) defects were effectively removed by the chemical etching process...
Article
A study was conducted to report the first evidence of enhanced external quantum efficiency in a Si QD (silicon quantum dot) light emitting diode (LED) resulting from the coupling between Si QDs and localized surface plasmons (LSP) and effective current tunneling into Si QDs from an Ag layer containing Ag particles inserted between the Si QD layer a...
Article
Full-text available
The effect of InGaN quantum dot (QD) size on the performance of light-emitting diodes (LEDs) was investigated by varying the QD size from 1.32 to 2.81 nm . The electroluminescence peak of the LEDs containing small QDs (1.32 nm ) was redshifted with increasing input current while that of large QDs (2.81 nm ) was blueshifted up to 40 mA due to the sc...
Article
Full-text available
The effect of Ni/Au metal contact on the carrier injection and the electroluminescence of silicon quantum dot light-emitting diodes (LEDs) was investigated. An LED with an annealed Ni/Au contact at 400 °C in air showed a lower threshold voltage compared to that of an as-deposited Ni/Au contact by forming a nickel silicide, which has a lower work fu...
Article
Full-text available
A room-temperature Coulomb blockade effect was observed in silicon quantum dots (Si QDs) spontaneously grown in a silicon nitride film. The metal-insulator-metal device containing the Si QDs showed a clear Coulomb staircase and differential conductance peaks at room temperature. The size distribution of the Si QDs determined by high-resolution tran...
Article
Full-text available
Crystalline silicon quantum dots (Si QDs) were spontaneously grown in the silicon nitride films by plasma-enhanced chemical vapor deposition using SiH4 and NH3 as precursors. When the size of the Si QDs was reduced from 4.9 to 2.9 nm, the photoluminescence peak energy was shifted from 1.73 to 2.77 eV. The photoluminescence peak energy was fitted to...
Article
Full-text available
The effect of hydrogen passivation on the charge storage characteristics of two types of silicon nitride films containing silicon quantum dots (Si QDs) grown by SiH4+N2 and SiH4+NH3 plasma was investigated. The transmission electron microscope analysis and the capacitance-voltage measurement showed that the silicon nitride film grown by SiH4+NH3 pl...
Article
Full-text available
The photoluminescence (PL) property of crystalline silicon quantum dots (Si QDs) in silicon nitride grown by using ammonia and silane gases is reported. The peak position of PL could be controlled in the wavelength range from 450 to 700 nm by adjusting the flow rates of ammonia and silane gases. The PL intensity of Si QDs grown by ammonia was more...
Conference Paper
A light emitting diode (LED) with transparent doping layer (TDL) is fabricated. The I-V characteristics and the electroluminescence intensity of a LED with TDL significantly increase more than that of a LED without TDL. The improvement of optical and electrical properties is attributed to the excellent carrier injection through the n-ZnO layer into...

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