H. Y. Hwang

University of Oxford

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Young-Dahl Jho

Gwangju Institute of Science and Technology

Akira Ohtomo

Tokyo Institute of Technology

David A. Muller

Cornell University

Dong‐Seon Lee

Gwangju Institute of Science and Technology

J. L. Grazul

Cornell University

Hyeonjun Baek

Sogang University

Gyu‐Chul Yi

Seoul National University

Jung‐Wook Min

Kumoh National Institute of Technology

Kwangwook Park

Jeonbuk National University

Hoon Jeong

Kwangwoon University

Cooperative Institutions

Gwangju Institute of Science and Technology

Seoul National University

Government of the Republic of Korea

Gwangju University

Korea Advanced Institute of Science and Technology

Samsung (South Korea)

Nagoya University

Korea Photonics Technology Institute

Tohoku University

Electronics and Telecommunications Research Institute

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Growth mode control of the free carrier density in SrTiO3−δ films

Journal of Applied Physics (2007)

Akira Ohtomo H. Y. Hwang

We have studied the growth dynamics and electronic properties of SrTiO3−δ homoepitaxial films by pulsed laser deposition. We find that the two dominant factors determining the growth mode are the kinetics of surface crystallization and of oxidation. When matched, persistent two-dimensional layer-by-layer growth can be obtained for hundreds of unit cells. By tuning these kinetic factors, oxygen vacancies can be frozen in the film, allowing controlled, systematic doping across a metal-insulator transition. Metallic films can be grown, exhibiting Hall mobilities as high as 25000cm2∕Vs.

Pulsed Laser Deposition

Free carrier

10.1063/1.2798385

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Citations (72)

Combined Effect of Carrier Localization and Polarity in InxGa1−xN/GaN Quantum Wells

Journal of Nanoscience and Nanotechnology (2014)

H. Y. Hwang Sang-Bae Choi Hoonill Jeong Dong‐Seon Lee Young-Dahl Jho

The influence of carrier localization and polarization-induced electric fields on the spectral variation of photoluminescence was comparatively studied in polar and semipolar InxGa1-x N/GaN strained quantum wells embedded in p-i-n diodes. Two representative structures with x = 0.16 for polar (0001) diodes and potential fluctuations for semipolar diodes grown along (1122) direction have been investigated with a reverse bias up to -4 V. From the s-shaped spectral shift as a function of temperature, the existence of single and triple localization traps was confirmed in polar and semipolar diodes. Within our bias range, we observed the monotonic blueshift with reverse bias in the polar sample, indicating that the carriers are laterally localized and thus influenced by the vertical piezoelectric fields. In clear contrast, the semipolar sample showed the blueshift of localized states only at low temperatures, while the deepest localization features were found at the highest available temperatures, overriding the influence of thermal activation and polarization fields.

Blueshift

Polarity (international relations)

10.1166/jnn.2015.10369

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Citations (2)

A Novel Asymmetric Vertical Directional Coupler Switch

Journal of the Institute of Electronics Engineers of Korea (2002)

Seong-Chan Jo Byeong-Min Jeong Bu-Gyun Kim Ji-Yeon Choe H. Y. Hwang

We propose a novel ultra-short asymmetric vertical directional coupler switch (VDCS) with high extinction ratios larger than 30㏈ composed of switching operation induced section (SOIS), extinction ratio adjusted section (ERAS), and extinction ratio enhanced section (ERES). In this VDCSs, switching operation is achieved by changing the refractive index of one core in SOIS. The improvement of extinction ratios larger than 30㏈ for both cross and bar states is achieved by controlling the asymmetry of refractive indices between both cores in ERES. After propagating through ERAS with symmetry in the structure, different extinction ratios between cross and bar states at the end of SOIS are changed to the same value. For this reason, the optimum asymmetry of the refractive indices of cores to have the maximum extinction ratios and the lengths of ERES are the same for cross and bar states. Design guidelines to achieve high extinction ratios with large tolerances are presented.

Extinction (optical mineralogy)

Extinction ratio

Bar (unit)

Source

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Artificial Charge Modulations in La-doped SrTiO3 Superlattices

Microscopy and Microanalysis (2002)

David A. Muller A. Ohtomo J. L. Grazul H. Y. Hwang

Journal Article Artificial Charge Modulations in La-doped SrTiO3 Superlattices Get access D A Muller, D A Muller Bell Labs, Lucent Technologies, 600 Mountain Ave, Murray Hill, NJ 07974 Search for other works by this author on: Oxford Academic Google Scholar A Ohtomo, A Ohtomo Bell Labs, Lucent Technologies, 600 Mountain Ave, Murray Hill, NJ 07974 Search for other works by this author on: Oxford Academic Google Scholar J Grazul, J Grazul Bell Labs, Lucent Technologies, 600 Mountain Ave, Murray Hill, NJ 07974 Search for other works by this author on: Oxford Academic Google Scholar H Y Hwang H Y Hwang Bell Labs, Lucent Technologies, 600 Mountain Ave, Murray Hill, NJ 07974 Search for other works by this author on: Oxford Academic Google Scholar Microscopy and Microanalysis, Volume 8, Issue S02, 1 August 2002, Pages 576–577, https://doi.org/10.1017/S1431927602105824 Published: 01 August 2002

10.1017/s1431927602105824

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Citations (1)

A gain‐clamped erbium‐doped fiber amplifier (GC–EDFA) for WDM optical packet‐switching system

Microwave and Optical Technology Letters (2002)

Choong-Reol Yang H. Y. Hwang Haitao Hong

Abstract The use of dual‐stage gain‐clamped erbium‐doped fiber amplifier (GC–EDFA) having a pump laser diode and 16‐channel wavelength‐division multiplexing (WDM) of 0.8 nm spacing in the C‐band of 1545–1560 nm wavelength was demonstrated in a burst packet‐mode optical switching system through an experimental setup. © 2002 John Wiley & Sons, Inc. Microwave Opt Technol Lett 32: 316–319, 2002.

Erbium

Laser diode

10.1002/mop.10165

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Asymmetric interface profiles in LaVO3∕SrTiO3 heterostructures grown by pulsed laser deposition

Applied Physics Letters (2007)

Lena F. Kourkoutis David A. Muller Yasushi Hotta H. Y. Hwang

Surface segregation effects play an important role in the growth of traditional III-V semiconductor heterointerfaces. Here we show that segregation processes can also set an upper limit to the obtainable interface sharpness in perovskite oxide heterostructures. In particular, the structure of LaVO3∕SrTiO3 superlattices was studied on the atomic scale by electron microscopy and spectroscopy. The vanadate layers exhibit a growth asymmetry, with diffuse lower and atomically abrupt upper interfaces, caused by preferential Sr surface segregation. Switching the SrTiO3 termination layer does not change the interface abruptness, which excludes the interfacial polar discontinuity as the driving force for the observed growth asymmetry.

Pulsed Laser Deposition

Discontinuity (linguistics)

Atomic units

Strontium titanate

10.1063/1.2798060

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Citations (38)

Strain relaxation and quantum size effect studied by two-photon laser scanning photoluminescence microscopy

H. Y. Hwang Hoon Jeong Hyeonjun Baek Gyu‐Chul Yi Hyoung Chan Kim

Nanoscale excitation by the simultaneous absorption of two photons was employed to investigate the spatially resolved role of strain relaxation and quantum size effect (QSE) in affecting luminescence from ZnO nanorods (NRs).

Nanorod

Strain (injury)

Photoluminescence excitation

Two-photon excitation microscopy

10.1109/cleopr.2015.7375897

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Distinctive mapping of strain and quantum size effects using depth-resolved photoluminescence in ZnO nanoneedles

AIP Advances (2016)

H. Y. Hwang Hyeonjun Baek Gyu‐Chul Yi Hyoung Chan Kim Young-Dahl Jho

In order to locate the spatially resolved influence of the strain, carrier localization, and quantum size effect (QSE) in tapered ZnO nanoneedles (NNs), the photoluminescence (PL) was measured as a function of the incident laser angle θ from 0∘ (normal to a surface) to 85∘. With increasing θ, the excitation point is spatially restricted along the axis of the NNs and varies from the ZnO buffer/sapphire interface to the tips of the NNs. In this way, we identified a strain-induced blue-shift of 25.3 meV at the ZnO buffer/sapphire interface, which corresponds to a tensile strain of 0.319%. The influence of strain and the concomitant indications of carrier localization decreased as the excitation point moved to a higher location along the NNs with increasing θ whereas the QSE revealed an abrupt blue-shift near the tips of the NNs. Furthermore, time-resolved PL measurement as a function of the excitation angle was used to distinguish the strain effect from the QSE. We observed two spatially competing tendencies: (1) the decay times are influenced by the increase in the interfacial strain and (2) the decay times are influenced by the decrease in the diameter-dependent QSE near the tips of the tapered ZnO NNs.

Strain (injury)

Tensile strain

Blueshift

Photoluminescence excitation

10.1063/1.4948452

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Citations (4)

Effects of nitrogen flow rate on the morphology and composition of AlGaN nanowires grown by plasma-assisted molecular beam epitaxy

Journal of Crystal Growth (2019)

Mun‐Do Park Jung‐Wook Min Jun Yeob Lee H. Y. Hwang Cihyun Kim

10.1016/j.jcrysgro.2019.125233

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