Investigation of optical properties in a single GaAs coupled quantum dots

Heedae Kim 한국자기학회 2023 한국자기학회 학술연구발표회 논문개요집 Vol.33 No.1

A Comparison Study in Productivity of Organically and Conventionally Grown Bulb Onion

Heedae Kim,Sangdae Lee,Jongtae Lee 한국원예학회 2012 한국원예학회 학술발표요지 Vol.2012 No.10

Temperature dependence of the radiative recombination time in laterally coupled GaAs quantum dots

Kim, Heedae,Murayama, Akihiro,Kim, Jongsu,Song, Jindong Elsevier 2018 APPLIED SURFACE SCIENCE - Vol.457 No.-

<P><B>Abstract</B></P> <P>We performed temperature dependent photoluminescence measurements of exciton states in GaAs laterally coupled quantum dots. The temperature dependence of the radiative decay time was used to investigate the density of states to study the intra-relaxation of thermally excited exciton states. We analyzed the density of states in laterally coupled quantum dots by observing the radiative decay time of exciton states as a function of temperature, where the decay time of exciton photoluminescence was calibrated with respect to photoluminescence intensity to extract the radiative decay time. In the case of laterally coupled quantum dots, a one-dimensional structure can be formed by elongation along the direction of coupling between two quantum dots. However, this assumption is not valid when the size in the uncoupled direction is comparable to that in the coupled direction. From experimental measurements, the power order of the temperature dependence was found to be 0.8, which corresponds to a quasi-one-dimensional system (∼T<SUP>α=0.8</SUP>), which is in between a two-dimensional (α = 1) and a one-dimensional (α = 0.5) density of states. This is due to several factors including a large size along the uncoupled direction, an extended wave function owing to optical coupling, and the presence of dark states.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The dimensionality of laterally coupled quantum dots is reported based on the measurement of temperature dependent radiative decay time. </LI> <LI> A quasi-one-dimensional density of states is observed with respect to the power order of the temperature dependence. </LI> <LI> Time-integrated photoluminescence spectral intensities are measured at various temperatures in laterally coupled quantum dots. </LI> </UL> </P>

Exciton Dipole–Dipole Interaction in a Single Coupled-Quantum-Dot Structure via Polarized Excitation

Kim, Heedae,Kim, Inhong,Kyhm, Kwangseuk,Taylor, Robert A.,Kim, Jong Su,Song, Jin Dong,Je, Koo Chul,Dang, Le Si American Chemical Society 2016 NANO LETTERS Vol.16 No.12

<P>We find that the exciton dipole dipole interaction in a single laterally coupled GaAs/AlGaAs quantum dot structure can be controlled by the linear polarization of a nonresonant optical excitation. When the excitation intensity is increased with the linearly polarized light parallel to the lateral coupling direction [1 (1) over bar0], excitons (X-1 and X-2) and local biexcitons (X1X1 and X2X2) of the two separate quantum dots (QD(1) and QD(2)) show a redshift along with coupled biexcitons (X1X2), while neither coupled biexcitons nor a redshift are observed when the polarization of the exciting beam is perpendicular to the coupling direction. The polarization dependence and the redshift are attributed to an optical nonlinearity in the exciton Forster resonant energy transfer interaction, whereby exciton population transfer between the two quantum dots also becomes significant with increasing excitation intensity. We have further distinguished coupled biexcitons from local biexcitons by their large diamagnetic coefficient.</P>

Growth of InAs and InGaAs Quantum Dots on (001) InP and their Photoluminescence Properties

Heedae Kim,정원국 한국물리학회 2005 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.47 No.3

InAs/InP and InGaAs/InGaAsP quantum dots (QDs) were grown by Metal-Organic Chemical Vapor Deposition and their photoluminescence (PL) properties are compared. InGaAs/InGaAsP QDs of high optical quality were grown by optimizing the compositions in the QD and the barrier. The PL spectral width is measured as 31 meV at 10 K without luminescence from the wetting layer. The integrated PL intensity at room temperature is measured to be 20 % of that measured at 10 K. The peak PL intensity of the QDs is measured to be 65 % of that of high quality 1.55 μm quantum wells. All these measured values indicate that the grown QDs are of high optical quality with minimal numbers of crystal defects around them. The areal density of spherical dome-shaped InGaAs/InGaAsP/InP QDs is measured to be as high as 1 × 1011 cm.2.

Light Controlled Optical Aharonov-Bohm Oscillations in a Single Quantum Ring

Kim, Heedae,Park, Seongho,Okuyama, Rin,Kyhm, Kwangseuk,Eto, Mikio,Taylor, Robert A.,Nogues, Gilles,Dang, Le Si,Potemski, Marek,Je, Koochul,Kim, Jongsu,Kyhm, Jihoon,Song, Jindong American Chemical Society 2018 NANO LETTERS Vol.18 No.10

<P>We found that optical Aharonov-Bohm oscillations in a single GaAs/GaAlAs quantum ring can be controlled by excitation intensity. With a weak excitation intensity of 1.2 kW cm<SUP>-2</SUP>, the optical Aharonov-Bohm oscillation period of biexcitons was observed to be half that of excitons in accordance with the period expected for a two-exciton Wigner molecule. When the excitation intensity is increased by an order of magnitude (12 kW cm<SUP>-2</SUP>), a gradual deviation of the Wigner molecule condition occurs with decreased oscillation periods and diamagnetic coefficients for both excitons and biexcitons along with a spectral shift. These results suggest that the effective orbit radii and rim widths of electrons and holes in a single quantum ring can be modified by light intensity via photoexcited carriers, which are possibly trapped at interface defects resulting in a local electric field.</P> [FIG OMISSION]</BR>

Temperature dependent activation energies of exciton states on a single GaAs laterally coupled-quantum-dot molecule and quantum dot

Kim Heedae 한국물리학회 2022 Current Applied Physics Vol.39 No.-

The objective of this study was to perform spectroscopy measurements of a single GaAs laterally coupled quantum dot molecule and quantum dot. Compared to photoluminescence spectra between a single GaAs laterally coupled quantum dot molecule and a single quantum dot, the presence of optical coupling was confirmed through dipole-dipole interactions in a single coupled quantum dot molecule. Based on temperature dependence measurements, weak exciton-phonon interactions (25 meV) were observed from the ground exciton state of a single GaAs laterally coupled quantum dot molecule in comparison with a strong exciton-phonon interaction (49 meV) from the ground exciton state of a single GaAs QD. Such weak interactions were due to reduced confinement at exciton states in a single laterally coupled quantum dot molecule. In addition, weaker activation energy (~15 meV) was observed in terms of confined electrons in a single laterally coupled quantum dot molecule, where a confinement effect became reduced due to enlarged dimensional area in one direction along [1 1 0].

Optical properties from a single GaAs quantum ring structure

Kim Heedae 한국물리학회 2023 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.82 No.8

We observed exciton and biexciton states in a single GaAs quantum ring at 4 K using micro photoluminescence system and investigated power/polarization dependent photoluminescence measurements to identify both exciton and biexciton states and fne structures states. The biexciton and exciton states showed quadratic (a~2.1) and linear (a~0.97) increasing power factors, respectively. As the excitation power is increased, the photoluminescence of exciton states shifts to higher energy slightly to fll the excited states gradually to confrm the existence of fne structure states. In addition, the large energy difer‑ ence (~0.7 meV) from exciton states and (~0.9 meV) from biexciton states for the perpendicular polarization was observed as a function of polarization angles.

Radiative decay time as a function of temperature in double GaAs quantum rings

Kim, Heedae,Kim, Jong Su,Kim, Inhong Elsevier 2019 APPLIED SURFACE SCIENCE - Vol.478 No.-

<P><B>Abstract</B></P> <P>This study examined the temperature-dependent, time-integrated/-resolved photoluminescence of the exciton states in double GaAs quantum rings. The density of states was analyzed from the temperature-dependent radiative decay time of exciton states to better understand the intra-relaxation process from thermally excited exciton states. To distinguish the radiative decay time from a non-radiative process, the decay time from the exciton states was calibrated by a comparison with the photoluminescence intensity at low temperatures, where the non-radiative process can be negligible. In ideal quantum ring structures, the ring width becomes almost zero. Therefore, one-dimensional nature would be expected. On the other hand, this assumption is not valid because widthless ring structures cannot be grown using current growth techniques. In other words, the quasi-one-dimensional nature (power order of the temperature dependence from radiative decay times ∼0.8 between 1.0 (two-dimensional nature) and 0.5 (one-dimensional nature)) was observed in quantum ring structures when the ring width was comparable to the radius of the ring structures. In the case of double quantum rings, however, the power order of the temperature dependence was obtained from the radiative decay times, which gave rise to 1.0, corresponding to a two-dimensional nature. This increased dimensional nature can be attributed to the appreciable ring width and ring size, extended wave function due to optical coupling, and the presence of dark exciton states.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The dimensionality of coupled quantum rings was investigated in terms of the radiative decay time as a function of temperature. </LI> <LI> Time-integrated photoluminescence intensity spectra were measured at various temperatures with a spectral redshift in coupled quantum rings. </LI> <LI> The two dimensional density of states was obtained in terms of the power order (α = 1.0) from temperature-dependent radiative decay times. </LI> </UL> </P>

Structuring the prediction model of project performance for international construction projects: A comparative analysis

Kim, Du Y.,Han, Seung H.,Kim, Hyoungkwan,Park, Heedae Elsevier 2009 expert systems with applications Vol.36 No.2

<P><B>Abstract</B></P> <P>Early understanding of project conditions is crucial so as to proactively respond to the variable situations of a project. Particularly, international construction projects are affected by more complex and dynamic factors than domestic projects; frequently being exposed to serious external uncertainties such as political, economical, social, and cultural risks, as well as internal risks from within the project itself. This study develops a structural equation model (SEM) to predict the project success of uncertain international construction projects. Through a comparative analysis of SEM with a multiple regression analysis and artificial neural network, SEM shows a more accurate prediction of performance because of its intrinsic ability to consider various risk variables in a systematic and realistic way. In addition, the use of SEM allows for visually depicting the paths of how those complicated variables are interrelated so as to promote the clear understanding of the complex system and its underpinned causes that critically affect the project success.</P>