• Proceedings of the Korean Vacuum Society Conference
• /
• 2014.02a
• /
• pp.297.2-297.2
• /
• 2014

Strong exciton-photon coupling in microcavities have generated an intense research effort since quasiparticles called exciton polaritons are produced and shows interesting phenomena. Most of studies have been done with GaAs based microcavities at cryogenic temperature. Recently, GaN material which has large exciton binding energy and oscillator strength has much attention because strong coupling between photon and exciton could be realized at room temperature. However, fabrication of high quality microcavity using GaN is challengeable due to the large mismatch between the lattice and the thermal expansion coefficient in GaN based distributed Bragg mirror. Here, we observed strong coupling regime of exciton-photon in GaN micro-rods which were grown by metalorganic vapour phase epitaxy (MOCVD) on Si substrate. Owing to the hexagonal cross-section of micro-rod, whispering gallery modes of photon are naturally formed and could be coupled with exciton in GaN. Using angle-resolved micro-photoluminescence measurement, exciton polariton dispersion curves were directly observed from GaN micro-rod. We expect room temperature exciton polariton condensation could be realized in high quality GaN micro-rod.

• Journal of Korean Vacuum Science & Technology
• /
• v.4 no.2
• /
• pp.41-43
• /
• 2000

We present a study of exciton relaxation in GaAs/AIGaAs quantum well structures by using time-resolved photoluminescence techniques.03 observed that light-hole exciton has a longer decay time than heavy-hole exciton, which results from the difference of the exciton population factor. We considered the thermal population time to explain the observed exciton dynamics.

• Proceedings of the Optical Society of Korea Conference
• /
• 2000.02a
• /
• pp.18-19
• /
• 2000

Recently, coherent control of exciton populations has been demonstrated through terahertz, reflection, and four-wave-mixing experiments. However, the most direct probe of exciton population control is the absorption, which has been lacking in previous studies. In this report, we probe the time evolution of exciton population directly through a transmission experiment. In particular, using upconversion technique with both narrow (spectrally broad) and long (spectrally narrow) pulses, we can obtain both the temporal and the spectral information. The main thrust of our report is that when phase controlled, the second pulse can be either greatly enhanced or completely destroyed by gaining energy from exciton (thus destroying the exciton population) or giving all of its energy to the system (thus greatly increasing the exciton population), respectively. (omitted)

• Current Optics and Photonics
• /
• v.1 no.1
• /
• pp.60-64
• /
• 2017

We have considered optical nonlinearities of coupled quantum dots theoretically, where an exciton dipole-dipole interaction is mediated between the adjacent large and small quantum dots. For increasing a pump pulse area in resonance with the large quantum dot exciton the induced nonlinear refractive index of the small quantum dot exciton has been obtained. As the exciton dipole-dipole interaction depends on the relative orientation of two exciton dipoles, the optical nonlinearities for the directions parallel and perpendicular to the coupling axis of the two quantum dots are compared. The directional imbalance of optical nonlinearities in coupled quantum dots can be utilized for a polarization phase modulator by controlling a pump pulse area and propagation length.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2010.02a
• /
• pp.119-119
• /
• 2010

We report strong exciton transition and exciton-phonon couplings in photoluminescence (PL) of ZnO thin films grown on MgO/sapphire (buffer/substrate) by plasma-assisted molecular beam epitaxy. The PL spectra at 10 K showed the intensity of the dominant emission, donor-bound exciton transition of front surface (top surface, the latter part in growth) is found to be about 100 times higher than that of back surface (in-depth bottom area, the initial part), while the room temperature PL spectra showed dominant contributions from the free exciton emissions and phonon-replicas of free excitons for front surface and back surface, respectively, It could be attributed to the strong contributions of exciton-phonon coupling. Time resolved PL spectra reveal that the life time of exciton recombination from the front surface are longer than those from back surface. This is most probably due to the fact that reduction of non-radiative recombination in the front surface. This investigation indicates that the existence of native defects or trap centers which can be reduced by the proper initial condition in growth and the exciton-phonon interaction couplings play an important role in optical properties and crystal quality of ZnO thin films.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.18 no.12
• /
• pp.1148-1151
• /
• 2005

Photovoltaic effects in organic solar cell were studied in a cell configuration of ITO/PEDOT:PSS/CuPc(20 nm)/$C_{60}$(40 nm)/BCP/Al(150 nm) at room temperature. Here, the BCP layer works as an exciton blocking layer. The exciton blocking layer must transport electrons from the acceptor layer to the metal cathode with minimal increase in the total cell series resistance and should absorb damage during cathode deposition. Therefore, a proper thickness of the exciton blocking layer is required for an optimized photovoltaic cell. Several thicknesses of BCP were made between $C_{60}$ and Al. And we obtained characteristic parameters such as short-circuit current, open-circuit voltage, and power conversion efficiency of the device under the illumination of AM 1.5.

• Journal of Sensor Science and Technology
• /
• v.14 no.6
• /
• pp.369-373
• /
• 2005

High quality CdTe single crystal for the solar cell fabrication was grown by vertical Bridgman method. The etch pits patterns of (111) surfaces of CdTe etched by Nakagawa solution was observed the (111)A compesed of Cd atoms with typical triangle etch pits of pyramid mode. From the photoluminescence measurement on (111)A, we observed free exciton ($E_{x}$) existing only high quality crystal and neutal acceptor bound exciton ($A^{0}$,X) having very strong peak intensity. Then, the full width at half maximum and binding energy of neutral acceptor bound exciton were 7 meV and 5.9 meV, respectively. By Haynes rule, an activation enery of impurity was 59 meV. Therefore, the origins on impurity level acting as a neutral acceptor were associated Ag or Cu elements.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2005.11a
• /
• pp.273-274
• /
• 2005

Photovoltaic effects in organic solar cell were studied in a cell configuration of ITO/PEDOT:PSS/CuPc(20nm)/$C_{60}$(40nm)/BCP/Al(150nm) at room temperature. Here, the BCP layer works as an exciton blocking layer. The exciton blocking layer must transport electrons from the acceptor layer to the metal cathode with minimal increase in the total cell series resistance and should absorb damage during cathode deposition. Therefore, a proper thickness of the exciton blocking layer is required for an optimized photovoltaic cell. Several thicknesses of BCP were made between $C_{60}$ and Al. And we obtained characteristic parameters such as short-circuit current, open-circuit voltage, and power conversion efficiency of the device under the illumination of AM 1.5.

• Journal of Integrative Natural Science
• /
• v.2 no.4
• /
• pp.265-269
• /
• 2009

The photoluminescence was measured in GaAs-AlGaAs double-quantum-well structure at high magnetic field. Although the phototransition characteristics displayed a free-particle transition at low magnetic field, the change of free-particle transition into bound-exciton transition was observed at high magnetic field (above 10 T). A charged exciton formation due to charge-unbalanced electron-hole was identified by using a spin-polarized photoluminescence method. An increase of exciton formation due to the localization of free-particle at magnetic field was observed according to the increase of magnetic field.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2009.06a
• /
• pp.45-45
• /
• 2009

우리는 ZnO Template를 사용한 열기상법을 이용하여 수직 배양한 ZnO nanorods와 ZnO Nanopencils를 성장하였고, Dependency temperature Photoluminescence(PL)의 분석을 통하여 광학적 특성에 대해 분석을 하였다. ZnO 나노구조는 100K 이하의 온도에서 donor-bound exciton가 dominant하고, 100K 이상의 온도에서는 free exciton과 그들의 phonon-replica emission이 dominant한 것을 알 수 있었다. 하지만, ZnO nanorods와 nanopencils은 다른 exciton-phonon coupling의 strength에 의한 surface defects에 의해 excitonic emissions의 다른 거동을 보이는 것을 알았다. 이것으로 인해 상온 PL에서 ZnO nanopencil은 nanorods에 비해 52meV의 red shift를 보였다.