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Quantum Confinement Effect of Thermoelectric Properties
제구철,Chang-Ho Cho 한국물리학회 2009 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.54 No.1
Using the quantum confinement effect based on the conduction band model, we theoretically determine the optimal concentration for the best figure-of-merit in n-type Bi2Te3 quantum well structures. The Bi2Te3 system has polycrystalline structures that can be prepared by using powders of hot-pressed alloys. The enhanced figure-of-merit due to the quantum confinement is almost caused by the enhanced Seebeck coefficient and by improved resistivity. It results from competition between the strong intrinsic characteristic and the enhancement of the volume ratio of the concentration in the quantum-confined system. The optimum concentration for the best figure-of-merit in the system amounts to 2.1 × 10^11 cm^-2 at room temperature. Control of the carrier concentration, as well as the quantum confinement effect, is also a very important effect to optimize the figure-of-merit in low-dimensional systems. Using the quantum confinement effect based on the conduction band model, we theoretically determine the optimal concentration for the best figure-of-merit in n-type Bi2Te3 quantum well structures. The Bi2Te3 system has polycrystalline structures that can be prepared by using powders of hot-pressed alloys. The enhanced figure-of-merit due to the quantum confinement is almost caused by the enhanced Seebeck coefficient and by improved resistivity. It results from competition between the strong intrinsic characteristic and the enhancement of the volume ratio of the concentration in the quantum-confined system. The optimum concentration for the best figure-of-merit in the system amounts to 2.1 × 10^11 cm^-2 at room temperature. Control of the carrier concentration, as well as the quantum confinement effect, is also a very important effect to optimize the figure-of-merit in low-dimensional systems.
Optical Excitonic Absorption Spectrum in Coupled Quantum Dots due to Dipole-dipole Interactions
제구철 한국물리학회 2015 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.67 No.5
We investigate the excitonic absorption spectrum induced by dipole-dipole interactions in two coupled quantum dots. The dipoles excited in neighboring quantum dots lead to constructive and destructive interference in excitonic polarizations. We find that the excitonic absorption peaks oscillate with the Rabi oscillation of the population and that two new peaks appear around the region where the bright excitonic state transfers to a dark state. The peaks result from a competition between the two types of interference. Therefore, the excitonic absorption spectrum in the coupled quantum dot system can be controlled by using the dipoles generated in neighboring quantum dots.
Optical Properties Induced by LO-Phonon Interactions in a Single Quantum Dot
제구철 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.53 No.2
We investigate the carrier dynamics induced by LO-phonon interactions with an effective phonon coupling constant in a strongly conned quantum dot. Broadening of the absorption spectra is induced by virtual states that suppress energy conservation events in the phonon interactions. We also find optical LO-phonon sidebands and a Rabi oscillation. The appearance of optical sidebands results from coherent phonons and the Rabi oscillation is closely related to the oscillating generation rate during the pulse. We can see that the LO-phonon interaction reduces the spontaneously emitting carrier density and re-excites carriers before arrival at complete emission.
Variation of Dynamic Fano Resonances in Semiconductor Superlattices Driven by Dc and THz Fields
제구철 한국물리학회 2010 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.56 No.3
We describe the dynamic Fano resonances in a biased three-dimensional semiconductor superlattice driven by combined dc and THz fields. The Fano resonances on the Wannier Stark ladders are dominantly changed by the THz field via the band collapse phenomenon. The Fano coupling matrix is closely related to the separated energy distance between the two types of exciton resonances produced by the dc and the THz fields. The dynamic Fano coupling strength increases as the exciton resonance induced by the THz field approaches the Wannier exciton states.
All-optical Polarization Phase Modulation in Coupled Quantum Dots
제구철,김광석 한국광학회 2017 Current Optics and Photonics Vol.1 No.1
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.
김지웅,박승한,Dae-Kyu Kim,Jason Han,윤종일,최중길,제구철,Thomas Fanghanel 한국물리학회 2006 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.49 No.1
CdSe/ZnS quantum dots (QDs) coated with mercaptoacetic acid (MAA) in an anqueous solution are investigated by means of highly sensitive laser-induced breakdown detection (LIBD). In particular, a size distribution analysis of QDs dispersed in ultra pure water is performed as a function of time until a steady state is reached. Freshly prepared CdSe/ZnS-MAA QDs are found to initially exist as relatively large (25.0 ± 1.2 nm) agglomerates that slowly disperse over days to small (6.5 ± 0.2 nm), but stable, single particles. These results of increasing breakdown probability with increasing particle density amply demonstrate that LIBD can be a promising analytical technique for size analysis of nanoparticle formation and stability.