• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.191.2-191.2
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• 2015

Details of carrier dynamics in self-assembled quantum dots (QDs) with a particular attention to nonradiative processes are not only interesting for fundamental physics, but it is also relevant to performance of optoelectronic devices and the exploitation of nanocrystals in practical applications. In general, the possible processes in such systems can be considered as radiative relaxation, carrier transfer between dots of different dimensions, Auger nonradiactive scattering, thermal escape from the dot, and trapping in surface and/or defects states. Authors of recent studies have proposed a mechanism for the carrier dynamics of time-resolved photoluminescence CdTe (a type II-VI QDs) systems. This mechanism involves the activation of phonons mediated by electron-phonon interactions. Confinement of both electrons and holes is strongly dependent on the thermal escape process, which can include multi-longitudinal optical phonon absorption resulting from carriers trapped in QD surface defects. Furthermore, the discrete quantized energies in the QD density of states (1S, 2S, 1P, etc.) arise mainly from ${\delta}$-functions in the QDs, which are related to different orbitals. Multiple discrete transitions between well separated energy states may play a critical role in carrier dynamics at low temperature when the thermal escape processes is not available. The decay time in QD structures slightly increases with temperature due to the redistribution of the QDs into discrete levels. Among II-VI QDs, wide-gap CdZnTe QD structures characterized by large excitonic binding energies are of great interest because of their potential use in optoelectronic devices that operate in the green spectral range. Furthermore, CdZnTe layers have emerged as excellent candidates for possible fabrication of ferroelectric non-volatile flash memory. In this study, we investigated the optical properties of CdZnTe/ZnTe QDs on Si substrate grown using molecular beam epitaxy. Time-resolved and temperature-dependent PL measurements were carried out in order to investigate the temperature-dependent carrier dynamics and the activation energy of CdZnTe/ZnTe QDs on Si substrate.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.451-451
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• 2012

Instead of a highly toxic CdSe and ZnScore-shell,InP/ZnSecore-shell quantum dots [1,2] were investigated as an active material for quantum dot light emitting diode (QD-LED). In this paper, aquantum dot light-emitting diode (QDLED), consisting of a InP/ZnS core-shell type materials, with the device structure of glass/indium-tin-oxide (ITO)/PEDOT:PSS/Poly-TPD/InP-ZnS core-shell quantum dot/Cesium carbonate(CsCO3)/Al was fabricated through a simple spin coating technique. The resulting InP/ZnS core-shell QDs, emitting near blue green wavelength, were more efficient than the above CdSe QDs, and their luminescent properties were comparable to those of CdSe QDs.Thebrightness ofInP/ZnS QDLED was maximumof 179cd/m2.

• Bulletin of the Korean Chemical Society
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• v.32 no.7
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• pp.2316-2318
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• 2011

A novel technology has been developed for the synthesis of thioglycolic acid (TGA)-capped CdSe quantum dots (QDs) in aqueous medium. The reaction was carried out in air atmosphere with one-pot by using $SeO_2$ to replace Se or $Na_2Se$. The technological parameters including refluxing time, pH values and molar ratios of selenium to cadmium had significant influence on the luminescence properties of CdSe QDs. Furthermore, the obtained QDs were characterized by fluorescent spectroscopy, X-ray powder diffraction (XRD) and transmission electron microscopy (TEM), respectively. The results demonstrated that the CdSe QDs were of zinc-blended crystal structure in a sphere-like shape.

• Journal of the Korean Vacuum Society
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• v.20 no.6
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• pp.442-448
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• 2011

Self-assembled InAs/InAlGaAs quantum dots (QDs) grown on an InP (001) substrate have been investigated by using photoluminescence (PL) and time-resolved PL measurements. The single layer (QD1) and seven stacks (QD2) of InAs/InAlGaAs QDs grown by the conventional S-K growth mode were used. The PL peak at 10 K was 1,320 nm for both QD1 and QD2. As the temperature increases from 10 to 300 K, the PL peaks for QD1 and QD2 were red-shifted in the amount of 178 and 264 nm, respectively. For QD1, the PL decay increased with increasing emission wavelength from 1,216 to 1,320 nm, reaching a maximum decay time of 1.49 ns at 1,320 nm, and then decreased as the emission wavelength was increased further. However, the PL decay time for QD2 decreased continuously from 1.83 to 1.22 ns as the emission wavelength was increased from 1,130 to 1,600 nm, respectively. These PL and TRPL results for QD2 can be explained by the large variation in the QD size with stacking number caused by the phase separation of InAlGaAs.

• Journal of the Korea Convergence Society
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• v.6 no.2
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• pp.49-55
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• 2015

Quantum dot technology can be complementary application of the bulk material, and that a wide range of applications that can take advantage of the characteristic convergence technology. With the development of quantum dot technology, it is important to analyze Marketability of quantum technology, business opportunity. In this study, patents, papers, market, analysis of the project will be to investigate the quantum information research trends. Research results are expected to be used as a basis for research and development path setting and strategic planning of the quantum dot. In particular, this study found the performance of quantum dot research through patents and papers analyzed. In addition, fast-growing field, the field to lead the commercialization were derived. Compared to the advanced research and national research was to diagnose the domestic research into quantum dots.

• Proceedings of the Korean Magnestics Society Conference
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• 2007.05a
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• pp.69.1-69.1
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• 2007

• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.265-265
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• 2011

자발형성법으로 InP (001) 기판에 성장한 InAs/InAlGaAs 양자점(QDs: quantum dots)의 광학적 특성을 PL (photoluminescence)와 TRPL (time-resolved PL)을 이용하여 분석하였다. InAs QDs 시료는 single layer InAs QDs (QD1)과 7-stacked InAs QDs (QD2)를 사용하였다. 두 시료 모두 저온 (10 K)에서 1,320 nm에서 PL 피크가 나타나고, 온도가 증가함에 따라 PL 피크는 적색편이 (red-shift)를 보였다. 양자점의 온도를 10 K에서 300 K까지 증가하였을 때 QD1은 178 nm 적색편이 하였으며, PL 스펙트럼 폭은 온도가 증가함에 따라 증가하였다. 그러나 QD2는 264 nm 적색편이를 보였으며 PL 스펙트럼의 폭은 QD1 시료와 반대로 온도가 증가함에 따라 감소하였다. QD2의 아주 넓은 PL 스펙트럼 폭과 매우 큰 적색편이는 InAs 양자점 크기의 변화가 QD1에 비해 훨씬 크기 때문이다. QD2의 경우 InAs 층수(layer number)가 증가함에 따라 InAs QD의 크기가 점차 증가하므로 QD 크기의 변화가 single layer인 QD1 시료보다 훨씬 크다. QD1의 PL 소멸은 파장이 증가함에 따라 점차 느려지다가 PL 피크 근처에서 가장 느린 소멸 곡선을 보이고, 파장이 더 증가하였을 때 PL 소멸은 점차 빠르게 소멸하였다. 그러나 QD2의 PL 소멸곡선은 파장이 증가함에 따라 점차 빠르게 소멸하였다. 이것은 QD2는 양자점 크기의 변화가 매우 크기 때문에 (lateral size=18~29 nm, height=2.8~5.9 nm) 방출파장이 증가함에 따라 양자점 사이의 파동함수의 겹침이 증가하여 캐리어의 이완이 증가하기 때문으로 설명된다. 온도에 따른 TRPL 결과는 두 시료 모두 10 K에서 150 K 까지는 소멸시간이 증가하였고, 150 K 이후부터는 소멸시간이 감소하였다. 온도가 증가함에 따라 소멸시간이 증가하는 것은 양자점에서 장벽과 WL (wetting layer)로 운반자(carrier)의 이동, 양자점들 사이에 열에 의해 유도된 운반자의 재분배 등으로 인한 발광 재결합으로 설명할 수 있다. 150 K 이상에서 소멸시간이 감소하는 것은 열적효과에 의한 비발광 재결합 과정에 의한 운반자의 소멸이 증가하기 때문이다. 온도에 따른 TRPL 결과는 두 시료 모두 150 K까지는 발광재결합이 우세하고, 150 K 이상에서 비발광재겹합이 우세하게 나타났다.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.08a
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• pp.276-276
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• 2010

Large-area micropatterned array of Co/Ni bilayer anti-dots was fabricated using photolithography and wet etching process. The surface morphology as well as the surface topography was checked by scanning electron microscopy and atomic force microscopy, whereas the magnetic properties were studied by magneto-optical Kerr effect (MOKE) and magnetic force microscopy (MFM). Systematic studies of the magnetic-reversal mechanism, the in-plane anisotropy and the switching field properties were carried out. To get a comprehensive knowledge about the domain configuration, we also employed OOMMF simulations. It was found from the MOKE measurements that a combined effect of configurational and the magneto-crystalline anisotropy simultaneously works in such micropatterned bilayer structures. In addition, the inclusion of holes in the uniform magnetic film drastically affected the switching field. The MFM images show well-defined domain structures which are periodic in nature. The micromagnetic simulations indicate that the magnetization reversal of such a structure proceeds by formation and annihilation of domain walls, which were equally manifested by the field-dependent MFM images. The observed changes in the magnetic properties are strongly related to both the patterning that hinders the domain-wall motion and to the magneto-anisotropic bilayered structure.

• Journal of the Korean Vacuum Society
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• v.15 no.3
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• pp.294-300
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• 2006

We fabricated the distributed feedback (DFB) InP/InGaAs/InP grating structures on InP (100) substrates by metal-organic chemical vapor deposition, and their structural properties were investigated by atomic force microscopy and scanning electron microscopy. Self-assembled InAs/InAlGaAs quantum dots (QDs) were grown on the InP/InGaAs/InP grating structures by molecular beam epitaxy, and their optical properties were compared with InAs/InAlGaAs QDs without grating structure. The duty of the grating structures was about 30%. The PL peak position of InAs/InAlGaAs QDs grown on the grating structure was 1605 nm, which was red-shifted by 18 nm from that of the InAs/InAlGaAs QDs without grating structure. This indicates that the formation of InAs/InAlGaAs QDs was affected by the existence of the DFB grating structures.

• Proceedings of the Korea Association of Crystal Growth Conference
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• 1999.06a
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• pp.81-114
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• 1999

The strain, surface and inerfacial energies of III-V ternary systems were calculated for three kinds of structure modes: the Frank-van der Merwe (FM) mode, the Stranski-Krastanov (SK) mode an the Volmer-Wever (VW) mode. The free energy for each mode was estimated as functions of the thickness and composition or lattice misfit. Through comparison of the free energy of each mode, it was found that the thickness-composition phase diagrams of III-V ternary systems can be determined only by considering the balance of the free energy and three kinds of structure modes appear in the phase diagrams. The SK mode appears only when the lattice misfit is large and/or the lattice layer is thick. The most stable structure of the SK mode is a cluster with four lattice layers or minimum thickness on a wetting layer of increasing lattice layers. The VW mode appears when the lattice misfit is large and the lattice layer is thin and only in the InPSb/InP and GaPSb/GaP systems which have the largest lattice misfit of III-V ternary systems. The stable region of the SK mode in the GaPSb/GaP and InPSb/InP phase diagrams is largest of all because the composition dependence of the strain energy of these systems is stronger than that of the other systems. The critical number of lattice layers below which tow-dimensional (2D) layers precede the three-dimensional (3D) nucleation in the SK mode at x=1.0 depnds on the lattice misfit.