• Bulletin of the Korean Chemical Society
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• v.32 no.1
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• pp.263-272
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• 2011

Highly luminescent and monodisperse InP quantum dots (QDs) were prepared by a non-organometallic approach in a non-coordinating solvent. Fatty acids with well-defined chain lengths as the ligand, a non coordinating solvent, and a thorough degassing process are all important factors for the formation of high quality InP QDs. By varying the molar concentration of indium to ligand, QDs of different size were prepared and their absorption and emission behaviors studied. By spin-coating a colloidal solution of InP QD onto a silicon wafer, InP QD thin films were obtained. The thickness of the thin films cured at 60 and $200^{\circ}C$ were nearly identical (approximately 860 nm), whereas at $300^{\circ}C$, the thickness of the thin film was found to be 760 nm. Different contrast regions (A, B, C) were observed in the TEM images, which were found to be unreacted precursors, InP QDs, and indium-rich phases, respectively, through EDX analysis. The optical properties of the thin films were measured at three different curing temperatures (60, 200, $300^{\circ}C$), which showed a blue shift with an increase in temperature. It was proposed that this blue shift may be due to a decrease in the core diameter of the InP QD by oxidation, as confirmed by the XPS studies. Oxidation also passivates the QD surface by reducing the amount of P dangling bonds, thereby increasing luminescence intensity. The dielectric properties of the thin films were also investigated by capacitance-voltage (C-V) measurements in a metal-insulator-semiconductor (MIS) device. At 60 and $300^{\circ}C$, negative flat band shifts (${\Delta}V_{fb}$) were observed, which were explained by the presence of P dangling bonds on the InP QD surface. At $300^{\circ}C$, clockwise hysteresis was observed due to trapping and detrapping of positive charges on the thin film, which was explained by proposing the existence of deep energy levels due to the indium-rich phases.

• Journal of the Korean Ceramic Society
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• v.54 no.6
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• pp.449-469
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• 2017

The development of quantum dots (QDs) has had a significant impact on various applications, such as solar cells, field-effect transistors, and light-emitting diodes (LEDs). Through successful engineering of the core/shell heterostructure of QDs, their photoluminescence (PL) quantum yield (QY) and stability have been dramatically enhanced. Such high-quality QDs have been regarded as key fluorescent materials in realizing next-generation display devices. Particularly, electrically driven (or electroluminescent, EL) QD light-emitting diodes (QLED) have been highlighted as an alternative to organic light-emitting diodes (OLED), mostly owing to their unbeatably high color purity. Structural optimizations in QD material as well as QLED architecture have led to substantial improvements of device performance, especially during the past decade. In this review article, we discuss QDs with various semiconductor compositions and describe the mechanisms behind the operation of QDs and QLEDs and the primary strategies for improving their PL and EL performances.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.13 no.2
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• pp.1100-1123
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• 2019

A code-based cryptosystem can resist quantum-computing attacks. However, an original system based on the Goppa code has a large key size, which makes it unpractical in embedded devices with limited sources. Many special error-correcting codes have recently been developed to reduce the key size, and yet these systems are easily broken through side channel attacks, particularly differential power analysis (DPA) attacks, when they are applied to hardware devices. To address this problem, a higher-order masking scheme for a McEliece cryptosystem based on the quasi-dyadic moderate density parity check (QD-MDPC) code has been proposed. The proposed scheme has a small key size and is able to resist DPA attacks. In this paper, a novel McEliece cryptosystem based on the QD-MDPC code is demonstrated. The key size of this novel cryptosystem is reduced by 78 times, which meets the requirements of embedded devices. Further, based on the novel cryptosystem, a higher-order masking scheme was developed by constructing an extension Ishai-Sahai-Wagne (ISW) masking scheme. The authenticity and integrity analysis verify that the proposed scheme has higher security than conventional approaches. Finally, a side channel attack experiment was also conducted to verify that the novel masking system is able to defend against high-order DPA attacks on hardware devices. Based on the experimental validation, it can be concluded that the proposed higher-order masking scheme can be applied as an advanced protection solution for devices with limited resources.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.293-294
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• 2011

It is known that semiconductor quantum-dot (QD) heterostructures have superior zero-dimensional quantum confinement, and they have been successfully applied to semiconductor laser diodes (QDLDs) for optical communication and infrared photodetectors (QDIPs) for thermal images [1]. The self-assembled QDs are normally formed at Stranski-Krastanov (S-K) growth mode utilizing the accumulated strain due to lattice-mismatch existing at heterointerfaces between QDs and cap layers. In order to increase the areal density and the number of stacks of QDs, recently, sub-monolayer (SML)-thick QDs (SQDs) with reduced strain were tried by equivalent thicknesses thinner than a wetting layer (WL) existing in conventional QDs (CQDs) by S-K mode. Despite that it is very different from CQDs with a well-defined WL, the SQD structure has been successfully applied to QDIP[2]. In this study, optical characteristics are investigated by using photoluminescence (PL) spectra taken from self-assembled InAs/GaAs QDs whose coverage are changing from submonolayer to a few monolayers. The QD structures were grown by using molecular beam epitaxy (MBE) on semi-insulating GaAs (100) substrates, and formed at a substrate temperature of 480$^{\circ}C$ followed by covering GaAs cap layer at 590$^{\circ}C$. We prepared six 10-period-stacked QD samples with different InAs coverages and thicknesses of GaAs spacer layers. In the QD coverage below WL thickness (~1.7 ML), the majority of SQDs with no WL coexisted with a small amount of CQDs with a WL, and multi-peak spectra changed to a single peak profile. A transition from SQDs to CQDs was found before and after a WL formation, and the sublevel of SQDs peaking at (1.32${\pm}$0.1) eV was much closer to the GaAs bandedge than that of CQDs (~1.2 eV). These revealed that QDs with no WL could be formed by near-ML coverage in InAs/GaAs system, and single-mode SQDs could be achieved by 1.5 ML just below WL that a strain field was entirely uniform.

• Journal of the Korean Vacuum Society
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• v.15 no.3
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• pp.301-307
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• 2006

We have investigated optical properties of p-modulation doped In(Ga)As quantum dots (QDs) on InP substrate with a comparison with the undoped QDs. Photoluminscence (PL) intensity of doped QDs at 10 K was about 10 times weaker than that of undoped QD sample. The decay time of doped QD sample at its PL peak, obtained from the time-resolved PL (TR-PL) experiment at 10 K, was very fast compared to that of undoped sample. We interpret that this fast decay time of the doped QD sample comes from the addition of non-radiative recombination paths, which are originated from the doping-related defects.

• Proceedings of the Optical Society of Korea Conference
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• 2003.02a
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• pp.152-153
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• 2003

최근 양자점 (Quantum Dot-QD)에 대한 관심이 기초 물리학뿐만 아니라 광전소자 응용 측면에서 많은 주목을 끌고 있다. 특히, 자발 형성방법으로 성장시킨 양자점 (Self-assembled QD)을 이용하여 Laser Diode와 같은 광소자에 응용한 결과가 발표되고 있다. 이러한 자발형성 방법으로 성장한 양자점을 광통신에 응용하기 위해서는 발광파장을 제어할 필요성이 있다. 따라서 본 연구에서는 단거리 광통신에 응용 될 수 있는 1.3 $\mu$m 영역과 장거리 광통신에 사용하는 1.55 $\mu$m 영역으로 InAs 양자점의 발광 파장을 변조한 결과에 대하여 분석하였다. (중략)

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.110-110
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• 2010

본 실험에서는 Silicon (001) 기판을 사용하여 silicon 기판상에 modified Stranski-Krastanow(S-K) 방식으로 InAs quantum dot (QD) 을 성장하고 그 위에 InSb layer를 형성하였다. 기판온도 $390^{\circ}$에서 In injection period를 4번 반복하여 제작된 InAs quantum dot layer를 buffer로 사용하였으며, QD layer의 밀도는 $1{\mu}m^2$ 당 600개, height가 $6.2\;{\pm}\;2.0\;nm$, width가 $36.1\;{\pm}\;9.2\;nm$ 정도이다. 성장된 $2.8{\mu}m$ 두께의 InSb film의 특성을 분석해 보면 AFM 상에서의 root mean square (rms) roughness는 5.142nm정도이며, electron mobility는 340 K 에서 $41,352cm^2/Vs$, 1.8 K에서는 $4,215cm^2/Vs$ 정도를 나타내었다. 본 실험에서는 다른 실험과는 달리 InAs QD 을 buffer layer로 사용하였으며, silicon기판도 아무런 처리가 되지 않은 (001)기판을 사용하였으므로 기존의 다른 연구 결과와는 차별성을 가진다. 또한 buffer로 사용된 InAs quantum dot layer의 종류를 한 가지로 고정하고 실험을 하였지만 추후 더욱 다양한 밀도와 크기의 quantum dot layer를 적용시키고, 기존의 다른 논문에서 적용된 방법들을 추가로 적용시켜 본다면 mobility값은 더욱 증가할 것으로 생각된다. 이러한 연구를 통해 값이 싸고 구하기 쉬운 silicon기판상에 silicon에 비하여 더 좋은 특성을 갖는 III-V족 화합물 반도체 소자를 구현 할 수 있을 것으로 생각된다.

• The Journal of Korean Medicine
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• v.24 no.2
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• pp.213-218
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• 2003

Objectives : There has been little report on the treatment of pulmonary hypertension on the basis of Oriental medicine. Several weeks ago we had a case of pulmonary hypertension, and found something in the treatment of the disease. A 60-year old man with hemoptysis was admitted to the Kyunghee Oriental Medical Center on April 23, 2002 and discharged May 4, 2002. During that time, we saw good results. Methods : On the oriental medical basis that Chuongsangboha-tang (Qingshangbuxia-tang) has an effect on chronic pulmonary disease, we treated him with that medicine three times a day for 12 days along with Roxithromycin 150mg/tab 1T qd, Digoxin 0.25mg/tab 0.5T qd, and Bambuterol Hel 1T qd. He was also given acupuncture therapy daily with tonifying SP3(太白), L9(太淵) and sedating H8(少府), L10(魚際). Results : The following data was observed from the therapy : hemoptysis volume decreased by 90%, general weakness by 40%m and ABGA results improved. Conclusions : As we managed pulmonary hypertension, we came to the conclusion that the oriental medical therapy can be of assistance to western medical therapy and can mitigate hemoptysis.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.221-221
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• 2013

Striving to replace the well known silicon nanocrystals embedded in oxides with solution-processable charge-trapping materials has been debated because of large scale and cost effective demands. Herein, a silicon quantum dot-polystyrene nanocomposite (SiQD-PS NC) was synthesized by postfunctionalization of hydrogen-terminated silicon quantum dots (H-SiQDs) with styrene using a thermally induced surface-initiated polymerization approach. The NC contains two miscible components: PS and SiQD@PS, which respectively are polystyrene and polystyrene chains-capped SiQDs. Spin-coated films of the nanocomposite on various substrate were thermally annealed at different temperatures and subsequently used to construct metal-insulator-semiconductor (MIS) devices and thin film field effect transistors (TFTs) having a structure p-$S^{++}$/$SiO_2$/NC/pentacene/Au source-drain. C-V curves obtained from the MIS devices exhibit a well-defined counterclockwise hysteresis with negative fat band shifts, which was stable over a wide range of curing temperature ($50{\sim}250^{\circ}C$. The positive charge trapping capability of the NC originates from the spherical potential well structure of the SiQD@PS component while the strong chemical bonding between SiQDs and polystyrene chains accounts for the thermal stability of the charge trapping property. The transfer curve of the transistor was controllably shifted to the negative direction by chaining applied gate voltage. Thereby, this newly synthesized and solution processable SiQD-PS nanocomposite is applicable as charge trapping materials for TFT based memory devices.

• Journal of Powder Materials
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• v.19 no.6
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• pp.442-445
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• 2012

The quantum dots (QD) have unique electrical and optical properties due to quantum dot confinement effect. The optical properties of QDs are decided by various synthesis conditions. In a prior QDs study, a study on the QDs size with synthesis condition such as synthesis time and temperature is being extensively researched. However, the research on QDs size with composition ratio has hitherto received scant attention. In order to evaluate the ratio dependence of CdSe crystal, synthesis ratio of Se precursor is changed from 16.7 mol%Se to 44 mol%Se. As the increasing Se ratio, the band gap was increased. This is caused by red shift of emission. We confirmed optical property of CdSe QDs with composition ratio.