• Title/Summary/Keyword: the dots

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Self-Assembled InAs/AlAs Quantum Dots Characterization Using Photoreflectance Spectroscopy (자연 성장된 InAs/AlAs 양자점의 Photoreflectance 특성)

  • Kim, Ki-Hong;Sim, Jun-Hyoung;Bae, In-Ho
    • Journal of the Korean Vacuum Society
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    • v.18 no.3
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    • pp.208-212
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    • 2009
  • The optical characterization of self-assembled InAs/AlAs quantum dots(QD) grown by MBE were investigated using photoreflectance spectroscopy. The intensities of the signals of the GaAs buffer and wetting layer(WL) changed with the width of the WL layer. The PR spectrum for the sample, in which QDs layer were etched off at room temperature, indicated that the broadened signal ranging $1.1{\sim}1.4\;eV$ was originated from InAs QDs and WL. The intensities of signals of GaAs buffer and the WL changed with the WL width. A red shift of the PR peak of WL are observed when the annealing temperatures range from $450^{\circ}C$ to $750^{\circ}C$, which indicates that the interdiffusion between dots and capping layer is caused by improvement in size uniformity of QDs.

Study on Sonochemical Synthesis and Characterization of CdTe Quatum Dot (초음파 방법을 이용한 CdTe 양자점의 합성 및 특성에 관한 연구)

  • Yoo, Jeong-yeol;Kim, Woo-seok;Park, Seon-A;Kim, Jong-Gyu
    • Applied Chemistry for Engineering
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    • v.28 no.5
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    • pp.571-575
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    • 2017
  • In this study, cadmium telluride (CdTe) quantum dots were synthesized by using ultrasonic irradiation method. Optical properties and structural characteristics of the CdTe quantum dots were analyzed by two main variables; the ratio of the precursor and the synthesis time. As the synthesis time increased, the band gap reduction was observed with the growth of CdTe quantum dots. As for the luminescence properties, the red shift appeared at 510~610 nm wavelength range. Also, it was confirmed that the red shift occurs rapidly as the ratio of Te increases. According to PL peak intensity, the highest intensity was shown at 180 to 240 min. Structural characteristics of CdTe quantum dots were investigated through XRD and TEM, and the cubic zinc blend structure was observed. The size of quantum dots was about 2.5 nm and uniformly dispersed when the synthesis time took 210 min. In addition, the apparent crystallinity was discovered in FFT image.

Improvement of Short-Circuit Current of Quantum Dot Sensitive Solar Cell Through Various Size of Quantum Dots (양자점 입도제어를 통한 양자점 감응형 태양전지 단락전류 향상)

  • Ji, Seung Hwan;Yun, Hye Won;Lee, Jin Ho;Kim, Bum-Sung;Kim, Woo-Byoung
    • Korean Journal of Materials Research
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    • v.31 no.1
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    • pp.16-22
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    • 2021
  • In this study, quantum dot-sensitized solar cells (QDSSC) using CdSe/ZnS quantum dots (QD) of various sizes with green, yellow, and red colors are developed. Quantum dots, depending their different sizes, have advantages of absorbing light of various wavelengths. This absorption of light of various wavelengths increases the photocurrent production of solar cells. The absorption and emission peaks and excellent photochemical properties of the synthesized quantum dots are confirmed through UV-visible and photoluminescence (PL) analysis. In TEM analysis, the average sizes of individual green, yellow, and red quantum dots are shown to be 5 nm, 6 nm, and 8 nm. The J-V curves of QDSSC for one type of QD show a current density of 1.7 mA/㎠ and an open-circuit voltage of 0.49 V, while QDSSC using three type of QDs shows improved electrical characteristics of 5.52 mA/㎠ and 0.52 V. As a result, the photoelectric conversion efficiency of QDSSC using one type of QD is as low as 0.53 %, but QDSSC using three type of QDs has a measured efficiency of 1.4 %.

The Structural and Optical Properties of GaAs- SiO2 Composite Thin Films With Varying GaAs Nano-particle Size (GaAs 나노입자 크기에 따른 SiO2 혼합박막의 구조적 광학적 특성)

  • Lee, Seong-Hun;Kim, Won-Mok;Sin, Dong-Uk;Jo, Seong-Hun;Jeong, Byeong-Gi;Lee, Taek-Seong;Lee, Gyeong-Seok
    • Korean Journal of Materials Research
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    • v.12 no.4
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    • pp.296-303
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    • 2002
  • For potential application to quantum mechanical devices, nano-composite thin films, consisting of GaAs quantum dots dispersed in SiO$_2$ glass matrix, were fabricated and studied in terms of structural, chemical, and optical properties. In order to form crystalline GaAs quantum dots at room temperature, uniformly dispersed in $SiO_2$matrix, the composite films were made to consist of alternating layers of GaAs and $SiO_2$in the manner of a superlattice using RF magnetron sputter deposition. Among different film samples, nominal thickness of an individual GaAs layer was varied with a total GaAs volume fraction fixed. From images of High Resolution Transmission Electron Microscopy (HRTEM), the formation of GaAs quantum dots on SiO$_2$was shown to depend on GaAs nominal thickness. GaAs deposits were crystalline and GaAs compound-like chemically according to HRTEM and XPS analysis, respectively. From measurement of optical absorbance using a spectrophotometer, absorption edges were determined and compared among composite films of varying GaAs nominal thicknesses. A progressively larger shift of absorption edge was noticed toward a blue wavelength with decreasing GaAs nominal thickness, i.e. quantum dots size. Band gaps of the composite films were also determined from Tauc plots as well as from PL measurements, displaying a linear decrease with increasing GaAs nominal thickness.

Size Control of PbS Colloidal Quantum Dots and Their Application to Photovoltaic Devices

  • Lee, Wonseok;Ryu, Ilhwan;Choi, Geunpyo;Yim, Sanggyu
    • Proceedings of the Korean Vacuum Society Conference
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    • 2015.08a
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    • pp.249.1-249.1
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    • 2015
  • Quantum dots (QDs) are attracting growing attention for photovoltaic device applications because of their unique electronic, optical and physical properties. Lead sulfide (PbS) QDs are one of the most widely studied materials for the devices and known to have size-tunable properties. In this context, we investigated the relationship between the size of PbS QDs and two synthesizing conditions, a concentration of ligand, oleic acid in this work, and injection temperature. The inverted colloidal quantum dot solar cells based on the heterojunction of n-type zinc oxide layer and p-type PbS QDs were also fabricated. The size of the QDs and cell properties were observed to depend on both the QD synthesizing conditions, and hence the overall efficiency of the cell could vary even though the size of QDs used was same. The QD synthesizing conditions were finally optimized for the maximum cell efficiency.

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Optical Properties of PbS Quantum Dots (QDs) Precipitated in Nd3+-Containing Glasses

  • Park, Won Ji;Heo, Jong
    • Journal of the Korean Ceramic Society
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    • v.52 no.2
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    • pp.146-149
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    • 2015
  • Silicate glasses with different $Nd_2O_3$ concentrations were prepared through conventional melt-quenching methods while PbS quantum dots (QDs) were precipitated through heat treatment. The peak wavelengths of absorption and the photoluminescence of PbS QDs shifted to the short-wavelength side as the concentration of $Nd_2O_3$ increased. The electron energy loss spectroscopy (EELS) indicated that $Nd^{3+}$ ions were preferentially distributed inside the PbS QDs instead of the glass matrix. In addition, there was no significant change in the lifetimes of the $Nd^{3+}:^4F_{3/2}$ fluorescence between the as-prepared glass ($607{\mu}s$) and the heat-treated glass($576{\mu}s$). $Nd^{3+}$ ions were surrounded by oxygen instead of sulfur and the Nd-O clusters probably acted as nucleating centers for the formation of PbS QDs inside the glasses.

Number Recognition of Dot Matrix LED Display Using Morphological Processing and Template Matching (영상 형태학적 처리와 원형 정합을 이용한 도트 매트릭스 LED 디스플레이의 숫자 인식)

  • Jung, Min Chul
    • Journal of the Semiconductor & Display Technology
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    • v.17 no.2
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    • pp.41-46
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    • 2018
  • This paper proposes a new method for the number recognition on dot matrix LED display. The proposed method uses morphological processing that dilates dots of numbers and connects the dots into strokes. The size of numbers is normalized using horizontal projection because the gaps of dots are different according to the size of numbers. The numbers are segmented by connected component analysis and finally, template matching method recognizes the segmented numbers. The proposed method is implemented using C language in Raspberry Pi system with a camera module for a real-time image processing. Experiments were conducted by using various dot matrix LED displays. The results show that the proposed method is successful for the number recognition on dot matrix LED display.

Field Effect Transistor of Vertically Stacked, Self-assembled InAs Quantum Dots with Nonvolatile Memory

  • Li, Shuwei;Koike, Kazuto;Yano, Mitsuaki
    • JSTS:Journal of Semiconductor Technology and Science
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    • v.2 no.3
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    • pp.170-172
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    • 2002
  • The epilayer of vertically stacked, self-assembled InAs Quantum Dots (QDs)was grown by MBE with solid sources in non-cracking K-cells, and the sample was fabricated to a FET structure using a conventional technology. The device characteristic and performance were studied. At 77K and room temperature, the threshold voltage shift values are 0.75V and 0.35 V, which are caused by the trapping and detrapping of electrons in the quantum dots. Discharging and charging curves form the part of a hysteresis loop to exhibit memory function. The electrical injection of confined electrons in QDs products the threshold voltage shift and memory function with the persistent electron trapping, which shows the potential use for a room temperature application.

Preparation and Characterization of CdTe Quantum Dots (CdTe 양자점 합성과 물리적 특성 분석)

  • 김현석;송현우;조경아;김상식;김성현
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.16 no.8
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    • pp.663-668
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    • 2003
  • CdTe quantum dots(QDs) were synthesized in aqueous solution by colloidal method. The synthesized CdTe QDs were identified to be cubic-structured ones by x-ray diffraction(XRD). The photoluminescence(PL) was performed for CdTe QDs prepared as a function of Te precursor concentration, condensation time and aging time. The PL intensity is strongly dependent on Te precursor concentration, indicating that the ratio of Te to Cd ions affects the particle size and size distribution of the CdTe QDs. Our PL study reveals that the intensity of PL peaks strengthens as the condensation time elongates, implying that annealing by thermal energy transferred during condensation would eliminate defects which act as killing centers in CdTe particles. Our photocurrent study suggests that the CdTe QDs materials are one of the prospective materials for optoelectronics including photodetectors.

Orbital Quantum Bit in Si Quantum Dots

  • Ahn, D.;Oh, J.H.;Hwnag, S.W.
    • Progress in Superconductivity
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    • v.8 no.1
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    • pp.16-21
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    • 2006
  • In this paper, current status of experimental and theoretical work on quantum bits based on the semiconductor quantum dots in the University of Seoul will be presented. A new proposal utilizing the multi-valley quantum state transitions in a Si quantum dot as a possible candidate for a quantum bit with a long decoherence time will be also given. Qubits are the multi-valley symmetric and anti-symmetric orbitals. Evolution of these orbitals is controlled by an external electric field, which turns on and off the inter-valley interactions. Initialization is achieved by turning on the inter-valley Hamiltonian to let the system settle down to the symmetric orbital state. Estimates of the decoherence time is made for the longitudinal acoustic phonon process.

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