• JSTS:Journal of Semiconductor Technology and Science
• /
• v.2 no.3
• /
• pp.170-172
• /
• 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.

• Applied Science and Convergence Technology
• /
• v.25 no.1
• /
• pp.1-6
• /
• 2016

Quantum dots (QDs) are considered as excellent color conversion and self-emitting materials for display and lighting applications. In this article, various technologies which can be used to realize white light emission with QDs are discussed. QDs have good color purity with a narrow emission spectrum and tunable optical properties with size control capabilities. For white light emission with a color-conversion approach, QDs are combined with blue-emitting inorganic and organic light-emitting diodes (LED) to generate white emission with high energy conversion efficiency and a high color rendering index for various display and lighting applications. Various device structures for self-emitting white QD light-emitting diodes (QD-LED) are also reviewed. Various stacking and patterning technologies are discussed in relation to QD-LED devices.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.27 no.2
• /
• pp.110-114
• /
• 2014

In this study, we report the doping effect of graphene quantum dots (QDs) in nematic liquid crystal (NLC) system on rubbed polyimide (PI) surface. The good LC alignment and high thermal stability in QD-LC cell system on rubbed PI surfaces can be measured. Also, the low threshold voltage of QD-TN cell was observed about 2.77 V. The fast response time of 13.2 ms for QD-TN cell can be achieved. Finally, the good voltage holding ratio of QD-TN cell on rubbed PI surface was measured.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.16 no.8
• /
• pp.663-668
• /
• 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.

• Bulletin of the Korean Chemical Society
• /
• v.29 no.9
• /
• pp.1729-1731
• /
• 2008

Colloidal solutions of crystalline PbSe nanoparticles have been synthesized by hot solution chemical process using PbO in oleic acid and tributylphosphine (TBP) bonded selenium. The use of TBP as a capping agent along with oleic acid gives a very good yield (around 10% at 180 ${^{\circ}C}$) with an average diameter of particle of about < 6.6 nm. The effects of temperature on size and production yield of PbSe quantum dots are studied. Xray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM) and UV/VIS/NIR absorption spectroscopy were used to characterize the samples.

• ETRI Journal
• /
• v.26 no.5
• /
• pp.475-480
• /
• 2004

Self-assembled InAs quantum dots (QDs) embedded in an InAlGaAs matrix were grown on an InP (001) using a solid-source molecular beam epitaxy and investigated using transmission electron microscopy (TEM) and photoluminescence (PL) spectroscopy. TEM images indicated that the QD formation was strongly dependent on the growth behaviors of group III elements during the deposition of InAlGaAs barriers. We achieved a lasing operation of around 1.5 ${\mu}m$ at room temperature from uncoated QD lasers based on the InAlGaAs-InAlAs material system on the InP (001). The lasing wavelengths of the ridge-waveguide QD lasers were also dependent upon the cavity lengths due mainly to the gain required for the lasing operation.

• Journal of the Korean Ceramic Society
• /
• v.52 no.2
• /
• pp.146-149
• /
• 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.

• Progress in Superconductivity and Cryogenics
• /
• v.24 no.4
• /
• pp.55-58
• /
• 2022

Carbon-based doping to MgB₂ superconductor is the simplest approach to enhance the critical current densities under magnetic fields. Carbon quantum dots is synthesized in this work as a carbon provider to MgB₂ superconductors. Polyvinyl Pyrrolidone is pyrolyzed and dispersed in dimethylfomamide solvent as a dopant to the mixture of Mg and B powders. Doped MgB₂ bulk samples clearly show the decrease of a-axis lattice constant, grain refinements, and broadening of FWHM of diffraction peaks compared to un-doped MgB₂ possibly due to the carbon substitution and/or boron vacancy at the boron site in MgB₂ lattice. Also, high-field J_c for the doped MgB₂ is enhanced significantly with the crossover about 3 T at 5 & 20 K when increasing the doping of carbon quantum dots.

• Journal of the Korean Vacuum Society
• /
• v.18 no.3
• /
• pp.208-212
• /
• 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.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2012.08a
• /
• pp.417-417
• /
• 2012

For desired optical properties of QDs, it is very important to reduce the presence of defects on their surfaces. Passivation of surface defects using larger band gap materials is the most effective way. Some groups successfully synthesized Cd based multi-shell structured quantum dots and improved its optical properties. However, its productivity has limit because of the amounts of glass ware and space. In this research, we try to synthesize Cd based multi-shell structured nanocrystal quantum dots to overcome demerits of conventional batch synthetic method. This reactor composed pump, SUS reaction part (3.2 mm stainless steel and furnace) and batch mixer. We successively synthesized CdSe/CdS/ZnS quantum dot at this reactor in one step.