• 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.

• Korean Journal of Optics and Photonics
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• v.32 no.5
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• pp.220-229
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• 2021

The optical characteristics of high-power direct-lit white light-emitting diode (LED) lighting were investigated, where a quantum dot (QD) film was adopted to enhance the color-rendering index (CRI). The transmittance of the diffuser plate and the concentration of the QD film were varied in this study. The color coordinates and the correlated color temperature (CCT) did not show any appreciable change, while the CRI values increased slightly as the transmittance of the diffuser plate decreased. The investigated optical properties were nearly independent of the viewing angle, and the luminance distribution was close to Lambertian. The CCT decreased from approximately 6000 K to approximately 4000 K as the concentration of the QD film increased from 0 to 7.5 wt%, which was due to the enhanced red component in the emission spectrum. The CRI increased to approximately 95 for some optical configurations of the lighting. These results demonstrate that glare-free, color-changeable, high-rendering LED lighting can be realized by using a combination of a diffuser plate of appropriate transmittance and a red QD film.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2010.05a
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• pp.177-178
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• 2010

• Proceedings of the Korean Vacuum Society Conference
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• 2006.02a
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• pp.217-217
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• 2006

• Proceedings of the Korean Vacuum Society Conference
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• 2007.08a
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• pp.61-61
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• 2007

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.11a
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• pp.205-205
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• 2009

As a p-type semiconductor NiO is potential material which can be used in many application including QD-LED. NiO films were deposited on glass substrates using rf-sputtering method. The properties of resistivity, surface roughness, etc in the NiO films were investigated at different sputtering parameters. The resistivity of $l.88{\times}10^{-2}{\sim}3.71{\times}10^{-2}{\Omega}cm$ with sputtering power(80~200 watts) and change was very low. The sputtering pressure at 3~60 mTorr resulted in rather broad change ofresistivity of $0.58{\times}10^{-2}{\sim}4.67{\Omega}cm$. The oxygen content in sputtering gas was found to be very effective to control the resistivity from $2.01{\times}10^{-2}$ to $1.22{\times}10^2{\Omega}cm$ with 100~2.5% $O_2$ in Ar gas. In addition, the surface roughness showed the RMS values of 0.6~1.1 nm and the dependence on sputtering parameters was weak.

• Advances in nano research
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• v.2 no.4
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• pp.211-217
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• 2014

The self-assembled strain-induced sub-micrometric islands and nanostructures are grown from In-As-Sb-P quaternary liquid phase on InAs (100) substrates in Stranski-Krastanow growth mode. Two samples are under consideration. The first sample consists of unencapsulated islands and lens-shape quantum dots (QDs) grown from expressly inhomogeneous liquid phase. The second sample is an n-InAs/p-InAsSbP heterostructure with QDs embedded in the p-n junction interface. The morphology, size and shape of the structures are investigated by high-resolution scanning electron (SEM) and transmission electron (TEM) microscopy. It is shown that islands, as they decrease in size, undergo shape transitions. Particularly, as the volume decreases, the following succession of shape transitions are detected: sub-micrometric truncated pyramid, {111} facetted pyramid, {111} and partially {105} facetted pyramid, completely unfacetted "pre-pyramid", hemisphere, lens-shaped QD, which then evolves again to nano-pyramid. A critical size of $5{\pm}2nm$ for the shape transformation of InAsSbP-based lens-shaped QD to nano-pyramid is experimentally measured and theoretically evaluated.

• Journal of the Korean Vacuum Society
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• v.15 no.5
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• pp.493-498
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• 2006

Superluminescent diodes (SLD) with the emitting wavelength of $1.55{\mu}m$ was fabricated on InGaAs quantum dot structure grown by MOCVD. The output power and 3-dB bandwidth at room temperature and continuous wave operation were 3 mw and 55 nm, respectively.

• 한국가시화정보학회:학술대회논문집
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• 2003.11a
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• pp.81-82
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• 2003

We have developed the method for the conjugation of biotinylated DNA to streptavidin-coated QDs. QD-DNA conjugates and a high-sensitive fluorescence imaging technique are adopted to visualize gene transport across the membrane of the live cell in real time. Endocytotic cellular uptake of oligonucleotide and electrically-mediated plasmid DNA transfer into the live cell are monitored by a quantitative microscopic imaging system. Long-term kinetic study enables us to reveal the unknown mechanisms and rate-limiting steps of extracellular and intracellular transport of biomolecules. We designed experimental protocols to conjugate the oligonucleotide or the plasmid DNA to commercially available streptavidin-coated QDs. Gel electrophoresis is used to verify the effect of incubation time and the molar ratio of QDs and DNA on the conjugation efficiency. It is possible to fractionate the QD-DNA conjugates according to the DNA concentration and obtain the purified conjugates by a gel extraction technique.

• Asian Journal of Business Environment
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• v.8 no.1
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• pp.23-29
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• 2018

Purpose - The purpose of this research is to make a comparative assessment of People Credit Funds (PCFs) ranking in Vietnam between the Circular No. 42/2016/TT-NHNN dated December 20, 2016 with the Decision No. 14/2007/QD-NHNN dated 09/4/2007 issued by the Governor of the State Bank. Research design, data, and methodology - This study is mainly based on the Circular No. 42/2016/TT-NHNN dated December 20, 2016 and the Decision No. 14/2007/QD-NHNN dated 09/4/2007 issued by the Governor of the State Bank on PCFs ranking. Results - The study paper has shown positive changes in PCFs ranking in Vietnam in accordance with the Circular No. 42/2016/TT-NHNN, such as increasing Capital Adequacy Ratio (CAR), maintaining CAR, improving assets quality, developing indicators of governance, management and control capability. These changes have implications for the development and efficient performance of PCFs in Vietnam. Conclusions - The classification and evaluation of PCFs will contribute to its healthy development. These finding support PCFs to understand more about rating methodology, significance of rating system and the importance of improving their rating. PCFs in Vietnam desire to develop their business effectively, they need to understand exactly and comply fully with regulations related to their field of operations.