• Applied Science and Convergence Technology
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• v.24 no.6
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• pp.257-261
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• 2015

We report on GaAs/AlGaAs quantum well infrared photodetectors (QWIPs) that can cover the spectral range of $3.6-25{\mu}m$. One advantage of the GaAs QWIPs is the wavelength tenability as a function of their structural parameters. We have performed a systematic calculation on the detection wavelength of a typical $GaAs/Al_xGa_{1-x}As$ multi-quantum-well photodetector, with the aluminum mole fraction (x) of $Al_xGa_{1-x}As$ barrier in the range of 0.15-0.43 and the quantum-well width range from 30 to 60 $60{\AA}$. Design and fabrication of a QWIP based on $GaAs/Al_{0.23}Ga_{0.77}As$ structure with $37{\AA}$-thick well width has been carried out. The calculated operation wavelength of the QWIP is in a good agreement with the experimental data taken by photo response and activation energy calculation from thermal quenching of integrated photoluminescence.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.477-477
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• 2011

In this paper, we synthesize ZnO wire on Si substrate by catalyst-free thermal chemical vapor deposition (CVD). Each ZnO wire is grew up at different condition such as temperature and O2 flow rate. The Young's modulus of individual ZnO wires were estimated using quasi-static and dynamic measurements, as well as resonance frequency measurements. Using this system, current-voltage characteristics of each ZnO wire structure fabricated on a trench were measured. A new concept of electromechanical device structure combined with the piezoelectric effect of ZnO will be suggested in the end of this paper.

• Journal of the Korean Vacuum Society
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• v.8 no.2
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• pp.148-152
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• 1999

the low temperature magnetoresistance effect, electron mobilities, and 2 Dimensional electron Gases (2DEG) properties were investigated in $Si/Si_{1-x}Ge_x$ quantum well devices. N-type $Si/Si_{1-x}Ge_x$ structures were fabricated by utilizing a gas source Molecular Beam Epitaxy (GSMBE). Thermal oxidation was carried out in a dry O atmosphere at $700^{\circ}C$ for 7 hours. Electron mobilities were measured by using a Hall effect and a magnetoresistant effect at low temperatures down to 0.4K. Pronounced Shubnikov-de Haas (SdH) oscillations were observed at a low temperature showing two dimensional electron gases (2DEG) in s tensile strained Si quantum well. The electron sheet density (ns) of $1.5\times10^{12}[\textrm{cm}^{-2}]$ and corresponding electron mobility of 14200 $[\textrm{cm}^2V^{-1}s^{-1}]$ were obtained at a low temperature of 0.4K from $Si/Si_{1-x}Ge_x$ structures with thermally grown oxides.

• 한국정보디스플레이학회:학술대회논문집
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• 2009.10a
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• pp.196-199
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• 2009

We report the multiple quantum well (MQW) structure for highly efficient red phosphorescent OLEDs. Various triplet quantum well devices from a single well to five quantum wells are realized using a wide band-gap hole and electron transporting layers, narrow band-gap host and dopant material, and charge control layers (CCL). The maximum external quantum efficiency of 14.8 % with a two quantum well device structure is obtained, which is the highest value among the red phosphorescent OLEDs using same dopant.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.24 no.1
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• pp.1-6
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• 2011

Optical gain characteristics of $1.3{\mu}m$ type-II GaAsSb/InGaNAs/GaAs trilayer quantum well structures were studied using multi-band effective mass theory. The results were compared with those of $1.3{\mu}m$ GaAsSb/InGaNAs/GaAs trilayer quantum well structures. In the case of $1.3{\mu}m$ GaAsSb/InGaNAs/GaAs trilayer quantum well structure, the energy difference between the first two subbands in the valence band is smaller than that of $1.3{\mu}m$ GaAsSb/InGaNAs/GaAs trilayer quantum well structure. Also, $1.3{\mu}m$ GaAsSb/InGaNAs/GaAs trilayer quantum well structure shows larger optical gain than $1.3{\mu}m$ GaAsSb/InGaNAs/GaAs trilayer quantum well structure. This means that GaAsSb/InGaNAs/GaAs system is promising as long-wavelength optoelectronic devices for optical communication.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.39 no.2
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• pp.14-26
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• 2002

A new model for degenerate semiconductor quantum well devices was developed. In this model, the multi-subband Boltzmann transport equation was formulated by applying the Pauli exclusion principle and coupled to the Schrodinger and Poisson equations. For the solution of the resulted nonlinear system, the finite difference method and the Newton-Raphson method was used and carrier energy distribution function was obtained for each subband. The model was applied to a Si MOSFET inversion layer. The results of the simulation showed the changes of the distribution function from Boltzmann like to Fermi-Dirac like depending on the electron density in the quantum well, which presents the appropriateness of this modeling, the effectiveness of the solution method, and the importance of the Pauli -exclusion principle according to the reduced size of semiconductor devices.

• Proceedings of the Optical Society of Korea Conference
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• 2000.02a
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• pp.258-259
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• 2000

Quantum Well Disordering (QWD) has drawn a considerable attention in recent years$^{(1-3)}$ due to its wide applicability to optoelectronic devices. QWD allows modification of the shape of QW in selected regions, hence it modifies the subband energies in conduction and valance bands$^{(4)}$ . This leads to changes in optical properties such as band gap, absorption coefficient and refractive index. Thus such disordering in selected areas enables monolithic integration of various optoelectronic devices such as lasers, EA/EO modulators, waveguides and optical amplifiers. In this paper, we investigate the quantum well disordering effects on photoluminescence spectra by using experimental measurements and theoretical analysis$^{(5)}$ . (omitted)

• 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.

• Applied Science and Convergence Technology
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• v.25 no.6
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• pp.158-161
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• 2016

Debye temperature is an important thermodynamical factor in quantum dots (QDs); it can be used to determine the degree of homogeneity of a QD structure as well as to study the interdiffusion mechanism during growth. Direct estimation of the Debye temperature can be obtained using the Varshni relation. The Varshni relation is an empirical formula that can interpret the change of emission energy with temperature as a result of phonon interaction. On the other hand, phonons energy can be calculated using the Fan Expression. The Fan expression and Varshni relation are considered equivalent at a temperature higher than Debye temperature for InAs quantum dot. We investigated InAs quantum dot optically, the photoluminescence spectra and peak position dependency on temperature has been discussed. We applied a mathematical treatment using Fan expression, and the Varshni relation to obtain the Debye temperature and the phonon energy for InAs quantum dots sample. Debye temperature increase about double compared to bulk crystal. We concluded that the In/Ga interdiffusion during growth played a major role in altering the quantum dot thermodynamical parameters.

• Journal of the Semiconductor & Display Technology
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• v.14 no.4
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• pp.45-49
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• 2015

Using a combined CVD and ALD equipment system, multi-layer quantum well structures of $Al_2O_3/a-Si/Al_2O_3$ were fabricated on silicon Schottky junction devices and implemented to quantum well solar cells, in which the 1~1.5 nm thicknesses of the aluminum oxide films and the a-Si thin film layers were deposited at $300^{\circ}C$ and $450^{\circ}C$, respectively. Fabricated solar cell was operated by tunneling phenomena through the inserted quantum well structure being generated electrons on the silicon surface. Efficiency of the fabricated solar cell inserted with multi-quantum well of 41 layers has been increased by about 10 times that of the solar cell of pure Schottky junction solar cell.