• Journal of Korean Vacuum Science & Technology
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• v.4 no.1
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• pp.23-26
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• 2000

We have fabricated by metal organic chemical vapor deposition (MOCVD) In$\_$0.13/Ga$\_$0.87/N/GaN multiple quantum well (MQW) with thickness as thin as 10 A and barriers also of th same width on (0001) sapphire substrate. We have investigated this thin MQW by steady-state and time-resolved photoluminescence(PL) in picosecond time scale in a wide temperature range from 10 to 290 K. In the PL at 10 K, we observed a broad peak at 3.134 eV which was attributed to the quantum well emission of InGaN. The full width at half maximum (FWHM) of this peak was 129 meV at 10 K and its broadening at low temperatures was considered to be due to compositional fluctuations and interfacial disorder in the alloy. The narrow width of the quantum well was mainly responsible for the broadening of the emission linewidth. We also observed an intense and sharp peak at 3.471 eV of GaN barrier. From the temperature dependent PL measurements, the activation energy of the InGaN quantum well emision peak was estimated to be 69 meV. The lifetime of the quantum well emission was found to be 720 ps at 10 K, which was explained in terms of the exciton localization arising from potential fluctuations.

• Korean Journal of Optics and Photonics
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• v.14 no.3
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• pp.279-285
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• 2003

Wide- and flat-gain laser diodes were designed and fabricated from asymmetric multiple quantum well (AMQW) structures which consist of three compressively strained InGaAsP wells of different thicknesses. For a 400 ${\mu}{\textrm}{m}$-long lasers with as-cleaved facets, -1 ㏈ and -3 ㏈ gain bandwidth were 45 nm and 80 nm, respectively. For this AMQW structure, calculated gain spectra with various line broadening functions were compared with experimental results. We confirmed the calculated gain spectra using an asymmetric line broadening function were in good agreement with the measured data.

• Applied Science and Convergence Technology
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• v.26 no.3
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• pp.52-54
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• 2017

An InGaN/GaN multiple quantum well (MQW) structure is grown on a GaN/sapphire template using a plasma-assisted molecular beam epitaxy (PA-MBE). The fluctuation of the quantum well thickness formed from roughly-grown InGaN layer results in a disordered photoluminescence (PL) spectrum. The surface morphologies of the InGaN layers with various In compositions are investigated by reflection high energy electron diffraction (RHEED) and atomic force microscopy (AFM). A blurred InGaN/GaN hetero-interface and the non-uniform QW size is confirmed by high resolution transmission electron microscopy (HR-TEM). Inhomogeneity of the quantum confinement results in a degradation of the quantum efficiency even though the InGaN layer has a uniform In composition.

• Journal of the Korean Vacuum Society
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• v.16 no.1
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• pp.27-32
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• 2007

We have investigated photoluminescence(PL) spectra of four $In_xGa_{1-x}N(x=0.15)/GaN$ multiple quantum well(MQW) structures with different well widths in order to study a phenomenon on crystal phase separation. The asymmetic behavior of PL spectra becomes stronger with increase of the well width from 1.5 nm to 6.0 nm, which indicates dual-peak nature. Analyzing the dual-peak fit PL spectra, we have observed that the intensity of low-energy shoulder peak rapidly becomes stronger, compared to that of high-energy peak corresponding to a transition in InGaN QW. It suggests that InGaN QW has two phases with tiny different In compositions, and that In-rich(InN-like) phase forms more and more relatively than stoichiometric InGaN(x=0.15) phase by the InN phase separation mechanism as the QW width increases. PL spectrum of 6.0-nm sample shows an additional peak at low-energy lesion(${\sim}2.0\;eV$) whose energy position is almost the same as a defect band of yellow luminescence frequently observed in GaN epilayers. It may be due to a defect resulted from In deficiency formed with development of the phase separation.

• Proceedings of the KIEE Conference
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• 1999.07d
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• pp.1747-1749
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• 1999

Organic electroluminescent devices (OLEDs) have received a great deal of attention due to their potential application as full-color displays. Europium complexes are known as excellent red color-emitting materials for OLEDs since they show intense photoluminescence at around 610 nm with a sharp spectral bandwidth. In this study, triple-layer and multiple quantum-well structures consisting of Eu$(TTA)_3$(bpy) complex well layer sandwiched triphenyldiamine derivative (TPD) layers were fabricated and their photoluminescent characteristics were investigated. Sharp emission at the wavelength of 615 nm has been observed from the triple-layer and multiple quantum-well structures containing Eu complex. Details on the electrical properties of these structures will be also discussed.

• Korean Journal of Optics and Photonics
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• v.10 no.4
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• pp.306-310
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• 1999

Electron intersubband absorption in Sb $\delta$-doped Si(110)/SiGe multiple quantum well structures is observed. Normally incident light can excite electrons in Si(110) quantum wells, which is not possible for Si(001) or GaAs quantum wells. The influence of Ge composition in SiGe barries is investigated. As the Ge composition in SiGe barriers increases, the absorption strength is decreased and the transition energy is increased. It is verifired by comparing the calculated and experimental results obtained at various incident and polarization angles that normally incident light and parallel incident light are absorbed in different processes.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.34D no.3
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• pp.60-73
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• 1997

By introducing a compressive-strained quanternary InGaAsP quantum-wells instead of a conventional ternary InGaAs quantum-wells in 1.55.mu.m DFB-LD, the lasing performances canb e improved and the problems caused by the thickness non-uniformity and the compositional abruptness among the hetero-interpaces canb e relaxed. In this paper, we investigated an iptimum InGaAsP/InGaAsP multiple-quantum-well(MQW) structure as an active layer in a direct-modulated 1.55.mu. DFB-LD from the view point of threshold current, chirping charcteristics, and resonance frequency. The optimum compressive-strained MQW structure was revealed as InGaAsP/InGaAsP structure with strain amount of about 1.2%, number of wells $N_{w}$ of 7, well width $L_{w}$ of 58.agns.. The threshold current density J of 500A/c $m^{2}$, the linewidth enhancement factor a of 1.8, and differential resonance frequency of d $f_{r}$/d(I-I)$^{1}$2/=2GHz/(mA)$^{1}$2/(atI=2 $I_{th}$) were expected in 1.55.mu.m .gamma./4-shifted DFB-LD with the cavity length of 400.mu.m long and kL value of 1.25. These values are considerably improved ones compared to those of 1.55um DFB-LD with InGaAs/InGaAsP MQW which have enhancement factor and the resonance frequence frequency by the detuning of lasing wavelength and gain-peak wavelength. It was found that the linewidth enhancement factor of 20% and differential resonance frequency of 35% without the degradation of the threshold current density could be enhanced in the range of -15nm~-20nm detuning which can be realized by controlling the thickness and Incomposition of InGaAsP well. well.and Incomposition of InGaAsP well. well.

• International Journal of Aeronautical and Space Sciences
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• v.15 no.2
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• pp.212-217
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• 2014

Micro Aerial Vehicles (MAVs) are useful devices to assess new features that may be utilized in a full size aircraft to enhance performance or to increase endurance. In this article, sources for energy saving in the micro air vehicles are initially addressed. Then, by specifying the important parameters on energy consumption of an aircraft, a feasibility study is conducted to assess the benefit of using solar cells to increase flight endurance. Next, a new solar cell has been designed and optimized for MAVs. This cell consists of a multiple quantum wells for which the quantum factor and the absorption coefficient are calculated by solving the Shrodinger equation using MATLAB software. Then, the manner and influence of MAVs parameters using the solar cells are examined to suggest optimal planform for different purposes. In order to increase flight endurance, it is noted that by using appropriate planform and the optimized solar cells, flight endurance can be increased by more than 30 percent.

• Proceedings of the Optical Society of Korea Conference
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• 1998.08a
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• pp.186-187
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• 1998

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.07a
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• pp.636-639
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• 2001

InGaN/GaN multiple quantum wells (MQWs) grown with various growth interruptions between the InGaN well and GaN barrier by metal-organic chemical vapor deposition were investigated using photoluminescence, high-resolution transmission electron microscopy, and energy filtered transmission electron microscopy (EFTEM). The luminescence intensity of the MQWs with growth interruptions is abruptly reduced compared to that of the MQW without growth interruption. Also, as the interruption time increases the peak emission shows a continuous blue shift. Evidence of indium clustering is directly observed both by using an indium ratio map of the MQWs and from indium composition measurements along an InGaN well using EFTEM. The higher intensity and lower energy emission of light from the MQW grown without interruption showing indium clustering is believed to be caused by the recombination of excitons localized in indium clustering regions and the increased indium composition in these recombination centers.