• Proceedings of the Optical Society of Korea Conference
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• 2003.02a
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• pp.38-39
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• 2003

The GaAs semiconductor whispering gallery modes, produced in the peripheral Rayleigh band region of W／sub Rayleigh／ ＝ (${\Phi}$／2)( 1-n／sub eff／n), exhibit novel properties of ultralow thresholds open to nano-ampere regime associated with photonic quantum ring (PQR) production (Fig 1 (a)). The PQR phenomena are associated with a photonic field-driven phase transition of quantum well(QW)-to-quantum wire (QWR) and hence the photonic (non-de Broglie) quantum corral effects, on the Rayleigh cavity confined carriers in dynamic steady state, occur as schematically shown in Fig 1. (omitted)

• Proceedings of the Korean Vacuum Society Conference
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• 2009.02a
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• pp.147.2-147.2
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• 2009

• Proceedings of the Korean Vacuum Society Conference
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• 1999.07a
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• pp.121-121
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• 1999

Gallium nitride (GaN) semiconductor is intensively under investigation for commercialization of short wavelength light emitting devices and laser diodes. One of serious obstacles to overcome is to reduce the defect density in GaN film grown by various techniques such as MOCVD, HVPE, etc. Many research groups including SAIT are trying to improve the defect density to 106-107/cm2 from the level of 108-1010/cm2. We have investigated epitaxial growth behaviour of GaN thin and thick films under hidride vapour phase epitaxy (HVPE) condition. In this report, we present the microstructural and crystallographical characteristics of the GaN films grown on sapphire (0001) substrate which were studied by both conventional and high-resolution transmission electron microscopy (TEM). Also we present some microscopic analysis results obtained from GaN films grown by ELO(dpitzsial lateral overgrowth)-HVPE and from GaN quantum well structures grown by MOCVD. Another serious problem in growing GaN thick film by HVPE is internal micro-cracks. We also comment the origin of the micro-crack.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.47-47
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• 2011

There have been numerous efforts to enhance the efficiency of light-emitting diodes (LEDs) by using low dimensional structures such as quantum dots (QDs), wire (QWRs), and wells (QWs). We demonstrate QD/QWR/QW hybrid structured LEDs by using nano-scaled pyramid structures of GaN with ~260 nm height. Photoluminescence (PL) showed three multi-peak spectra centered at around 535 nm, 600 nm, 665 nm for QWs, QWRs, and QDs, respectively. The QD emission survived at room temperature due to carrier localization, whereas the QW emission diminished from 10 K to 300 K. We confirmed that hybrid LEDs had zero-, one-, and two-dimensional behavior from a temperature-dependent time-resolved PL study. The radiative lifetime of the QDs was nearly constant over the temperature, while that of the QWs increased with increasing temperature, due to low dimensional behavior. Cathodoluminescence revealed spatial distributions of InGaN QDs, QWRs, and QWs on the vertices, edges, and sidewalls, respectively. We investigated the blue-shifted electroluminescence with increasing current due to the band-filling effect. The hybrid LEDs provided broad-band spectra with high internal quantum efficiency, and color-tunability for visible light-emitting sources.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.31A no.8
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• pp.62-71
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• 1994

A novel semiconductor device is proposed to be used as a processing element for the implementation of pulse-mode neural networks which consists of alternating n' GaAs quantum wells and undoped AlGaAs barriers sandwitched between n' GaAs cathode and P' GaAs anode and in simple circuit in conjunction with a parallel capacitive and resistive load the trigger circuit generates neuron-like pulse train output mimicking the function of axon hillock of biological neuron. It showed the sigmoidal relationship between the frequency of the pulse-train and the applied input DC voltage. In conjunction with MQWIMD the various neural circuits are proposed especially a neural chip monolithically integrated with photodetectors in order to perfrom the pattern recognition.

• ETRI Journal
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• v.44 no.3
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• pp.504-511
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• 2022

Monte Carlo simulations show that, as temperature increases, the average kinetic energy of channel electrons in a GaN transistor first decreases and then increases. According to the calculations, the relative energy change reaches 40%. This change leads to a reduced barrier height due to quantum coupling among the three-dimensional motions of channel electrons. Thus, an analysis and physical model of the gate leakage current that includes drift velocity is proposed. Numerical calculations show that the negative and positive temperature dependence of gate leakage currents decreases across the barrier as the field increases. They also demonstrate that source-drain voltage can have an effect of 1 to 2 orders of magnitude on the gate leakage current. The proposed model agrees well with the experimental results.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.31A no.3
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• pp.46-52
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• 1994

We investigated theoretically the current-voltage characteristics of resonant tunneling diodes with a single quantum well structure. using a self-consistent method. This method is a numerical analysis which is able to include the effects of the undoped spacer layer and the band bending by charge accumulation and depletion on the contact layers which have not been considered in the flat-band model reported by Esaki. so that it is better suited to explain experimental results. The structure used is an $AL_{0.5}Ga_{0.5}AS/GaAs/Al_{0.5}Ga_{0.5}AS$ single quantum well. In this work. we estimate the theoretical current-voltage characteristics of the same structure, and then, the dependence of the current-voltage curves on the thickness of undoped spacer layers sandwiched between the barrier and highly n-doped GaAs contact layer.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.317-318
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• 2013

Terahertz (THz) wave는 광학 영역과 방송파 영역 사이에 광대역 주파수 스펙트럼을 차지하고 있다. X선과는 달리 비이온화 광원으로 직진성, 투과성, 낮은 에너지 (meV)를 가지고 있어 비파괴적이고 무해한 장점을 지니고 있다. 본 연구에서는 In0.53Ga0.47As:Be/In0.52Al0.48As의 multi quantum well (MQW)을 Semi-insulting InP:Fe substrate 위에 active layer의 두께와 적층을 변화주어서 성장하였고Au (200 nm)/Ti (30 nm)의 금속전극으로 공정을 하였다. Ti:Sapphire femtosecond pulse laser를 조사하여 THz time-domain spectrometer 시스템을 이용하여 광전도검출법으로 THz 검출 특성을 연구하였다. THz 검출은 짧은 전하수명과 높은 저항을 요구한다. LTInGaAs의 경우 AsGa antisite로 인하여 짧은 전하수명을 얻게 되면 n-type의 높은 전하밀도를 가지게 되어서 저항이 낮아지게 된다. 높은 저항을 만들기 위하여 Be doping을 이용하여 과잉의 전자들을 보상하고 InAlAs layer를 삽입시켜 보다 높은 저항을 얻었다. LT-InGaAs:Be는 LT-GaAs보다 1/70 정도의 amplitude를 보이는데 LT-InGaAs/InAlAs MQW의 경우 LT-GaAs 대비 약 3/4 정도의 큰 amplitude를 얻었다. 또 active layer의 두께가 얇고 적층이 많을수록 신호가 커지는 것을 알 수 있었다. 이는 상대적으로 band gap이 큰 InAlAs층이 더 높은 저항을 만든 것으로 사료된다.

• Proceedings of the Korean Society Of Semiconductor Equipment Technology
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• 2006.05a
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• pp.127-130
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• 2006

사파이어 기판위에 MOCVD (metal organic chemical vapor deposition)를 이용하여 8주기의 InGaN/GaN 다중양자우물(multiple quantum well : MQW)구조가 성장되어졌고 이 구조 위에 p-GaN층이 형성됐다. 다시 p-GaN 위에 200nm의 두께를 갖는 PMMU 박막을 도포하고 electron beam lithography system을 이용하여 직경이 150nm가 되도록 나노단위의 삼각격자 구조를 가진 구멍을 패턴하고 inductively coupled plasma(ICP)를 이용하여 식각을 하여 광결정을 제작하였다. 광결정은 두께가 26nm이고 격자간격은 460nm로서 파장이 450nm인 파란빛을 나노회절 시켜서 photoluminescence(PL)의 세기를 강화시킨다.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.08a
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• pp.234-234
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• 2010

The PR transitions in asymmetric dot-in-double-quantum-well (DdWELL) photodetector is identified by bias-dependent spectral behaviors. Discrete n-i-n infrared photodetectors were fabricated on a 30-period asymmetric InAs-QD/[InGaAs/GaAs]/AlGaAs DdWELL wafer that was prepared by MBE technique. A 2.0-monolayer (ML) InAs QD ensemble was embedded in upper combined well of InGaAs/GaAs and each stack is separated by a 50-nm AlGaAs barrier. Each pixel has circular aperture of 300 um in diameter, and the mesa cell ($410{\times}410\;{\mu}m^2$) was defined by shallow etching. PR measurements were performed in the spectral range of $3{\sim}13\;{\mu}m$ (~ 100-400 meV) by using a Fourier-transform infrared (FTIR) spectrometer and a low-noise preamplifier. The asymmetric photodetector exhibits unique transition behaviors that near-/far-infrared (NIR/FIR) photoresponse (PR) bands are blue/red shifted by the electric field, contrasted to mid-infrared (MIR) with no dependence. In addition, the MIR-FIR dual-band spectra change into single-band feature by the polarity. A four-level energy band model is proposed for the transition scheme, and the field dependence of FIR bands numerically calculated by a simplified DdWELL structure is in good agreement with that of the PR spectra. The wavelength shift by the field strength and the spectral change by the polarity are discussed on the basis of four-level transition.