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Comparison of Quantum Nature in InAs/GaAs Quantum Dots
장유동,U. H. Lee,H.Lee,D. Lee,J. S. Kim,J. Y. Leem,노삼규 한국물리학회 2003 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.42 No.III
We calculate the energy level spacing of InAs/GaAs quantum dots. From the calculations, as the size of quantum dot becomes larger, the spacing between ground state and 1st excited state increases. At a fixed quantum dot diameter, there is a height that gives the maximum level spacing. This interesting behavior comes from the small height to diameter ratio of typical quantum dots. From these results, the InAs/GaAs quantum dot emitting at a longer wavelength is typically the better QD system in view of dimensionality.
반도체 양자점 연구를 위한 광대역 고효율 발광 구조의 수치해석적 분석
장유동,이동한 한국물리학회 2019 새물리 Vol.69 No.7
단일 양자점은 반도체 영차원 양자구조에서의 물리현상을 연구하기 위한 이상적인 구조이다. 그러나, 발광 신호가 광자 하나씩 나오기 때문에 극히 약해 단일 양자점 연구를 위해서는 양자점에서 나오는 광자의 집광효율을 극대화할 필요가 있다. 본 연구에서는 광자집광효율이 높으면서 대역폭이 넓은 집광구조를 선정하기 위하여 평면 마이크로 공진기 구조와 하부층만 분산형 브래그 반사경 (distributed Bragg reflector, DBR) 를 두었을 때의 집광 특성을 수치해석 방법을 통해 조사하였다. 각 구조로부터 광추출효율, 원거리장 (far-field) 분포 등을 계산하여 비교적 작은 조리개수 (numerical aperture) 를 가지는렌즈를 사용할 때의 광자집광효율을 계산하고 비교하였다. 바람직한 구조는 하부층만 DBR 층을 가진구조로 조리개수 0.5에서 8.7%의 광자집광효율을 보여 DBR이 없는 구조의 0.5%에 비해 크게 증가했고, 27.5 nm의 넓은 대역폭을 가진다. A semiconductor single quantum dot is an ideal system for studying the physics of zerodimensional quantum structures. However, emission from a single quantum dot is extremely weak because it emits single photons, so maximizing photon collection from the quantum dot is crucial. In this work, we investigated, by using numerical simulations, an efficient single quantum dot structure that had a high photon collection efficiency and a broad bandwidth. The Purcell enhancement, photon-extraction efficiency, far-field pattern, and photon-collection efficiency were calculated and compared among candidates. A broadband structure with a bottom distributed Bragg reflector (DBR) provided a bandwidth of 27.5 nm with a lens having a NA of 0.5. The expected photoncollection efficiency was 8.7% for a NA of 0.5, which was greatly improved from 0.5% in a bulk structure without a DBR.
Simulation Study of an Apertured Planar Microcavity for Efficient Single-Photon Sources
장유동,D. Lee 한국물리학회 2019 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.75 No.1
An efficient single-photon source is one of the key components in quantum secure communication systems. In this work, a clean quantum-dot single-photon source without side walls, consisting of a planar microcavity structure with an aperture in the light-blocking top metal layer, is designed to prevent spectral diffusion of single-photon emission. Such a source with an aperture diameter of 1000 nm provides a photon collection efficiency of 14\%, increased from 0.5\% for a quantum dot in GaAs, and one with an 800-nm aperture provides a Purcell enhancement of 1.7 with an excellent far-field radiation pattern. The dependences of the emission characteristics on the aperture size and the quantum dot misplacement are also investigated.
Dependence of the Carrier Lifetime on the Level Spacing in Semiconductor Quantum Dots
장유동,D. Lee,D. K. Oh,H. Lee,S. U. Hong 한국물리학회 2005 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.47 No.1
We have found that the carrier lifetime in a quantum dot is shorter when the level spacing between the ground and the first excited states is larger. We interpret this observation with the improved wavefunction overlap between an electron and a hole at a large level spacing. The existence of an optimum point for zero dimensionality is found for tall quantum dots.
P 변조도핑한 In(Ga)As/InGaAsP 양자점에 대한 운반자 동역학
장유동,박재규,이동한,홍성의,오대곤,Jang, Y.D.,Park, J.,Lee, D.,Hong, S.U.,Oh, D.K. 한국진공학회 2006 Applied Science and Convergence Technology Vol.15 No.3
P-modulation doping된 In(Ga)As/InGaAsP 양자점에서의 decay time 특성을 undoped 양자점 시료와의 비교를 통해 살펴보았다. 10 K 에서의 photoluminescence (PL) 세기는 doping 된 양자점이 doping되지 않은 양자점에 비해 약 10배 정도 약하게 나왔다. 또한 Time resolved PL (TR-PL) 실험을 통해 얻은 양자점 시료의 기저상태 PL peak 에서의 decay time은 doping된 양자점이 doping 되지 않은 양자점에 비해 매우 짧게 나왔다. 이러한 PL 세기와 decay time 특성을 통해서 본 연구에서 측정한 doping 된 양자점의 경우에는 doping에 의해 결함이 증가하게 되고, 그로 인해 운반자의 비발광 경로가 증가하게 되어 doping 된 양자점의 경우에 decay time이 짧게 나타나는 것으로 분석하였다. We have investigated optical properties of p-modulation doped In(Ga)As quantum dots (QDs) on InP substrate with a comparison with the undoped QDs. Photoluminscence (PL) intensity of doped QDs at 10 K was about 10 times weaker than that of undoped QD sample. The decay time of doped QD sample at its PL peak, obtained from the time-resolved PL (TR-PL) experiment at 10 K, was very fast compared to that of undoped sample. We interpret that this fast decay time of the doped QD sample comes from the addition of non-radiative recombination paths, which are originated from the doping-related defects.
張幼冬(Zhang You-Dong) 대한중국학회 2006 중국학 Vol.27 No.-
The theory of Task-based Approach has effected the teaching field greatly after it was put forward, which is regarded as the most effective means for language training currently. Teaching Chinese to foreigners as a second language can also draw lessons from this theory. This paper aims to explore the application of Task-based Approach in Chinese teaching by teaching practice.