입방형 GaAs 양자점에 인가된 스트레인 효과 연구

홍우표,박승환,양정민 한국물리학회 2007 새물리 Vol.55 No.5

We investigate the strain effects on the valence energy band structures of cuboidal GaAs quantum dots (QDs) modeled by using a six-band Luttinger-Kohn Hamiltonian and a calculation procedure based on a finite-element method (FEM). We show that the combined effect of the strain and the size of the QD can be very sensitive to the energy structure of the valence band. In the case of the initial tensile misfit strain, the lowest energy of the strained QD is larger than that of the nonstrained QD in the range of relatively small QD size. However, we found that as the QD size increased further, the difference between the two energies gradually decreased. We show that depending on the nature of the strain, i.e., a compressive or tensile strain, the valence band energy can vary from a negative to a positive value. 6-밴드 루틴저-콘 (Luttinger-Kohn) 해밀토니안으로 모델링 될 수 있는입방형 GaAs 양자점의 원자가띠 (valence band)의 에너지 구조를유한요소법을 적용하여 수치적으로 구하고, 스트레인에 의한 양자점원자가띠의 에너지 구조에 대한 효과를 조사하였다. 양자점의 크기와스트레인이 결합된 효과는 에너지띠 구조에 매우 민감하게 작용함을 알수 있었다. 양자점의 초기 인장 스트레인 차가 있는 경우, 가장 낮은원자가띠의 에너지가 스트레인이 없는 양자점 경우보다 크다는 것을밝혔다. 하지만, 양자점의 크기가 더욱 커지는 경우, 스트레인 효과에의한 에너지 차가 점차 줄게 됨을 확인할 수 있었다. 또한, 양자점에가해진 스트레인의 성격에 따라 , 즉 압축력 또는 장력, 원자가 띠의에너지가 음의 값에서 양의 값으로 바뀐다는 것을 알 수 있었다.

Thermal Loading Effects on the Electronic and the Optical Properties of CdTe/ZnTe Quantum Dots

홍우표,박승환 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.59 No.5

We study the effects of the thermal loading on the straindistributions, the electronic structure, and the optical propertiesof CdTe/ZnTe self-assembled quantum dots with a finite elementmethod based on the linear elasticity theory of solids and theeight-band k·p Hamiltonian. Thermal expansion of the QDand its surrounding matrix is shown to significantly alter themagnitude of the strain distribution at high temperatures. It isdemonstrated that the gain spectra have different polarizationdistributions due to the structure of the optical matrix elements.It can be concluded that the thermal loading effect has to be takeninto account for analyzing the shapes of optical gain polarizationsat high temperatures.

On the Existence Condition for Paired Stationary Bright Solitons Obtained by Using the Paraxial-Ray Approximation Method in Coupled Photovoltaic Photorefractive Crystal Circuit Systems

홍우표 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.53 No.6

We report the existence of new families of stable stationary paired solitons in the coupled pho- tovoltaic photorefractive crystal circuit system. By applying the paraxial-ray approximation, we obtain the relation betwen the width and the peak amplitude of the stationary paired soliton in terms of the system parameters. We verify the analytical results by direct numerical simulations for the LiNbO3 crystal as a photovoltaic photorefractive medium to show the stability of the paired solitons. The stability of the bright paired solitons for different crystal temperatures has ben investigated. We conclude that the existence condition obtained by using the paraxial-ray approximation method may serve as a more reliable initial condition for understanding coupled photovoltaic photorefractive circuit systems.

원시 블랙홀 증발과 일치하는 BATSE 감마광선 폭사 데이터 분석

홍우표 대구효성가톨릭대학교 1997 연구논문집 Vol.56 No.2

We previously identified tat some short burst events from the BATSE 1B catalogue that were consistent with an origin of primordial black hole evaporation at the quark-gluon phase transition. We showed that these events are also consistent with those arising from a homogeneous spatial distrbution. Recently, the PHEBUS group has also indicated that the short bursts are consistent with V/V max ~1/2. In paper we describe the results of the study of the BATSE 3B catalogue shape that confirm the results from BATSE 1B.

Structural Effects on the Electronic Properties of Vertically-coupled CdTe/ZnTe Quantum-dot Molecules

홍우표,박승환,Mark R. A. Shegelski 한국물리학회 2012 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.61 No.12

We study the effects of structure parameters such as the vertical distance between two quantum dots (QDs) and the size of QDs on the electronic properties of vertically separated self-assembled CdTe/ZnTe quantum-dot molecules (QDMs) by using a finite-element method based on the elasticity theory of solids and the effective mass Hamiltonian. A QD-size-dependent switching between the ground and the first excited electron states is shown to occur as the vertical distance increases, even under the assumption of symmetric QDMs, due to a strain induced deformation of the conduction-band edge. A more complex valence-band-edge deformation causes the bonding and the anti-bonding states of the hole wave functions to switch with each other with increasing vertical distance between the QDs. We explicitly identify why the switching can occur in CdTe/ZnTe QDMs by analyzing the strain-induced conduction and valence-band-edge deformations.

절단된 피라미드형 GaN/AIN 반도체 양자점의 크기에 따른 내부 전기 퍼텐셜 분포 /

홍우표,김종재 한국물리학회 2010 새물리 Vol.60 No.10

Mole Fraction Effect on the Interband Transition Energy of CdTe/CdxZn1−xTe Nanostructures

홍우표,박승환 한국물리학회 2010 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.57 No.1

The electrical properties of strained CdTe quantum dots (QDs) grown on a CdTe/CdxZn1−xTe substrate layer were studied using an eight-band strain-dependent k·p Hamiltonian and the theory of linear elasticity. The combined effect of the Cd mole fraction of the CdxZn1−xTe substrate and the wetting layer thickness is found to have an influence on the energies of the conduction and the valence subbands. We find that at the wetting layer thickness used in the PL spectra, the calculated interband transition energy shows a reasonable agreement with the experiment data when a pyramidally shaped nanostructure is assumed.

Surface Multipole Solitons on Photorefractive Media with Bessel Optical Lattices

홍우표 한국물리학회 2015 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.66 No.6

We find the existence conditions for new surface crescent, dipole, tripole, and quadrupole solitonsformed at the interface of a focusing photorefractive medium and a medium imprinted with aBessel optical lattice. We demonstrate by using numerical simulations that the crescent and thedipole solitons show oscillatory behaviors in their amplitude and shape while the tripole and thequadrupole solitons maintain a remarkable rigidity during propagation. Based on a linear stabilityanalysis, we classify the stability region of the tripole and the quadrupole surface solitons in termsof the Bessel optical lattice strength and the Bessel index.

GaN/AlN 반도체 양자점들의 기하학적 구조에 따른 내부 전기 퍼텐셜 분포

홍우표,박승환 한국물리학회 2011 새물리 Vol.61 No.2

The electric potentials as functions of the shapes of GaN/AlN semiconductor quantum dots are investigated using the theory of continuum elasticity based on a three-dimensional ¯nite element method. The total electric potential caused by the strain-induced piezoelectric and the spontaneous potentials is shown to be sensitive to the height rather than the shape of the quantum dots. The hydrostatic strain distribution also depends strongly on the height of the quantum dots and is closely related with the energy band gap. 모양이 다른 GaN/AlN 반도체 양자점 구조들에 대해, 탄성체의 연속체이론과 3차원 유한요소방법을 이용한 수치계산을 통하여, 자발 분극과압전 퍼텐셜 및 내부 퍼텐셜의 크기와 공간변화 양상을 양자점의 모양변화에 따른 의존성을 조사하였다. 양자점의 분극 및 압전 퍼텐셜은양자점들의 부피가 같은 경우 그 높이에 크게 의존함을 확인하였다. 양자점의 체적이 같은 경우 양자점의 모양 보다 높이가 양자점의 에너지밴드갭의 중요 요소인 물정역학적 변형 성분의 값과 모양에 영향을미치게 됨을 확인하였다.

Finite Element Analysis of Strain Effects on Cuboidal CdTe/ZnTe Quantum Dots by Using the Eight-Band Strained k· p Hamiltonian

홍우표 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.53 No.6

The strain effects on the conduction and the valence subband energy structures of cuboidal CdTe/ZnTequantumdots(QDs)are analyzed by using a three dimensional finite-elementmethod formulation with the eight-band strained Lutinger-Kohn Hamiltonian. Both the conduction and the valance subband energies of the strained QD are shown to decrease more slowly than those of the unstrained cases with increasing QD size. For both the conduction and the valence subbands, the energy difference between the first and the second excited states diminishes with increasing QD size. We demonstrate that the combined effect of the strain and the size of QD can be sensitive to the transition energy between the conduction and the valence subbands.