Quantum Confinement Effect of Thermoelectric Properties

제구철,Chang-Ho Cho 한국물리학회 2009 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.54 No.1

Using the quantum confinement effect based on the conduction band model, we theoretically determine the optimal concentration for the best figure-of-merit in n-type Bi2Te3 quantum well structures. The Bi2Te3 system has polycrystalline structures that can be prepared by using powders of hot-pressed alloys. The enhanced figure-of-merit due to the quantum confinement is almost caused by the enhanced Seebeck coefficient and by improved resistivity. It results from competition between the strong intrinsic characteristic and the enhancement of the volume ratio of the concentration in the quantum-confined system. The optimum concentration for the best figure-of-merit in the system amounts to 2.1 × 10^11 cm^-2 at room temperature. Control of the carrier concentration, as well as the quantum confinement effect, is also a very important effect to optimize the figure-of-merit in low-dimensional systems. Using the quantum confinement effect based on the conduction band model, we theoretically determine the optimal concentration for the best figure-of-merit in n-type Bi2Te3 quantum well structures. The Bi2Te3 system has polycrystalline structures that can be prepared by using powders of hot-pressed alloys. The enhanced figure-of-merit due to the quantum confinement is almost caused by the enhanced Seebeck coefficient and by improved resistivity. It results from competition between the strong intrinsic characteristic and the enhancement of the volume ratio of the concentration in the quantum-confined system. The optimum concentration for the best figure-of-merit in the system amounts to 2.1 × 10^11 cm^-2 at room temperature. Control of the carrier concentration, as well as the quantum confinement effect, is also a very important effect to optimize the figure-of-merit in low-dimensional systems.

GaAs/AlGaAs 양자 우물 구조의 제한적 특성 해석

윤기정,김원호 동의공업대학 1999 論文集 Vol.25 No.1

The impact ionization rates of GaAs/AlGaAs quantum well at temperature 77, 100, 150, 200, 250, 300 [K] are calculated. These are important parameters to design the infrared detector APD. The effects on the impact ionization rates by the parameters of quantum well structure, such as well-width, barrier-width, barrier-height and doping density m the well, are analyzed, using Ensemble Monte Carlo method, scattering and tunneling effects. As the width of the quantum well increases, the impact ionization rate increases in the range of the small well width but gradually the increment slows down. Due to the effect of the energy of the injected electrons into the well from the barrier, as well as the tunneling effect in the barrier, the impact ionization rate increases with the range of the smaller barrier width and decreases with the range of the larger barrier width. Thus, there exists a barrier width to maximize the impact ionization rate. The impact ionization rate is very sensitive to the variation of the doping density. It is found that there is a limit to the doping density to confine the electrons in the quantum well effectively.

Numerical Study of Strained GaAs 1−x N x /GaAs Quantum-Well Laser

M. Lahoual,A. Gueddim,N. Bouarissa 한국전기전자재료학회 2019 Transactions on Electrical and Electronic Material Vol.20 No.4

The optical gain of a strained GaAs 1−x N x /GaAs quantum-well laser has been calculated for a nitrogen concentration of 0.03 corresponding to a so-called dilute alloy. The eff ect of the density of carriers along with that of the quantum well width on the optical gain of the considered laser have been investigated and analyzed. Besides, the emitted wavelength has been also derived as a function of the quantum well width. Numerical results clearly show that by increasing the density of carriers and the quantum well width the optical gain is increased. The emitted wavelength is also enhanced as the quantum well width is augmented. The laser diode being studied here is shown to emit in the infrared-red region of the electromagnetic spectrum.

Modulation of Quantum Well Optical Properties by Illumination above the Barrier Bandgap

D. Wolverson,A. V. Koudinov,Yu. G. Kusrayev,L. C. Smith,J. J. Davies,M. Wiater,G. Karczewski,T. Wojtowicz 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.53 No.5

The spin flip Raman scattering signals associated with the Mn2+ 3d5 electrons in a range of CdTe-based dilute magnetic semiconductor quantum well structures is shown to be sensitive to even very weak above-barrier illumination, as are the quantum-well photoluminescence from exciton and trion recombination and acoustic phonon Raman scattering signals excited in resonance with the quantum well. This surprising degree of sensitivity is discussed in terms of the modulation of the carrier densities in the quantum wells, leading to a modulation of the resonant intermediate state for Raman scattering and, therefore, of the scattering cross section. Depending on the majority intrinsic carrier type in the quantum wells, we show that either enhancing or quenching of the Raman signals can result.

다양한 In 조성을 가진 InGaN/GaN Multi Quantum Well의효과적인 광전기화학적 물분해

배효정,방승완,주진우,하준석 한국마이크로전자및패키징학회 2018 마이크로전자 및 패키징학회지 Vol.25 No.3

In this study, the effects of indium (In) doping in InGaN/GaN multi quantum well (MQW) on photoelectrochemical (PEC) properties were investigated. Each quantum well (QW) layer with controlled In content were grown on sapphire substrate. Before growth of MQW, GaN growth consisted of various stages in the following order: buffer GaN growth, undoped GaN growth, and Si-doped n-type GaN growth. Absorbance of InGaN/GaN MQW having different In composition was higher than that of the InGaN/GaN MQW having a constant In composition. It indicates that InGaN layer having different In composition absorbs light having a broad spectrum energy. These results are in agreement with those in photoluminescence (PL). After evaluation of PEC properties, it demonstrated that InGaN/GaN MQW having different In composition was improved InGaN/GaN MQW having constant In composition in PEC water splitting ability. 본 연구에서는 InGaN/GaN multi quantum well (MQW)에서 Indium (In) 도핑효과에 따른 광전기화학적 특성을 관찰하였다. 기판으로는 Sapphire을 사용하였고, 각 Quantum well (QW)을 구성하고 있는 InGaN의 조성을 다르게 하였다. 투과도 측정 결과 일정한 In 조성을 가진 InGaN/GaN MQW에 비해 각 QW의 In 조성을 다르게 한 InGaN/GaN MQW에서 흡수도가 향상되는 것을 확인할 수 있었다. 이는 각각 다른 In 조성을 가진 InGaN 층이 더 넓은 영역의 스펙트럼 에너지를 가지는 빛을 흡수하기 때문인 것으로 생각된다. 광학적 특성을 평가하기 위해 진행한 상온photoluminescence (PL) 실험을 진행한 결과, 역시 다양한 In 조성을 가진 InGaN/GaN MQW이 더 넓은 파장에서 발광이 나타나는 것을 확인할 수 있었다. 이들 샘플에 대한 광전기화학적 특성평가를 통하여, gradation In 조성을 가지고 있는 InGaN/GaN MQW이 일정한 In 조성을 가지는 InGaN/GaN MQW에 비해 광전기화학적 물분해 능력이 월등히 향상됨을 확인하였다.

A Model for the InGaAs/InP Single Photon Avalanche Diodes with Multiple-Quantum Wells in the Charge Multiplication Region

H. S. Seo,S. H. Park,S. Kwak,안도열 한국물리학회 2018 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.72 No.2

In this work, we study the InP-InGaAs single photon avalanche diodes with multiple InGaAs quantum wells in the multiplication region for quantum information and communication. The compositions of InGaAs quantum wells are adjusted to give transition wavelength of 1.55. Simulation results show that three orders of magnitude improvement of dark count probability and an order of magnitude improvement of single photon quantum efficiency are expected with the adaption of multiple quantum-wells in the multiplication region. The improvement dark count probability is due to the difference of ionization coefficients for electrons and holes caused by the large difference between the conduction and valence band edge of multiple quantum-well layers inserted in the multiplication layer.

Magneto-optical Measurements of Semiconductor Quantum Structures in Pulsed-magnetic Fields

김용민 한국진공학회 2014 Applied Science and Convergence Technology Vol.23 No.1

Semiconductor quantum structures are often characterized by their energy gaps which are modified by the quantum size effect. Energy levels in semiconductors can be realized by optical transitions within confined structures. Photoluminescence spectroscopy in magnetic fields at low temperatures has proved to be a powerful technique for investigating the electronic states of quantum semiconductor heterostructures and offers a complimentary tool to electrical transport studies. In this review, we examine comprehensive investigations of magneto-excitonic and Landau transitions in a large variety of undoped and doped quantum-well structures. Strong magnetic fields change the diamagnetic energy shift of free excitons from quadratic to linear in B in undoped single quantum well samples. Twodimensional electron gas induced by modulation doping shows pronounce quantum oscillations in integer quantum Hall regime and discontinuous transition at ν=1. Such discontinuous transition can be explained as the formation of spin waves or Skyrmions.

Magneto-optical Measurements of Semiconductor Quantum Structures in Pulsed-magnetic Fields

Kim, Yongmin The Korean Vacuum Society 2014 Applied Science and Convergence Technology Vol.23 No.1

Semiconductor quantum structures are often characterized by their energy gaps which are modified by the quantum size effect. Energy levels in semiconductors can be realized by optical transitions within confined structures. Photoluminescence spectroscopy in magnetic fields at low temperatures has proved to be a powerful technique for investigating the electronic states of quantum semiconductor heterostructures and offers a complimentary tool to electrical transport studies. In this review, we examine comprehensive investigations of magneto-excitonic and Landau transitions in a large variety of undoped and doped quantum-well structures. Strong magnetic fields change the diamagnetic energy shift of free excitons from quadratic to linear in B in undoped single quantum well samples. Two-dimensional electron gas induced by modulation doping shows pronounce quantum oscillations in integer quantum Hall regime and discontinuous transition at ${\nu}=1$. Such discontinuous transition can be explained as the formation of spin waves or Skyrmions.

Magneto-optical Measurements of Semiconductor Quantum Structures in Pulsed-magnetic Fields

Yongmin Kim 한국진공학회(ASCT) 2014 Applied Science and Convergence Technology Vol.23 No.1

Semiconductor quantum structures are often characterized by their energy gaps which are modified by the quantum size effect. Energy levels in semiconductors can be realized by optical transitions within confined structures. Photoluminescence spectroscopy in magnetic fields at low temperatures has proved to be a powerful technique for investigating the electronic states of quantum semiconductor heterostructures and offers a complimentary tool to electrical transport studies. In this review, we examine comprehensive investigations of magneto-excitonic and Landau transitions in a large variety of undoped and doped quantum-well structures. Strong magnetic fields change the diamagnetic energy shift of free excitons from quadratic to linear in B in undoped single quantum well samples. Twodimensional electron gas induced by modulation doping shows pronounce quantum oscillations in integer quantum Hall regime and discontinuous transition at ν=1. Such discontinuous transition can be explained as the formation of spin waves or Skyrmions.

Optical Properties of a ZnO-MgZnO Quantum-Well

Doyeol Ahn,Seoung-Hwan Park 대한전자공학회 2006 Journal of semiconductor technology and science Vol.6 No.3

The optical gain and the luminescence of a ZnO quantum well with MgZnO barriers is studied theoretically. We calculated the non-Markovian optical gain and the luminescence for the strainedlayer wurtzite quantum well taking into account of the excitonic effects. It is predicted that both optical gain and luminescence are enhanced for the ZnO quantum well when compared with those of InGaNAlGaN quantum well structure due to the significant reduction of the piezoelectric effects in the ZnOMgZnO systems.