WorldWideScience

Sample records for double quantum-well nanostructure

  1. Terahertz detection using double quantum well devices

    Science.gov (United States)

    Khodier, Majid; Christodoulou, Christos G.; Simmons, Jerry A.

    2001-12-01

    This paper discusses the principle of operation of an electrically tunable THz detector, working around 2.54 THz, integrated with a bowtie antenna. The detection is based on the idea of photon-assisted tunneling (PAT) in a double quantum well (DQW) device. The bowtie antenna is used to collect the THz radiation and feed it to the detector for processing. The Bowtie antenna geometry is integrated with the DQW device to achieve broadband characteristic, easy design, and compatibility with the detector fabrication process. The principle of operation of the detector is introduced first. Then, results of different bowtie antenna layouts are presented and discussed.

  2. Bose Condensation of Interwell Excitons in Double Quantum Wells

    DEFF Research Database (Denmark)

    Larionov, A. V.; Timofeev, V. B.; Ni, P. A.

    2002-01-01

    The luminescence of interwell excitons in double quantum wells GaAs/AlGaAs (n–i–n heterostructures) with large-scale fluctuations of random potential in the heteroboundary planes was studied. The properties of excitons whose photoexcited electron and hole are spatially separated in the neighboring...

  3. Transient Intersubband Optical Absorption in Double Quantum Well Structure

    Institute of Scientific and Technical Information of China (English)

    WU Bin-He

    2005-01-01

    The microscopic equations of motion including many-body effects are derived to study the intersubband polarization in the double quantum well structure induced by an ultrafast pumping infrared light. Based on the selfconsistent field theory, the transient probe absorption coefficient is calculated. These calculations are beyond the previous steady-state assumption. Transient probe absorption spectra are calculated under different pumping intensity and various pump probe delay.

  4. Polarization converters on double hetero structures containing strained quantum wells

    Science.gov (United States)

    Khalique, U.; van der Tol, J. J. G. M.; Nötzel, R.; Smit, M. K.

    2009-02-01

    The importance of polarization manipulation is increased as optical fiber systems evolve to higher data rates. Photonic integrated circuits should be insensitive to the state of polarization of the light emanating from fibers if they are to be used as detectors, add-drop mutiplexers or cross connects. Either all the integrated components have to be polarization independent or only one polarization direction should be used. For either method, a compact polarization converter is useful. A model is developed for the mode propagation in the waveguide of the slanted side polarization converter based on double hetero structures. The model is extended to include polarization dependent absorption and mismatch. Polarization converters on different double heterostructures (with and without quantum wells) have been designed and are realized by contact optical lithography. The performance of the realized converters is well described with the model.

  5. Electron transport in coupled double quantum wells and wires

    Energy Technology Data Exchange (ETDEWEB)

    Harff, N.E.; Simmons, J.A.; Lyo, S.K. [and others

    1997-04-01

    Due to inter-quantum well tunneling, coupled double quantum wells (DQWs) contain an extra degree of electronic freedom in the growth direction, giving rise to new transport phenomena not found in single electron layers. This report describes work done on coupled DQWs subject to inplane magnetic fields B{sub {parallel}}, and is based on the lead author`s doctoral thesis, successfully defended at Oregon State University on March 4, 1997. First, the conductance of closely coupled DQWs in B{sub {parallel}} is studied. B{sub {parallel}}-induced distortions in the dispersion, the density of states, and the Fermi surface are described both theoretically and experimentally, with particular attention paid to the dispersion anticrossing and resulting partial energy gap. Measurements of giant distortions in the effective mass are found to agree with theoretical calculations. Second, the Landau level spectra of coupled DQWs in tilted magnetic fields is studied. The magnetoresistance oscillations show complex beating as Landau levels from the two Fermi surface components cross the Fermi level. A third set of oscillations resulting from magnetic breakdown is observed. A semiclassical calculation of the Landau level spectra is then performed, and shown to agree exceptionally well with the data. Finally, quantum wires and quantum point contacts formed in DQW structures are investigated. Anticrossings of the one-dimensional DQW dispersion curves are predicted to have interesting transport effects in these devices. Difficulties in sample fabrication have to date prevented experimental verification. However, recently developed techniques to overcome these difficulties are described.

  6. Bose condensation of interwell excitons in double quantum wells

    CERN Document Server

    Larionov, A V; Ni, P A; Dubonos, S V; Hvam, I; Soerensen, K

    2002-01-01

    The luminescence of the interwell excitons in the GaAs/AlGaAs double quantum wells, containing large-scale fluctuations of the random potential in the heteroboundary planes, is studied. The properties of the excitons, wherein the excited electron and hole are spatially separated between the neighboring quantum wells by the density and temperature variation within the domain limits of the scale below one micron, are investigated. The interwell excitons by low pumping (below 50 mW) are strongly localized due to the small-scale fluctuations of the random potential. The localized excitons line grows by increase in the resonance excitation capacity through the threshold method. With the temperature growth this line disappears in the spectrum (T sub c <= 3.4 K). The above phenomenon is related to the Bose-Einstein condensation in the quasi-two-dimensional system of the interwell excitons. The critical values of the exciton density and temperature in the studied temperature range (1.5-3.4 K) grow according to the...

  7. Indirect excitons in (111) GaAs double quantum wells

    Science.gov (United States)

    Hubert, C.; Biermann, K.; Hernández-Mínguez, A.; Santos, P. V.

    2017-08-01

    We study the dynamics of indirect (or dipolar) excitons (interwell IXs) in GaAs (111) double quantum wells (DQWs) subjected to a transverse electric field. In comparison with single (111) QWs, these DQWs can store, for a comparable applied fields and optical excitation density, a density of interwell IXs much larger than in SQWs, thus leading to stronger interwell IX- IX repulsive interactions. We show by means of spatially-resolved optical spectroscopy that interwell IXs in (111) DWQs can be transported over distances exceeding 60 μm. From the spectral dependence of the interwell IX spatial distribution profiles, we show that the long transport distances are due to drift forces arising from the strong interwell IX- IX interactions.

  8. Quantum wells, wires and dots theoretical and computational physics of semiconductor nanostructures

    CERN Document Server

    Harrison, Paul

    2016-01-01

    Quantum Wells, Wires and Dots provides all the essential information, both theoretical and computational, to develop an understanding of the electronic, optical and transport properties of these semiconductor nanostructures. The book will lead the reader through comprehensive explanations and mathematical derivations to the point where they can design semiconductor nanostructures with the required electronic and optical properties for exploitation in these technologies. This fully revised and updated 4th edition features new sections that incorporate modern techniques and extensive new material including: - Properties of non-parabolic energy bands - Matrix solutions of the Poisson and Schrodinger equations - Critical thickness of strained materials - Carrier scattering by interface roughness, alloy disorder and impurities - Density matrix transport modelling -Thermal modelling Written by well-known authors in the field of semiconductor nanostructures and quantum optoelectronics, this user-friendly guide is pr...

  9. Collective Behavior of a Spin-Aligned Gas of Interwell Excitons in Double Quantum Wells

    DEFF Research Database (Denmark)

    Larionov, A. V.; Bayer, M.; Hvam, Jørn Märcher;

    2005-01-01

    The kinetics of a spin-aligned gas of interwell excitons in GaAs/AlGaAs double quantum wells (n–i–n heterostructure) is studied. The temperature dependence of the spin relaxation time for excitons, in which a photoexcited electron and hole are spatially separated between two adjacent quantum wells...... is associated with indirect evidence of the coherence of the collective phase of interwell excitons at temperatures below the critical value....

  10. A New Type of Photoelectric Response in a Double Barrier Structure with a Wide Quantum Well

    Institute of Scientific and Technical Information of China (English)

    ZHOU Xia; ZHENG Hou-Zhi

    2005-01-01

    @@ We have calculated the photoelectric response in a specially designed double barrier structure. It has been verified that a transfer of the internal photovoltaic effect in the quantum well to the tunnelling transport through above-barrier quasibound states of the emitter barrier may give rise to a remarkable photocurrent.

  11. Collective Behavior of Interwell Excitons in GaAs/AlGaAs Double Quantum Wells

    DEFF Research Database (Denmark)

    Larionov, A. V.; Timofeev, V. B.; Hvam, Jørn Märcher;

    2000-01-01

    Photoluminescence spectra of interwell excitons in double GaAs/AlGaAs quantum wells (n-i-n structures) have been investigated (an interwell excition in these systems is an electron-hole pair spatially separated by a narrow AlAs barrier). Under resonance excitation by circular polarized light, the...

  12. Closed form solution for a double quantum well using Gr\\"obner basis

    CERN Document Server

    Acus, A

    2011-01-01

    Analytical expressions for spectrum, eigenfunctions and dipole matrix elements of a square double quantum well (DQW) are presented for a general case when the potential in different regions of the DQW has different heights and effective masses are different. This was achieved by Gr\\"obner basis algorithm which allows to disentangle the resulting coupled polynomials without explicitly solving the transcendental eigenvalue equation.

  13. Transversal confined polar optical phonons in spherical quantum-dot/quantum-well nanostructures

    Science.gov (United States)

    Comas, F.; Trallero-Giner, C.; Prado, S. J.; Marques, G. E.; Roca, E.

    2006-02-01

    Confined polar optical phonons are studied in a spherical quantum-dot/quantum-well (QD/QW) nanostructure by using an approach that takes into account the coupling of electromechanical oscillations and is valid in the long-wave limit. This approach was developed a few years ago and provides results beyond the usually applied dielectric continuum approach (DCA), where just the electric aspect of the oscillations is considered. In the present paper we limit ourselves to the study of the so-called uncoupled modes, having a purely transversal character and not involving an electric potential. We display the dispersion curves for the frequencies considering three possible nanostructures, which show different bulk phonon curvatures near the Brillouin zone -point and have been actually grown: ZnS/CdSe, CdSe/CdS and CdS/HgS. A detailed discussion of the results obtained is made, emphasizing the novelties provided by our treatment and the relevance of infrared spectroscopy in the characterization of the geometrical features of the QD/QW nanostructure.

  14. Asymmetric double quantum well structure as a tunable detector in the far-infrared range

    CERN Document Server

    Shin, U; Park, M J; Lee, S J

    1999-01-01

    The eigenvalues and the wave functions of GaAs/Al sub x Ga sub 1 sub - sub x As asymmetric double quantum well structure have been calculated by using of complex energy method. Based on theoretical calculations, tuning ranges from 9 to 14 mu m are predicted for the proposed asymmetric coupled-quantum-well structure. In addition we calculated the energy eigenvalues and the wave functions of an electron in GaAs/Al sub x Ga sub 1 sub - sub x As single quantum well structure (including delta-perturbation). the variation in E sub 1 , the ground state energy eigenvalue of the electron, depends on the strength and position of the perturbation within the well.

  15. Element-free Galerkin method applied to quantum dot and quantum well nanostructures

    Energy Technology Data Exchange (ETDEWEB)

    Sperotto, Lucas Kriesel [Instituto Tecnologico de Aeronautica (ITA/IEAv), Sao Jose dos Campos, SP (Brazil). Instituto de Estudos Avancados; Passaro, Angelo; Tanaka, Roberto Y. [Instituto de Estudos Avancados (IEAv), Sao Jose dos Campos, SP (Brazil); Marques, Gleber N. [Universidade do Estado de Mato Grosso (UNEMAT), MT (Brazil)

    2012-07-01

    Full text: The development of native technologies for the fabrication of infrared photodetectors based on quantum wells and quantum dots is the goal of a set of Brazilian Research Institutes and Universities gathered in a National Institute for Science and Technology. The research covers all phases of the production of such devices in Brazil, from the design to the growing of nanostructured semiconductors, processing and characterization of samples. In this context, a set of computer programs have been developed in the recent years in order to assist the design of such structures, some of them based on the Finite Element Methods (FEM). The Element-Free Galerkin Method (EFGM) is an attractive numerical alternative to the FEM. To perform an EFGM approximation it is required a set of nodal points and the shape functions associated to each node. In this sense its similar to FEM. In the EFGM, the Moving Least Squares (MLS) is used to build highly continuous shape functions, which also result in approximations (solutions) highly continuous. The assembling of the final linear system requires support for numerical integration, which in this work is the same triangular mesh generated for the FEM. One of the main drawbacks of the EFGM is the reproduction of the physical discontinuities inherent to each phenomenon, which means discontinuities of the state variable and/or of its spatial derivatives. If no additional numerical treatment is adopted, spurious oscillations arise in the approximation nearby the discontinuity lines. For instance, some aid techniques such as the domain truncation have been successfully applied for the treatment of material interfaces in the computation of electrostatic and electromagnetic fields. Although the EFGM has been successfully tested for one-dimensional quantum well structures, additional techniques are required for ensuring the Dirichlet boundary conditions, e.g. Lagrange multipliers, which spoil the symmetrical character of the final

  16. Closed form solution for a double quantum well using Groebner basis

    Energy Technology Data Exchange (ETDEWEB)

    Acus, A [Institute of Theoretical Physics and Astronomy, Vilnius University, A Gostauto 12, LT-01108 Vilnius (Lithuania); Dargys, A, E-mail: dargys@pfi.lt [Center for Physical Sciences and Technology, Semiconductor Physics Institute, A Gostauto 11, LT-01108 Vilnius (Lithuania)

    2011-07-01

    Analytical expressions for the spectrum, eigenfunctions and dipole matrix elements of a square double quantum well (DQW) are presented for a general case when the potential in different regions of the DQW has different heights and the effective masses are different. This was achieved by using a Groebner basis algorithm that allowed us to disentangle the resulting coupled polynomials without explicitly solving the transcendental eigenvalue equation.

  17. Correlation Effects on the Coupled Plasmon Modes of a Double Quantum Well

    DEFF Research Database (Denmark)

    Hill, N. P. R.; Nicholls, J. T.; Linfield, E. H.;

    1997-01-01

    At temperatures comparable to the Fermi temperature, we have measured a plasmon enhanced Coulomb drag in a GaAs/AlGaAs double quantum well electron system. This measurement provides a probe of the many-body corrections to the coupled plasmon modes, and we present a detailed comparison between...... experiment and theory testing the validity of local field theories. Using a perpendicular magnetic field to raise the magnetoplasmon energy we can induce a crossover to single-particle Coulomb scattering....

  18. Simultaneous generation of intersubband absorption and quantum well intermixing through silicon ion implantation in undoped InGaAs/AlAsSb coupled double quantum wells

    Science.gov (United States)

    Cong, G. W.; Akimoto, R.; Gozu, S.; Mozume, T.; Hasama, T.; Ishikawa, H.

    2010-03-01

    We demonstrated the intersubband absorption in undoped InGaAs/AlAsSb coupled double quantum wells through silicon ion implantation and rapid thermal annealing. For an implantation dose of 1×1014 cm-2, the actual carrier density of a sample annealed at 600 °C for 1 min was ˜7.5×1013 cm-2 (˜75% activation efficiency); the activation energy was ˜1.41 eV. The simultaneously generated quantum well intermixing (QWI) was nonuniform due to the silicon ion distribution. The effects of QWI nonuniformity on both intersubband and interband transitions were explained by eight-band k ṡp calculation. This study will open a route for monolithic integration of intersubband-transition-based high-speed all-optical switches.

  19. InGaAsP/InP Double Quantum Well Intermixing Induced by Phosphorus Ion Implantation

    Institute of Scientific and Technical Information of China (English)

    CHEN Jie; ZHAO Jie; WANG Yong-chen; HAN De-jun

    2005-01-01

    A quantum well intermixing(QWI) investigation on double quantum well(DQW) structure with two different emitting wavelength caused by phosphorus ion implantation and following rapid thermal annealing (RTA) was carried out by means of photoluminescence(PL). The ion implantation was performed at the energy of 120 kev with the dose ranging from 1 × 1011 cm-2 to 1× 1014 cm-2. The RTA was performed at the temperature of 700 ℃ for 30 s under pure nitrogen protection. The PL measurement implied that the band gap blue-shift from the upper well increases with the ion dose faster than that from lower well and the PL peaks from both QWs remained well separated under the lower dose implantation(~1×1011 cm-2 ) indicating that the implant vacancy distribution affects the QWI. When the ion dose is over ~ 1 × 1012 cm-2 , the band gap blue-shift from both wells increases with the ion dose and finally the two peaks merge together as one peak indicating the ion implantation caused a total intermixing of both quantum wells.

  20. Collective Behavior of Interwell Excitons in GaAs/AlGaAs Double Quantum Wells

    DEFF Research Database (Denmark)

    Larionov, A. V.; Timofeev, V. B.; Hvam, Jørn Märcher

    2000-01-01

    Photoluminescence spectra of interwell excitons in double GaAs/AlGaAs quantum wells (n-i-n structures) have been investigated (an interwell excition in these systems is an electron-hole pair spatially separated by a narrow AlAs barrier). Under resonance excitation by circular polarized light......, the luminescence line of interwell excitions exhibits a significant narrowing and a drastic increase in the degree of circular polarization of photoluminescence with increasing exciton concentration. It is found that the radiative recombination rate significantly increases under these conditions. This phenomenon...

  1. Hole subband structure in single and double p-type {delta}-doped diamond quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Rodriguez-Vargas, I. [Facultad de Ciencias, Univ. Autonoma del Estado de Morelos, Av. Universidad 1001, C.P. 62209, Cuernavaca (Mexico); Duque, C.A. [Inst. de Fisica, Universidad de Antioquia, AA 1226, Medellin (Colombia); Mora-Ramos, M.E. [Facultad de Ciencias, Univ. Autonoma del Estado de Morelos, Av. Universidad 1001, C.P. 62209, Cuernavaca (Mexico); Inst. de Ciencia de Materiales de Madrid, CSIC, Sor Juana Ines de la Cruz 3, 28049 Madrid (Spain); Velasco, V.R. [Inst. de Ciencia de Materiales de Madrid, CSIC, Sor Juana Ines de la Cruz 3, 28049 Madrid (Spain)

    2007-07-01

    Heavy, light, and split-off hole states in single and double p-{delta}-doped diamond quantum wells are studied with the use of a 6 x 6 k.p model. The effective mass Hamiltonian is solved using a local density Thomas-Fermi-Dirac approximation for the description of the band bending profile. The features of the valence band spectrum are briefly discussed in both cases. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  2. Temperature-dependent exciton recombination in asymmetrical ZnCdSe/ZnSe double quantum wells

    CERN Document Server

    Yu Guang You; Zhang, J Y; Zheng, Z H; Yang, B J; Zhao Xiao Wei; Shen De Zhen; Kong Xiang Gui

    1999-01-01

    Temperature-dependent exciton recombination in asymmetrical ZnCdSe/ZnSe double quantum wells is studied by recording photoluminescence spectra and photoluminescence decay spectra. The exciton tunnelling from the wide well to the narrow well and the thermal dissociation of excitons are two factors that influence the exciton recombination in this structure. In the narrow well, both of the two processes decrease the emission intensity, whereas, in the wide well, these two processes have contrary influences on the exciton density. The change of the emission intensity depends on which is the stronger one. (author)

  3. Electromagnetically induced transparency in an asymmetric double quantum well under non-resonant, intense laser fields

    Science.gov (United States)

    Niculescu, E. C.

    2017-02-01

    Electromagnetically induced transparency in an asymmetric double quantum well subjected to a non-resonant, intense laser field is theoretically investigated. We found that the energy levels configuration could be switched between a Λ-type and a ladder-type scheme by varying the non-resonant radiation intensity. This effect is due to the laser-induced electron tunneling between the wells and it allows a substantial flexibility in the manipulation of the optical properties. The dependence of the susceptibilities on the control field Rabi frequency, intensity of the nonresonant laser, and the control field detuning for both configurations are discussed and compared.

  4. Voltage-controlled wavelength conversion by terahertz electro-optic modulation in double quantum wells

    CERN Document Server

    Su, M Y; Sherwin, M S; Huntington, A S; Coldren, L A

    2002-01-01

    An undoped double quantum well (DQW) was driven with a terahertz (THz) electric field of frequency \\omega_{THz} polarized in the growth direction, while simultaneously illuminated with a near-infrared (NIR) laser at frequency \\omega_{NIR}. The intensity of NIR upconverted sidebands \\omega_{sideband}=\\omega_{NIR} + \\omega_{THz} was maximized when a dc voltage applied in the growth direction tuned the excitonic states into resonance with both the THz and NIR fields. There was no detectable upconversion far from resonance. The results demonstrate the possibility of using gated DQW devices for all-optical wavelength shifting between optical communication channels separated by up to a few THz.

  5. Tunneling-Induced Transient Gain in an Asymmetric Double Quantum Well

    Institute of Scientific and Technical Information of China (English)

    XU Wei-Hua; WU Jin-Hui; GAO Jin-Yue

    2004-01-01

    @@ We investigate the transient behaviour of a weak probe in asymmetric double quantum well structures, where two excited states are coupled by resonant tunnelling through a thin barrier in a three-level system of electronic subbands. There is no external coherent coupling field applied, and we find that probe gain can be achieved during the transient process, which is induced by the coherent coupling of the upper states via the resonant tunnelling.We show that the transient behaviour of the probe depends on the coupling strength and the dephasing rate and can be tuned by changing the width of the tunnelling barrier.

  6. Controllable optical bistability and multistability in asymmetric double quantum wells via spontaneously generated coherence

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Yuan; Deng, Li [Department of Applied Physics, East China Jiaotong University, Nanchang, 330013 (China); Chen, Aixi, E-mail: aixichen@ecjtu.jx.cn [Department of Applied Physics, East China Jiaotong University, Nanchang, 330013 (China); Institute for Quantum Computing, University of Waterloo, Ontario N2L 3G1 (Canada)

    2015-02-15

    We investigate the nonlinear optical phenomena of the optical bistability and multistability via spontaneously generated coherence in an asymmetric double quantum well structure coupled by a weak probe field and a controlling field. It is shown that the threshold and hysteresis cycle of the optical bistability can be conveniently controlled only by adjusting the intensity of the SGC or the controlling field. Moreover, switching between optical bistability and multistability can be achieved. These studies may have practical significance for the preparation of optical bistable switching device.

  7. Optical absorption in asymmetric double quantum wells driven by two intense terahertz fields

    Institute of Scientific and Technical Information of China (English)

    Wu Hong-Wei; Mi Xian-Wu

    2013-01-01

    Optical absorption is investigated for asymmetric double quantum wells driven by a resonant terahertz field and a varied terahertz field,both polarized along the growth direction.Rich nonlinear dynamics of the replica peak and the Autler-Townes splitting of various dressed states are systematically studied in undoped asymmetric double quantum wells by taking account of multiple factors,such as the frequency of the varied terahertz field and the strength of the resonant terahertz field.Each electron subband splits into two dressed states when the resonant terahertz field is applied in the absence of the varied terahertz field,the optical absorption spectrum shows the first-order Autler-Townes splitting of the electron subbands.When a varied terahertz field is added into the resonant system,the replica peak and the second-order Autler-Townes splitting of the dressed states near the band edge respectively emerge when the varied terahertz field is non-resonant and resonant with these dressed states.Wben the strength of the resonant terahertz field is increased,the first-order Autler-Townes double peaks and the replica peak in the optical absorption spectrum shift with the shifts of the dressed states.The presented results have potential applications in electro-optical devices.

  8. Impurity-assisted terahertz luminescence in quantum well nanostructures under interband photoexсitation

    Directory of Open Access Journals (Sweden)

    Ivan S. Makhov

    2016-12-01

    Full Text Available The paper presents the results of an experimental study of impurity-assisted photoluminescence in the far- (terahertz and near-infrared spectral ranges in n-GaAs/AlGaAs quantum well structures with different well widths under interband photoexcitation of electron–hole pairs. The optical electron transitions between the first electron subband and donor ground state as well as between excited and ground donor states were revealed in the far-infrared photoluminescence spectra. Observation of these optical electron transitions became possible because of the depopulation of the donor ground state in the quantum well due to the non-equilibrium charge carrier radiative transitions from the donor ground state to the first heavy hole subband. The opportunity to tune the terahertz radiation wavelength in structures with doped quantum wells by changing the quantum well width was demonstrated experimentally.

  9. Mobility modulation in inverted delta doped coupled double quantum well structure

    Science.gov (United States)

    Sahoo, N.; Sahu, T.

    2016-10-01

    We have studied the modulation of electron mobility μ as a function of the electric field perpendicular to the interface plane Fp in a GaAs/AlGaAs double quantum well structure near the resonance of subband states. The functional dependence of μ on Fp exhibits a minimum near the anticrossing of subband states leading to an oscillatory behavior of μ. We show that the oscillatory enhancement of μ becomes more pronounced with increase in the difference between the doping concentrations in the side barriers. The oscillation of μ also increases by varying the widths of the two wells through shifting of the position of the middle barrier. It is interesting to show that the oscillation of μ is always larger when there is doping in barrier towards the substrate side compared to that of the surface side due to the difference in the influence of the interface roughness scattering potential. Further, broadening of the central barrier width increases the peaks of the oscillation of μ mostly due to the changes in the ionized impurity scattering potential. Our results can be utilized for the performance enhancement of quantum well field effect transistor devices.

  10. Mobility modulation in inverted delta doped coupled double quantum well structure

    Energy Technology Data Exchange (ETDEWEB)

    Sahoo, N. [Department of Electronic Science, Berhampur University, 760007, Odisha (India); Sahu, T., E-mail: tsahu_bu@rediffmail.com [Department of Electronics and Communication Engineering, National Institute of Science and Technology, Palur Hills, Berhampur 761008, Odisha (India)

    2016-10-01

    We have studied the modulation of electron mobility μ as a function of the electric field perpendicular to the interface plane F{sub p} in a GaAs/AlGaAs double quantum well structure near the resonance of subband states. The functional dependence of μ on F{sub p} exhibits a minimum near the anticrossing of subband states leading to an oscillatory behavior of μ. We show that the oscillatory enhancement of μ becomes more pronounced with increase in the difference between the doping concentrations in the side barriers. The oscillation of μ also increases by varying the widths of the two wells through shifting of the position of the middle barrier. It is interesting to show that the oscillation of μ is always larger when there is doping in barrier towards the substrate side compared to that of the surface side due to the difference in the influence of the interface roughness scattering potential. Further, broadening of the central barrier width increases the peaks of the oscillation of μ mostly due to the changes in the ionized impurity scattering potential. Our results can be utilized for the performance enhancement of quantum well field effect transistor devices.

  11. Molecular states in double quantum wells: nanochemistry for metatmaterials with new optical properties

    Science.gov (United States)

    Gutierrez, Rafael M.; Castañeda, Arcesio

    2009-08-01

    Quantum mechanics explains the existence and properties of the chemical bond responsible for the formation of molecules from isolated atoms. In this work we study quantum states of Double Quantum Wells, DQW, formed from isolated Single Quantum Wells, SQWs, that can be considered metamaterials. Using the quantum chemistry definition of the covalent bond, we discuss molecular states in DQW as a kind of nanochemistry of metamaterials with new properties, in particular new optical properties. An important particularity of such nanochemistry, is the possible experimental control of the geometrical parameters and effective masses characterizing the semiconductor heterostructures represented by the corresponding DQW. This implies a great potential for new applications of the controlled optical properties of the metamaterials. The use of ab initio methods of intensive numerical calculations permits to obtain macroscopic optical properties of the metamaterials from the fundamental components: the spatial distribution of the atoms and molecules constituting the semiconductor layers. The metamaterial new optical properties emerge from the coexistence of many body processes at atomic and molecular level and complex quantum phenomena such as covalent-like bonds at nanometric dimensions.

  12. Bandgap Engineering of 1300 nm Quantum Dots/Quantum Well Nanostructures Based Devices

    KAUST Repository

    Alhashim, Hala H.

    2016-05-29

    The main objectives of this thesis are to develop viable process and/or device technologies for bandgap tuning of 1300-nm InGaAs/GaAs quantum-dot (QD) laser structures, and broad linewidth 1300-nm InGaAsP/InP quantum well (QW) superluminescent diode structures. The high performance bandgap-engineered QD laser structures were achieved by employing quantum-dot intermixing (QDI) based on impurity free vacancy diffusion (IFVD) technique for eventual seamless active-passive integration, and bandgap-tuned lasers. QDI using various dielectric-capping materials, such as HfO2, SrTiO3, TiO2, Al2O3 and ZnO, etc, were experimented in which the resultant emission wavelength can be blueshifted to ∼ 1100 nm ─ 1200 nm range depending on process conditions. The significant results extracted from the PL characterization were used to perform an extensive laser characterization. The InAs/GaAs quantum-dot lasers with QDs transition energies were blueshifted by ~185 nm, and lasing around ~1070 – 1190 nm was achieved. Furthermore, from the spectral analysis, a simultaneous five-state lasing in the InAs/InGaAs intermixed QD laser was experimentally demonstrated for the first time in the very important wavelength range from 1030 to 1125 nm. The QDI methodology enabled the facile formation of a plethora of devices with various emission wavelengths suitable for a wide range of applications in the infrared. In addition, the wavelength range achieved is also applicable for coherent light generation in the green – yellow – orange visible wavelength band via frequency doubling, which is a cost-effective way of producing compact devices for pico-projectors, semiconductor laser based solid state lighting, etc. [1, 2] In QW-based superluminescent diode, the problem statement lies on achieving a flat-top and ultra-wide emission bandwidth. The approach was to design an inhomogeneous active region with a comparable simultaneous emission from different transition states in the QW stacks, in

  13. THz Acoustic Spectroscopy by using Double Quantum Wells and Ultrafast Optical Spectroscopy

    Science.gov (United States)

    Wei, Fan Jun; Yeh, Yu-Hsiang; Sheu, Jinn-Kong; Lin, Kung-Hsuan

    2016-06-01

    GaN is a pivotal material for acoustic transducers and acoustic spectroscopy in the THz regime, but its THz phonon properties have not been experimentally and comprehensively studied. In this report, we demonstrate how to use double quantum wells as a THz acoustic transducer for measuring generated acoustic phonons and deriving a broadband acoustic spectrum with continuous frequencies. We experimentally investigated the sub-THz frequency dependence of acoustic attenuation (i.e., phonon mean-free paths) in GaN, in addition to its physical origins such as anharmonic scattering, defect scattering, and boundary scattering. A new upper limit of attenuation caused by anharmonic scattering, which is lower than previously reported values, was obtained. Our results should be noteworthy for THz acoustic spectroscopy and for gaining a fundamental understanding of heat conduction.

  14. Photoluminescence study of InGaN/GaN double quantum wells with varying barrier widths

    CERN Document Server

    Ryu, M Y; Shin, E J; Lee, J I; Yu, S K; Oh, E S; Park, Y J; Park, H S; Kim, T I

    2000-01-01

    We report the results of photoluminescence (PL) and time-resolved PL studies on InGaN/GaN double quantum well (DQW) samples with different barrier widths. The barrier-width dependence of the PL emission energy and intensity are discussed. The PL as a function of excitation density can be well explained in terms of the quantum-confined Stark effect (QCSE). The temporal behavior of the PL was also studied. As the barrier width increases, the decay times tau sub 1 and tau sub 2 , decrease from 1.02 ns and 6.99 ns to 0.32 ns and 1.09 ns, respectively. The PL efficiency and the decay lifetime depend on the barrier width.

  15. Enhancement of multisubband electron mobility in asymmetrically doped coupled double quantum well structure

    Energy Technology Data Exchange (ETDEWEB)

    Das, S.; Nayak, R.K.; Sahu, T., E-mail: tsahu_bu@rediffmail.com; Panda, A.K.

    2015-11-01

    We study the effect of coupling of subband wave functions on the multisubband electron mobility in a barrier delta doped GaAs/Al{sub x}Ga{sub 1−x}As asymmetric double quantum well structure. We use selfconsistent solution of the coupled Schrödinger equation and Poisson's equation to calculate the subband wave functions and energy levels. The low temperature mobility is considered by using scatterings due to ionized impurities, interface roughness and alloy disorder. We show that variation of the width of the central barrier considerably affect the interplay of different scattering mechanisms on electron mobility through intersubband effects. Under single subband occupancy, the mobility increases with decrease in the barrier width as functions of doping concentration as well as function of well width. However, in case of double subband occupancy, effect of intersubband interaction yields opposite trend, i.e., increase in mobility with increase in barrier width. It is gratifying to show that in case of asymmetric variation of well widths the mobility shows nonmonotonic behavior which varies with change in the width of the central barrier under double subband occupancy.

  16. Photoelectric Characteristics of Double Barrier Quantum Dots-Quantum Well Photodetector

    Directory of Open Access Journals (Sweden)

    M. J. Wang

    2015-01-01

    Full Text Available The photodetector based on double barrier AlAs/GaAs/AlAs heterostructures and a layer self-assembled InAs quantum dots and In0.15Ga0.85As quantum well (QW hybrid structure is demonstrated. The detection sensitivity and detection ability under weak illuminations have been proved. The dark current of the device can remain at 0.1 pA at 100 K, even lower to 3.05×10-15 A, at bias of −1.35 V. Its current responsivity can reach about 6.8×105 A/W when 1 pw 633 nm light power and −4 V bias are added. Meanwhile a peculiar amplitude quantum oscillation characteristic is observed in testing. A simple model is used to qualitatively describe. The results demonstrate that the InAs monolayer can effectively absorb photons and the double barrier hybrid structure with quantum dots in well can be used for low-light-level detection.

  17. Quantum Wells, Wires and Dots Theoretical and Computational Physics of Semiconductor Nanostructures

    CERN Document Server

    Harrison, Paul

    2011-01-01

    Quantum Wells, Wires and Dots, 3rd Edition is aimed at providing all the essential information, both theoretical and computational, in order that the reader can, starting from essentially nothing, understand how the electronic, optical and transport properties of semiconductor heterostructures are calculated. Completely revised and updated, this text is designed to lead the reader through a series of simple theoretical and computational implementations, and slowly build from solid foundations, to a level where the reader can begin to initiate theoretical investigations or explanations of their

  18. Infrared Supercontinuum Generation in Multiple Quantum Well Nanostructures under Electromagnetically Induced Transparency

    CERN Document Server

    Borgohain, Nitu; Konar, S

    2015-01-01

    Mid-infrared spectral broadening is of great scientific and technological interest, which till date is mainly achieved using non-silica glass fibers, primarily made of tellurite, fluoride and chalcogenide glasses. We investigate broadband mid-infrared supercontinuum generation at very low power in semiconductor multiple quantum well (MQW) systems facilitated by electromagnetically induced transparency. 100 femto-seconds pulses of peak power close to a Watt have been launched in the electromagnetically induced transparency window of a 30 period 1.374 {\\mu}m long MQW system. Broadband supercontinuum spectra, attributed to self phase modulation and modulation instability, is achievable at the end of the MQW system. The central part of the spectra is dominated by several dips and the far infra-red part of the spectra is more broadened in comparison to the infra-red portion. Key advantage of the proposed scheme is that the supercontinuum source could be easily integrated with other semiconductor devices.

  19. Quantum wells based on Si/SiO{sub x} stacks for nanostructured absorbers

    Energy Technology Data Exchange (ETDEWEB)

    Berghoff, B.; Suckow, S.; Roelver, R.; Spangenberg, B.; Kurz, H. [Institute of Semiconductor Electronics, RWTH Aachen University, Sommerfeldstr. 24, 52074 Aachen (Germany); Sologubenko, A.; Mayer, J. [Central Facility for Electron Microscopy, RWTH Aachen University, Ahornstr. 55, 52074 Aachen (Germany); Ernst Ruska Centre for Microscopy and Spectroscopy with Electrons, Research Centre Juelich, 52426 Juelich (Germany)

    2010-11-15

    We report on electrical transport and quantum confinement in thermally annealed Si/SiO{sub x} multiple quantum well (QW) stacks. Results are correlated with the morphology of the stacks. High temperature annealing of Si/SiO{sub x} stacks leads to precipitation of excess Si from the SiO{sub x} layers, which enhances the degree of crystallization and increases the grain sizes in the Si QWs compared to the conventional Si/SiO{sub 2} system. Moreover, the excess Si forms highly conductive pathways between adjacent Si QWs that are separated by ultrathin silicon oxide barriers. This results in an increase of conductivity by up to 10 orders of magnitude compared to the tunneling dominated transport in Si/SiO{sub 2} stacks. The stacks exhibit a distinct quantum confinement as confirmed by photoluminescence measurements. (author)

  20. Phase Diagram of the Bose Condensation of Interwell Excitons in GaAs/AlGaAs Double Quantum Wells

    DEFF Research Database (Denmark)

    Dremin, A. A.; Timofeev, V. B.; Larionov, A. V.

    2002-01-01

    The luminescence of interwell excitons in GaAs/AlGaAs double quantum wells (n–i–n heterostructures) with large-scale fluctuations of random potential in the heteroboundary planes was studied at low temperatures down to 0.5 K. The properties of excitons whose photoexcited electron and hole...

  1. Hybrid InGaAs quantum well-dots nanostructures for light-emitting and photo-voltaic applications

    Science.gov (United States)

    Mintairov, S. A.; Kalyuzhnyy, N. A.; Lantratov, V. M.; Maximov, M. V.; Nadtochiy, A. M.; Rouvimov, Sergei; Zhukov, A. E.

    2015-09-01

    Hybrid quantum well-dots (QWD) nanostructures have been formed by deposition of 7-10 monolayers of In0.4Ga0.6As on a vicinal GaAs surface using metal-organic chemical vapor deposition. Transmission electron microscopy, photoluminescence and photocurrent analysis have shown that such structures represent quantum wells comprising three-dimensional (quantum dot-like) regions of two kinds. At least 20 QWD layers can be deposited defect-free providing high gain/absorption in the 0.9-1.1 spectral interval. Use of QWD media in a GaAs solar cell resulted in a photocurrent increment of 3.7 mA cm-2 for the terrestrial spectrum and by 4.1 mA cm-2 for the space spectrum. Diode lasers based on QWD emitting around 1.1 μm revealed high saturated gain and low transparency current density of about 15 cm-1 and 37 A cm-2 per layer, respectively.

  2. Barrier and well-width dependence of optical emission of GaN/AlGaN quantum well nanostructures

    Directory of Open Access Journals (Sweden)

    H. Haratizadeh

    2007-06-01

    Full Text Available Internal polarizations field which take place in quantum structures of group-III nitrides have an important consequence on their optical properties. Optical properties of wurtzite AlGaN/GaN quantum well (QW structures grown by MBE and MOCVD on c-plane sapphire substrates have been investigated by means of photoluminescence (PL and time resolved photoluminescence (TRPL at low-temperature. PL spectra exhibit a blue-shifted emission of AlGaN/GaN quantum well (QW nanostructures by decreasing the barrier width contrary to the arsenide system. The trend of the barrier-width dependence of the internal polarization field is reproduced by using simple electrostatic arguments. In addition the effect of well width variation on the optical transition and decay time of GaN MQWs have been investigated and it has been shown that the screening of the piezoelectric field and the electron-hole separation are strongly dependent on the well thickness and have a profound effect on the optical properties of the GaN/AlGaN MQWs.

  3. Hybrid InGaAs quantum well-dots nanostructures for light-emitting and photo-voltaic applications.

    Science.gov (United States)

    Mintairov, S A; Kalyuzhnyy, N A; Lantratov, V M; Maximov, M V; Nadtochiy, A M; Rouvimov, Sergei; Zhukov, A E

    2015-09-25

    Hybrid quantum well-dots (QWD) nanostructures have been formed by deposition of 7-10 monolayers of In0.4Ga0.6As on a vicinal GaAs surface using metal-organic chemical vapor deposition. Transmission electron microscopy, photoluminescence and photocurrent analysis have shown that such structures represent quantum wells comprising three-dimensional (quantum dot-like) regions of two kinds. At least 20 QWD layers can be deposited defect-free providing high gain/absorption in the 0.9-1.1 spectral interval. Use of QWD media in a GaAs solar cell resulted in a photocurrent increment of 3.7 mA cm(-2) for the terrestrial spectrum and by 4.1 mA cm(-2) for the space spectrum. Diode lasers based on QWD emitting around 1.1 μm revealed high saturated gain and low transparency current density of about 15 cm(-1) and 37 A cm(-2) per layer, respectively.

  4. Ultraslow optical solitons in tunnel-coupled double semiconductor quantum well

    Institute of Scientific and Technical Information of China (English)

    Chen Ai-Xi; Xu Yan-Qiu; Deng Li; Zhou Su-Yun

    2009-01-01

    This paper investigates the nonlinear evolution of the pulse probe field in an asymmetric coupled-quantum well driven coherently by a pulse probe field and two controlled fields.This study shows that,by choosing appropriate physical parameters,self-modulation can precisely balance group velocity dispersion in the investigated system,leading to the formation of ultraslow optical solitons of the probe field.The proposed scheme may lead to the development of the controlled technique of optical buffers and optical delay lines.

  5. Continuous-Variable Entanglement in Tunnel-Coupled Double Quantum Wells

    Institute of Scientific and Technical Information of China (English)

    L(U) Xin-You; LIU Ji-Bing; HAO Xiang-Ying; HUANG Pei; YANG Xiao-Xue

    2009-01-01

    This paper investigates the generation and evolution of continuous-variable entanglement in an asymmetric coupled-quantum well (CQW) system. Our numerical results show that this CQW system can be regarded as a source of macroscopic entangled light over a wide range of initial states of the cavity field. This investigation can be used for achieving the macroscopic entangled light in the CQW solid-state medium, which is much more practical than that in an atomic medium because of its flexible design and the controllable interference strength.

  6. Partial hybridisation of electron-hole states in an InAs/GaSb double quantum well heterostructure

    Science.gov (United States)

    Knox, C. S.; Morrison, C.; Herling, F.; Ritchie, D. A.; Newell, O.; Myronov, M.; Linfield, E. H.; Marrows, C. H.

    2017-10-01

    InAs/GaSb coupled quantum well heterostructures are important semiconductor systems with applications ranging from spintronics to photonics. Most recently, InAs/GaSb heterostructures have been identified as candidate two-dimensional topological insulators, predicted to exhibit helical edge conduction via fully spin-polarised carriers. We study an InAs/GaSb double quantum well heterostructure with an AlSb barrier to decouple partially the 2D electrons and holes, and find conduction consistent with a 2D hole gas, with an effective mass of 0.235 ± 0.005 m 0, existing simultaneously with hybridised carriers with an effective mass of 0.070 ± 0.005 m 0, where m 0 is the bare electron mass.

  7. Two-dimensional double-quantum spectroscopy: peak shapes as a sensitive probe of carrier interactions in quantum wells

    CERN Document Server

    Tollerud, Jonathan O

    2016-01-01

    We identify carrier scattering at densities below which it has previously been observed in semiconductor quantum wells. These effects are evident in the peakshapes of 2D double-quantum spectra, which change as a function of excitation density. At high excitation densities ($\\geq 10^{9}$ carriers/,cm$^{-2}$) we observe untilted peaks similar to those reported in previous experiments. At low excitation densities (<$10^{8}$ carriers cm$^{-2}$) we observe narrower, tilted peaks. Using a simple simulation, we show that tilted peak-shapes are expected in double-quantum spectra when inhomogeneous broadening is much larger than homogeneous broadening, and that fast pure-decoherence of the double-quantum coherence can obscure this peak tilt. These results show that carrier interactions are important at lower densities than previously expected, and that the `natural' double-quantum peakshapes are hidden by carrier interactions at the excitation densities typically used. Furthermore, these results demonstrate that an...

  8. Electron Raman scattering in a double quantum well tuned by an external nonresonant intense laser field

    Science.gov (United States)

    Tiutiunnyk, A.; Mora-Ramos, M. E.; Morales, A. L.; Duque, C. M.; Restrepo, R. L.; Ungan, F.; Martínez-Orozco, J. C.; Kasapoglu, E.; Duque, C. A.

    2017-02-01

    In this work we shall present a study of inelastic light scattering involving inter-subband electron transitions in coupled GaAs-(Ga,Al)As quantum wells. Calculations include the electron related Raman differential cross section and Raman gain. The effects of an external nonresonant intense laser field are used in order to tune these output properties. The confined electron states will be described by means of a diagonalization procedure within the effective mass and parabolic band approximations. It is shown that the application of the intense laser field can produce values of the intersubband electron Raman gain above 400 cm-1. The system proposed here is an alternative choice for the development of AlxGa1-xAs semiconductor laser diodes that can be tuned via an external nonresonant intense laser field.

  9. Giant Spin-Orbit Splitting in Inverted InAs /GaSb Double Quantum Wells

    Science.gov (United States)

    Nichele, Fabrizio; Kjaergaard, Morten; Suominen, Henri J.; Skolasinski, Rafal; Wimmer, Michael; Nguyen, Binh-Minh; Kiselev, Andrey A.; Yi, Wei; Sokolich, Marko; Manfra, Michael J.; Qu, Fanming; Beukman, Arjan J. A.; Kouwenhoven, Leo P.; Marcus, Charles M.

    2017-01-01

    Transport measurements in inverted InAs /GaSb quantum wells reveal a giant spin-orbit splitting of the energy bands close to the hybridization gap. The splitting results from the interplay of electron-hole mixing and spin-orbit coupling, and can exceed the hybridization gap. We experimentally investigate the band splitting as a function of top gate voltage for both electronlike and holelike states. Unlike conventional, noninverted two-dimensional electron gases, the Fermi energy in InAs /GaSb can cross a single spin-resolved band, resulting in full spin-orbit polarization. In the fully polarized regime we observe exotic transport phenomena such as quantum Hall plateaus evolving in e2/h steps and a nontrivial Berry phase.

  10. Collective behavior of interwell excitons laterally confined in GaAs/AlGaAs double quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Timofeev, V.B.; Gorbunov, A.V. [Institute of Solid State Physics, Russian Academy of Sciences, Chernogolovka 142432 (Russian Federation)

    2005-02-01

    The luminescence of interwell excitons laterally confined by long range potential fluctuations and with the use of inhomogeneous electric field in n-i-n GaAs/AlGaAs heterostructures double quantum wells has been investigated under variation of excitation power and temperature. Above mobility threshold very narrow interwell exciton line has been observed and its intensity decrease is linearly dependent on temperature growth. The observed phenomena, which were critical to exciton density and temperature, are attributed to the Bose-condensation in laterally confined quasi-two dimensional system of interwell excitons. (copyright 2005 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  11. Effects of electromagnetic fields on the nonlinear optical properties of asymmetric double quantum well under intense laser field

    Science.gov (United States)

    Yesilgul, U.; Sari, H.; Ungan, F.; Martínez-Orozco, J. C.; Restrepo, R. L.; Mora-Ramos, M. E.; Duque, C. A.; Sökmen, I.

    2017-03-01

    In this study, the effects of electric and magnetic fields on the optical rectification and second and third harmonic generation in asymmetric double quantum well under the intense non-resonant laser field is theoretically investigated. We calculate the optical rectification and second and third harmonic generation within the compact density-matrix approach. The theoretical findings show that the influence of electric, magnetic, and intense laser fields leads to significant changes in the coefficients of nonlinear optical rectification, second and third harmonic generation.

  12. Collective State of Interwell Excitons in GaAs/AlGaAs Double Quantum Wells under Pulse Resonance Excitation

    DEFF Research Database (Denmark)

    Larionov, A. V.; Timofeev, V. B.; Hvam, Jørn Märcher

    2002-01-01

    The time evolution and kinetics of photoluminescence (PL) spectra of interwell excitons in double GaAs/AlGaAs quantum wells (n–i–n structures) have been investigated under the pulse resonance excitation of intrawell 1sHH excitons using a pulsed tunable laser. It is found that the collective exciton......, and a significant increase in the radiative decay rate of the condensed phase. The collective exciton phase arises at temperatures T properties of the collective phase of interwell excitons and experimental manifestations of this coherence...

  13. Enhanced performance of InGaN/GaN multiple quantum well solar cells with double indium content

    Institute of Scientific and Technical Information of China (English)

    Zhao Bi-Jun; Chen Xin; Ren Zhi-Wei; Tong Jin-Hui; Wang Xing-Fu; Li Dan-Wei; Zhuo Xiang-Jing

    2013-01-01

    The performance of a multiple quantum well (MQW) InGaN solar cell with double indium content is investigated.It is found that the adoption of a double indium structure can effectively broaden the spectral response of the external quantum efficiencies and optimize the overall performance of the solar cell.Under AM1.5G illumination,the short-circuit current density (Jsc) and conversion efficiency of the solar cell are enhanced by 65% and 13% compared with those of a normal single-indium-content MQW solar cell.These improvements are mainly attributed to the expansion of the absorption spectrum and better extraction efficiency of the photon-generated carriers induced by higher polarization.

  14. Dispersive properties of tunnelling-induced transparency in an asymmetric double quantum well

    Institute of Scientific and Technical Information of China (English)

    苏雪梅; 卓仲畅; 王立军; 高锦岳

    2002-01-01

    We have investigated the dispersive properties of tunnelling-induced transparency in asymmetric double quantumwell structures where two excited states are coupled by resonant tunnelling through a thin barrier in a three-levelsystem of electronic subbands. The intersubband transitions exhibit high dispersion at zero absorption, which leads tothe slow light velocity in this medium as compared with that in vacuum (c=3× 108). The group velocity in a specificGaAs/AlGaAs sample is calculated to be vg=c/4.30. This structure can be used to compensate for the dispersion andenergy loss in fibre optical communications.

  15. Nonmonotonous electron mobility due to structurally induced resonant coupling of subband states in an asymmetric double quantum well

    Energy Technology Data Exchange (ETDEWEB)

    Nayak, R. K.; Das, S.; Panda, A. K.; Sahu, T., E-mail: tsahu-bu@rediffmail.com [Department of Electronics and Communication Engineering, National Institute of Science and Technology, Palur Hills, Berhampur-761 008, Odisha (India)

    2015-11-15

    We show that sharp nonmonotic variation of low temperature electron mobility μ can be achieved in GaAs/Al{sub x}Ga{sub 1-x}As barrier delta-doped double quantum well structure due to quantum mechanical transfer of subband electron wave functions within the wells. We vary the potential profile of the coupled structure as a function of the doping concentration in order to bring the subbands into resonance such that the subband energy levels anticross and the eigen states of the coupled structure equally share both the wells thereby giving rise to a dip in mobility. When the wells are of equal widths, the dip in mobility occurs under symmetric doping of the side barriers. In case of unequal well widths, the resonance can be obtained by suitable asymmetric variation of the doping concentrations. The dip in mobility becomes sharp and also the wavy nature of mobility takes a rectangular shape by increasing the barrier width. We show that the dip in mobility at resonance is governed by the interface roughness scattering through step like changes in the subband mobilities. It is also gratifying to show that the drop in mobility at the onset of occupation of second subband is substantially supressed through the quantum mechanical transfer of subband wave functions between the wells. Our results can be utilized for performance enhancement of coupled quantum well devices.

  16. Magnetophotoluminescence study of GaAs/AlGaAs coupled double quantum wells with bimodal heterointerface roughness

    Energy Technology Data Exchange (ETDEWEB)

    Lopes, E.M., E-mail: eldermantovani@yahoo.com.br [Departamento de Fisica, Quimica e Biologia, Universidade Estadual Paulista, CP 266, CEP 19060-900, Presidente Prudente, Sao Paulo (Brazil); Duarte, J.L.; Dias, I.F.L.; Laureto, E. [Departamento de Fisica, Universidade Estadual de Londrina, CP 6001, CEP 86051-970, Londrina, Parana (Brazil); Guimaraes, P.S.S.; Subtil, A.G.S. [Departamento de Fisica, Instituto de Ciencias Exatas, Universidade Federal de Minas Gerais, CP 702, CEP 30123-970, Belo Horizonte, Minas Gerais (Brazil); Quivy, A.A. [Laboratorio de Novos Materiais Semicondutores, Instituto de Fisica, Universidade de Sao Paulo, CP 66318, CEP 05315-970, Sao Paulo (Brazil)

    2012-05-15

    This work reports on the results of magnetophotoluminescence (MPL) measurements carried out in a sample containing two Al{sub 0.35}Ga{sub 0.65}As/GaAs, coupled double quantum wells (CDQWs), with inter-well barriers of different thicknesses, which have the heterointerfaces characterized by a distribution of bimodal roughness. The MPL measurements were performed at 4 K, with magnetic fields applied parallel to the growth direction, and varying from 0 to 12 T. The diamagnetic shift of the photoluminescence (PL) peaks is more sensitive to changes in the confinement potential, due to monolayer variations in the mini-well thickness, rather than to the exciton localization at the local potential fluctuations. As the magnetic field increases, the relative intensities of the two peaks in each PL band inverts, what is attributed to the reduction in the radiative lifetime of the delocalized excitons, which results in the radiative recombination, before the excitonic migration between the higher and lower energy regions in each CDQW occurs. The dependence of the full width at half maximum (FWHM) on magnetic field shows different behaviors for each PL peak, which are attributed to the different levels and correlation lengths of the potential fluctuations present in the regions associated with each recombination channel. - Highlights: Black-Right-Pointing-Pointer Magnetophotoluminescence results from two coupled double quantum wells are reported. Black-Right-Pointing-Pointer Each structure shows two emission channels due to bimodal heterointerface roughness. Black-Right-Pointing-Pointer Little variations on thickness have greater effect than local potential fluctuations. Black-Right-Pointing-Pointer With increasing B the excitonic migration changes between the bimodal regions. Black-Right-Pointing-Pointer The FWHM depends on level and correlation length of the potential fluctuations.

  17. 双量子阱中的子带光吸收%Intersubband Optical Absorption in Double Quantum Wells

    Institute of Scientific and Technical Information of China (English)

    邓永晴; 郭康贤; 于凤梅; 俞友宾; 王瑞强

    2005-01-01

    Recently, much attention has been focus on the investigation of the electroabsorption in the GaAs/AlGaAs quantum wells (QW's) because of its possibility of designing new types of electro-optic modulators. Much optical properties of the single QW's with different potential has been and being investigated experimently and theoriticaly with different methods. In these few years, the double quantum wells (DQWs) became the focus of the research. In this paper, by using the density matrix formalism and iterated method, the first-and the third-order intersubband optical absorption of double quantum well with infinit boundary was investigated theoretically. Thereafter, a typical GaAs/AlGaAs DQWs is presented to get the results. The results show that the peak absorption varies with the width of the intermediate potential barrier. And it also shows that the absorption decrease as the incident optical intensity increasing.%由于微制造技术的不断发展,如液相外延(LPE),气相外延(VPE),金属有机化学气相沉积(MOCVD)以及分子束外延技术(MBE)等先进的材料生长技术方法也日趋完善,从而使得各种低维半导体量子器件(如半导体、超晶格、量子阱、量子线和量子点等)制造日趋成熟.由于这些低维半导体量子器件具有很强的非线性光效应,而且随着材料、外形、尺寸等的不同,非线性光效应也有很大的差别,更由于其可能存在的广泛的应用前景,所以近年来,一直是人们研究的重点.近来,由于人们相信,利用GaAs/AlGaAs量子阱有可能制造出一些新型的光学仪器,如光开关、光限幅器、光调制器等,所以,对不同势形的GaAs/AlGaAs量子阱的非线性光学特性一直吸引着人们进行理论和实验的研究.而在最近几年,对双量子阱的研究也成为了人们的研究重点.通过密度矩阵和迭代的方法,得到双量子阱中的第一、第三阶子带光吸收表达式,我们将用一个典型的GaAs/AlGaAs双

  18. Donor states in a semimagnetic Cd1 -xinMnxin Te /Cd1 -xoutMnxout Te Double Quantum Well

    Science.gov (United States)

    Kalpana, Panneer Selvam; Nithiananthi, Perumal; Jayakumar, Kalyanasundaram

    2017-02-01

    The theoretical investigation has been carried out on the binding energy of donor associated with the electrons confined in a Cd1 -xinMnxin Te /Cd1 -xoutMnxout Te Double Quantum Well (DQW) as a function of central barrier width for various well dimensions and impurity locations in the barrier and the well. The magnetic field can act as a tool to continuously change the interwell coupling inside this DQW systems and its effect on donor binding has also been studied. Moreover, the polaronic corrections, which is due to the strong exchange interaction between the magnetic moment of Mn2+ ion and the spin of the confined carrier, to the binding energy of the hydrogenic donor impurity has also been estimated with and without the application of magnetic field. The binding energy of the donor impurity is determined by solving the Schrodinger equation variationally in the effective mass approximation and the effect due to Bound Magnetic Polaron (BMP) is included using mean field theory with the modified Brillouin function. The results are reported and discussed.

  19. Transport properties of double-gate SiO{sub 2}-Si-SiO{sub 2} quantum well

    Energy Technology Data Exchange (ETDEWEB)

    Prunnila, Mika; Ahopelto, Jouni [VTT Information Technology, Microelectronics, P.O. Box 1208, 02044 VTT (Finland); Sakaki, Hiroyuki [University of Tokyo, Institute of Industrial Science, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8503 (Japan)

    2005-05-01

    We report on fabrication and low temperature transport properties of double-gate SiO{sub 2}-Si-SiO{sub 2} quantum well with a 16.5 nm thick Si layer. The device is fabricated on a silicon-on-insulator substrate utilizing wafer bonding, which enables us to use heavily doped back gate. Transport properties of the device are characterized by low field Hall and high field magnetotransport measurements at 4.2 K and at 0.38 K, respectively. Top (back) Si-SiO{sub 2} interface peak mobility of 1.9 m{sup 2}/Vs (1.0 m{sup 2}/Vs) is measured at 4.2 K. When both gates have a (large) positive bias the Hall carrier density is observed to fall below the value of the expected total carrier density, which is interpreted to arise from the occupancy of the second sub-band in the Si well. This is confirmed by the high field magnetotransport measurements. In quantizing magnetic fields the longitudinal resistivity minima show Landau level filling factor behavior which is typical for weakly coupled bi-layers. (copyright 2005 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  20. Charged excitonic complexes in GaAs/Al0.35Ga0.65As p-i-n double quantum wells

    DEFF Research Database (Denmark)

    Timofeev, V. B.; Larionov, A. V.; Alessi, M. Grassi

    1999-01-01

    Photoluminescence (PL) and PL excitation measurements (PLE) have been performed in GaAs/AlxGa1-xAs double quantum well (QW) structures under different applied electric fields. An emission due to charged excitons (trions) has been identified in the PL spectra similar to 3 meV below the heavy...

  1. Interwell radiative recombination in the presence of random potential fluctuations in GaAs/AlGaAs biased double quantum wells

    DEFF Research Database (Denmark)

    Timofeev, V.B.; Larionov, A.V.; Ioselevich, A.S.;

    1998-01-01

    The interwell radiative recombination from biased double quantum wells (DQW) in pin GaAs/AlGaAs heterostructures is investigated at different temperatures and external electrical fields. The luminescence line of interwell recombination of spatially separated electron-hole pairs exhibits systemati...

  2. HgTe/CdHgTe double quantum well with a spectrum of bilayer graphene and peculiarities of its magnetotransport

    Science.gov (United States)

    Yakunin, M. V.; Krishtopenko, S. S.; Podgornykh, S. M.; Popov, M. R.; Neverov, V. N.; Mikhailov, N. N.; Dvoretsky, S. A.

    2016-09-01

    The quantum Hall effect (QHE) in a HgTe/CdHgTe double quantum well (DQW) with a tunneling-transparent barrier and the energy spectrum resembling the band structure of bilayer graphene has been investigated. An experimental manifestation of a tunnel gap between the states of light carriers seen as a magnetoresistance (MR) peak in the in-plane magnetic field has been discovered. An unusual structure of the QHE has been observed in a sample with hole conductivity: there is a pronounced peak on a plateau with the number i = 2 and the slopes of this anomalous peak correspond to two peaks of the longitudinal MR. On the other hand, a stable 2-1 plateau-plateau transition has been observed in much higher fields with the position of this transition corresponding to a considerably higher hole density than follows from the pattern of the QHE in weak fields. The anomalous peak is interpreted as a reentrant QHE between the 2-1-2 states. The position of the anomalous peak is immune to IR illumination and the tilting angle of the magnetic field, although these factors strongly affect its amplitude. According to comparison with the calculated structure of magnetic levels, the anomalous peak is attributed to crossing of electron-like and hole-like levels in the valence band. The difference between the hole densities found in weak field and from the 2-1 transition in strong fields is attributed to the effects of redistribution of holes between the localized states in sideband maxima of the valence subband and the ones delocalized in the overlapping levels of light holes.

  3. Persistent photoeffects in p-i-n GaAs/AlGaAs heterostructures with double quantum wells

    DEFF Research Database (Denmark)

    Dorozhkin, S.I.; Timofeev, V.B.; Hvam, Jørn Märcher

    2001-01-01

    Abrupt changes in the capacitance between the p and n regions were observed in a planar p-i-n GaAs/AlGaAs heterostructure with two tunneling-coupled quantum wells exposed to laser irradiation (lambda = 633 nm). These changes can be caused by variations in both temperature (in the vicinity of T...

  4. Photoluminescence energy transitions in GaAs-Ga{sub 1-x}Al{sub x}As double quantum wells: Electric and magnetic fields and hydrostatic pressure effects

    Energy Technology Data Exchange (ETDEWEB)

    Lopez, S.Y. [Grupo de Educacion en Ciencias Experimentales y Matematicas-GECEM, Facultad de Educacion, Universidad de Antioquia, AA 1226 Medellin (Colombia); Mora-Ramos, M.E. [Facultad de Ciencias, Universidad Autonoma del Estado de Morelos, Av. Universidad 1001, CP 62209, Cuernavaca, Morelos (Mexico); Duque, C.A., E-mail: cduque@fisica.udea.edu.c [Instituto de Fisica, Universidad de Antioquia, AA 1226 Medellin (Colombia)

    2009-12-15

    The photoluminescence energy transitions in GaAs-Ga{sub 1-x}Al{sub x}As coupled double quantum wells are presented by considering the simultaneous effects of applied electric and magnetic fields and hydrostatic pressure. Calculations have been made in the framework of the effective mass and parabolic band approximations and using a variational procedure. The electric field is taken to be oriented along the growth direction of the heterostructure whereas for the magnetic field both in-plane and in-growth directions have been considered. The results show that the hydrostatic pressure and the applied electric field are two useful tools to tune the direct and indirect exciton transitions in such heterostructures. Our results are in good agreement with previous experimental findings in double quantum wells under applied electric field and hydrostatic pressure.

  5. Second-order nonlinear optical susceptibilities induced by built-in electric field in wurtzite nitride double quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, L. [State Key Laboratory for Mesoscopic Physics, and School of Physics, Peking University, Beijing 100871 (China) and Department of Mechanism and Electron, Panyu Polytechnic, Panyu 511483 (China)]. E-mail: zhangli-gz@263.net; Chi Yuemeng [State Key Laboratory for Mesoscopic Physics, and School of Physics, Peking University, Beijing 100871 (China); Shi, J.-J. [State Key Laboratory for Mesoscopic Physics, and School of Physics, Peking University, Beijing 100871 (China)

    2007-06-25

    Based on the density matrix method and the iterative treatment, the second-harmonic generation (SHG) susceptibility of a wurtzite nitride coupling quantum well (CQW) with strong built-in electric fields have been theoretically investigated. The effect of the band non-parabolicity effect has been taken into account. A typical wurtzite GaN/In{sub x}Ga{sub 1-x}N CQW are chosen to perform numerical calculations. The localized properties of the electronic ground state and the low-excited states in the system are analyzed in detail. The calculated SHG coefficients reach the order of magnitude of 10{sup -7}m/V, which is two-order larger than the corresponding values in wurtzite single quantum wells. Moreover, it is confirmed that the SHG coefficients are not monotonic functions of the well width, barrier width and the doped concentration of the CQW systems, but have complicated dependent relations on them. The reasons resulting in these characteristics can be attributed to the intense competition between the strong built-in electric field effect and the quantum size effect for the electronic confined situation in the wurtzite CQWs. The calculated results also show that a strong SHG effect can be realized in the nitride CQW by choosing a group of optimized structural parameters and doped fraction.

  6. Residual electric fields of InGaAs/AlAs/AlAsSb (001) coupled double quantum wells structures assessed by photoreflectance anisotropy

    Science.gov (United States)

    González-Fernández, J. V.; Herrera-Jasso, R.; Ulloa-Castillo, N. A.; Ortega-Gallegos, J.; Castro-García, R.; Lastras-Martínez, L. F.; Lastras-Martínez, A.; Balderas-Navarro, R. E.; Mozume, T.; Gozu, S.

    2016-12-01

    We report on photoreflectance anisotropy (PRA) spectroscopy of InGaAs/AlAs/AlAsSb coupled double quantum wells (CDQWs) with extremely thin coupling AlAs barriers grown by molecular beam epitaxy (MBE), with no intentional doping. By probing the in-plane interfacial optical anisotropies (OAs), it is shown that PRA spectroscopy has the ability to detect and distinguish semiconductor layers with quantum dimensions, as the anisotropic photoreflectance (PR) signal stems entirely from buried quantum wells (QWs). In order to account for the experimental PRA spectra, a theoretical model at k = 0, based on a linear electro-optic effect through a piezoelectric shear strain, has been employed to quantify the internal electric fields across the QWs. The dimensionalities of the PR lineshapes were tested by using reciprocal (Fourier) space analysis. Such a complementary test is used in order to correctly employ the PRA model developed here.

  7. Nonlinear absorption coefficient and relative refraction index change for an asymmetrical double δ-doped quantum well in GaAs with a Schottky barrier potential

    Energy Technology Data Exchange (ETDEWEB)

    Rojas-Briseño, J.G.; Martínez-Orozco, J.C.; Rodríguez-Vargas, I. [Unidad Académica de Física, Universidad Autónoma de Zacatecas, Calzada Solidaridad esquina con Paseo la Bufa S/N, C.P. 98060, Zacatecas, Zac. (Mexico); Mora-Ramos, M.E. [Facultad de Ciencias, Universidad Autónoma del Estado de Morelos, Av. Universidad 1001, CP 62209, Cuernavaca, Morelos (Mexico); Instituto de Física, Universidad de Antioquia, AA 1226, Medellín (Colombia); Duque, C.A., E-mail: cduque@fisica.udea.edu.co [Instituto de Física, Universidad de Antioquia, AA 1226, Medellín (Colombia)

    2013-09-01

    In this work we are reporting the energy level spectrum for a quantum system consisting of an n-type double δ-doped quantum well with a Schottky barrier potential in a Gallium Arsenide matrix. The calculated states are taken as the basis for the evaluation of the linear and third-order nonlinear contributions to the optical absorption coefficient and to the relative refractive index change, making particular use of the asymmetry of the potential profile. These optical properties are then reported as a function of the Schottky barrier height (SBH) and the separation distance between the δ-doped quantum wells. Also, the effects of the application of hydrostatic pressure are studied. The results show that the amplitudes of the resonant peaks are of the same order of magnitude of those obtained in the case of single δ-doped field effect transistors; but tailoring the asymmetry of the confining potential profile allows the control the resonant peak positions.

  8. A Numerical Investigation of the Strain Effect on Saturation Optical Intensity in Electroabsorption Modulators Based on Asymmetric Intra-step-barrier Coupled Double Strained Quantum Wells

    Science.gov (United States)

    Abedi, Kambiz

    2011-12-01

    In this paper, the strain effect on saturation optical intensity in electroabsorption modulators (EAMs) based on asymmetric intra-step-barrier coupled double strained quantum well (AICD-SQWs) active region is theoretically investigated and compared with intra-step quantum well (IQW) structure. For this purpose, the thermionic emission and tunneling escape processes are taken into account and the escape times of photogenerated carriers are calculated. Then, the electroabsorption coefficient is calculated for different well strains for TE input light polarization. Finally, the saturation optical intensity of electroabsorption modulators with AICD-SQW structures in comparison with IQW structure is evaluated. Numerical results show that the tensile strain of well has the most significant effect on the saturation optical intensity of electroabsorption modulators with AICD-SQW structures due to reduction in escape times.

  9. Collective state of interwall excitons on GaAs/AlGaAs double quantum wells under pulse resonant excitation

    CERN Document Server

    Larionov, A V; Hvam, J; Soerensen, K

    2002-01-01

    The time evolution and kinetics of the photoluminescence (PL) spectra of the interwall excitons under the pulse resonant excitation of the interwall excitons are studied in the GaAs/AlGaAs binary quantum well. It is established, that the collective exciton phase originates with the time delay relative to the exciting pulse (several nanoseconds), which is conditioned by the density and temperature relaxation to the equilibrium values.The origination of the collective phase of the interwall excitons is accompanied by the strong narrowing of the corresponding photoluminescence line, the superlinear growth of its intensity and large time of change in the degree of the circular polarization.The collective exciton phase originates at the temperatures < 6 K and the interwall excitons densities 3 x 10 sup 1 sup 0 cm sup - sup 2

  10. Investigation of surface-plasmon coupled red light emitting InGaN/GaN multi-quantum well with Ag nanostructures coated on GaN surface

    Energy Technology Data Exchange (ETDEWEB)

    Li, Yi; Liu, Bin, E-mail: bliu@nju.edu.cn, E-mail: rzhang@nju.edu.cn; Zhang, Rong, E-mail: bliu@nju.edu.cn, E-mail: rzhang@nju.edu.cn; Xie, Zili; Zhuang, Zhe; Dai, JiangPing; Tao, Tao; Zhi, Ting; Zhang, Guogang; Chen, Peng; Ren, Fangfang; Zhao, Hong; Zheng, Youdou [Jiangsu Provincial Key Laboratory of Advanced Photonic and Electronic Materials, School of Electronic Science and Engineering, Nanjing University, Nanjing 210093, People' s Republic of China and Nanjing National Laboratory of Microstructures, Nanjing University, Nanjing 210093 (China)

    2015-04-21

    Surface-plasmon (SP) coupled red light emitting InGaN/GaN multiple quantum well (MQW) structure is fabricated and investigated. The centre wavelength of 5-period InGaN/GaN MQW structure is about 620 nm. The intensity of photoluminescence (PL) for InGaN QW with naked Ag nano-structures (NS) is only slightly increased due to the oxidation of Ag NS as compared to that for the InGaN QW. However, InGaN QW with Ag NS/SiO{sub 2} structure can evidently enhance the emission efficiency due to the elimination of surface oxide layer of Ag NS. With increasing the laser excitation power, the PL intensity is enhanced by 25%–53% as compared to that for the SiO{sub 2} coating InGaN QW. The steady-state electric field distribution obtained by the three-dimensional finite-difference time-domain method is different for both structures. The proportion of the field distributed in the Ag NS for the GaN/Ag NS/SiO{sub 2} structure is smaller as compared to that for the GaN/naked Ag NS structure. As a result, the energy loss of localized SP modes for the GaN/naked Ag NS structure will be larger due to the absorption of Ag layer.

  11. Characterization of nonpolar a-plane InGaN/GaN multiple quantum well using double nanopillar SiO2 mask

    Science.gov (United States)

    Son, Ji-Su; Honda, Yoshio; Yamaguchi, Masahito; Amano, Hiroshi

    2014-01-01

    The characteristics of nonpolar a-plane (11\\bar{2}0) GaN (a-GaN) grown using single and double nanopillar SiO2 masks were investigated. The two nanopillar SiO2 masks were directly fabricated on an r-plane sapphire substrate and a-GaN by the epitaxial lateral overgrowth (ELOG) technique. Through the use of the single and double nanopillar SiO2 masks, the crystalline quality and optical properties of a-GaN were markedly improved because of the nanoscale ELOG effect and a number of voids in the single and double nanopillar SiO2 mask areas in comparison with the planar sample. The submicron pit densities of the planar, single, and double nanopillar mask samples were ˜2 × 109, ˜7 × 108, and ˜4 × 108 cm-2, respectively. The internal quantum efficiency (IQE) values at room temperature of three-period InGaN/GaN multiple quantum wells (MQWs) grown using the planar, single, and double nanopillar masks were 45, 60, and 68% at a carrier concentration of 1.0 × 1018 cm-3, respectively.

  12. Influence of Width of left Well on Intersubband Transitions in AlxGa1-x N/GaN Double Quantum Wells

    Institute of Scientific and Technical Information of China (English)

    LEI Shuang-Ying; SHEN Bo; ZHANG Guo-Yi

    2008-01-01

    Influence of width of lett well in Alx Ga1-x N/GaN double quantum wells (DQWs) on absorption coefficients and wavelengths of the intersubband transitions (ISBTs) is investigated by solving the SchrSdinger and Poisson equations self-consistently. When the width of lett well is 1.79nm, three-energy-level DQ, Ws are realized. The ISBT between the first odd and second odd order subbands (the lodd-2odd ISBT) has a comparable absorption coeffcient with the 1odd-2even ISBT. Their wavelengths are located at 1.3 and 1.55μm, respectively. When the width of lett well is 1.48nm, a four-energy-level DQWs is realized. The calculated results have a possible application to ultrafast two-colour optoeleetronic devices operating within the optical communication wavelength range.

  13. Exciton-related nonlinear optical absorption and refractive index change in GaAs-Ga{sub 1-x}Al{sub x}As double quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Miranda, Guillermo L. [Fisica Teorica y Aplicada, Escuela de Ingenieria de Antioquia, A.A. 7516 Medellin (Colombia); Instituto de Fisica, Universidad de Antioquia, AA 1226 Medellin (Colombia); Mora-Ramos, Miguel E., E-mail: memora@uaem.mx [Fisica Teorica y Aplicada, Escuela de Ingenieria de Antioquia, A.A. 7516 Medellin (Colombia); Facultad de Ciencias, Universidad Autonoma del Estado de Morelos, Av. Universidad 1001, C.P. 62209 Cuernavaca, Morelos (Mexico); Instituto de Fisica, Universidad de Antioquia, AA 1226 Medellin (Colombia); Duque, Carlos A. [Instituto de Fisica, Universidad de Antioquia, AA 1226 Medellin (Colombia)

    2013-01-15

    In this work the variations of the exciton-related optical absorption and the change of the refractive index in a GaAs-(Ga,Al)As double quantum well as functions of the geometric parameters of the heterostructure are investigated. The variational method is applied within the framework of the parabolic band and effective mass approximations, in order to obtain the 1s-like exciton energy spectrum. The outcome for the related optical coefficients shows a quenched and redshifted light absorption as a result of the increment in the inner barrier and right-hand well widths, with the possibility of an enhancement of the excitonic contribution to the relative change in the refractive index.

  14. Nanostructure surface patterning of GaN thin films and application to AlGaN/AlN multiple quantum wells: A way towards light extraction efficiency enhancement of III-nitride based light emitting diodes

    Energy Technology Data Exchange (ETDEWEB)

    Guo, Wei, E-mail: wguo2@ncsu.edu; Kirste, Ronny; Bryan, Zachary; Bryan, Isaac; Collazo, Ramón; Sitar, Zlatko [Department of Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina 27695-7919 (United States); Gerhold, Michael [Engineering Science Directorate, Army Research Office, Research Triangle Park, North Carolina 27703 (United States)

    2015-03-21

    Enhanced light extraction efficiency was demonstrated on nanostructure patterned GaN and AlGaN/AlN Multiple-Quantum-Well (MQW) structures using mass production techniques including natural lithography and interference lithography with feature size as small as 100 nm. Periodic nanostructures showed higher light extraction efficiency and modified emission profile compared to non-periodic structures based on integral reflection and angular-resolved transmission measurement. Light extraction mechanism of macroscopic and microscopic nanopatterning is discussed, and the advantage of using periodic nanostructure patterning is provided. An enhanced photoluminescence emission intensity was observed on nanostructure patterned AlGaN/AlN MQW compared to as-grown structure, demonstrating a large-scale and mass-producible pathway to higher light extraction efficiency in deep-ultra-violet light-emitting diodes.

  15. Nanostructure surface patterning of GaN thin films and application to AlGaN/AlN multiple quantum wells: A way towards light extraction efficiency enhancement of III-nitride based light emitting diodes

    Science.gov (United States)

    Guo, Wei; Kirste, Ronny; Bryan, Zachary; Bryan, Isaac; Gerhold, Michael; Collazo, Ramón; Sitar, Zlatko

    2015-03-01

    Enhanced light extraction efficiency was demonstrated on nanostructure patterned GaN and AlGaN/AlN Multiple-Quantum-Well (MQW) structures using mass production techniques including natural lithography and interference lithography with feature size as small as 100 nm. Periodic nanostructures showed higher light extraction efficiency and modified emission profile compared to non-periodic structures based on integral reflection and angular-resolved transmission measurement. Light extraction mechanism of macroscopic and microscopic nanopatterning is discussed, and the advantage of using periodic nanostructure patterning is provided. An enhanced photoluminescence emission intensity was observed on nanostructure patterned AlGaN/AlN MQW compared to as-grown structure, demonstrating a large-scale and mass-producible pathway to higher light extraction efficiency in deep-ultra-violet light-emitting diodes.

  16. Correlation of the nanostructure with optoelectronic properties during rapid thermal annealing of Ga(NAsP) quantum wells grown on Si(001) substrates

    Energy Technology Data Exchange (ETDEWEB)

    Wegele, Tatjana; Beyer, Andreas; Gies, Sebastian; Zimprich, Martin; Heimbrodt, Wolfram; Stolz, Wolfgang; Volz, Kerstin [Faculty of Physics and Material Sciences Center, Philipps-Universität Marburg, 35032 Marburg (Germany)

    2016-01-14

    Ga(NAsP) quantum wells grown pseudomorphically on Si substrate are promising candidates for optically active light sources in future optoelectronically integrated circuits on Si substrates. As the material is typically grown at low temperatures, it has to be thermally annealed after growth to remove defects and optimize optoelectronic properties. Here we show by quantitative transmission electron microscopy that two different kinds of structural development are associated with the annealing. First of all, the quantum well homogeneity improves with increasing annealing temperature. For annealing temperatures above 925 °C the composition becomes less homogeneous again. Second, voids form in the quantum well for annealing temperatures above 850 °C. Their density and size increase continuously with increasing annealing temperature. These results are correlated to the optical properties of the samples, where we find from temperature-dependent photoluminescence measurements two scales of disorder, which show the same temperature dependence as the structural properties.

  17. Bias-tunable IR photodetector based on asymmetrically doped GaAs/AlGaAs double-quantum-well nanomaterial for remote temperature sensing

    Science.gov (United States)

    Zhang, Xiang; Mitin, Vladimir; Choi, Jae Kyu; Sablon, Kimberly; Sergeev, Andrei

    2016-05-01

    We designed, fabricated, and characterized multi-color IR photodetectors with asymmetrical doping of GaAs/AlGaAs double quantum wells (DQW). We measured and analyzed spectral and noise characteristics to evaluate feasibility of these photodetectors for remote temperature sensing at liquid nitrogen temperatures. The bias voltage controls the charge distribution between the two wells in a DQW unit and provides effective tuning of IR induced electron transitions. We have found that the responsivity of our devices is symmetrical and weakly dependent on the bias voltage because the doping asymmetry compensates the effect of dopant migration in the growth direction. At the same time, the asymmetrical doping strongly enhances the selectivity and tunability of spectral characteristics by bias voltage. Multicolor detection of our QWIP is realized by varying the bias voltage. Maximum detection wavelength moves from 7.5 μm to 11.1 μm by switching applied bias from -5 V to 4 V. Modeling shows significant dependence of the photocurrent ratio on the object temperature regardless of its emissivity and geometrical factors. We also experimentally investigated the feasibility of our devices for remote temperature sensing by measuring the photocurrent as a response to blackbody radiation with the temperature from 300°C to 1000°C in the range of bias voltages from -5 V to 5 V. The agreement between modelling and experimental results demonstrates that our QWIP based on asymmetrically doped GaAs/AlGaAs DQW nanomaterial is capable of remote temperature sensing. By optimizing the physical design and varying the doping level of quantum wells, we can generalize this approach to higher temperature measurements. In addition, continuous variation of bias voltage provides fast collection of large amounts of photocurrent data at various biases and improves the accuracy of remote temperature measurements via appropriate algorithm of signal processing.

  18. Theoretical and experimental study of the excitonic binding energy in GaAs/AlGaAs single and coupled double quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Lopes, E.M., E-mail: eldermantovani@yahoo.com.br [Departamento de Física, Química e Biologia, Universidade Estadual Paulista, C. P. 266, Presidente Prudente, São Paulo 17700-000 (Brazil); César, D.F. [Departamento de Física, Universidade Federal de São Carlos, C. P. 676, São Carlos, São Paulo (Brazil); Franchello, F.; Duarte, J.L.; Dias, I.F.L.; Laureto, E. [Departamento de Física, Universidade Estadual de Londrina, C. P. 6001, Londrina, Paraná (Brazil); Elias, D.C.; Pereira, M.V.M.; Guimarães, P.S.S. [Departamento de Física, Instituto de Ciências Exatas, Universidade Federal de Minas Gerais, C. P. 702, Belo Horizonte, Minas Gerais (Brazil); Quivy, A.A. [Laboratório de Novos Materiais Semicondutores, Instituto de Física, Universidade de São Paulo, C. P. 66318, São Paulo (Brazil)

    2013-12-15

    This paper discusses the theoretical and experimental results obtained for the excitonic binding energy (E{sub b}) in a set of single and coupled double quantum wells (SQWs and CDQWs) of GaAs/AlGaAs with different Al concentrations (Al%) and inter-well barrier thicknesses. To obtain the theoretical E{sub b} the method proposed by Mathieu, Lefebvre and Christol (MLC) was used, which is based on the idea of fractional-dimension space, together with the approach proposed by Zhao et al., which extends the MLC method for application in CDQWs. Through magnetophotoluminescence (MPL) measurements performed at 4 K with magnetic fields ranging from 0 T to 12 T, the diamagnetic shift curves were plotted and adjusted using two expressions: one appropriate to fit the curve in the range of low intensity fields and another for the range of high intensity fields, providing the experimental E{sub b} values. The effects of increasing the Al% and the inter-well barrier thickness on E{sub b} are discussed. The E{sub b} reduction when going from the SQW to the CDQW with 5 Å inter-well barrier is clearly observed experimentally for 35% Al concentration and this trend can be noticed even for concentrations as low as 25% and 15%, although the E{sub b} variations in these latter cases are within the error bars. As the Zhao's approach is unable to describe this effect, the wave functions and the probability densities for electrons and holes were calculated, allowing us to explain this effect as being due to a decrease in the spatial superposition of the wave functions caused by the thin inter-well barrier. -- Highlights: • Magnetophotoluminescence results from coupled double quantum wells are reported. • Theoretical and experimental values for excitonic binding energy (E{sub b}) are obtained. • The effects of increasing the inter-well barrier height and thickness on E{sub b} are discussed. • An E{sub b} reduction is observed when going from zero to the 5 Å inter-well barrier

  19. Nonequilibrium Green's function theory of resonant steady state photoconduction in a double quantum well FET subject to THz radiation at plasmon frequency

    Science.gov (United States)

    Morgenstern Horing, Norman J.; Popov, Vyacheslav V.

    2006-04-01

    Recent experimental observations by X.G. Peralta and S.J. Allen, et al. of dc photoconductivity resonances in steady source-drain current subject to terahertz radiation in a grid-gated double-quantum well FET suggested an association with plasmon resonances. This association was definitively confirmed for some parameter ranges in our detailed electrodynamic absorbance calculations. In this paper we propose that the reason that the dc photoconductance resonances match the plasmon resonances in semiconductors is based on a nonlinear dynamic screening mechanism. In this, we employ a shielded potential approximation that is nonlinear in the terahertz field to determine the nonequilibrium Green's function and associated density perturbation that govern the nonequilibrium dielectric polarization of the medium. This ''conditioning'' of the system by the incident THz radiation results in resonant polarization response at the plasmon frequencies which, in turn, causes a sharp drop of the resistive shielded impurity scattering potentials and attendant increase of the dc source-drain current. This amounts to disabling the impurity scattering mechanism by plasmon resonant behavior in nonlinear screening.

  20. Band edge tailoring of InGaAs/AlAsSb coupled double quantum wells for a monolithically integrated all-optical switch.

    Science.gov (United States)

    Feng, Jijun; Akimoto, Ryoichi; Gozu, Shin-ichiro; Mozume, Teruo; Hasama, Toshifumi; Ishikawa, Hiroshi

    2013-07-01

    We demonstrate a compact all-optical Michelson interferometer (MI) gating switch with monolithic integration of two different bandgap energies. Based on the ion-induced intermixing in InGaAs/AlAsSb coupled double quantum wells, the blueshift of the band edge can be tailored. Through phosphorus ion implantation with a dose of 5 × 10(14) cm(-2) and subsequent annealing at 720 °C for 60 s, an implanted sample can acquire a high transmittance compared with the as-grown one. Meanwhile, the cross-phase modulation (XPM) efficiency of a non-implanted sample undergoing the same annealing process decreases little. An implanted part for signal propagation and a non-implanted section for XPM are thus monolithically integrated for an MI switch by an area-selective manner. Full switching of a π-rad nonlinear phase shift is achieved with pump pulse energy of 5.6 pJ at a 10-GHz repetition rate.

  1. Influence of applied electric field on the absorption coefficient and subband distances in asymmetrical AIN/GaN coupled double quantum wells

    Institute of Scientific and Technical Information of China (English)

    Cen Long-Bin; Shen Bo; qin Zhi-Xin; Zhang Guo-Yi

    2009-01-01

    The influence of applied electric fields on the absorption coefficient and subband distances in asymmetrical AlN/GaN coupled double quantum wells (CDQWs) has been investigated by solving Schrodinger and Poisson equations self-consistently. It is found that the absorption coefficient of the intersubband transition (ISBT) between the ground state and the third excited state (1odd -2even) can be equal to zero when the electric fields are applied in asymmetrical A1N/GaN CDQWs,which is related to applied electric fields induced symmetry recovery of these states. Meanwhile,the energy distances between 1odd -2even and 1even - 2even subbands have different relationships from each other with the increase of applied electric fields due to the different polarization-induced potential drops between the lett and the right wells. The results indicate that an electrical-optical modulator operated within the opto-communication wavelength range can be realized in spite of the strong polarization-induced electric fields in asymmetrical AIN/GaN CDQWs.

  2. Influence of the technological parameters of growth on the characteristics of double tunnel-coupled InGaAs/GaAs quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Khazanova, S. V., E-mail: khazanova@phys.unn.ru; Degtyarev, V. E.; Malekhonova, N. V.; Pavlov, D. A. [Nizhni Novgorod State University (Russian Federation); Baidus, N. V. [Nizhni Novgorod State University, Physical Technical Research Institute (Russian Federation)

    2015-01-15

    A comprehensive analysis of double tunnel-coupled InGaAs/GaAs quantum well heterostructures is carried out. The real composition profiles of the structures are obtained by high-resolution transmission electron microscopy and energy-dispersive spectrometry. The resultant profiles are compared with the profile obtained by computer simulation. By solving the Schrödinger equation in combination with the Poisson equation, the energy states for quantum-confined heterostructures with initially specified and real composition profiles are calculated. The influence of a number of factors, such as the well width, barrier thickness, and the background doping level on the properties of the heterostructure is thoroughly analyzed. In this manner, the optical characteristics and their dependence on the growth technology and geometric parameters of the structures are studied. Such an approach makes it possible to refine the real geometric parameters of wells and barriers and to correct the parameters of the structure and growth technology in order to improve the optical characteristics.

  3. Quantum well lasers

    CERN Document Server

    Zory, Jr, Peter S; Kelley, Paul

    1993-01-01

    This book provides the information necessary for the reader to achieve a thorough understanding of all aspects of QW lasers - from the basic mechanism of optical gain, through the current technolgoical state of the art, to the future technologies of quantum wires and quantum dots. In view of the growing importance of QW lasers, this book should be read by all those with an active interest in laser science and technology, from the advanced student to the experienced laser scientist.* The first comprehensive book-length treatment of quantum well lasers* Provides a detailed treatment

  4. Modeling Quantum Well Lasers

    Directory of Open Access Journals (Sweden)

    Dan Alexandru Anghel

    2012-01-01

    Full Text Available In semiconductor laser modeling, a good mathematical model gives near-reality results. Three methods of modeling solutions from the rate equations are presented and analyzed. A method based on the rate equations modeled in Simulink to describe quantum well lasers was presented. For different signal types like step function, saw tooth and sinus used as input, a good response of the used equations is obtained. Circuit model resulting from one of the rate equations models is presented and simulated in SPICE. Results show a good modeling behavior. Numerical simulation in MathCad gives satisfactory results for the study of the transitory and dynamic operation at small level of the injection current. The obtained numerical results show the specific limits of each model, according to theoretical analysis. Based on these results, software can be built that integrates circuit simulation and other modeling methods for quantum well lasers to have a tool that model and analysis these devices from all points of view.

  5. Quantum well nonlinear microcavities

    Science.gov (United States)

    Oudar, J. L.; Kuszelewicz, R.; Sfez, B.; Pellat, D.; Azoulay, R.

    We report on recent progress in reducing the power threshold of all-optical bistable quantum well vertical microcavities. Significant improvements are achieved through an increase of the cavity finesse, together with a reduction of the device active layer thickness. A critical intensity of 5 μW/μm 2 has been observed on a microcavity of finesse 250, with a nonlinear medium of only 18 GaAs quantum wells of 10 nm thickness. Further improvements of the Bragg mirror quality resulted in a finesse of 700 and a power-lifetime product of 15 fJ/μm 2. Microresonator pixellation allows to obtain 2-dimensional arrays. A thermally-induced alloy-mixing technique is described, which produced a 110 meV carrier confinement energy, together with a refractive index change of -.012, averaged over the 2.6 μm nonlinear medium thickness. The resulting electrical and optical confinement is shown to improve the nonlinear characteristics, by limiting lateral carrier diffusion and light diffraction.

  6. Asymmetric GaAs n-type double δ-doped quantum wells as a source of intersubband-related nonlinear optical response: Effects of an applied electric field

    Energy Technology Data Exchange (ETDEWEB)

    Rodríguez-Magdaleno, K.A.; Martínez-Orozco, J.C.; Rodríguez-Vargas, I. [Unidad Académica de Física, Universidad Autónoma de Zacatecas, Calz. Solidaridad Esq. Paseo a La Bufa S/N. C.P. 98060 Zacatecas (Mexico); Mora-Ramos, M.E. [Facultad de Ciencias, Universidad Autónoma del Estado de Morelos, Av. Universidad 1001, CP 62209 Cuernavaca, Morelos (Mexico); Física Teórica y Aplicada, Escuela de Ingeniería de Antioquia, AA 7516 Medellín (Colombia); Grupo de Materia Condensada-UdeA, Instituto de Física, Facultad de Ciencias Exactas y Naturales, Universidad de Antioquia UdeA, Calle 70 No. 52-21, Medellín (Colombia); Duque, C.A., E-mail: cduque@fisica.udea.edu.co [Grupo de Materia Condensada-UdeA, Instituto de Física, Facultad de Ciencias Exactas y Naturales, Universidad de Antioquia UdeA, Calle 70 No. 52-21, Medellín (Colombia)

    2014-03-15

    In this work, the conduction band electron states and the associated intersubband-related linear and nonlinear optical absorption coefficient and relative refractive index change are calculated for an asymmetric double n-type δ-doped quantum well in a GaAs-matrix. The effects of an external applied static electric field are included. Values of the two-dimensional impurities density (N{sub 2d}) of each single δ-doped quantum well are taken to vary within the range of 1.0×10{sup 12} to 7.0×10{sup 12} cm{sup −2}, consistent with the experimental data growth regime. The optical responses are reported as a function of the δ-doped impurities density and the applied electric field. It is shown that single electron states and the related optical quantities are significantly affected by the structural asymmetry of the double δ-doped quantum well system. In addition, a brief comparison with the free-carrier-related optical response is presented. -- Highlights: • Nonlinear optics in asymmetric double n-type δ-doped quantum well in a GaAs-matrix. • The system is considered under external applied electric field in growth direction. • The 2D impurity density is consistent with the experimental data growth regime. • The optical quantities are significantly affected by the structural asymmetry of the system.

  7. Electromagnetically induced grating via coherently driven the n-doped In0.47Ga0.53As semiconductor quantum well nanostructure

    Science.gov (United States)

    Naseri, Tayebeh

    2016-06-01

    A new scheme for investigating electromagnetically induced grating (EIG) in the vanishing two-photon absorption condition in a three-level ladder-configuration n-doped semiconductor quantum well is presented. By applying a standing-wave field interacting with the system, the absorption and dispersion of the probe field will change with the spatial periodical modulation. It is shown that the first-order diffraction intensity sensitively depends on the intensity of coupling fields, detuning of applied laser fields and interaction length. Moreover, it can reach its maximum on varying the system parameters. A novel result shows the considerable efficiency of higher order diffractions is significantly improved via relative phase between applied laser fields. Furthermore, it is found that the intensity of the switching and coupling fields can increase the efficiency of the phase grating in the present model. Such a unique feature of the cooperative Electromagnetic Induced Grating may be extended to further develop diffraction based new photonic devices in quantum information networks and new photonic devices in all-optical switching and optical imaging.

  8. Refraction index modulation induced with transverse electric field in double tunnel-coupled GaAs/AlGaAs quantum wells

    Science.gov (United States)

    Shumilov, A. A.; Vinnichenko, M. Ya; Balagula, R. M.; Vorobjev, L. E.; Firsov, D. A.; Kulagina, M. M.; Vasil'iev, A. P.; Duque, C. A.; Tiutiunnyk, A.; Akimov, V.; Restrepo, R. L.; Tulupenko, V. N.; Ter-Martirosyan, A. L.

    2015-11-01

    Modulation of refraction index under transverse electric field was studied in structures with multiple tunnel-coupled GaAs/AlGaAs quantum wells in the spectral range corresponding to intersubband light absorption. The change of refraction index in electric field was calculated using Kramers-Kronig relation and experimentally determined spectra of intersubband light absorption in equilibrium conditions and under transverse electric field.

  9. Comparative study of the hydrostatic pressure and temperature effects on the impurity-related optical properties in single and double GaAs-Ga{sub 1-x}Al{sub x}As quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Odhiambo Oyoko, H. [Department of Physics, Westville Campus, University of KwaZulu-Natal, Private Bag X 54001, Durban 4000 (South Africa); Porras-Montenegro, N. [Departamento de Fisica, Universidad del Valle, AA 25360, Cali (Colombia); Lopez, S.Y. [Facultad de Educacion, Universidad de Antioquia, AA 1226, Medellin (Colombia); Duque, C.A. [Instituto de Fisica, Universidad de Antioquia, AA 1226, Medellin (Colombia)

    2007-07-01

    Using a variational technique within the effective mass approximation we have carried out a comparative study of the effect of hydrostatic pressure and temperature on the shallow-impurity related optical absorption spectra in GaAs-Ga{sub 1-x}Al{sub x}As single and double quantum wells. The results show a pressure dependent read-shift and a temperature dependent blue-shift in the optical absorption spectra. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  10. Exciton-related energies of the 1s-like states of excitons in GaAs-Ga{sub 1-x}Al{sub x}As double quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Miranda, Guillermo L. [Fisica Teorica y Aplicada, Escuela de Ingenieria de Antioquia, A.A. 7516, Medellin (Colombia); Mora-Ramos, M.E. [Facultad de Ciencias, Universidad Autonoma del Estado de Morelos, Av. Universidad 1001, C.P. 62209, Cuernavaca, Morelos (Mexico); Duque, C.A., E-mail: cduque_echeverri@yahoo.es [Instituto de Fisica, Universidad de Antioquia, AA 1226, Medellin (Colombia)

    2012-10-15

    The dependencies of the binding energies of the lowest four 1s-like exciton states in GaAs-(Ga,Al)As coupled double quantum wells (CDQW) on the geometric parameters of the system are theoretically studied. A variational approach, together with the parabolic band and effective mass approximations, were considered in order to perform the numerical calculations. It is shown that in the case of a symmetric system there is a degeneracy between the heavy-hole even and odd states and this degeneracy can be removed by the presence of a sufficiently narrow middle barrier. In contrast to this fact, the electron even and odd states are never degenerated. It is detected that, if the system is asymmetric, there will appear binding energies anticrossings between the heavy-hole states at the point of the asymmetric {yields} symmetric QW transition. - Highlights: Black-Right-Pointing-Pointer Study of 1s-like exciton states in double quantum wells. Black-Right-Pointing-Pointer Binding energy decreases with the presence of second well. Black-Right-Pointing-Pointer Binding energy of (2,2) state can be larger than (1,1) state. Black-Right-Pointing-Pointer Central barrier can remove degeneracy of states. Black-Right-Pointing-Pointer Anticrossing between states can be induced via symmetries.

  11. Quantum-Well Thermophotovoltaic Cells

    Science.gov (United States)

    Freudlich, Alex; Ignatiev, Alex

    2009-01-01

    Thermophotovoltaic cells containing multiple quantum wells have been invented as improved means of conversion of thermal to electrical energy. The semiconductor bandgaps of the quantum wells can be tailored to be narrower than those of prior thermophotovoltaic cells, thereby enabling the cells to convert energy from longer-wavelength photons that dominate the infrared-rich spectra of typical thermal sources with which these cells would be used. Moreover, in comparison with a conventional single-junction thermophotovoltaic cell, a cell containing multiple narrow-bandgap quantum wells according to the invention can convert energy from a wider range of wavelengths. Hence, the invention increases the achievable thermal-to-electrical energy-conversion efficiency. These thermophotovoltaic cells are expected to be especially useful for extracting electrical energy from combustion, waste-heat, and nuclear sources having temperatures in the approximate range from 1,000 to 1,500 C.

  12. ASYMMETRICAL COUPLING DOUBLE QUANTUM WELL INTERMIXING INDUCED BY COMBINATORIAL PROTON IMPLANTATION%组合注入质子导致不对称耦合双量子阱界面混合效应研究

    Institute of Scientific and Technical Information of China (English)

    缪中林; 陈平平; 蔡炜颖; 李志锋; 袁先漳; 刘平; 史国良; 徐文兰; 陆卫; 陈昌明; 朱德彰; 潘浩昌; 胡军; 李明乾

    2001-01-01

    用分子束外延系统(MBE)生长了GaAs/AlGaAs不对称耦合双量子阱(ACDQW),采用组合注入质子的方法,在同一块衬底上获得了不同注入剂量的GaAs/AlGaAs不对称耦合双量子阱单元,没有经过快速热退火的过程,在常温下测量了不同注入剂量量子阱单元的显微光荧光谱和光调制反射光谱,发现了各区域子带间跃迁能量最大变化范围达到81meV.由于样品未作高温热退火处理,为此由Al组分误差函数模型推导的扩散长度要大大高于扩散系数公式.耦合量子阱的界面混合效应对于质子注入非常敏感.%With combinatorial proton implantation, we obtained several areas with different implantation doses in single wafer of GaAs/AlGaAs asymmetry coupling double quantum well grown by MBE, and studied the optical characteristics with photoluminescence (PL) and photo-modulated reflectance(PR). Without rapid thermal annealing, maximum transition energy shift 81 meV was obtained in single wafer. The diffusion lengths of Al component calculated from error function were larger than that calculated from coefficient of diffusion formula. The interface effect of double quantum well is sensitive to proton implantation.

  13. Coherent excitonic nonlinearity versus inhomogeneous broadening in single quantum wells

    DEFF Research Database (Denmark)

    Langbein, Wolfgang Werner; Borri, Paola; Hvam, Jørn Märcher;

    1998-01-01

    The coherent response of excitons in semiconductor nanostructures, as measured in four wave mixing (FWM) experiments, depends strongly on the inhomogeneous broadening of the exciton transition. We investigate GaAs-AlGaAs single quantum wells (SQW) of 4 nm to 25 nm well width. Two main mechanisms...

  14. Quantum Wells in Photovoltaic Cells

    CERN Document Server

    Rohr, C; Ballard, I M; Bushnell, D B; Connolly, J P; Daukes, N J Ekins-; Barnham, K W J

    2016-01-01

    The fundamental efficiency limit of a single bandgap solar cell is about 31% at one sun with a bandgap of about Eg = 1.35 eV (1), determined by the trade-off of maximising current with a smaller bandgap and voltage with a larger bandgap. Multiple bandgaps can be introduced to absorb the broad solar spectrum more efficiently. This can be realised in multi- junction cells, for example, where two or more cells are stacked on top of each other either mechanically or monolithically connected by a tunnel junction. An alternative or complementary (see section 1.4) approach is the quantum well cell (QWC).

  15. Silicon Germanium Quantum Well Solar Cell Project

    Data.gov (United States)

    National Aeronautics and Space Administration — Quantum-well structures embodied on single crystal silicon germanium drastically enhanced carrier mobilities.  The cell-to-cell circuits of quantum-well PV...

  16. Ultra Thin Quantum Well Materials

    Energy Technology Data Exchange (ETDEWEB)

    Dr Saeid Ghamaty

    2012-08-16

    This project has enabled Hi-Z technology Inc. (Hi-Z) to understand how to improve the thermoelectric properties of Si/SiGe Quantum Well Thermoelectric Materials. The research that was completed under this project has enabled Hi-Z Technology, Inc. (Hi-Z) to satisfy the project goal to understand how to improve thermoelectric conversion efficiency and reduce costs by fabricating ultra thin Si/SiGe quantum well (QW) materials and measuring their properties. In addition, Hi-Z gained critical new understanding on how thin film fabrication increases the silicon substrate's electrical conductivity, which is important new knowledge to develop critical material fabrication parameters. QW materials are constructed with alternate layers of an electrical conductor, SiGe and an electrical insulator, Si. Film thicknesses were varied, ranging from 2nm to 10nm where 10 nm was the original film thickness prior to this work. The optimum performance was determined at a Si and SiGe thickness of 4nm for an electrical current and heat flow parallel to the films, which was an important conclusion of this work. Essential new information was obtained on how the Si substrate electrical conductivity increases by up to an order of magnitude upon deposition of QW films. Test measurements and calculations are accurate and include both the quantum well and the substrate. The large increase in substrate electrical conductivity means that a larger portion of the electrical current passes through the substrate. The silicon substrate's increased electrical conductivity is due to inherent impurities and thermal donors which are activated during both molecular beam epitaxy and sputtering deposition of QW materials. Hi-Z's forward looking cost estimations based on future high performance QW modules, in which the best Seebeck coefficient and electrical resistivity are taken from separate samples predict that the electricity cost produced with a QW module could be achieved at <$0.35/W

  17. Double electromagnetically induced transparency phenomenon in an asymmetric N-type semiconductor quantum well%非对称半导体双量子阱中的双电磁感应透明现象

    Institute of Scientific and Technical Information of China (English)

    张蔚曦; 张愉; 金慧

    2016-01-01

    The characteristics of optical absorption in an asymmetric four-level N-type semiconductor quantum well with the cross-coupling longitude-optical phonons (CCLOP) relaxation were studied. In the linear range, it shows that the electromagnetically induced transparency (EIT) relies on the coherence control of the optical fields and the CCLOP relaxation. Especially, there exhibits a double-EIT when the transition frequency between the hole and anti-bonding states is rather large. Interestingly, there appears a near-perfect double-EIT phenomenon when increasing the CCLOP relaxation. It is expected that these results may exhibit some potential applications in the all-optical switching and other optical information engineering related issues.%对在交叉耦合纵波光学声子(Cross-coupling Longitude-optical Phonons,简称CCLOP)弛豫时四能级非对称N型半导体量子阱系统的光吸收特性进行了研究。研究表明,在线性范围内,在该系统中能够实现电磁感应透明效应(Electromagnetically Induced Transparency,简称EIT),并且这种EIT效应依赖于光场与系统的谐振控制和CCLOP 弛豫;尤其是当空穴态和反键态之间的跃迁频率较大时,系统会出现双EIT现象。有趣的是,当CCLOP弛豫增大时,将出现近乎完美的双EIT现象。研究结果在全光开关和其他的光信息工程中有着潜在的应用。

  18. Excitons in asymmetric quantum wells

    Science.gov (United States)

    Grigoryev, P. S.; Kurdyubov, A. S.; Kuznetsova, M. S.; Ignatiev, I. V.; Efimov, Yu. P.; Eliseev, S. A.; Petrov, V. V.; Lovtcius, V. A.; Shapochkin, P. Yu.

    2016-09-01

    Resonance dielectric response of excitons is studied for the high-quality InGaAs/GaAs heterostructures with wide asymmetric quantum wells (QWs). To highlight effects of the QW asymmetry, we have grown and studied several heterostructures with nominally square QWs as well as with triangle-like QWs. Several quantum confined exciton states are experimentally observed as narrow exciton resonances. A standard approach for the phenomenological analysis of the profiles is generalized by introducing different phase shifts for the light waves reflected from the QWs at different exciton resonances. Good agreement of the phenomenological fit to the experimentally observed exciton spectra for high-quality structures allowed us to reliably obtain parameters of the exciton resonances: the exciton transition energies, the radiative broadenings, and the phase shifts. A direct numerical solution of the Schrödinger equation for the heavy-hole excitons in asymmetric QWs is used for microscopic modeling of the exciton resonances. Remarkable agreement with the experiment is achieved when the effect of indium segregation is taken into account. The segregation results in a modification of the potential profile, in particular, in an asymmetry of the nominally square QWs.

  19. Spin photocurrents in quantum wells

    CERN Document Server

    Ganichev, S D

    2003-01-01

    Spin photocurrents generated by homogeneous optical excitation with circularly polarized radiation in quantum wells (QWs) are reviewed. The absorption of circularly polarized light results in optical spin orientation due to the transfer of the angular momentum of photons to electrons of a two-dimensional electron gas. It is shown that in QWs belonging to one of the gyrotropic crystal classes a non-equilibrium spin polarization of uniformly distributed electrons causes a directed motion of electrons in the plane of the QW. A characteristic feature of this electric current, which occurs in unbiased samples, is that it reverses its direction upon changing the radiation helicity from left-handed to right-handed and vice versa. Two microscopic mechanisms are responsible for the occurrence of an electric current linked to a uniform spin polarization in a QW: the spin polarization-induced circular photogalvanic effect and the spin-galvanic effect. In both effects the current flow is driven by an asymmetric distribut...

  20. Quantum wells for high-efficiency photovoltaics

    Science.gov (United States)

    Alonso-Álvarez, Diego; Ekins-Daukes, Nicholas

    2016-03-01

    Over the last couple of decades, there has been an intense research on strain balanced semiconductor quantum wells (QW) to increase the efficiency of multi-junction solar (MJ) solar cells grown monolithically on germanium. So far, the most successful application of QWs have required just to tailor a few tens of nanometers the absorption edge of a given subcell in order to reach the optimum spectral position. However, the demand for higher efficiency devices requiring 3, 4 or more junctions, represents a major difference in the challenges QWs must face: tailoring the absorption edge of a host material is not enough, but a complete new device, absorbing light in a different spectral region, must be designed. Among the most important issues to solve is the need for an optically thick structure to absorb enough light while keeping excellent carrier extraction using highly strained materials. Improvement of the growth techniques, smarter device designs - involving superlattices and shifted QWs, for example - or the use of quantum wires rather than QWs, have proven to be very effective steps towards high efficient MJ solar cells based on nanostructures in the last couple of years. But more is to be done to reach the target performances. This work discusses all these challenges, the limitations they represent and the different approaches that are being used to overcome them.

  1. Current-Enhanced Quantum Well Solar Cells

    Institute of Scientific and Technical Information of China (English)

    LOU Chao-Gang; SUN Qiang; XU Jun; ZHANG Xiao-Bing; LEI Wei; WANG Bao-Ping; CHEN Wen-Jun; QIAO Zai-Xiang

    2006-01-01

    We present the experimental results that demonstrate the enhancement of the short-circuit current of quantum well solar cells. The spectral response shows that the introduction of quantum wells extends the absorption spectrum of solar cells. The current densities under different truncated spectrums significantly increase, showing that quantum well solar cells are suitable to be the middle cells of GaInP/GaAs/Ge triple-junction solar cells to increase their overall conversion efficiency.

  2. Pyroelectric Quantum Well Energy Harvesters Project

    Data.gov (United States)

    National Aeronautics and Space Administration — We propose the investigation of pyroelectric energy harvesters with enhanced efficiencies through quantum wells induced by a multilayer design.  Pyroelectric...

  3. Self-assembly of double helical nanostructures inside carbon nanotubes.

    Science.gov (United States)

    Lv, Cheng; Xue, Qingzhong; Shan, Meixia; Jing, Nuannuan; Ling, Cuicui; Zhou, Xiaoyan; Jiao, Zhiyong; Xing, Wei; Yan, Zifeng

    2013-05-21

    We use molecular dynamics (MD) simulations to show that a DNA-like double helix of two poly(acetylene) (PA) chains can form inside single-walled carbon nanotubes (SWNTs). The computational results indicate that SWNTs can activate and guide the self-assembly of polymer chains, allowing them to adopt a helical configuration in a SWNT through the combined action of the van der Waals potential well and the π-π stacking interaction between the polymer and the inner surface of SWNTs. Meanwhile both the SWNT size and polymer chain stiffness determine the outcome of the nanostructure. Furthermore, we also found that water clusters encourage the self-assembly of PA helical structures in the tube. This molecular model may lead to a better understanding of the formation of a double helix biological molecule inside SWNTs. Alternatively, it could form the basis of a novel nanoscale material by utilizing the 'empty' spaces of SWNTs.

  4. Magnetoluminescence characterization of quantum well structures

    Energy Technology Data Exchange (ETDEWEB)

    Jones, E.D.; Kurtz, S.R.

    1995-03-01

    Three applications of magnetic field effects upon the photoluminescence spectrum which provide unique information about semiconductor quantum well structures are presented. The first example shows data which provide a quantitative measure of both the conduction and valence-band the energy dispersion curves for an InGaAs/GaAs single-strained-quantum well and a GaAs/AlGaAs lattice-matched single quantum well. The second subject discusses magnetoluminescence data which provides a clear demonstration for the existence of spectral shifts related to ionized-impurity scattering and the third study involves infrared magnetoluminescence measurements on narrow bandgap semiconductor alloys and heterostructures.

  5. Energy transfer in organic multilayer quantum well structure and its application to OLEDs

    Institute of Scientific and Technical Information of China (English)

    ZHAO De-wei; SONG Shu-fang; ZHAO Su-ling; XU Zheng

    2007-01-01

    We fabricate a series of samples and OLEDs with organic multilayer quantum well structure, which consist of alternate PBD and Alq3. Both PBD and Alq3 are electron-transporting materials, and PBD is used as potential barrier layer, while Alq3 is used as potential well layer and emitting layer. Compared with double-layer structure, the luminescent characteristics of organic samples and diodes with quantum well structure are investigated and the quantum well structure helps the energy transfer between well layer and barrier layer. The quantum well structure makes carriers disperse in the different well layers and then increases the number of excitons to enhance the efficiency of the recombination.

  6. Anisotropic Spin Splitting in Step Quantum Wells

    Institute of Scientific and Technical Information of China (English)

    HAO Ya-Fei; CHEN Yong-Hai; HAO Guo-Dong; WANG Zhan-Guo

    2009-01-01

    By the method of finite difference,the anisotropic spin splitting of the Alx Ga1-x As/GaAs/Aly Ga1-y As/Alx Ga1-x As step quantum wells (QWs) are theoretically investigated considering the interplay of the bulk inversion asymmetry and structure inversion asymmetry induced by step quantum well structure and external electric field.We demonstrate that the anisotropy of the total spin splitting can be controlled by the shape of the QWs and the external electric field.The interface related Rashba effect plays an important effect on the anisotropic spin splitting by influencing the magnitude of the spin splitting and the direction of electron spin.The Rashba spin splitting presents in the step quantum wells due to the interface related Rashba effect even without external electric field or magnetic field.

  7. Photonic crystal slab quantum well infrared photodetector

    Science.gov (United States)

    Kalchmair, S.; Detz, H.; Cole, G. D.; Andrews, A. M.; Klang, P.; Nobile, M.; Gansch, R.; Ostermaier, C.; Schrenk, W.; Strasser, G.

    2011-01-01

    In this letter we present a quantum well infrared photodetector (QWIP), which is fabricated as a photonic crystal slab (PCS). With the PCS it is possible to enhance the absorption efficiency by increasing photon lifetime in the detector active region. To understand the optical properties of the device we simulate the PCS photonic band structure, which differs significantly from a real two-dimensional photonic crystal. By fabricating a PCS-QWIP with 100x less quantum well doping, compared to a standard QWIP, we are able to see strong absorption enhancement and sharp resonance peaks up to temperatures of 170 K.

  8. Mixed biexcitons in single quantum wells

    DEFF Research Database (Denmark)

    Wagner, Hans Peter; Langbein, Wolfgang Werner; Hvam, Jørn Märcher

    1999-01-01

    Biexcitonic complexes in a ZnSe single quantum well are investigated by spectrally resolved four-wave mixing (FWM). The formation of heavy-heavy-hole XXh and of mixed heavy-light-hole XXm biexcitons showing binding energies of Delta(h) = 4.8 meV and Delta(m)= 2.8 meV is identified by polarization...

  9. Spectroscopy of GaAs quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    West, L.C.

    1985-07-01

    A new type of optical dipole transition in GaAs quantum wells has been observed. The dipole occurs between two envelope states of the conduction band electron wavefunction, and is called a quantum well envelope state transition (QWEST). The QWEST is observed by infrared absorption in three different samples with quantum well thicknesses 65, 82, and 92 A and resonant energies of 152, 121, and 108 MeV, respectively. The oscillator strength is found to have values of over 12, in good agreement with prediction. The linewidths are seen as narrow as 10 MeV at room temperature and 7 MeV at low temperature, thus proving a narrow line resonance can indeed occur between transitions of free electrons. Techniques for the proper growth of these quantum well samples to enable observation of the QWEST have also been found using (AlGa)As compounds. This QWEST is considered to be an ideal material for an all optical digital computer. The QWEST can be made frequency matched to the inexpensive Carbon Dioxide laser with an infrared wavelength of 10 microns. The nonlinearity and fast relaxation time of the QWEST indicate a logic element with a subpicosecond switch time can be built in the near future, with a power level which will eventually be limited only by the noise from a lack of quanta to above approximately 10 microwatts. 64 refs., 35 figs., 6 tabs.

  10. Recombination Dynamics in Quantum Well Semiconductor Structures

    Science.gov (United States)

    Fouquet, Julie Elizabeth

    Time-resolved and time-integrated photoluminescence as a function of excitation energy density have been observed in order to study recombination dynamics in GaAs/Al(,x)Ga(,1 -x)As quantum well structures. The study of room temperature photoluminescence from the molecular beam epitaxy (MBE) -grown multiple quantum well structure and photoluminescence peak energy as a function of tem- perature shows that room temperature recombination at excitation densities above the low 10('16) cm('-3) level is due to free carriers, not excitons. This is the first study of time-resolved photoluminescence of impurities in quantum wells; data taken at different emission wave- lengths at low temperatures shows that the impurity-related states at photon energies lower than the free exciton peaks luminesce much more slowly than the free exciton states. Results from a similar structure grown by metal -organic chemical vapor deposition (MOCVD) are explained by saturation of traps. An unusual increase in decay rate observed tens of nanoseconds after excitation is probably due to carriers falling out of the trap states. Since this is the first study of time-resolved photoluminescence of MOCVD-grown quantum well structures, this unusual behavior may be realted to the MOCVD growth process. Further investigations indi- cate that the traps are not active at low temperatures; they become active at approximately 150 K. The traps are probably associated with the (hetero)interfaces rather than the bulk Al(,x)Ga(,1-x)As material. The 34 K photoluminescence spectrum of this sample revealed a peak shifted down by approximately 36 meV from the main peak. Time-resolved and time-integrated photoluminescence results here show that this peak is not a stimulated phonon emission sideband, but rather is an due to an acceptor impurity, probably carbon. Photo- luminescence for excitation above and below the barrier bandgap shows that carriers are efficiently collected in the wells in both single and multiple

  11. Strained quantum well photovoltaic energy converter

    Science.gov (United States)

    Freundlich, Alexandre (Inventor); Renaud, Philippe (Inventor); Vilela, Mauro Francisco (Inventor); Bensaoula, Abdelhak (Inventor)

    1998-01-01

    An indium phosphide photovoltaic cell is provided where one or more quantum wells are introduced between the conventional p-conductivity and n-conductivity indium phosphide layer. The approach allows the cell to convert the light over a wider range of wavelengths than a conventional single junction cell and in particular convert efficiently transparency losses of the indium phosphide conventional cell. The approach hence may be used to increase the cell current output. A method of fabrication of photovoltaic devices is provided where ternary InAsP and InGaAs alloys are used as well material in the quantum well region and results in an increase of the cell current output.

  12. Quantum Well Infrared Photodetectors Physics and Applications

    CERN Document Server

    Schneider, Harald

    2007-01-01

    Addressed to both students as a learning text and scientists/engineers as a reference, this book discusses the physics and applications of quantum-well infrared photodetectors (QWIPs). It is assumed that the reader has a basic background in quantum mechanics, solid-state physics, and semiconductor devices. To make this book as widely accessible as possible, the treatment and presentation of the materials is simple and straightforward. The topics for the book were chosen by the following criteria: they must be well-established and understood; and they should have been, or potentially will be, used in practical applications. The monograph discusses most aspects relevant for the field but omits, at the same time, detailed discussions of specialized topics such as the valence-band quantum wells.

  13. Entangled States and the Gravitational Quantum Well

    CERN Document Server

    Alves, Rui; Bertolami, Orfeu

    2016-01-01

    We study the continuous variable entanglement of a system of two particles under the influence of Earth's gravitational field. We determine a phase-space description of this bipartite system by calculating its Wigner function and verify its entanglement by applying a generalization of the PPT criterion for non-Gaussian states. We also examine the influence of gravity on an idealized entanglement protocol to be shared between stations at different potentials based on the correlation of states of the gravitational quantum well.

  14. Photoemission of switchable mirrors and quantum wells

    OpenAIRE

    Koitzsch, Christian; Aebi, Philippe

    2005-01-01

    This thesis focuses on the electronic properties of materials, which were explored with Angle Resolved Photoemission (ARPES) and Density Functional Theory (DFT). The natural fingerprint of electronic phenomena in crystalline solids, e.g. in this thesis the hydrogen-induced metal-insulator transition and the formation of standing electron waves in quantum wells, is the k-resolved band structure or in short the E(k) relation in the solid. The experimental technique to explore the occupied band ...

  15. Resonant Optical Absorption in Semiconductor Quantum Wells

    Institute of Scientific and Technical Information of China (English)

    YU Li-Yuan; CAO Jun-Cheng

    2004-01-01

    @@ We have calculated the intraband photon absorption coefficients of hot two-dimensional electrons interacting with polar-optical phonon modes in quantum wells. The dependence of the photon absorption coefficients on the photon wavelength λ is obtained both by using the quantum mechanical theory and by the balance-equation theory. It is found that the photon absorption spectrum displays a local resonant maximum, corresponding to LO energy, and the absorption peak vanishes with increasing the electronic temperature.

  16. Raman spectroscopy of single quantum well wires

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    We used the micro-Raman spectroscopy to investigate the V-grooved quantum well wires (QWWs), and first observed and assigned the Raman spectra of single QWW. They were the disorder induced modes at 223 and 243 cm-1, confined LO mode of GaAs QWW at 267 cm1, and higher order peaks of disorder induced modes at 488 and 707 cm-1.

  17. Energy loss rate in disordered quantum well

    Energy Technology Data Exchange (ETDEWEB)

    Tripathi, P.; Ashraf, S. S. Z. [Centre of Excellence in Nanomaterials, Faculty of Engineering and Technology, Aligarh Muslim University, Aligarh-202002 (India); Hasan, S. T. [Physics Department, Faculty of Science, The M.S. University of Baroda, Vadodara-390002 (India); Sharma, A. C. [Physics Department, Sibli National College, Azamgarh-276128 (India)

    2014-04-24

    We report the effect of dynamically screened deformation potential on the electron energy loss rate in disordered semiconductor quantum well. Interaction of confined electrons with bulk acoustic phonons has been considered in the deformation coupling. The study concludes that the dynamically screened deformation potential coupling plays a significant role as it substantially affects the power dependency of electron relaxation on temperature and mean free path.

  18. Wave-packet dynamics in quantum wells

    DEFF Research Database (Denmark)

    Kuznetsov, A. V.; Sanders, G. D.; Stanton, C. J.

    1995-01-01

    It has been recently recognized that in bulk semiconductors the displacement current caused by ultrafast optical generation of ''polarized pairs'' in the applied de field is an important mechanism of charge transport in addition to the usual transport current. In quantum-well systems, this polari......It has been recently recognized that in bulk semiconductors the displacement current caused by ultrafast optical generation of ''polarized pairs'' in the applied de field is an important mechanism of charge transport in addition to the usual transport current. In quantum-well systems......, this polarized pair creation is thought to be the only source of photocurrent at the early stages of photoexcitation since the bulk like transport current is inhibited by the barriers. In this work we perform a full quantum-mechanical analysis of ultrafast optical excitation in a de-biased quantum well. We take...... larger than the well width (for long pulses and/or narrow wells), we recover the polarized pairs behavior of the photocurrent. For shorter pulses, when the coherence length becomes comparable to the well width, the photocurrent exhibits quantum beats. Finally, for very short pulses (around 10 fs) we find...

  19. Probing light emission from quantum wells within a single nanorod

    Science.gov (United States)

    Bruckbauer, Jochen; Edwards, Paul R.; Bai, Jie; Wang, Tao; Martin, Robert W.

    2013-09-01

    Significant improvements in the efficiency of optoelectronic devices can result from the exploitation of nanostructures. These require optimal nanocharacterization techniques to fully understand and improve their performance. In this study we employ room temperature cathodoluminescence hyperspectral imaging to probe single GaN-based nanorods containing multiple quantum wells (MQWs) with a simultaneous combination of very high spatial and spectral resolution. We have investigated the strain state and carrier transport in the vicinity of the MQWs, demonstrating the high efficiencies resulting from reduced electric fields. Power-dependent photoluminescence spectroscopy of arrays of these nanorods confirms that their fabrication results in partial strain relaxation in the MQWs. Our technique allows us to interrogate the structures on a sufficiently small length scale to be able to extract the important information.

  20. The Physics of Quantum Well Infrared Photodetectors

    CERN Document Server

    Choi, K K

    1999-01-01

    In the past, infrared imaging has been used exclusively for military applications. In fact, it can also be useful in a wide range of scientific and commercial applications. However, its wide spread use was impeded by the scarcity of the imaging systems and its high cost. Recently, there is an emerging infrared technology based on quantum well intersubband transition in III-V compound semiconductors. With the new technology, these impedances can be eliminated and a new era of infrared imaging is in sight. This book is designed to give a systematic description on the underlying physics of the ne

  1. Intermixing effects on emission properties of InGaN/GaN coupled Quantum wells

    KAUST Repository

    Susilo, Tri B.

    2015-02-01

    Intermixing processes in quantum wells have been extensively studied in order to modify characteristic of semiconductor devices such as LEDs. Controlling the band gap of material by introducing intermixing process can be used to enable broadband and controllable emission of LEDs. Quantum well intermixing (QWI) in InGaN/GaN double quantum well (DQW) is discussed in this paper. By varying the interdiffusion and separation lengths, the effects of intermixing process on the quantum eigen energies of the wells are studied. The investigation is carried out using a homegrown Quantum-FDTD simulator. © 2015 IEEE.

  2. Physics of strained quantum well lasers

    CERN Document Server

    Loehr, John P

    1998-01-01

    When this publisher offered me the opportunity to \\\\Tite a book, some six years ago, I did not hesitate to say yes. I had just spent the last four years of graduate school struggling to understand the physics of strained quantum well lasers, and it seemed to me the whole experience was much more difficult that it should have been. For although many of the results I needed were easy to locate, the underlying physical premises and intervening steps were not. If only I had a book providing the derivations, I could have absorbed them and gone on my way. Such a book lies before you. It provides a unified and self-contained descrip­ tion of the essential physics of strained quantum well lasers, starting from first principles whenever feasible. The presentation I have chosen requires only the standard introductory background in quantum mechanics, solid state physics, and electromagnetics expected of entering graduate students in physics or elec­ trical engineering. A single undergraduate course in each of these su...

  3. Wavelength sensitive detector based on ICD in two coupled quantum wells

    Science.gov (United States)

    Goldzak, Tamar; Gilary, Ido; Moiseyev, Nimrod

    2014-05-01

    We design a wavelength sensitive detector based on inter coulombic decay (ICD) mechanism in a two-quantum well nano-structure. The two coupled quantum wells are designed to satisfy the specific conditions which allow the ICD to occur. In this setup, by absorbing light an electron in one well is excited. Its relaxation back to the ground state is a non-radiative process which transfers the excess energy to the ionization of the electron in the neighboring well into the continuum. Only radiation with a specific wavelength will be absorbed, when the wavelength matches the excitation energy in the quantum well. By applying a weak bias a current is obtained even when light with a very low intensity is absorbed. For the ICD to be dominant decay mechanism it must prevail over all other possible competitive decay processes. We have found that the lifetime of the ICD is on the timescale of picoseconds. Control over the ICD lifetime can be achieved by variation of different parameters in the two quantum well nano-structure. The most useful parameter is the distance between the two quantum wells. We show that as the distance decreases the decay rate of the ICD increases. Furthermore the distance can be tuned such that the emitted electron would be in a metastable state in the continuum (a resonance state); this causes the life time of the ICD to be an order of magnitude smaller, and improves the efficiency of the ICD.

  4. Electrical injection to contactless near-surface InGaN quantum well

    Energy Technology Data Exchange (ETDEWEB)

    Riuttanen, L., E-mail: lauri.riuttanen@aalto.fi; Svensk, O.; Suihkonen, S. [Department of Micro- and Nanosciences, Aalto University, P.O. Box 13500, FI-00076 Aalto (Finland); Kivisaari, P.; Oksanen, J. [Department of Biomedical Engineering and Computational Science, Aalto University, P.O. Box 12200, FI-00076 Aalto (Finland)

    2015-08-03

    Charge injection to the prevailing and emerging light-emitting devices is almost exclusively based on the double heterojunction (DHJ) structures that have remained essentially unchanged for decades. In this letter, we report the excitation of a near surface indium gallium nitride (InGaN) quantum well (QW) by bipolar carrier diffusion from a nearby electrically excited pn-homojunction. The demonstrated near surface QW emitter is covered only by a 10 nm GaN capping leaving the light-emitting mesa perfectly free of metals, other contact, or current spreading structures. The presented proof-of-principle structure, operating approximately with a quantum efficiency of one fifth of a conventional single QW reference structure, provides conclusive evidence of the feasibility of using diffusion injection to excite near surface light-emitting structures needed, e.g., for developing light emitters or photo-voltaic devices based on nanoplasmonics or free-standing nanowires. In contrast to the existing DHJ solutions or optical pumping, our approach allows exciting nanostructures without the need of forming a DHJ, absorbing layers or even electrical contacts on the device surface.

  5. Experimental signatures of the inverted phase in InAs/GaSb coupled quantum wells

    Science.gov (United States)

    Karalic, Matija; Mueller, Susanne; Mittag, Christopher; Pakrouski, Kiryl; Wu, QuanSheng; Soluyanov, Alexey A.; Troyer, Matthias; Tschirky, Thomas; Wegscheider, Werner; Ensslin, Klaus; Ihn, Thomas

    2016-12-01

    Transport measurements are performed on InAs/GaSb double quantum wells at zero and finite magnetic fields applied parallel and perpendicular to the quantum wells. We investigate a sample in the inverted regime where electrons and holes coexist, and compare it with another sample in the noninverted semiconducting regime. The activated behavior in conjunction with a strong suppression of the resistance peak at the charge neutrality point in a parallel magnetic field attest to the topological hybridization gap between electron and hole bands in the inverted sample. We observe an unconventional Landau level spectrum with energy gaps modulated by the magnetic field applied perpendicular to the quantum wells. This is caused by a strong spin-orbit interaction provided jointly by the InAs and the GaSb quantum wells.

  6. 对称双势垒量子阱中自旋极化输运的时间特性%Time of spin-polarized tunneling through a symmetric double-barrier quantum well structure∗

    Institute of Scientific and Technical Information of China (English)

    王瑞琴; 宫箭†; 武建英; 陈军

    2013-01-01

      电子的隧穿时间是描述量子器件动态工作范围的重要指标。本文考虑k3 Dresselhaus自旋轨道耦合效应对系统哈密顿量的修正,结合转移矩阵方法和龙格-库塔法来解含时薛定谔方程,进而讨论了电子在非磁半导体对称双势垒结构中的透射系数及隧穿寿命等问题。研究结果发现:由于k3 Dresselhaus自旋轨道耦合效应使自旋简并消除,并在时间域内得到了表达,导致自旋向上和自旋向下电子的透射峰发生了自旋劈裂;不同自旋取向的电子构建时间和隧穿寿命不同,这是导致自旋极化的原因之一;电子的自旋极化在时间上趋于稳定。%Tunneling time is an important factor to describe quantum electronic device. In this paper, the dynamic problem of spin-dependent tunneling is investigated by solving the time-dependent Schr¨odinger equation. The transmission coefficient and tunneling lifetime are discussed by use of mixing transfer-matrix and Runge-Kutta method. The k3 Dresselhaus term is considered to correct the effective Hamiltonian of the system in our calculation. The results show that the transmission peak of the electrons with different spin orien-tations split obviously. The building time and the tunneling lifetime through the double-barrier structure of AlxGa1−xSb material are different for the spin-down electron and spin-up electron. These time-dependent properties depend on the electronic spin orientation. It can be considered as one of reasons for spin polarization to appear. Additionally, the steady spin-polarization emerges in the well due to the k3 Dresselhaus spin-orbit coupling.

  7. Quantum well intermixing for photonic integrated circuits

    Science.gov (United States)

    Sun, Xiaolan

    2007-12-01

    In this thesis, several aspects of GaAsSb/AlSb multiple quantum well (MQW) heterostructures have been studied. First, it was shown that the GaAsSb MQWs with a direct band gap near 1.5 mum at room temperature could be monolithically integrated with AlGaSb/AlSb or AlGaAsSb/AlAsSb Bragg mirrors, which can be applied to Vertical Cavity Surface Emitting Lasers (VCSELs). Secondly, an enhanced photoluminescence from GaAsSb MQWs was reported. The photoluminescence strength increased dramatically with arsenic fraction as conjectured. The peak photoluminescence from GaAs0.31Sb 0.69 was 208 times larger than that from GaSb. Thirdly, the strong photoluminescence from GaAsSb MQWs and the direct nature of the band gap near 1.5 mum at room temperature make the material favorable for intermixing studies. The samples were treated with ion implantation followed by rapid thermal annealing (RTA). A band gap blueshift as large as 198 nm was achieved with a modest ion dose and moderate annealing temperature. Photoluminescence strength for implanted samples generally increased with the annealing temperature. The energy blueshift was attributed to the interdiffusion of both the group III and group V sublattices. Finally, based on the interesting properties of GaAsSb MQWs, including the direct band gap near 1.5 mum, strong photoluminescence, a wide range of wavelength (1300--1500 nm) due to ion implantation-induced quantum well intermixing (QWI), and subpicosecond spin relaxation reported by Hall et al, we proposed to explore the possibilities for ultra-fast optical switching by investigating spin dynamics in semiconductor optical amplifiers (SOAs) containing InGaAs and GaSb MQWs. For circularly polarized pump and probe waves, the numerical simulation on the modal indices showed that the difference between the effective refractive index of the TE and TM modes was quite large, on the order of 0.03, resulting in a significant phase mismatch in a traveling length larger than 28 mum. Thus the

  8. Contribution of double scattering to structural coloration in quasiordered nanostructures of bird feathers

    Energy Technology Data Exchange (ETDEWEB)

    Noh, Heeso; Liew, Seng Fatt; Saranathan, Vinodkumar; Prum, Richard O.; Mochrie, Simon G.J.; Dufresne, Eric R.; Cao, Hui (Yale)

    2010-07-28

    We measured the polarization- and angle-resolved optical scattering and reflection spectra of the quasiordered nanostructures in the bird feather barbs. In addition to the primary peak that originates from single scattering, we observed a secondary peak which exhibits depolarization and distinct angular dispersion. We explained the secondary peak in terms of double scattering, i.e., light is scattered successively twice by the structure. The two sequential single-scattering events are considered uncorrelated. Using the Fourier power spectra of the nanostructures obtained from the small-angle x-ray scattering experiment, we calculated the double scattering of light in various directions. The double-scattering spectrum is broader than the single-scattering spectrum, and it splits into two subpeaks at larger scattering angle. The good agreement between the simulation results and the experimental data confirms that double scattering of light makes a significant contribution to the structural color.

  9. Generation of acoustic terahertz waves in hybrid InGaN/GaN quantum wells

    Science.gov (United States)

    Mahat, Meg; Llopis, Antonia; Choi, Tae Youl; Periera, Sergio; Watson, Ian; Neogi, Arup

    2015-03-01

    We have carried out differential transmission measurements on InGaN/ GaN quantum wells with Au nanoparticles inserted inside V-pits with high filling fraction. We have observed acoustic wave packets generated with multiple THz frequencies as 0.12 THz from GaN buffer layer, 0.22 THz from Au-InGaN multiple quantum wells region, 0.07 THz from sapphire substrate, and 0.17 THz mixed signals from the sample. These THz wave packets are observed as a result of generation of coherent acoustic phonons propagating in hybrid Au-InGaN quantum wells. The study of these acoustic THz wave generation is crucial for the imaging of nanostructures.

  10. Bandedge-engineered quantum well laser

    Science.gov (United States)

    Asryan, Levon V.; Kryzhanovskaya, Natalia V.; Maximov, Mikhail V.; Egorov, Anton Yu; Zhukov, Alexey E.

    2011-05-01

    A promising type of quantum well (QW) lasers is discussed—bandedge-engineered (BE) QW lasers. The use of two asymmetric barrier layers (one on each side of the QW) in such lasers prevents establishing a bipolar population in the optical confinement layer (OCL) and thus suppresses the parasitic electron-hole recombination there. We discuss semiconductor alloys suitable for pseudomorphic growth of BE QW lasers on GaAs substrates and propose material compositions for such lasers. We use an analytical model to calculate the device characteristics. Due to suppression of the recombination in the OCL, the threshold current density of a BE QW laser is considerably reduced and the characteristic temperature T0 is increased compared to conventional QW lasers. Ideally, T0 of a BE QW laser can be as high as 300 K at room temperature. In more realistic BE QW lasers incorporating thin indent layers (located between the QW and each of the asymmetric barrier layers), the threshold current density is still low, and T0 is above 200 K for practical cavity lengths. Our results suggest that BE QW lasers offer major advantages over conventional QW lasers for low-threshold and high-temperature-stable operation.

  11. Bose-Einstein condensation of dipolar excitons in quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Timofeev, V B; Gorbunov, A V, E-mail: timofeev@issp.ac.r [Institute of Solid State Physics, Russian Academy of Sciences, 142432, Chernogolovka, Moscow region (Russian Federation)

    2009-02-01

    The experiments on Bose-Einstein condensation (BEC) of dipolar (spatially-indirect) excitons in the lateral traps in GaAs/AlGaAs Schottky-diode heterostructures with double and single quantum wells are presented. The condensed part of dipolar excitons under detection in the far zone is placed in k-space in the range which is almost two orders of magnitude less than thermal exciton wave vector. BEC occurs spontaneously in a reservoir of thermalized excitons. Luminescence images of Bose-condensate of dipolar excitons exhibit along perimeter of circular trap axially symmetrical spatial structures of equidistant bright spots which strongly depend on excitation power and temperature. By means of two-beam interference experiments with the use of cw and pulsed photoexcitation it was found that the state of dipolar exciton Bose-condensate is spatially coherent and the whole patterned luminescence configuration in real space is described by a common wave function.

  12. Phonons in Quantum-Dot Quantum Well

    Institute of Scientific and Technical Information of China (English)

    QINGuo-Yi

    2004-01-01

    Phonon modes of A1As/GaAs/A1As and GaAs/A1As/metal Pb quantum-dot quantum wells (QDQW's) with the whole scale up to 90 AО are calculated by using valence force field model (VFFM) based on group theory.Their optical frequency spectra are divided into two nonoverlapping bands, the AlAs-like band and the GaAs-like band,originated from and having frequency interval inside the bulk AlAs optical band and bulk GaAs optical band, respectively.The GaAs-LO (Г)-like modes of QDQW's that have maximum bulk GaAs-LO (Г) parentages in all modes covering thewhole frequency region and all symmetries have always A1 symmetry. Its frequency is controllable by adjusting thestructure parameters. In A1As/GaAs/A1As, it may be controlled to meet any designed frequency in GaAs-like band.The results on GaAs/A1As/metal Pb QDQW's show the same effect of reducing in interface optical phonons by using the metal/semiconductor interface revealed ever by macroscopic model The frequency spectra in both GaAs-like andAlAs-like optical phonon bands are independent of the thickness of Pb shell as long as the thickness of Pb shell is no less than 5 AО Defects at metal/A1As interface have significant influence to AlAs-like optical modes but have only minor influence to GaAs-like optical modes. All these results are important for the studying of the e-ph interaction in QD structures.

  13. Phonons in Quantum-Dot Quantum Well

    Institute of Scientific and Technical Information of China (English)

    QIN Guo-Yi

    2004-01-01

    Phonon modes of AlAs/GaAs/AlAs and GaAs/AlAs/metal Pb quantum-dot quantum wells (QDQW's)with the whole scale up to 90 A are calculated by using valence force field model (VFFM) based on group theory.Their optical frequency spectra are divided into two nonoverlapping bands, the AMs-like band and the GaAs-like band,originated from and having frequency interval inside the bulk AlAs optical band and bulk GaAs optical band, respectively.The GaAs-LO (F)-like modes of QDQW's that have maximum bulk GaAs-LO (F) parentages in all modes covering the whole frequency region and all symmetries have always A1 symmetry. Its frequency is controllable by adjusting the structure parameters. In AlAs/GaAs/AlAs, it may be controlled to meet any designed frequency in GaAs-like band.The results on GaAs/AMs/metal Pb QDQW's show the same effect of reducing in interface optical phonons by using the metal/semiconductor interface revealed ever by macroscopic model. The frequency spectra in both GaAs-like and AlAs-like optical phonon bands are independent of the thickness of Pb shell as long as the thickness of Pb shell is no less than 5 A. Defects at metal/AlAs interface have significant influence to AMs-like optical modes but have only minor influence to GaAs-like optical modes. All these results are important for the studying of the e-ph interaction in QD structures.

  14. Bose Condensation of Interwell Excitons in Double Quantum Wells

    DEFF Research Database (Denmark)

    Larionov, A. V.; Timofeev, V. B.; Ni, P. A.

    2002-01-01

    in the domain. With a rise in temperature, this line disappears from the spectrum (Tc 3.4 K). The observed phenomenon is attributed to Bose–Einstein condensation in a quasi-two-dimensional system of interwell excitons. In the temperature range studied (1.5–3.4 K), the critical exciton density and temperature...

  15. Spatially indirect excitons in coupled quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Lai, Chih-Wei Eddy [Univ. of California, Berkeley, CA (United States)

    2004-03-01

    Microscopic quantum phenomena such as interference or phase coherence between different quantum states are rarely manifest in macroscopic systems due to a lack of significant correlation between different states. An exciton system is one candidate for observation of possible quantum collective effects. In the dilute limit, excitons in semiconductors behave as bosons and are expected to undergo Bose-Einstein condensation (BEC) at a temperature several orders of magnitude higher than for atomic BEC because of their light mass. Furthermore, well-developed modern semiconductor technologies offer flexible manipulations of an exciton system. Realization of BEC in solid-state systems can thus provide new opportunities for macroscopic quantum coherence research. In semiconductor coupled quantum wells (CQW) under across-well static electric field, excitons exist as separately confined electron-hole pairs. These spatially indirect excitons exhibit a radiative recombination time much longer than their thermal relaxation time a unique feature in direct band gap semiconductor based structures. Their mutual repulsive dipole interaction further stabilizes the exciton system at low temperature and screens in-plane disorder more effectively. All these features make indirect excitons in CQW a promising system to search for quantum collective effects. Properties of indirect excitons in CQW have been analyzed and investigated extensively. The experimental results based on time-integrated or time-resolved spatially-resolved photoluminescence (PL) spectroscopy and imaging are reported in two categories. (i) Generic indirect exciton systems: general properties of indirect excitons such as the dependence of exciton energy and lifetime on electric fields and densities were examined. (ii) Quasi-two-dimensional confined exciton systems: highly statistically degenerate exciton systems containing more than tens of thousands of excitons within areas as small as (10 micrometer)2 were

  16. Conductance of graphene-based double-barrier nanostructures

    Energy Technology Data Exchange (ETDEWEB)

    Setare, M R [Department of Campus of Bijar, University of Kurdistan, Bijar (Iran, Islamic Republic of); Jahani, D, E-mail: Rezakord@ipm.co, E-mail: Dariush110@gmail.co [Department of Physics, Razi University, Kermanshah (Iran, Islamic Republic of)

    2010-12-22

    The effect of a mass gap on the conductance of graphene double-barrier heterojunctions is studied. By obtaining the 2D expression for the electronic transport of the low energy excitations of pure graphene through double-barrier systems, it is found that the conductivity of these structures does not depend on the type of charge carriers in the zones of the electric field. However, a finite induced gap in the graphene spectrum makes conductivity dependent on the energy band index. We also discuss a few controversies concerning double-barrier systems stemming from an improper choice of the scattering angle. Then it is observed that, for some special values of the incident energy and potential's height, graphene junctions behave like left-handed materials, resulting in a maximum value for the conductivity.

  17. Theoretical Studies of the Optoelectronic Properties of Semiconductor Quantum Wells.

    Science.gov (United States)

    Chao, Calvin Yi-Ping

    The valence-band structure of a semiconductor quantum well is calculated based on the multiband effective -mass theory. A unitary transformation is found to diagonalize the six-by-six Luttinger-Kohn Hamiltonian into two three -by-three blocks, making the computation more efficient. With this new formulation, the effect of strain on the band structure is studied systematically for both the compressional and tensile strain. The importance of the coupling between the heavy-hole, light-hole bands and the spin-orbit split -off bands is especially pointed out. The resonant tunneling of holes through a double -barrier structure is investigated using a transfer-matrix technique. It is shown that the strong mixing between the heavy holes and the light holes results in a totally different I-V characteristic from that predicted previously by the parabolic-band model. The exciton equation in momentum space is solved by using a modified Gaussian quadrature method. The exact solutions for a pure-two-dimensional exciton are derived by means of the Mehler-Fock transform, and the accuracy of the quadrature method is checked by comparing the numerical solutions against the exact solutions. A complete theory for quantum-well excitons is developed taking into account the effects of the valence -band mixing and the intersubband Coulomb interaction. Optical absorption spectra are calculated and compared to experimental data. The comparison demonstrates that the theory explains very well the quantum-confined Stark effect, the polarization selection rule, the coupling between the interwell and intrawell excitons in a multiwell structure, and the anticrossing between the ground state of a light-hole exciton and the excited state of a heavy-hole exciton observed experimentally.

  18. 组份变化的InGaAsSb/AIGaAsSb多量子阱结构对其X射线衍射及发光性质的影响%Effects of Structure of InGaAsSb/AIGaAsSb Multi-quantum Well Based on AL and In Change on X-ray Double Crystal Diffraction and Photoluminescence Properties

    Institute of Scientific and Technical Information of China (English)

    单含; 李梅

    2012-01-01

    Due to the basic characteristics of InGaAsSb/AlGaAsSb, based on the calculate lattice constant and energy band of quaternary system through the calculation of structure constants of binary system and ternary system, and analyze the MBE growth parameters and process, we design and grow the InGaAsSb/AlGaAsSb multi-quantum-wells epitaxial materials. The characterization of the layers has been carried out by X-ray double crystal diffraction and photo luminescence. There are several satellite peaks in X-ray double crystal diffraction results which indicate that these prepared InGaAsSb/AlGaAsSb multi-quantum-Wells are with high crystallized quality. The results of PL spec tra at the room temperature indicate that the wave length are modulated from 1.6 to 2. 28 u.m, the narrowest PL FWHM is 22 meV.%通过二元系和三元系结构参数计算四元系量子阱结构的晶格常数、禁带宽度等,设计了InGaAsSb/AlGaAsSb结构的MBE生长参数及工艺,利用X射线双晶衍射和PL谱研究了InGaAsSb/AlGaAsSb多量子阱结构特性和光学特性.X射线双晶衍射谱中出现了8条卫星峰,表明制备的InGaAsSb/AlGaAsSb多量子阱结构具有良好的结晶质量.利用光致发光光谱方法对制备的样品的光学性质进行了表征,结果表明,不同组份的InGaAsSb/AlGaAsSb多量子阱的发光峰波长随组份的变化在1.6~2.28 μm范围内可调,样品PL谱的半峰宽最窄可达22 meV.

  19. Noble metal nanostructures for double plasmon resonance with tunable properties

    Science.gov (United States)

    Petr, M.; Kylián, O.; Kuzminova, A.; Kratochvíl, J.; Khalakhan, I.; Hanuš, J.; Biederman, H.

    2017-02-01

    We report and compare two vacuum-based strategies to produce Ag/Au materials characterized by double plasmon resonance peaks: magnetron sputtering and method based on the use of gas aggregation sources (GAS) of nanoparticles. It was observed that the double plasmon resonance peaks may be achieved by both of these methods and that the intensities of individual localized surface plasmon resonance peaks may be tuned by deposition conditions. However, in the case of sputter deposition it was necessary to introduce a separation dielectric interlayer in between individual Ag and Au nanoparticle films which was not the case of films prepared by GAS systems. The differences in the optical properties of sputter deposited bimetallic Ag/Au films and coatings consisted of individual Ag and Au nanoparticles produced by GAS is ascribed to the divers mechanisms of nanoparticles formation.

  20. Morphologies, Preparations and Applications of Layered Double Hydroxide Micro-/Nanostructures

    Directory of Open Access Journals (Sweden)

    Mingdong Dong

    2010-12-01

    Full Text Available Layered double hydroxides (LDHs, also well-known as hydrotalcite-like layered clays, have been widely investigated in the fields of catalysts and catalyst support, anion exchanger, electrical and optical functional materials, flame retardants and nanoadditives. This feature article focuses on the progress in micro-/nanostructured LDHs in terms of morphology, and also on the preparations, applications, and perspectives of the LDHs with different morphologies.

  1. Self-assembly of fully addressable DNA nanostructures from double crossover tiles.

    Science.gov (United States)

    Wang, Wen; Lin, Tong; Zhang, Suoyu; Bai, Tanxi; Mi, Yongli; Wei, Bryan

    2016-09-19

    DNA origami and single-stranded tile (SST) are two proven approaches to self-assemble finite-size complex DNA nanostructures. The construction elements appeared in structures from these two methods can also be found in multi-stranded DNA tiles such as double crossover tiles. Here we report the design and observation of four types of finite-size lattices with four different double crossover tiles, respectively, which, we believe, in terms of both complexity and robustness, will be rival to DNA origami and SST structures.

  2. Energy level spectroscopy of InSb quantum wells using quantum-well LED emission

    Science.gov (United States)

    Tenev, T. G.; Palyi, A.; Mirza, B. I.; Nash, G. R.; Fearn, M.; Smith, S. J.; Buckle, L.; Emeny, M. T.; Ashley, T.; Jefferson, J. H.; Lambert, C. J.

    2009-02-01

    We have investigated the low-temperature optical properties of InSb quantum-well (QW) light-emitting diodes, with different barrier compositions, as a function of well width. Three devices were studied: QW1 had a 20 nm undoped InSb quantum well with a barrier composition of Al0.143In0.857Sb , QW2 had a 40 nm undoped InSb well with a barrier composition of Al0.077In0.923Sb , and QW3 had a 100 nm undoped InSb well with a barrier composition of Al0.025In0.975Sb . For QW1, the signature of two transitions (CB1-HH1 and CB1-HH2) can be seen in the measured spectrum, whereas for QW2 and QW3 the signature of a large number of transitions is present in the measured spectra. In particular transitions to HH2 can be seen, the first time this has been observed in AlInSb/InSb heterostructures. To identify the transitions that contribute to the measured spectra, the spectra have been simulated using an eight-band k.p calculation of the band structure together with a first-order time-dependent perturbation method (Fermi golden rule) calculation of spectral emittance, taking into account broadening. In general there is good agreement between the measured and simulated spectra. For QW2 we attribute the main peak in the experimental spectrum to the CB2-HH1 transition, which has the highest overall contribution to the emission spectrum of QW2 compared with all the other interband transitions. This transition normally falls into the category of “forbidden transitions,” and in order to understand this behavior we have investigated the momentum matrix elements, which determine the selection rules of the problem.

  3. Polaron Energy and Effective Mass in Parabolic Quantum Wells

    Institute of Scientific and Technical Information of China (English)

    WANG Zhi-Ping; LIANG Xi-Xia

    2005-01-01

    @@ The energy and effective mass of a polaron in a parabolic quantum well are studied theoretically by using LLP-like transformations and a variational approach. Numerical results are presented for the polaron energy and effective mass in the GaAs/Al0.3Ga0.7As parabolic quantum well. The results show that the energy and the effective mass of the polaron both have their maxima in the finite parabolic quantum well but decrease monotonously in the infinite parabolic quantum well with the increasing well width. It is verified that the bulk longitudinal optical phonon mode approximation is an adequate formulation for the electron-phonon coupling in parabolic quantum well structures.

  4. InGaN/GaN laser diode characterization and quantum well number effect

    Institute of Scientific and Technical Information of China (English)

    S. M. Thahab; H. Abu Hassan; Z. Hassan

    2009-01-01

    The effect of quantum well number on the quantum efficiency and temperature characteristics of In-GaN/GaN laser diodes (LDs) is determined and investigated. The 3-nm-thick In0.13Ga0.87TN wells and two 6-nm-thick GaN barriers are selected as an active region for Fabry-Perot (FP) cavity waveguide edge emitting LD. The internal quantum efficiency and internal optical loss coefficient are extracted through the simulation software for single, double, and triple InGaN/GaN quantum wells. The effects of device temperature on the laser threshold current, external differential quantum efficiency (DQE), and output wavelength are also investigated. The external quantum efficiency and characteristic temperature are improved significantly when the quantum well number is two. It is indicated that the laser structures with many quantum wells will suffer from the inhomogeneity of the carrier density within the quantum well itself which affects the LD performance.

  5. Modeling of novel lateral AlGaAs/GaAs quantum well solar cell

    CERN Document Server

    Rashidi, M

    2016-01-01

    In this paper, a novel lateral quantum well solar cell has been introduced, and the structural parameters effects of these nano-structures on the performance of the device have been investigated. For modeling, the continuity equation has been solved in the quasi neutral regions. However, to analyze the quantum wells' effects, first the Schrodinger and Poisson equations have been solved self-consistently. To find the absorption coefficient derived from the Fermi's golden rule, the obtained Eigen states and energies and also the effects of multilayers using Transfer Matrix Method have been employed. Then, to find the solar cell performance parameters, all radiative and non-radiative recombinations have been accounted. It is found that modifying different geometrical parameters, including the thickness of the system, the widths of the wells and barriers, and also some structural parameters such as the barriers' mole fraction could noticeably influence the characteristics of the device. So, optimizing these param...

  6. Lateral shifts of spin electron beams in antiparallel double {delta}-magnetic-barrier nanostructure

    Energy Technology Data Exchange (ETDEWEB)

    Kong Yonghong [Department of Electronic Engineering, Hunan University Science and Engineering, Hunan 425100 (China); Lu Maowang, E-mail: m_w_lu@126.com [Department of Electronic Engineering, Hunan University Science and Engineering, Hunan 425100 (China); Chen Saiyan; Zhang Guilian [Department of Electronic Engineering, Hunan University Science and Engineering, Hunan 425100 (China)

    2012-08-15

    We investigate the Goos-Haenchen (GH) effect of spin electron beams in a magnetic-barrier (MB) nanostructure consisting of antiparallel double {delta}-MBs, which can be experimentally realized by depositing two ferromagnetic (FM) stripes on top and bottom of the semiconductor heterostructure. GH shifts for spin electron beams across this type of MB nanostructures, is derived exactly, with the help of the stationary phase method. It is shown that GH shifts depend strongly on the spin directions for double {delta}-MBs with unidentical magnetic strengths, giving rise to a considerable spin polarization effect. It also is shown that spin polarization of GH shifts is closely relative to the separation and magnetic-strength difference of two {delta}-MBs. These interesting properties may provide an alternative scheme to spin-polarize electrons into the semiconductor, and the devices can serve as tunable spin beam splitters. - Highlights: Black-Right-Pointing-Pointer Spin Goos-Haenchen effect of electron beams through a kind of MB nanostructures. Black-Right-Pointing-Pointer GH shift depends greatly on electron-spins, which is used to spin polarize electrons in semiconductor. Black-Right-Pointing-Pointer Spin polarization in GH shift is tunable. Black-Right-Pointing-Pointer A tunable spin beam splitter is achieved.

  7. Comparison of resonant tunneling in AlGaAs/GaAs parabolic and diffusion modified quantum wells

    Indian Academy of Sciences (India)

    Sudhira Panda; B K Panda; S Fung

    2003-07-01

    Double barrier resonant tunneling diode using annealing induced diffusion modified quantum well is proposed as a viable alternative to that using parabolic quantum well which requires complex techniques to fabricate it. The transmission coefficients are calculated using the hybrid incremental airy function plane wave approach. The room temperature current–voltage characteristics have been calculated using transmission coefficients. The current–voltage characteristics are found to be similar in both diodes.

  8. Multichannel scattering of charge carriers on quantum well heterostructures

    CERN Document Server

    Galiev, V I; Polupanov, A F; Goldis, E M; Tansli, T L

    2002-01-01

    An efficient numerical analytical method has been developed for finding continuum spectrum states in quantum well systems with arbitrary potential profiles that are described by coupled Schroedinger equations. Scattering states and S matrix have been built for the case of multichannel scattering in one-dimensional systems with quantum wells and their symmetry properties are obtained and analyzed. The method is applied for studying hole scattering by strained GaInAs-InGaAsP quantum wells. Coefficients of the hole transmission and reflection as well as delay time are calculated as functions of the energy of the incident hole for various values of parameters of structures and values of the momentum

  9. Toward high-energy laser-driven ion beams: Nanostructured double-layer targets

    Science.gov (United States)

    Passoni, M.; Sgattoni, A.; Prencipe, I.; Fedeli, L.; Dellasega, D.; Cialfi, L.; Choi, Il Woo; Kim, I. Jong; Janulewicz, K. A.; Lee, Hwang Woon; Sung, Jae Hee; Lee, Seong Ku; Nam, Chang Hee

    2016-06-01

    The development of novel target concepts is crucial to make laser-driven acceleration of ion beams suitable for applications. We tested double-layer targets formed of an ultralow density nanostructured carbon layer (˜7 mg/cm 3 , 8 - 12 μ m -thick) deposited on a μ m -thick solid Al foil. A systematic increase in the total number of the accelerated ions (protons and C6 + ) as well as enhancement of both their maximum and average energies was observed with respect to bare solid foil targets. Maximum proton energies up to 30 MeV were recorded. Dedicated three-dimensional particle-in-cell simulations were in remarkable agreement with the experimental results, giving clear indication of the role played by the target nanostructures in the interaction process.

  10. Study of optical non-linear properties of a constant total effective length multiple quantum wells system

    Energy Technology Data Exchange (ETDEWEB)

    Solaimani, M.; Morteza, Izadifard [Faculty of Physics, Shahrood University of technology, Shahrood (Iran, Islamic Republic of); Arabshahi, H., E-mail: arabshahi@um.ac.ir [Department of Physics, Ferdowsi University of Mashhad, Mashhad (Iran, Islamic Republic of); Physics Department, Payame Noor University, P.O. Box 19395-3697, Tehran (Iran, Islamic Republic of); Reza, Sarkardehi Mohammad [Physics Department, Al-Zahra University, Vanak, Tehran (Iran, Islamic Republic of)

    2013-02-15

    In this work, we have studied the effect of the number of the wells, in a multiple quantum wells structure with constant total effective length, on the optical properties of multiple quantum wells like the absorption coefficient and the refractive index by means of compact density matrix approach. GaAs/Al{sub x}Ga{sub (1-x)}As multiple quantum wells systems was selected as an example. Besides, the effect of varying number of wells on the subband energies, wave functions, number of bound states, and the Fermi energy have been also investigated. Our calculation revealed that the number of wells in a multiple quantum well is a criterion with which we can control the amount of nonlinearity. This study showed that for the third order refractive index change there is two regimes of variations and the critical well number was six. In our calculations, we have used the same wells and barrier thicknesses to construct the multiple quantum wells system. - Highlights: Black-Right-Pointing-Pointer OptiOptical Non-Linear. Black-Right-Pointing-Pointer Total Effective Length. Black-Right-Pointing-Pointer Multiple Quantum Wells System - genetic algorithm Black-Right-Pointing-Pointer Schroedinger equation solution. Black-Right-Pointing-Pointer Nanostructure.

  11. Photoluminescence from narrow InAs-AlSb quantum wells

    Science.gov (United States)

    Brar, Berinder; Kroemer, Herbert; Ibbetson, James; English, John H.

    1993-01-01

    We report on photoluminescence spectra from narrow InAs-AlSb quantum wells. Strong, clearly resolved peaks for well widths from 2 to 8 monolayers were observed. Transmission electron micrographs show direct evidence for the structural quality of the quantum well structures. The transition energies of the narrowest wells suggest a strong influence of the AlSb X-barrier on the electronic states in the conduction band.

  12. Double scattering of light from biophotonic nanostructures with short-range order

    CERN Document Server

    Noh, Heeso; Saranathan, Vinodkumar; Prum, Richard O; Mochrie, Simon G J; Dufresne, Eric R; Cao, Hui

    2009-01-01

    We investigate the physical mechanism for color production by isotropic nanostructures with short-range order in bird feather barbs. While the primary peak in optical scattering spectra results from constructive interference of singly-scattered light, many species exhibit secondary peaks with distinct characteristic. Our experimental and numerical studies show that these secondary peaks result from double scattering of light by the correlated structures. Without an analog in periodic or random structures, such a phenomenon is unique for short-range ordered structures, and has been widely used by nature for non-iridescent structural coloration.

  13. Advantages of InGaN/GaN multiple quantum well solar cells with stepped-thickness quantum wells

    Institute of Scientific and Technical Information of China (English)

    Chen Xin; Zhao Bi-Jun; Ren Zhi-Wei; Tong Jin-Hui; Wang Xing-Fu; Zhuo Xiang-Jing; Zhang Jun

    2013-01-01

    InGaN/GaN multiple quantum well (MQW) solar cells with stepped-thickness quantum wells (SQW) are designed and grown by metal-organic chemical vapor deposition.The stepped-thickness quantum wells structure,in which the well thickness becomes smaller and smaller along the growth direction,reveals better crystalline quality and better spectral overlap with the solar spectrum.Consequently,the short-circuit current density (Jsc) and conversion efficiency of the solar cell are enhanced by 27.12% and 56.41% compared with the conventional structure under illumination of AM1.5G (100 mW/cm2).In addition,approaches to further promote the performance of InGaN/GaN multiple quantum well solar cells are discussed and presented.

  14. From Zn-Al layered double hydroxide to ZnO nanostructure:Gradually etching by sodium hydroxide

    Institute of Scientific and Technical Information of China (English)

    Gang Qiang Wan; Dong Xiang Li; Chun Fang Li; Jie Xu; Wan Guo Hou

    2012-01-01

    Zn-Al layered double hydroxide (LDH) was used as precursor to produce ZnO nanostructures through dissolution of aluminum hydroxide in caustic soda.The Zn-Al LDH could transform into different nanostructures of ZnO on LDH nanosheets and even pure ZnO nanorods under various NaOH concentration.The formed ZnO nanorods vertically aligned on both LDH sides.UV-vis diverse reflectance spectra show that the obtained ZnO nanorods have a band gap of approximately 3.05 eV.Such ZnO/LDH nanostructures might be used as photocatalyst in the organic pollutant decomposition.

  15. From layered double hydroxide to spinel nanostructures: facile synthesis and characterization of nanoplatelets and nanorods.

    Science.gov (United States)

    Sun, Genban; Sun, Lingna; Wen, He; Jia, Zhiqian; Huang, Kunlin; Hu, Changwen

    2006-07-13

    Mg-Al spinel (MgAl2O4) nanorods and nanoplatelets transformed from Mg-Al layered double hydroxide (Mg-Al-LDHs) were synthesized via a combined hydrothermal method and calcination route using Al(NO3).9H2O and Mg(NO3)2.6H2O as raw materials. The nanorods and nanoplatelets were characterized by means of physical techniques, including powder X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microcopy (HRTEM), selected-area electron diffraction (SAED), Fourier transform infrared spectra (FT-IR), thermogravimetric (TG), and nitrogen adsorption-desorption isotherms. XRD patterns reveal that the Mg-Al-LDHs nanostructures were obtained under a hydrothermal reaction temperature of 200 degrees C and Mg-Al spinel nanostructures were fabricated via calcination of the Mg-Al-LDHs nanostructures at 750 degrees C. It can be seen from TEM that the sizes of the Mg-Al-LDHs nanoplatelets were about 20-40 nm and the diameters of the MgAl2O4 nanorods were ca. 6 nm. The HRTEM images indicate that the crystal lattice spaces of the MgAl2O4 nanorods and nanoplatelets are 0.282 and 0.287 nm, respectively.

  16. Double-layered ZnO nanostructures for efficient perovskite solar cells

    KAUST Repository

    Mahmood, Khalid

    2014-01-01

    To date, a single layer of TiO2 or ZnO has been the most successful implementations of any electron transport layer (ETL) in solution-processed perovskite solar cells. In a quest to improve the ETL, we explore a new nanostructured double-layer ZnO film for mesoscopic perovskite-based thin film photovoltaics. This approach yields a maximum power conversion efficiency of 10.35%, which we attribute to the morphology of oxide layer and to faster electron transport. The successful implementation of the low-temperature hydrothermally processed double-layer ZnO film as ETL in perovskite solar cells highlights the opportunities to further improve the efficiencies by focusing on the ETL in this rapidly developing field. This journal is

  17. Quantum well electronic states in a tilted magnetic field

    Science.gov (United States)

    Trallero-Giner, C.; Padilha, J. X.; Lopez-Richard, V.; Marques, G. E.; Castelano, L. K.

    2017-08-01

    We report the energy spectrum and the eigenstates of conduction and uncoupled valence bands of a quantum well under the influence of a tilted magnetic field. In the framework of the envelope approximation, we implement two analytical approaches to obtain the nontrivial solutions of the tilted magnetic field: (a) the Bubnov-Galerkin spectral method and b) the perturbation theory. We discuss the validity of each method for a broad range of magnetic field intensity and orientation as well as quantum well thickness. By estimating the accuracy of the perturbation method, we provide explicit analytical solutions for quantum wells in a tilted magnetic field configuration that can be employed to study several quantitative phenomena.

  18. Microscopic Theory and Simulation of Quantum-Well Intersubband Absorption

    Science.gov (United States)

    Li, Jianzhong; Ning, C. Z.

    2004-01-01

    We study the linear intersubband absorption spectra of a 15 nm InAs quantum well using the intersubband semiconductor Bloch equations with a three-subband model and a constant dephasing rate. We demonstrate the evolution of intersubband absorption spectral line shape as a function of temperature and electron density. Through a detailed examination of various contributions, such as the phase space filling effects, the Coulomb many-body effects and the non-parabolicity effect, we illuminate the underlying physics that shapes the spectra. Keywords: Intersubband transition, linear absorption, semiconductor heterostructure, InAs quantum well

  19. GaSbBi/GaSb quantum well laser diodes

    Science.gov (United States)

    Delorme, O.; Cerutti, L.; Luna, E.; Narcy, G.; Trampert, A.; Tournié, E.; Rodriguez, J.-B.

    2017-05-01

    We report on the structural and optical properties of GaSbBi single layers and GaSbBi/GaSb quantum well heterostructures grown by molecular beam epitaxy on GaSb substrates. Excellent crystal quality and room-temperature photoluminescence are achieved in both cases. We demonstrate laser operation from laser diodes with an active zone composed of three GaSb0.885Bi0.115/GaSb quantum wells. These devices exhibit continuous-wave lasing at 2.5 μm at 80 K, and lasing under pulsed operation at room-temperature near 2.7 μm.

  20. Detection of electromagnetic radiation using micromechanical multiple quantum wells structures

    Science.gov (United States)

    Datskos, Panagiotis G [Knoxville, TN; Rajic, Slobodan [Knoxville, TN; Datskou, Irene [Knoxville, TN

    2007-07-17

    An apparatus and method for detecting electromagnetic radiation employs a deflectable micromechanical apparatus incorporating multiple quantum wells structures. When photons strike the quantum-well structure, physical stresses are created within the sensor, similar to a "bimetallic effect." The stresses cause the sensor to bend. The extent of deflection of the sensor can be measured through any of a variety of conventional means to provide a measurement of the photons striking the sensor. A large number of such sensors can be arranged in a two-dimensional array to provide imaging capability.

  1. Superradiant modes in Fibonacci quantum wells under resonant conditions

    Science.gov (United States)

    Chang, C. H.; Tsao, C. W.; Hsueh, W. J.

    2014-11-01

    It is first presented that superradiant modes exist in Fibonacci quantum wells within the exact regions that are obtained using the gap map diagram, rather than the traditional resonant Bragg condition. The results show that three limited regions are derived from the diagram, which correspond to bandgaps with widths that differ from each other. The regions in which the superradiant modes do not occur are also defined clearly. Moreover, the proposed method can be used to determine whether superradiant modes occur in multiple quantum wells that have non-periodical arrangements, including quasiperiodic sequences and correlated disorder sequences.

  2. Neutron quantum well states in Fe/Co/Fe trilayers

    Science.gov (United States)

    Feygenson, M.; Toperverg, B. P.; Rücker, U.; Kentzinger, E.; Brückel, Th.

    2004-07-01

    We report on neutron quantum well states in Fe/Co/Fe trilayers, in which the reflection potential exhibits a quantum well for both spin states of the neutron. It is shown, that the resonance state in such a system exists and manifests itself as a dip in the reflectivity plateau below the critical angle of total reflection. The range of trilayer parameters was numerically analyzed to find optimal experimental conditions for the enhancement of the neutron wave field in the Co spacer. Enhancement of the wave field by a resonance is suggested as a way to substantially increase the off-specular scattering signal from lateral domains in buried layers of Co.

  3. Neutron quantum well states in Fe/Co/Fe trilayers

    Energy Technology Data Exchange (ETDEWEB)

    Feygenson, M.; Toperverg, B.P.; Ruecker, U.; Kentzinger, E.; Brueckel, Th

    2004-07-15

    We report on neutron quantum well states in Fe/Co/Fe trilayers, in which the reflection potential exhibits a quantum well for both spin states of the neutron. It is shown, that the resonance state in such a system exists and manifests itself as a dip in the reflectivity plateau below the critical angle of total reflection. The range of trilayer parameters was numerically analyzed to find optimal experimental conditions for the enhancement of the neutron wave field in the Co spacer. Enhancement of the wave field by a resonance is suggested as a way to substantially increase the off-specular scattering signal from lateral domains in buried layers of Co.

  4. Spontaneous polarizations, electrical properties, and phononic properties of GaN nanostructures and systems

    Science.gov (United States)

    Yamanaka, Takayuki; Sun, Ke; Li, Yang; Dutta, Mitra; Stroscio, Michael A.

    2007-02-01

    Spontaneous polarizations of GaN nanostructures and quantum dots are calculated for different surface terminations. In addition, dimensionally-confined phonons in GaN-based nanostructures are discussed. GaN-based nanostructures have applications in a variety of systems and concepts including: non-charge-transfer-based devices and single-photon detectors based on GaN-based double-barrier quantum-well injectors, conductive-polymer collectors, and colloidal quantum dot recombination regions. In this paper, application of photodetectors is considered along with the related application of using colloidal quantum-dot-based ensembles for solar cell applications.

  5. Time-dependent tunneling of spin-polarized electrons in coupled quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Cruz, H; Luis, D [Departamento de Fisica Basica, Universidad de La Laguna, 38204 La Laguna, Tenerife (Spain)], E-mail: hcruz@ull.es

    2008-02-15

    We have solved the in-plane momentum-dependent effective-mass nonlinear Schroedinger equation for a spin-polarized electron wave packet in a InAs double quantum well system with an interlayer voltage. Considering a time-dependent Hartree potential, we have calculated the spin-polarized nonlinear electron dynamics between both quantum wells at different in-plane momentum values and applied bias. The spin-splitting caused by the Rashba effect is combined with the level matching between the spin dependent resonant tunneling levels making possible the observed local spin density oscillations which depend on the applied bias value. The filtering efficiency has been studied using time-dependent calculations.

  6. Spatial Light Modulators with Arbitrary Quantum Wells Profiles

    Science.gov (United States)

    1993-09-27

    SUPPLEMENTARY NOTES A 12a. DISTRIBUTION/AVAILABILITY STATEMENT . 12b. DISTRIBUTION CODE Approved for public release; distribution unlimited 13. ABSTRACT...2.1O.References ............................................................ 61 C. Publications in technical journals...Livescu, J. E. Cunningham, and W. Y. Jan , "Quantum Well Czrrier Sweep Out: Relatino to Electroabsorption and Exciton Saturation, "JEEE J.. Qunaturn

  7. Minimal length uncertainty relation and gravitational quantum well

    NARCIS (Netherlands)

    Brau, F.; Buisseret, F.

    2006-01-01

    The dynamics of a particle in a gravitational quantum well is studied in the context of nonrelativistic quantum mechanics with a particular deformation of a two-dimensional Heisenberg algebra. This deformation yields a new short-distance structure characterized by a finite minimal uncertainty in pos

  8. A Polaron in a Quantum Dot Quantum Well

    Institute of Scientific and Technical Information of China (English)

    ZHANG Li; XIE HongJing; CHEN ChuanYu

    2002-01-01

    The polaron effect in a quantum dot quantum well (QDQW)system is investigated by using the perturbation method. Both the bound electron states outside and inside the shell well are taken into account . Numerical calculation on the CdS/HgS QDQW shows that the phonon correction to the electron ground state energy is quite significant and cannot be neglected.

  9. Frictional drag between quantum wells mediated by phonon exchange

    DEFF Research Database (Denmark)

    Bønsager, M.C.; Flensberg, Karsten; Hu, Ben Yu-Kuang;

    1998-01-01

    lattice imperfections or electronic excitations is accounted for. In the case of GaAs quantum wells, we find that for a phonon mean free path l(ph) smaller than a critical value, imperfection scattering dominates and the drag rate varies as ln(l(ph)/d) over many orders of magnitude of the layer separation...

  10. Development of an infrared detector: Quantum well infrared photodetector

    Institute of Scientific and Technical Information of China (English)

    LU Wei; LI Ling; ZHENG HongLou; XU WenLan; XIONG DaYuan

    2009-01-01

    The progress in the quantum well infrared photo-detector (QWIP) based on quantum confinement in semiconductor in recent 10 years has been reviewed. The differences between QWlP and the HgCdTe (HCT) infrared detector as well as their compensation are analyzed. The outlook for near-future trends in QWIP technologies is also presented.

  11. Multiple Quantum Wells for P T -Symmetric Phononic Crystals

    Science.gov (United States)

    Poshakinskiy, A. V.; Poddubny, A. N.; Fainstein, A.

    2016-11-01

    We demonstrate that the parity-time symmetry for sound is realized in laser-pumped multiple-quantum-well structures. Breaking of the parity-time symmetry for the phonons with wave vectors corresponding to the Bragg condition makes the structure a highly selective acoustic wave amplifier. Single-mode distributed feedback phonon lasing is predicted for structures with realistic parameters.

  12. Electrooptical modulation in multiple quantum well hetero nipi waveguides

    DEFF Research Database (Denmark)

    Thirstrup, C.; Robson, P. N.; Li Kam Wa, P.

    1994-01-01

    An optical intensity modulator based on multiple quantum well hetero (MQW-H) nipi waveguides is reported. In the low optical power regime (~10-5 W), the modulator exhibits an extinction ratio in excess of 100:1 at low drive voltage (4 V) and 5-B attenuation. Modelling and experimental results of ...

  13. Absorption recovery in strongly saturated quantum-well electroabsorption modulators

    DEFF Research Database (Denmark)

    Højfeldt, Sune; Romstad, F.; Mørk, Jesper

    2003-01-01

    We observe experimentally that a quantum-well electroabsorption modulator, when strongly saturated by a highly energetic optical pulse, may exhibit an absorption recovery time much longer than for excitation with a low-energy pulse. Using a comprehensive drift-diffusion. type model, we are able...

  14. Development of an infrared detector: Quantum well infrared photodetector

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    The progress in the quantum well infrared photo-detector (QWIP) based on quantum confinement in semiconductor in recent 10 years has been reviewed. The differences between QWIP and the HgCdTe (HCT) infrared detector as well as their compensation are analyzed. The outlook for near-future trends in QWIP technologies is also presented.

  15. Double-dark-resonance-enhanced Kerr nonlinearity in a single layer of graphene nanostructure

    Science.gov (United States)

    Solookinejad, Gh.; Panahi, M.; Ahmadi Sangachin, E.; Hossein Asadpour, Seyyed

    2016-08-01

    In this paper, a novel scheme is proposed for the giant enhanced Kerr nonlinearity in a single layer of graphene nanostructure based on quantum optics and nonlinear optical sciences. The linear and the nonlinear susceptibility of the monolayer graphene system are presented in details by using the density matrix method and perturbation theory. After deriving the equations of motion in the steady-state regime, we analytically solve the linear and nonlinear susceptibility of the system. Our numerical results show that the giant enhanced Kerr nonlinearity can be obtained in the double-dark-resonance condition with zero linear and nonlinear absorption. Our results may have potential applications in quantum information science in infrared and terahertz regimes.

  16. Synthesis and characterization of metal (Core) - layered double hydroxide (Shell) nanostructures

    Science.gov (United States)

    Noh, Woo C.

    Layered double hydroxides (LDH) which belong to a class of inorganic ceramic layered materials have been studied since the mid-19th century for a variety of applications including catalysis, anion exchange, adsorbents and antacid, but more recently as a potential drug and gene delivery platform. Drug delivery platforms based on nano-sized geometries are nanovectors which promise a revolutionary impact on the therapy and imaging of various types of cancers and diseases. To date, various polymeric platforms have been the focus of intense research, but the development of inorganic, bio-hybrid nanoparticles for therapeutics and molecular imaging are at a stage of infancy. The hybridization of LDH with bioactive agents or the fabrication of metal (Core)---LDH (Shell) nanostructures could have many beneficial effects including multimodality, active targetability, and efficacy. For example, Core---Shell nanostructures may be designed to have a high scattering optical cross-section for imaging, but may also be tailored to strongly absorb near infrared (NIR) light for hyperthermic ablation. The central theme of this thesis was to demonstrate proof-of-concept of spherical silver and gold metal (Core)---LDH (Shell) nanostructures that have uniform size distribution and are agglomeration free. The effects of processing parameters on the characteristics of LDH as well as LDH-coated spherical metal (Ag, Au) nanoparticles have been evaluated using X-ray Diffraction, Dynamic Light Scattering, Scanning Electron Microscopy, Transmission Electron Microscopy, Rutherford Backscattering Spectrometry, and Inductively Coupled Plasma Emission Spectrometry to arrive at appropriate process windows. The core---shell nanostructures were also characterized for their optical properties in the ultra---violet---visible region, and the data were compared with simulated data, computed by using a quasi static model from Mie scattering theory. Moreover, in order to achieve a strong plasmon resonance

  17. Characteristics of surface plasmon coupled quantum well infrared photodetectors

    Science.gov (United States)

    Hsu, Wei-Cheng; Ling, Hong-Shi; Wang, Shiang-Yu; Lee, Chien-Ping

    2017-06-01

    Quantum Well Infrared Photodetectors (QWIPs) with different structures were characterized for the study of surface plasmon wave coupling. Detailed comparisons between surface plasmon coupled and etched grating coupled devices were investigated. A bias dependence for the enhancement of the responsivity of surface plasmon coupled devices was found, especially for the samples with non-uniform quantum wells. The non-uniform QWIPs with surface plasmon coupling showed an asymmetric enhancement with respect to the bias directions. Stronger enhancements were shown under the biases when a higher effective electric field region is close to the collector. The change of the photocarrier escape probability due to the narrow coupling bandwidth of the surface plasmon wave is attributed to this unexpected bias dependence.

  18. Storage and retrieval of light pulse in coupled quantum wells

    Directory of Open Access Journals (Sweden)

    Jibing Liu

    2016-03-01

    Full Text Available In this paper, we propose an effective scheme to create a frequency entangled states based on bound-to-bound inter-subband transitions in an asymmetric three-coupled quantum well structure. A four-subband cascade configuration quantum well structure is illuminated with a pulsed probe field and two continuous wave control laser fields to generate a mixing field. By properly adjusting the frequency detunings and the intensity of coupling fields, the conversion efficiency can reach 100%. A maximum entangled state can be achieved by selecting a proper length of the sample. We also numerically investigate the propagation dynamics of the probe pulse and mixing pulse, the results show that two frequency components are able to exchange energy through a four-wave mixing process. Moreover, by considering special coupling fields, the storage and retrieval of the probe pulse is also numerically simulated.

  19. Performance evaluation of quantum well infrared phototransistor instrumentation through modeling

    Science.gov (United States)

    El-Tokhy, Mohamed S.; Mahmoud, Imbaby I.

    2014-05-01

    This paper presents a theoretical analysis for the characteristics of quantum well infrared phototransistors (QWIPTs). A mathematical model describing this device is introduced under nonuniformity distribution of quantum wells (QWs). MATLAB environment is used to devise this model. Furthermore, block diagram models through the VisSim environment were used to describe the device characteristics. The developed models are used to investigate the behavior of the device with different values of performance parameters such as bias voltage, spacing between QWs, and temperature. These parameters are tuned to enhance the performance of these quantum phototransistors through the presented modeling. Moreover, the resultant performance characteristics and comparison between both QWIPTs and quantum wire infrared phototransistors are investigated. Also, the obtained results are validated against experimental published work and full agreements are obtained.

  20. Development of high power quantum well lasers at RRCAT

    CERN Document Server

    Sharma, T K; Dixit, V K; Singh, S D; Pal, S; Porwal, S; Kumar, Ravi; Khakha, Alexander; Jangir, R; Kheraj, V; Rawat, P; Nath, A K

    2014-01-01

    We at RRCAT have recently developed high power laser diodes in the wavelength range of 740 to 1000 nm. A typical semiconductor laser structure is consisted of about 10 epilayers with different composition, thickness and doping values. For example, a laser diode operating at 0.8 micron has either GaAs or GaAsP quantum well as an active layer. The quantum well is sandwiched between AlGaAs wider bandgap waveguide and cladding layers. The complete laser structure is grown by metal organic vapour phase epitaxy technique and devices are fabricated through standard procedure using photolithography. We recently achieved about 5.3 Watt peak power at 853 nm. These laser diodes were tested under pulsed operation at room temperature for 500 nanosecond pulse duration with a duty cycle of 1:1000. Laser diode arrays consisting of 6-10 elements were also developed and tested for operation in pulsed mode at room temperature.

  1. Piezo-Phototronic Effect in a Quantum Well Structure.

    Science.gov (United States)

    Huang, Xin; Du, Chunhua; Zhou, Yongli; Jiang, Chunyan; Pu, Xiong; Liu, Wei; Hu, Weiguo; Chen, Hong; Wang, Zhong Lin

    2016-05-24

    With enhancements in the performance of optoelectronic devices, the field of piezo-phototronics has attracted much attention, and several theoretical works have been reported based on semiclassical models. At present, the feature size of optoelectronic devices are rapidly shrinking toward several tens of nanometers, which results in the quantum confinement effect. Starting from the basic piezoelectricity equation, Schrödinger equation, Poisson equation, and Fermi's golden rule, a self-consistent theoretical model is proposed to study the piezo-phototronic effect in the framework of perturbation theory in quantum mechanics. The validity and universality of this model are well-proven with photoluminescence measurements in a single GaN/InGaN quantum well and multiple GaN/InGaN quantum wells. This study provides important insight into the working principle of nanoscale piezo-phototronic devices as well as guidance for the future device design.

  2. The Quantum Well of One-Dimensional Photonic Crystals

    Directory of Open Access Journals (Sweden)

    Xiao-Jing Liu

    2015-01-01

    Full Text Available We have studied the transmissivity of one-dimensional photonic crystals quantum well (QW with quantum theory approach. By calculation, we find that there are photon bound states in the QW structure (BA6(BBABBn(AB6, and the numbers of the bound states are equal to n+1. We have found that there are some new features in the QW, which can be used to design optic amplifier, attenuator, and optic filter of multiple channel.

  3. Magnetization dynamics in (Cd,Mn)Te quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Goryca, M.; Nawrocki, M. [Institute of Experimental Physics, Warsaw University, Hoza 69, 00-681 Warsaw (Poland); Ferrand, D.; Tatarenko, S. [Joined group ' ' Nanophysique et semiconducteurs' ' , CNRS/CEA/Universite Joseph Fourier-Grenoble, Laboratoire de Spectrometrie Physique, BP 87, 38402 Saint Martin d' Heres cedex (France); Kossacki, P.; Pacuski, W.; Maslana, W. [Institute of Experimental Physics, Warsaw University, Hoza 69, 00-681 Warsaw (Poland); Joined group ' ' Nanophysique et semiconducteurs' ' , CNRS/CEA/Universite Joseph Fourier-Grenoble, Laboratoire de Spectrometrie Physique, BP 87, 38402 Saint Martin d' Heres cedex (France); Cibert, J. [Laboratoire Louis Neel, CNRS, BP166, 38042 Grenoble cedex 9 (France)

    2006-03-15

    The relaxation of the magnetization change induced by a short pulse of magnetic field in p-doped (Cd,Mn)Te quantum wells is determined from the giant Zeeman shift of the photoluminescence line. The characteristic times change by three orders of magnitude upon application of a static magnetic field. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  4. Quantum-well-induced ferromagnetism in thin films

    DEFF Research Database (Denmark)

    Niklasson, A.M.N.; Mirbt, S.; Skriver, Hans Lomholt;

    1997-01-01

    We have used a first-principles Green's-function technique to investigate the magnetic properties of thin films of Rh, Pd, and Pt deposited on a fee Ag (001) substrate. We find that the magnetic moment of the film is periodically suppressed and enhanced as a function of film thickness....... The phenomenon is explained in terms of quantum-well states moving through the Fermi level with increasing film thickness....

  5. Spin structure of electron subbands in (110)-grown quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Nestoklon, M. O.; Tarasenko, S. A. [Ioffe Physical-Technical Institute, Russian Academy of Sciences, St. Petersburg 194021 (Russian Federation); Jancu, J.-M. [FOTON-INSA Laboratory, UMR 6082 au CNRS, INSA de Rennes, 35043 Rennes Cedex (France); Voisin, P. [CNRS-Laboratoire de Photonique et de Nanostructures, 91460 Marcoussis (France)

    2013-12-04

    We present the theory of fine structure of electron states in symmetric and asymmetric zinc-blende-type quantum wells with the (110) crystallographic orientation. By combining the symmetry analysis, sp{sup 3}d{sup 5}s* tight-binding method, and envelope-function approach we obtain quantitative description of in-plane wave vector, well width and applied electric field dependencies of the zero-magnetic-field spin splitting of electron subbands and extract spin-orbit-coupling parameters.

  6. Density of states in an electrically biased quantum well

    Indian Academy of Sciences (India)

    A Khan; S Sinha; P Panchadhyayee

    2007-10-01

    Density of states in a quantum well has been studied in the presence of an electric field applied perpendicular to the growth direction. We have shown that an extra quantization is introduced to the motion of the electron due to the discrete energy levels known as Wannier–Stark ladder states and the nature of density of electronic states changes from quasi two-dimensional to quasi one-dimensional.

  7. SWKB Quantization Rules for Bound States in Quantum Wells

    CERN Document Server

    Sinha, A K; Sinha, Anjana; Roychoudhury, Rajkumar

    2000-01-01

    In a recent paper by Gomes and Adhikari (J.Phys B30 5987(1997)) a matrix formulation of the Bohr-Sommerfield quantization rule has been applied to the study of bound states in one dimension quantum wells. Here we study these potentials in the frame work of supersymmetric WKB (SWKB) quantization approximation and find that SWKB quantization rule is superior to the modified Bohr-Sommerfield or WKB rules as it exactly reproduces the eigenenergies.

  8. Hole transport simulations in SiGe cascade quantum wells

    Science.gov (United States)

    Ikonić, Z.; Harrison, P.; Kelsall, R. W.

    2004-03-01

    Hole transport in p-Si/SiGe quantum well cascade structures has been analyzed using a rate equation method with thermal balancing (self-consistent energy balance method). The carrier and energy relaxation due to alloy disorder, acoustic and optical phonon scattering are included. The model includes the in-plane k-space anisotropy. The results are compared to those obtained from Monte Carlo simulations and from the basic particle rate equation method.

  9. High signal-to-noise ratio quantum well bolometer materials

    Science.gov (United States)

    Wissmar, Stanley; Höglund, Linda; Andersson, Jan; Vieider, Christian; Savage, Susan; Ericsson, Per

    2006-09-01

    Novel single crystalline high-performance temperature sensing materials (quantum well structures) have been developed for the manufacturing of uncooled infrared bolometers. SiGe/Si and AlGaAs/GaAs quantum wells are grown epitaxially on standard Si and GaAs substrates respectively. The former use holes as charge carriers utilizing the discontinuities in the valence band structure, whereas the latter operate in a similar manner with electrons in the conduction band. By optimizing parameters such as the barrier height (by variation of the germanium/aluminium content respectively) and the fermi level E f (by variation of the quantum well width and doping level) these materials provide the potential to engineer layer structures with a very high temperature coefficient of resistance, TCR, as compared with conventional thin film materials such as vanadium oxide and amorphous silicon. In addition, the high quality crystalline material promises very low 1/f-noise characteristics promoting an outstanding signal to noise ratio and well defined and uniform material properties, A comparison between the two (SiGe/Si and AlGaAs/GaAs) quantum well structures and their fundamental theoretical limits are discussed and compared to experimental results. A TCR of 2.0%/K and 4.5%/K have been obtained experimentally for SiGe/Si and AlGaAs/GaAs respectively. The noise level for both materials is measured as being several orders of magnitude lower than that of a-Si and VOx. These uncooled thermistor materials can be hybridized with read out circuits by using conventional flip-chip assembly or wafer level adhesion bonding. The increased bolometer performance so obtained can either be exploited for increasing the imaging system performance, i. e. obtaining a low NETD, or to reduce the vacuum packaging requirements for low cost applications (e.g. automotive).

  10. Design and Analysis of a Quantum Well Light Emitting Triode.

    Science.gov (United States)

    Rajagopalan, Bharath

    1992-01-01

    We present, for the first time, the design and analysis of a novel, quantum well light emitting triode (QWLET), based on a bipolar junction transistor with a quantum well in the base. Modulation of the collector -base voltage controls the radiation emission from the quantum well by sweeping the space-charge region across the well. Detailed analysis is provided for an npn-Al_{.35 }Ga_{.65}As transistor with an undoped GaAs quantum well. Calculations indicate that modulation rates in excess of 1 GHz are possible. The switching-off process is limited by thermionic emission of majority carriers out of the well, whereas the turn -on is controlled by the recombination lifetime in the well. Our calculations reveal that the thermionic emission lifetime of these carriers is ~0.1 ns at an applied field of 5 times 10 ^4 V/cm, while the radiative lifetime is approximately 1-2 ns for carrier densities in excess of 10^{12} cm ^{-2} in the well. For material systems, or choice of parameters, where thermionic emission is insignificant, field induced tunneling of carriers out of the well is considered as a quenching mechanism. However, the tunneling lifetime is ~3.1 mus at a field of 1 times 10^5 V/cm, and therefore we propose a novel scheme to reduce this lifetime to ~3.3 ns through impurity assisted tunneling. Our calculated results also include a capture cross-section of 10^{-14} cm ^2 for carriers into the well, a B coefficient for radiative recombination of 2.4 times 10^{-10} cm ^3/s, and optical power generation of 0.15 muW per μm of length per mA of drive current and peaked at 855 nm. The voltage amplitude needed to modulate the radiation is on the order of 1 to 2 volts.

  11. Photonic integrated circuits based on quantum well intermixing techniques

    OpenAIRE

    Hou, Lianping; Marsh, John H.

    2016-01-01

    The passive sections of a monolithic device must have a wider bandgap than the active regions to reduce losses due to direct interband absorption. Such bandgap engineering is usually realized by complicated regrown butt-joint or selective-area growth techniques. We, however, have developed a simple, flexible and low-cost alternative technique – quantum well intermixing (QWI) – to increase the bandgap in selected areas of an integrated device post-growth. To verify the QWI process, we have fab...

  12. Optical Detection Properties of Silicon-Germanium Quantum Well Structures

    Science.gov (United States)

    2011-07-28

    discrete index N labels energies that correspond to bound hole states in the growth direction. The EFA proceeds by first determining the bulk...dashed line designated by the label, HHl-cont, represents the EFA zone center energy difference between the ground state and the edge of the quantum well...points out the absolute necessity of performing the EFA theoretical calculations. Without them the correct number of bound states would be 5-32 0.25

  13. Voltage controlled terahertz transmission through GaN quantum wells

    OpenAIRE

    Laurent, T.; Sharma, R.; Torres, J.; Nouvel, P; Blin, S.; Varani, L.; Cordier, Y.; Chmielowska, M.; Chenot, S.; Faurie, JP; Beaumont, B.; P. Shiktorov; Starikov, E.; Gruzinskis, V.; Korotyevyev, V.

    2011-01-01

    We report measurements of radiation transmission in the 0.220--0.325 THz frequency domain through GaN quantum wells grown on sapphire substrates at room and low temperatures. A significant enhancement of the transmitted beam intensity with the applied voltage on the devices under test is found. For a deeper understanding of the physical phenomena involved, these results are compared with a phenomenological theory of light transmission under electric bias relating the transmission enhancement ...

  14. Photonic Integrated Circuits Based on Quantum well Intermixing Techniques

    OpenAIRE

    Hou, Lianping; John H. Marsh

    2016-01-01

    The passive sections of a monolithic device must have a wider bandgap than the active regions to reduce losses due to direct interband absorption. Such bandgap engineering is usually realized by complicated regrown butt-joint or selective-area growth techniques. We, however, have developed a simple, flexible and low-cost alternative technique – quantum well intermixing (QWI) – to increase the bandgap in selected areas of an integrated device post-growth. To verify the QWI process, we have fab...

  15. Crystal Phase Quantum Well Emission with Digital Control.

    Science.gov (United States)

    Assali, S; Lähnemann, J; Vu, T T T; Jöns, K D; Gagliano, L; Verheijen, M A; Akopian, N; Bakkers, E P A M; Haverkort, J E M

    2017-09-18

    One of the major challenges in the growth of quantum well and quantum dot heterostructures is the realization of atomically sharp interfaces. Nanowires provide a new opportunity to engineer the band structure as they facilitate the controlled switching of the crystal structure between the zinc-blende (ZB) and wurtzite (WZ) phases. Such a crystal phase switching results in the formation of crystal phase quantum wells (CPQWs) and quantum dots (CPQDs). For GaP CPQWs, the inherent electric fields due to the discontinuity of the spontaneous polarization at the WZ/ZB junctions lead to the confinement of both types of charge carriers at the opposite interfaces of the WZ/ZB/WZ structure. This confinement leads to a novel type of transition across a ZB flat plate barrier. Here, we show digital tuning of the visible emission of WZ/ZB/WZ CPQWs in a GaP nanowire by changing the thickness of the ZB barrier. The energy spacing between the sharp emission lines is uniform and is defined by the addition of single ZB monolayers. The controlled growth of identical quantum wells with atomically flat interfaces at predefined positions featuring digitally tunable discrete emission energies may provide a new route to further advance entangled photons in solid state quantum systems.

  16. High-Performance Water Electrolysis System with Double Nanostructured Superaerophobic Electrodes.

    Science.gov (United States)

    Xu, Wenwen; Lu, Zhiyi; Wan, Pengbo; Kuang, Yun; Sun, Xiaoming

    2016-05-01

    Catalysts screening and structural optimization are both essential for pursuing a high-efficient water electrolysis system (WES) with reduced energy supply. This study demonstrates an advanced WES with double superaerophobic electrodes, which are achieved by constructing a nanostructured NiMo alloy and NiFe layered double hydroxide (NiFe-LDH) films for hydrogen evolution and oxygen evolution reactions, respectively. The superaerophobic property gives rise to significantly reduced adhesion forces to gas bubbles and thereby accelerates the hydrogen and oxygen bubble releasing behaviors. Benefited from these metrics and the high intrinsic activities of catalysts, this WES affords an early onset potential (≈1.5 V) for water splitting and ultrafast catalytic current density increase (≈0.83 mA mV(-1) ), resulting in ≈2.69 times higher performance compared to the commercial Pt/C and IrO2 /C catalysts based counterpart under 1.9 V. Moreover, enhanced performance at high temperature as well as prominent stability further demonstrate the practical application of this WES. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  17. Thickness and local field effects on energy transfer rate in coupled quantum wells system: Linear regime

    Energy Technology Data Exchange (ETDEWEB)

    Vazifehshenas, T.; Bahrami, B. [Department of Physics, Shahid Beheshti University, G.C., Evin, 1983963113 Tehran (Iran, Islamic Republic of); Salavati-fard, T., E-mail: taha@udel.edu [Department of Physics and Astronomy, University of Delaware, Newark, DE 19716 (United States)

    2012-12-15

    We investigate theoretically the dependence of energy transfer rate in Double-Quantum-Well system on the well thickness by using the balance equation formalism. Also, by including the local field correction in our calculations through the zero- and finite-temperature Hubbard approximations, we study the effect of the short-range interactions on the energy transfer phenomenon. Calculations consider both the static and dynamic screening approximations. Our numerical results predict that the energy transfer rate increases considerably by increasing the layers' thicknesses and by taking into account the short-range interactions, as well.

  18. Giant kerr nonlinearity, controlled entangled photons and polarization phase gates in coupled quantum-well structures.

    Science.gov (United States)

    Zhu, Chengjie; Huang, Guoxiang

    2011-11-07

    We study linear and nonlinear propagations of probe and signal pulses in a multiple quantum-well structure with a four-level, double Λ-type configuration. We show that slow, mutually matched group velocities and giant Kerr nonlinearity of the probe and the signal pulses may be achieved with nearly vanishing optical absorption. Based on these properties we demonstrate that two-qubit quantum polarization phase gates can be constructed and highly entangled photon pairs may be produced. In addition, we show that coupled slow-light soliton pairs with very low generation power can be realized in the system.

  19. Harsh photovoltaics using InGaN/GaN multiple quantum well schemes

    KAUST Repository

    Lien, Derhsien

    2015-01-01

    Harvesting solar energy at extremely harsh environments is of practical interest for building a self-powered harsh electronic system. However, working at high temperature and radiative environments adversely affects the performance of conventional solar cells. To improve the performance, GaN-based multiple quantum wells (MQWs) are introduced into the solar cells. The implementation of MQWs enables improved efficiency (+0.52%/K) and fill factor (+0.35%/K) with elevated temperature and shows excellent reliability under high-temperature operation. In addition, the GaN-based solar cell exhibits superior radiation robustness (lifetime >30 years under solar storm proton irradiation) due to their strong atomic bonding and direct-bandgap characteristics. This solar cell employing MQW nanostructures provides valuable routes for future developments in self-powered harsh electronics.

  20. Arbitrary tunable spaser based on double-Fano resonance of two sets of disk-ring nanostructure

    CERN Document Server

    Huo, Y; Zheng, C; Zhao, H; Jiang, S; Ning, T; Yang, C; Tan, C; Jiao, Y; Man, B

    2015-01-01

    This paper demonstrates an arbitrary tunable spaser based on double-Fano resonance of a plasmonic nanostructure consisting of two sets of disk-ring (TSDR) nanostructure. TSDR nanostructure supports two Fano resonances, which can be served as the lasing mode and the pumping mode of a spaser. These two mode can be tuned in a very wide wavelength range because of the good tunability of the two nanorings. The tuning range of the lasing mode and the pumping mode can be reached to 710 nm and 620 nm. These results represent a significant step in the pursuit of ultimate spasers and propose a approach to manipulate lasing mode and pumping mode over a broad spectral range.

  1. All-optically induced ultrafast currents in GaAs quantum wells: Excitonic effects and dependence on quantum well width

    Energy Technology Data Exchange (ETDEWEB)

    Priyadarshi, Shekhar; Maria Racu, Ana; Pierz, Klaus; Siegner, Uwe; Bieler, Mark [Physikalisch-Technische Bundesanstalt, Braunschweig (Germany); Dawson, Philip [School of Physics and Astronomy, University of Manchester (United Kingdom)

    2009-07-01

    We have studied the influence of excitonic effects on ultrafast current transients that are induced in unbiased GaAs quantum wells by all-optical excitation. The ultrafast current transients result from second-order nonlinear optical effects and were detected by measuring the simultaneously emitted THz radiation. Experiments were performed on (110)-oriented GaAs/AlGaAs quantum well samples with different well widths and with 150 fs excitation laser pulses at room temperature. By studying the dependence of the current amplitude and phase on excitation photon energy in the different samples, we find that Coulomb effects and the quantum well width substantially affect the properties of these ultrafast currents. This becomes most prominently visible when exciting light-hole exciton transitions. The phase data shows that for excitation of light-hole-type transitions a current reversal occurs as compared to excitation of heavy-hole-type transitions. The amplitude dependence of the current transients on excitation photon energy is influenced by the reversed current contribution from heavy- and light-hole-type transitions, the complex bandstructure, and non-instantaneous effects contributing to the current dynamics.

  2. An Emphasis of Electron Energy Calculation in Quantum Wells

    Institute of Scientific and Technical Information of China (English)

    GAOShao-Wen; CAOJun-Cheng; FENGSong-Lin

    2004-01-01

    We investigate various methods for the calculation of the electron energy in semiconductor quantum wells and focus on a matrix algorithm method. The results show better fitness of the factor -h2/2 э/эz 1/m*(z) э/эz than that of -h2/2 1/m*(z) э2/эz2 in the first part of the Schroedinger equation. The effect of nonparabolicity in the conduction band is also discussed.

  3. Quantum-well thickness dependence of spin polarization of excitons

    Directory of Open Access Journals (Sweden)

    M. Idrish Miah

    2011-07-01

    Full Text Available The optical orientation of exciton spins in semiconductor quantum wells (SQWs was investigated by observing the circular polarization of the photoluminescence (PL. The left/right circularly polarized PL in SQWs was measured. It was found that there is a difference between the two different polarization conditions, which is caused by spin-dependent phase-space filling. The PL polarization was estimated from the signals of the left and right circularly polarized PL and was found to depend on the well thickness of SQWs as well as on the sample temperature. The influence of an electric field on the PL polarization was studied.

  4. Ordered Dissipative Structures in Exciton Systems in Semiconductor Quantum Wells

    Directory of Open Access Journals (Sweden)

    Andrey A. Chernyuk

    2006-02-01

    Full Text Available A phenomenological theory of exciton condensation in conditions of inhomogeneous excitation is proposed. The theory is applied to the study of the development of an exciton luminescence ring and the ring fragmentation at macroscopical distances from the central excitation spot in coupled quantum wells. The transition between the fragmented and the continuous ring is considered. With assumption of a defect in the structure, a possibility of a localized island of the condensed phase in a fixed position is shown. Exciton density distribution is also analyzed in the case of two spatially separated spots of the laser excitation.

  5. Quantum-well-driven magnetism in thin films

    DEFF Research Database (Denmark)

    Mirbt, S.; Johansson, B.; Skriver, Hans Lomholt

    1996-01-01

    We have performed local spin-density calculations for an fee (100) Ag substrate covered by 1 to 16 monolayers (ML) of Pd. We find that thin films of Pd are magnetic with a moment of the order of 0.3 mu(B) except for films of 1-2 ML and 5-7 ML where magnetism is completely suppressed. We present...... a physically transparent explanation of this behavior in terms of the Stoner picture and magnetic quantum-well states....

  6. Dynamics of electron in a surface quantum well

    Institute of Scientific and Technical Information of China (English)

    Wang Li-Fei; Yang Guang-Can

    2009-01-01

    This paper studies the quantum dynamics of electrons in a surface quantum well in the time domain with autocorrelation of wave packet. The evolution of the wave packet for different manifold eigenstates with finite and infinite lifetimes is investigated analytically. It is found that the quantum coherence and evolution of the surface electronic wave packet can be controlled by the laser central energy and electric field. The results show that the finite lifetime of excited states expedites the dephasing of the coherent electronic wave packet significantly. The correspondence between classical and quantum mechanics is shown explicitly in the system.

  7. Strong photoluminescence emission from resonant Fibonacci quantum wells.

    Science.gov (United States)

    Chang, C H; Chen, C H; Hsueh, W J

    2013-06-17

    Strong photoluminescence (PL) emission from a resonant Fibonacci quantum well (FQW) is demonstrated. The maximum PL intensity in the FQW is significantly stronger than that in a periodic QW under the Bragg or anti-Bragg conditions. Moreover, the peaks of the squared electric field in the FQW are located very near each of the QWs. The optimal PL spectrum in the FQW has an asymmetrical form rather than the symmetrical one in the periodic case. The maximum PL intensity and the corresponding thickness filling factor in the FQW become greater with increasing generation order.

  8. Relative Intensity Noise in the Single Quantum Well Diode

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    Based on the mathematical model of quantum well laser diode(QW-LDs) developed, the paper presents a relative intensity noise(RIN) model, which employs Gaussian form random noise with its average being to zero. It can be straightforwardly used to describe the effect of the noise on the performance of QW-LDs. The RIN becomes notable in the frequency range of interests and therefore affects the device modulation property. The results are in good agreement of the published data. The RIN model proposed and the results can be used for purpose of device technique improvement and performance simulation of optical communication systems and networks.

  9. Reliability assessment of multiple quantum well avalanche photodiodes

    Science.gov (United States)

    Yun, Ilgu; Menkara, Hicham M.; Wang, Yang; Oguzman, Isamil H.; Kolnik, Jan; Brennan, Kevin F.; May, Gray S.; Wagner, Brent K.; Summers, Christopher J.

    1995-01-01

    The reliability of doped-barrier AlGaAs/GsAs multi-quantum well avalanche photodiodes fabricated by molecular beam epitaxy is investigated via accelerated life tests. Dark current and breakdown voltage were the parameters monitored. The activation energy of the degradation mechanism and median device lifetime were determined. Device failure probability as a function of time was computed using the lognormal model. Analysis using the electron beam induced current method revealed the degradation to be caused by ionic impurities or contamination in the passivation layer.

  10. Photoluminescence efficiency in AlGaN quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Tamulaitis, G.; Mickevičius, J. [Institute of Applied Research and Semiconductor Physics Department, Vilnius University, Sauletekio av. 9-III, Vilnius LT-10222 (Lithuania); Jurkevičius, J., E-mail: jonas.jurkevicius@ff.vu.lt [Institute of Applied Research and Semiconductor Physics Department, Vilnius University, Sauletekio av. 9-III, Vilnius LT-10222 (Lithuania); Shur, M.S. [Department of ECE and CIE, Rensselaer Polytechnic Institute (United States); Shatalov, M.; Yang, J.; Gaska, R. [Sensor Electronic Technology, Inc. (United States)

    2014-11-15

    Photoluminescence spectroscopy of AlGaN/AlGaN multiple quantum wells under quasi-steady-state conditions in the temperature range from 8 to 300 K revealed a strong dependence of droop onset threshold on temperature that was explained by the influence of carrier delocalization. The delocalization at room temperature results predominantly in enhancement of bimolecular radiative recombination, while being favorable for enhancement of nonradiative recombination at low temperatures. Studies of stimulated emission confirmed the strong influence of carrier localization on droop.

  11. Thermopower enhancement in quantum wells with the Rashba effect

    Energy Technology Data Exchange (ETDEWEB)

    Wu, Lihua [State Key Laboratory of High Performance Ceramics and Superfine Microstructure, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050 (China); Materials Science and Engineering Department, University of Washington, Seattle, Washington 98195 (United States); University of Chinese Academy of Sciences, Beijing 100049 (China); Yang, Jiong; Wang, Shanyu; Wei, Ping; Yang, Jihui, E-mail: jihuiy@uw.edu, E-mail: wqzhang@mail.sic.ac.cn [Materials Science and Engineering Department, University of Washington, Seattle, Washington 98195 (United States); Zhang, Wenqing, E-mail: jihuiy@uw.edu, E-mail: wqzhang@mail.sic.ac.cn [State Key Laboratory of High Performance Ceramics and Superfine Microstructure, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050 (China); Materials Genome Institute, Shanghai University, Shanghai 200444 (China); Chen, Lidong [State Key Laboratory of High Performance Ceramics and Superfine Microstructure, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050 (China)

    2014-11-17

    We theoretically demonstrate that the thermopower in two-dimensional quantum wells (QWs) can be significantly enhanced by its Rashba spin-splitting effect, governed by the one-dimensional density of states in the low Fermi energy region. The thermopower enhancement is due to the lower Fermi level for a given carrier concentration in Rashba QWs, as compared with that in normal two-dimensional systems without the spin-splitting effect. The degenerate approximation directly shows that larger strength of Rashba effect leads to higher thermopower and consequently better thermoelectric performance in QWs.

  12. Binding energy of donors in symmetric triangular quantum wells

    Institute of Scientific and Technical Information of China (English)

    ZHANG Ji-ye; LIANG Xi-xia

    2005-01-01

    Hydrogen-like donor impurity states in symmetric triangular quantum wells are investigated by using a variational method.Both the effects of the variable effective mass of electrons and the spatially dependent dielectric constant are considered in the calculation.The numerical results show that the binding energy depends on not only the effective mass and dielectric constant but also the spatial distribution of electron probability density.The binding energies of donor states get the maximums at the well-center.The results are also compared with those obtained in parabolic and square wells.It is seen that the triangular well support the highest binding energies for donor states.

  13. Intersubband infrared absorption in stepped quantum wells under intense irradiation

    Energy Technology Data Exchange (ETDEWEB)

    Aceituno, P [Departamento de Fisica Basica, Universidad de La Laguna, La Laguna 38206-Tenerife, Canary Islands (Spain); Hernandez-Cabrera, A [Departamento de Fisica Basica, Universidad de La Laguna, La Laguna 38206-Tenerife, Canary Islands (Spain); Vasko, F T [Institute of Semiconductor Physics, NAS of Ukraine, Kiev 252650 (Ukraine)

    2005-11-02

    The effect of an intense THz irradiation on the relative intersubband absorption of electrons in stepped quantum wells of GaAs-GaAlAs is theoretically studied. Analytical expressions for the induced current are obtained by means of the adiabatic and resonant approximations within the matrix density formalism. This method allows one to predict the presence of a marked fine structure on the absorption, together with a shift and broadening of the absorption peaks, when the pump intensity is around the megawatts level.

  14. Interface Roughness Scattering on Electronic Transport in a Quantum Well

    Institute of Scientific and Technical Information of China (English)

    郑以松; 吕天全; 张程祥; 苏文辉

    2003-01-01

    Several theoretical models are established to simulate the interface roughness in a quantum well. The numerical result shows that the roughness correlation function always deviates from the extensively used Gaussian form to some extent, which depends on what a model is used. The influence of such a deviation on the electronic transport property is investigated by assuming several different analytical forms of the correlation function. It is found that the Fermi wavevector is crucial to determine whether the conductivity depends sensitively on the details of the correlation function.

  15. Ground- and excited-state impurity bands in quantum wells

    Science.gov (United States)

    Ghazali, A.; Gold, A.; Serre, J.

    1989-02-01

    The density of states and the spectral density of electrons in quantum wells with charged impurities are calculated with use of a multiple-scattering method. The impurity-density-dependent broadening and the gradual merging of the ground (1s) and excited (2p+/-,2s) impurity levels into impurity bands are investigated. At low density the shapes of the 1s, 2p+/-, and 2s spectral densities are found to be in excellent agreement with the analytical results obtained for the ideal two-dimensional Coulomb problem.

  16. Surface photovoltage spectroscopy of quantum wells and superlattices

    Energy Technology Data Exchange (ETDEWEB)

    Bachrach-Ashkenasy, N.; Kronik, L.; Shapira, Y. [Department of Physical Electronics, Faculty of Engineering, Tel-Aviv University, Ramat-Aviv 69978 (Israel); Rosenwaks, Y.; Hanna, M.C. [National Renewable Energy Laboratory, Golden, Colorado 80401 (United States); Leibovitch, M.; Ram, P. [Physics Department, Brooklyn College of the City University of New York, Brooklyn, New York 11210 (United States)

    1996-02-01

    Surface photovoltage spectroscopy (SPS) has been employed to monitor optical transitions in quantum well and superlattice structures at room temperature. Excellent agreement is found between theoretical predictions of heavy hole and electron energy level positions and the observed transitions. The results show that using this technique, the complete band diagram of the quantum structure may be constructed. SPS emerges as a powerful tool capable of monitoring optical transitions above the lowest one in a simple to interpret, contactless, and nondestructive way. {copyright} {ital 1996 American Institute of Physics.}

  17. Highly efficient metallic optical incouplers for quantum well infrared photodetectors

    Science.gov (United States)

    Liu, Long; Chen, Yu; Huang, Zhong; Du, Wei; Zhan, Peng; Wang, Zhenlin

    2016-01-01

    Herein, we propose a highly efficient metallic optical incoupler for a quantum well infrared photodetector (QWIP) operating in the spectrum range of 14~16 μm, which consists of an array of metal micropatches and a periodically corrugated metallic back plate sandwiching a semiconductor active layer. By exploiting the excitations of microcavity modes and hybrid spoof surface plasmons (SSPs) modes, this optical incoupler can convert infrared radiation efficiently into the quantum wells (QWs) layer of semiconductor region with large electrical field component (Ez) normal to the plane of QWs. Our further numerical simulations for optimization indicate that by tuning microcavity mode to overlap with hybrid SSPs mode in spectrum, a coupled mode is formed, which leads to 33-fold enhanced light absorption for QWs centered at wavelength of 14.5 μm compared with isotropic absorption of QWs without any metallic microstructures, as well as a large value of coupling efficiency (η) of |Ez|2 ~ 6. This coupled mode shows a slight dispersion over ~40° and weak polarization dependence, which is quite beneficial to the high performance infrared photodetectors. PMID:27456691

  18. Highly efficient metallic optical incouplers for quantum well infrared photodetectors

    Science.gov (United States)

    Liu, Long; Chen, Yu; Huang, Zhong; Du, Wei; Zhan, Peng; Wang, Zhenlin

    2016-07-01

    Herein, we propose a highly efficient metallic optical incoupler for a quantum well infrared photodetector (QWIP) operating in the spectrum range of 14~16 μm, which consists of an array of metal micropatches and a periodically corrugated metallic back plate sandwiching a semiconductor active layer. By exploiting the excitations of microcavity modes and hybrid spoof surface plasmons (SSPs) modes, this optical incoupler can convert infrared radiation efficiently into the quantum wells (QWs) layer of semiconductor region with large electrical field component (Ez) normal to the plane of QWs. Our further numerical simulations for optimization indicate that by tuning microcavity mode to overlap with hybrid SSPs mode in spectrum, a coupled mode is formed, which leads to 33-fold enhanced light absorption for QWs centered at wavelength of 14.5 μm compared with isotropic absorption of QWs without any metallic microstructures, as well as a large value of coupling efficiency (η) of |Ez|2 ~ 6. This coupled mode shows a slight dispersion over ~40° and weak polarization dependence, which is quite beneficial to the high performance infrared photodetectors.

  19. Optimized photonic crystal design for quantum well infrared photodetectors

    Science.gov (United States)

    Reininger, P.; Kalchmair, S.; Gansch, R.; Andrews, A. M.; Detz, H.; Zederbauer, T.; Ahn, S. I.; Schrenk, W.; Strasser, G.

    2012-06-01

    The performance of quantum well infrared photodetectors (QWIP) can be significantly enhanced combining it with a photonic crystal slab (PCS) resonator. In such a system the chosen PCS mode is designed to coincide with the absorption maximum of the photodetector by adjusting the lattice parameters. However there is a multitude of parameter sets that exhibit the same resonance frequency of the chosen PCS mode. We have investigated how the choice of the PC design can be exploited for a further enhancement of QWIPs. Several sets of lattice parameters that exhibit the chosen PCS mode at the same resonance frequency have been obtained and the finite difference time domain method was used to simulate the absorption spectra of the different PCS. A photonic crystal slab quantum well infrared photodetector with three different photonic crystal lattice designs that exhibit the same resonance frequency of the chosen PCS mode were designed, fabricated and measured. This work shows that the quality factor of a PCS-QWIP and therefore the absorption enhancement can be increased by an optimized PCS design. The improvement is a combined effect of a changed lattice constant, PC normalized radius and normalized slab thickness. An enhancement of the measured photocurrent of more than a factor of two was measured.

  20. Characterization of the nanostructure of complexes formed by single- or double-stranded oligonucleotides with a cationic surfactant.

    Science.gov (United States)

    Liu, Xiaoyang; Abbott, Nicholas L

    2010-12-02

    We report the use of dynamic light scattering (DLS), small-angle neutron scattering (SANS), and small-angle X-ray scattering (SAXS) to characterize the nanostructure of complexes formed by either single- or double-stranded oligonucleotides with a cationic surfactant (cetyltrimethylammonium bromide, CTAB) in aqueous solution (1 mM Li(2)SO(4)). For single-stranded oligonucleotides 5'-A(20)-3' and 5'-CCCCATTCTAGCAGCCCGGG-3', both the appearance of two Bragg peaks (at 0.14 and 0.28 Å(-1)) in SAXS spectra with a spacing of 1:2 and form factor fits to SANS spectra are consistent with the presence of multilamellar vesicles (with, on average, 6-9 layers with a periodicity of 45-48 Å). Some samples showed evidence of an additional Bragg peak (at 0.20 Å(-1)) associated with periodic packing (with a periodicity of 31 Å) of the oligonucleotides within the lamellae of the nanostructure. The nucleotide composition of the single-stranded oligonucleotides was also found to impact the number and size of the complexes formed with CTAB. In contrast to 5'-A(20)-3' and 5'-CCCCATTCTAGCAGCCCGGG-3', 5'-T(20)-3' did not change the state of aggregation of CTAB (globular micelles) over a wide range of oligonucleotide:CTAB charge ratios. These results support the proposition that hydrophobic interactions, as well as electrostatics, play a central role in the formation of complexes between cationic amphiphiles and single-stranded oligonucleotides and thus give rise to nanostructures that depend on nucleotide composition. In contrast to the single-stranded oligonucleotides, for double-stranded oligonucleotides mixed with CTAB, three Bragg peaks (0.13, 0.23, and 0.25 Å(-1)) in SAXS spectra with a spacing ratio of 1:√3:√4 and characteristic changes in SANS spectra indicate formation of a hexagonal nanostructure. Also, the composition of the double-stranded oligonucleotides did not measurably impact the nanostructure of complexes formed with CTAB, suggesting that electrostatic

  1. Multiple quantum wells for passive ultra short laser pulse generation

    CERN Document Server

    Quintero-Torres, R; Rodriguez-Rodriguez, E; Stintz, Andreas; Diels, Jean-Claude

    2007-01-01

    Solid state lasers are demanding independent control in the gain media and cavity loss to achieve ultra short laser pulses using passive mode-locking. Recently, laser mode-locking is achieved with a MBE structure with multiple quantum wells, designed to achieve two functions; Bragg mirror and changes in absorption to control the cavity dynamics. The use of an AlGaAs/AlAs Bragg mirror with a 15 nm GaAs saturable absorber used in a Cr:LiSAF tuneable laser proved to be effective to produce femtosecond pulses. The use of saturable absorbers thus far is a trial and error procedure that is changing due to the correlation with more predictive procedures.

  2. High frequency modeling for quantum-well laser diodes

    Institute of Scientific and Technical Information of China (English)

    GAO JianJun

    2009-01-01

    High frequency modeling of quantum-well (OW) laser diodes for optoelectronic integrated circuit (OEIC) design is discussed in this paper. Modeling of the intrinsic device and the extrinsic components is discussed by accounting for important physical effects at both de and high frequency. The concepts of equivalent circuits representing both intrinsic and extrinsic components in a QW laser diode are ana-lyzed to obtain a physics-based high frequency model. The model is based on the physical rate equa-tions, and is versatile in that it permits both small-and large-signal simulations to be performed. Sev-eral procedures of the high frequency model parameter extraction are also discussed. Emphasis here is placed on validating the model via a comparison of simulated results with measured data of the small-signal modulation response, obtained over a wide range of optical output powers.

  3. Bound polarons in quantum dot quantum well structures

    Institute of Scientific and Technical Information of China (English)

    Xing Yan; Wang Zhi-Ping; Wang Xu

    2009-01-01

    The problem of bound polarons in quantum dot quantum well (QDQW) structures is studied theoretically. The eigenfrequencies of bulk longitudinal optical (LO) and surface optical (SO) modes are derived in the framework of the diclectric continuum approximation. The electron-phonon interaction Hamiltonian for QDQW structures is obtained and the exchange interaction between impurity and LO-phonons is discussed. The binding energy and the trapping energy of the bound polaron in CdS/HgS QDQW structures are calculated. The numcrical results reveal that there exist three branches of eigenfrequcncies of surface optical vibration in the CdS/HgS QDQW structure. It is also shown that the binding energy and the trapping energy increase as the inner radius of the QDQW structure decreases, with the outer radius fixed, and the trapping energy takes a major part of the binding energy when the inner radius is very small.

  4. Excitons in quantum-dot quantum-well nanoparticles

    Institute of Scientific and Technical Information of China (English)

    史俊杰

    2002-01-01

    A variational calculation is presented for the ground-state properties of excitons confined in spherical core-shell quantum-dot quantum-well (QDQW) nanoparticles. The relationship between the exciton states and structure parameters of QDQW nanoparticles is investigated, in which both the heavy-hole and the light-hole exciton states are considered. The results show that the confinement energies of the electron and hole states and the exciton binding energies depend sensitively on the well width and core radius of the QDQW structure. A detailed comparison between the heavy-hole and light-hole exciton states is given. Excellent agreement is found between experimental results and our calculated 1se-1sh transition energies.

  5. Integrated photonic crystals and quantum well infrared photodetector

    Science.gov (United States)

    Zhou, T.; Tsui, D. C.; Choi, K. K.

    2004-03-01

    GaAs/AlGaAs based quantum well infrared photodetectors (QWIP) are becoming very reliable technologies that are widely used to detect mid-infrared light. Photonic crystals, on the other hand, are very powerful tools to manipulate light and thus are very crucial elements in future optical integration circuits. have fabricated a series of devices that incorporate QWIP and 2d photonic crystals together on a single GaAs based chip. These devices work at the 7-13 μ m range. Compared with the conventional photonic crystals designed for fiber communication, these devices have the advantage that they only require photolithography instead of e-beam lithography. The fabrication of such devices is thus far less costly and time-consuming.

  6. Eigenstate localization in an asymmetric coupled quantum well pair

    DEFF Research Database (Denmark)

    Mialitsin, Aleksej; Schmult, Stefan; Solov'yov, Ilia;

    2012-01-01

    exclusively either in the wide or the narrow parts of the well pair. The energy of the narrow-well localized state determines the minimal excitation energy for optically pumped charge carriers separation. In a previously used design [Guliamov et al., PRB 64 035314 (2001)] this narrow well transition energy......Optical pumping of a type-I/type-II coupled asymmetric quantum well pair induces a spatially separated two dimensional charge carriers plasma in the well’s wide and narrow parts. Treating the two coupled wells as a single system we find that the eigenstate probability distribution localizes...... was measured to correspond to a wavelength of 646 nm. We propose modifications to the design suggested earlier with the purpose of pushing up the energy required for the optical pumping of the two-dimensional plasma into the green and blue regions of the visible spectrum....

  7. Quantum wells under an in-plane magnetic field

    Energy Technology Data Exchange (ETDEWEB)

    Hernandez-Cabrera, A. [Dpto. Fisica Basica, Universidad de La Laguna, La Laguna, 38206 Tenerife (Spain)], E-mail: ajhernan@ull.es; Aceituno, P. [Dpto. Fisica Basica, Universidad de La Laguna, La Laguna, 38206 Tenerife (Spain); Vasko, F.T. [Institute of Semiconductor Physics, NAS Ukraine, Pr. Nauki 41, Kiev 03028 (Ukraine)

    2008-05-15

    The dependence of the electronic spin-splitting energy on the composition parameters (x,y) in In{sub x}Ga{sub 1-x}As-In{sub y}Al{sub 1-y}As-based quantum wells, has been calculated. InGaAs narrow gap structures, subjected to in-plane magnetic fields, have been selected because these structures have a big Lande factor. The dependence of the Lande factor both on the applied fields and composition parameters has been included for fixed well width and external electric field. Contributions from the interfaces and strain, which also depend on the composition, are included. Spin-splitting energy and density of states show a strong dependence on the above parameters.

  8. Impurity binding energy for -doped quantum well structures

    Indian Academy of Sciences (India)

    V Tulupenko; C A Duque; R Demediuk; O Fomina; V Akimov; V Belykh; T Dmitrichenko; V Poroshin

    2014-10-01

    The binding energy of an impurity delta layer situated either in the centre or at the edge of a quantum well (QW) is theoretically considered for the example of -type Si0.8Ge0.2/Si/Si0.8Ge0.2 QW doped with phosphorus. Calculations are made for the case of not so big impurity concentrations, when impurity bands are not yet formed and it is still possible to treat impurity as isolated ones. It is shown on the base of self-consistent solution of Schrödinger, Poisson and electro-neutrality equations that impurity binding energy is dependent on the degree of impurity ionization and the most noticeably for the case of edge-doped QWs.

  9. Coulomb correlation effects and density dependence of radiative recombination rates in polar AlGaN quantum wells

    Science.gov (United States)

    Rupper, Greg; Rudin, Sergey; Bertazzi, Francesco; Garrett, Gregory; Wraback, Michael

    2013-03-01

    AlGaN narrow quantum wells are important elements of deep-ultraviolet light emitting devices. The electron-hole radiative recombination rates are important characteristics of these nanostructures. In this work we evaluated their dependence on carrier density and lattice temperature and compared our theoretical results with the experimentally determined radiative lifetimes in the c-plane grown AlGaN quantum wells. The bands were determined in the k .p approximation for a strained c-plane wurtzite quantum well and polarization fields were included in the model. In order to account for Coulomb correlations at relatively high densities of photo-excited electron-hole plasma and arbitrary temperature, we employed real-time Green's function formalism with self-energies evaluated in the self-consistent T-matrix approximation. The luminescence spectrum was obtained from the susceptibility by summing over scattering in-plane directions and polarization states. The recombination coefficient was obtained from the integrated photo-luminescence. The density dependence of the radiative recombination rate shows effects of strong screening of the polarization electric field at high photo-excitation density.

  10. Frequency up-conversion in nonpolar a-plane GaN/AlGaN based multiple quantum wells optimized for applications with silicon solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Radosavljević, S.; Radovanović, J., E-mail: radovanovic@etf.bg.ac.rs; Milanović, V. [School of Electrical Engineering, University of Belgrade, Bulevar kralja Aleksandra 73, 11200 Belgrade (Serbia); Tomić, S. [Joule Physics Laboratory, School of Computing, Science and Engineering, University of Salford, Manchester M5 4WT (United Kingdom)

    2014-07-21

    We have described a method for structural parameters optimization of GaN/AlGaN multiple quantum well based up-converter for silicon solar cells. It involves a systematic tuning of individual step quantum wells by use of the genetic algorithm for global optimization. In quantum well structures, the up-conversion process can be achieved by utilizing nonlinear optical effects based on intersubband transitions. Both single and double step quantum wells have been tested in order to maximize the second order susceptibility derived from the density matrix formalism. The results obtained for single step wells proved slightly better and have been further pursued to obtain a more complex design, optimized for conversion of an entire range of incident photon energies.

  11. Frequency up-conversion in nonpolar a-plane GaN/AlGaN based multiple quantum wells optimized for applications with silicon solar cells

    Science.gov (United States)

    Radosavljević, S.; Radovanović, J.; Milanović, V.; Tomić, S.

    2014-07-01

    We have described a method for structural parameters optimization of GaN/AlGaN multiple quantum well based up-converter for silicon solar cells. It involves a systematic tuning of individual step quantum wells by use of the genetic algorithm for global optimization. In quantum well structures, the up-conversion process can be achieved by utilizing nonlinear optical effects based on intersubband transitions. Both single and double step quantum wells have been tested in order to maximize the second order susceptibility derived from the density matrix formalism. The results obtained for single step wells proved slightly better and have been further pursued to obtain a more complex design, optimized for conversion of an entire range of incident photon energies.

  12. Terahertz quantum-well photodetectors: Design, performance, and improvements

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, S., E-mail: phybuff@sjtu.edu.cn; Wang, T. M.; Hao, M. R.; Yang, Y.; Zhang, Y. H.; Shen, W. Z.; Liu, H. C. [Department of Physics and Astronomy, Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education), Shanghai Jiao Tong University, Shanghai 200240 (China)

    2013-11-21

    Theoretical studies and numerical simulations on design, performance, and improvements of terahertz quantum-well photodetector (THz QWP) are presented. In the first part of this paper, we discuss the device band structure resulting from a self-consistent solution and simulation results. First, the temperature dependence of device characteristics is analyzed. Next, we deduce the condition of optimal doping concentration for maximizing dark current limited detectivity D{sub det}* when QWP is lightly doped. Accordingly, unlike in previously published reports, doping concentration is not fixed and is selected by the above condition. In the second part of this paper, we propose two schemes for improving operation temperature. The first is to incorporate an optical antenna which focuses incident THz wave. Numerical results show that the QWP with peak frequency higher than 5.5 THz is expected to achieve background-noise-limited performance at 77 K or above when employing a 10{sup 6} times enhancement antenna. The second scheme is to use a laser as the signal source to achieve photon-noise-limited performance (PLIP) at high temperatures. Simulations show that when operating below critical temperature QWPs in the range of 1 ∼ 7 THz can reach PLIP under practical illumination intensities.

  13. Fractal quantum well heterostructures for broadband light emitters

    Energy Technology Data Exchange (ETDEWEB)

    Crawford, M.H.; Gourley, P.L.; Meissner, K.E.; Sinclair, M.B.; Jones, E.D.; Chow, W.W.; Schneider, R.P. Jr.

    1994-12-31

    We examine carrier relaxation and radiative recombination in AlGaAs based near IR and AlGaInP based visible fractal quantum well heterostructures. Through temperature dependent photoluminescence, we demonstrate that enhanced population of higher lying energy levels can be achieved by varying the thickness of the layers in the fractal heterostructurd. This distribution of carriers results in room temperature emission over a relatively broad range of wavelengths: approximately 700--855 nm for AlGaAs structures and 575--650 nm for AlGaInP structures. Spectra are compared to theoretical calculations to evaluate the non-equilibrium nature of the carrier distributions. Time resolved photoluminescence measurements demonstrate an approximately linear relationship between the radiative decay time and the layer thickness of the structure. Correspondingly, integrated luminescence measurements at room temperature reveal a factor of four increase in the light output efficiency of the structure as the fractal layer thickness is increased from 50 {angstrom} to 400 {angstrom}. The applicability of these heterostructures to broadband LEDs is discussed.

  14. Nanostructured Double Hydrophobic Poly(Styrene-b-Methyl Methacrylate) Block Copolymer Membrane Manufactured Via Phase Inversion Technique

    KAUST Repository

    Karunakaran, Madhavan

    2016-03-11

    In this paper, we demonstrate the formation of nanostructured double hydrophobic poly(styrene-b-methyl methacrylate) (PS-b-PMMA) block copolymer membranes via state-of-the-art phase inversion technique. The nanostructured membrane morphologies are tuned by different solvent and block copolymer compositions. The membrane morphology has been investigated using FESEM, AFM and TEM. Morphological investigation shows the formation of both cylindrical and lamellar structures on the top surface of the block copolymer membranes. The PS-b-PMMA having an equal block length (PS160K-b-PMMA160K) exhibits both cylindrical and lamellar structures on the top layer of the asymmetric membrane. All membranes fabricated from PS160K-b-PMMA160K shows an incomplete pore formation in both cylindrical and lamellar morphologies during the phase inversion process. However, PS-b-PMMA (PS135K-b-PMMA19.5K) block copolymer having a short PMMA block allowed us to produce open pore structures with ordered hexagonal cylindrical pores during the phase inversion process. The resulting PS-b-PMMA nanostructured block copolymer membranes have pure water flux from 105-820 l/m2.h.bar and 95% retention of PEG50K

  15. Emergence of the Persistent Spin Helix in Semiconductor Quantum Wells

    Energy Technology Data Exchange (ETDEWEB)

    Koralek, Jake; Weber, Chris; Orenstein, Joe; Bernevig, Andrei; Zhang, Shoucheng; Mack, Shawn; Awschalom, David

    2011-08-24

    According to Noether's theorem, for every symmetry in nature there is a corresponding conservation law. For example, invariance with respect to spatial translation corresponds to conservation of momentum. In another well-known example, invariance with respect to rotation of the electron's spin, or SU(2) symmetry, leads to conservation of spin polarization. For electrons in a solid, this symmetry is ordinarily broken by spin-orbit (SO) coupling, allowing spin angular momentum to flow to orbital angular momentum. However, it has recently been predicted that SU(2) can be recovered in a two-dimensional electron gas (2DEG), despite the presence of SO coupling. The corresponding conserved quantities include the amplitude and phase of a helical spin density wave termed the 'persistent spin helix' (PSH). SU(2) is restored, in principle, when the strength of two dominant SO interactions, the Rashba ({alpha}) and linear Dresselhaus ({beta}{sub 1}), are equal. This symmetry is predicted to be robust against all forms of spin-independent scattering, including electron-electron interactions, but is broken by the cubic Dresselhaus term ({beta}{sub 3}) and spin-dependent scattering. When these terms are negligible, the distance over which spin information can propagate is predicted to diverge as {alpha} {yields} {beta}{sub 1}. Here we observe experimentally the emergence of the PSH in GaAs quantum wells (QW's) by independently tuning {alpha} and {beta}{sub 1}. Using transient spin-grating spectroscopy (TSG), we find a spin-lifetime enhancement of two orders of magnitude near the symmetry point. Excellent quantitative agreement with theory across a wide range of sample parameters allows us to obtain an absolute measure of all relevant SO terms, identifying {beta}{sub 3} as the main SU(2) violating term in our samples. The tunable suppression of spin-relaxation demonstrated in this work is well-suited for application to spintronics.

  16. Enhancement of carrier lifetimes in type-II quantum dot/quantum well hybrid structures

    Energy Technology Data Exchange (ETDEWEB)

    Couto, O. D. D., E-mail: odilon@ifi.unicamp.br; Almeida, P. T. de; Santos, G. E. dos; Balanta, M. A. G.; Andriolo, H. F.; Brum, J. A.; Brasil, M. J. S. P.; Iikawa, F. [Instituto de Física “Gleb Wataghin,” Universidade Estadual de Campinas, 13083-859 Campinas, São Paulo (Brazil); Liang, B. L., E-mail: bliang@cnsi.ucla.edu; Huffaker, D. L. [California NanoSystems Institute, UCLA, Los Angeles, California 90095 (United States)

    2016-08-28

    We investigate optical transitions and carrier dynamics in hybrid structures containing type-I GaAs/AlGaAs quantum wells (QWs) and type-II GaSb/AlGaAs quantum dots (QDs). We show that the optical recombination of photocreated electrons confined in the QWs with holes in the QDs and wetting layer can be modified according to the QW/QD spatial separation. In particular, for low spacer thicknesses, the QW optical emission can be suppressed due to the transference of holes from the QW to the GaSb layer, favoring the optical recombination of spatially separated carriers, which can be useful for optical memory and solar cell applications. Time-resolved photoluminescence (PL) measurements reveal non-exponential recombination dynamics. We demonstrate that the PL transients can only be quantitatively described by considering both linear and quadratic terms of the carrier density in the bimolecular recombination approximation for type-II semiconductor nanostructures. We extract long exciton lifetimes from 700 ns to 5 μs for QDs depending on the spacer layer thickness.

  17. Enhanced Luminescence Performance of Quantum Wells by Coupling Piezo-Phototronic with Plasmonic Effects.

    Science.gov (United States)

    Huang, Xin; Jiang, Chunyan; Du, Chunhua; Jing, Liang; Liu, Mengmeng; Hu, Weiguo; Wang, Zhong Lin

    2016-12-27

    With a promising prospect of light-emitting diodes as an attractive alternative to conventional light sources, remaining challenges still cannot be addressed owing to their limited efficiency. Among the continued scientific efforts, significant improvement on the emission efficiency has been achieved via either piezo-phototronic effect-based strain modulation or resonant excitation of plasmons in metallic nanostructures. Here, we present the investigation on the coupling process between piezo-phototronic effect and localized surface plasmonic resonance for enhancing the photoluminescence of InGaN/GaN quantum wells coated with Ag nanoparticles. The underlying physical mechanism of experimental results originates from tuning plasmonic resonance controlled by the shift of emission wavelength via piezo-phototronic effect, and it is further confirmed with the support of theoretical calculations. As a result, our research provides an approach to the integration of plasmonics with piezo-phototronic effect and brings widespread applications to high-efficiency artificial lighting, on-chip integrated plasmonic circuits, subwavelength optical communication, and micro-optoelectronic mechanical systems.

  18. Anticrossing double Fano resonances generated in metallic/dielectric hybrid nanostructures using nonradiative anapole modes for enhanced nonlinear optical effects.

    Science.gov (United States)

    Zhai, Wu-Chao; Qiao, Tie-Zhu; Cai, Dong-Jin; Wang, Wen-Jie; Chen, Jing-Dong; Chen, Zhi-Hui; Liu, Shao-Ding

    2016-11-28

    Third-harmonic generation with metallic or dielectric nanoparticles often suffer from, respectively, small modal volumes and weak near-field enhancements. This study propose and demonstrate that a metallic/dielectric hybrid nanostructure composed of a silver double rectangular nanoring and a silicon square nanoplate can be used to overcome these obstacles for enhanced third-harmonic generation. It is shown that the nonradiative anapole mode of the Si plate can be used as a localized source to excite the dark subradiant octupole mode of the Ag ring, and the mode hybridization leads to the formation of an antibonding and a bonding subradiant collective mode, thereby forming anticrossing double Fano resonances. With the strong coupling between individual particles and the effectively suppressed radiative losses of the Fano resonances, several strong hot spots are generated around the Ag ring due to the excitation of the octupole mode, and electromagnetic fields within the Si plate are also strongly amplified, making it possible to confine more incident energy inside the dielectric nanoparticle. Calculation results reveal that the confined energy inside the Si plate and the Ag ring for the hybrid structures can be about, respectively, more than three times and four orders stronger than that of the corresponding isolated nanoparticles, which makes the designed hybrid nanostructure a promising platform for enhanced third-harmonic generation.

  19. Double-layered TiO2-SiO2 nanostructured films with self-cleaning and antireflective properties.

    Science.gov (United States)

    Zhang, Xintong; Fujishima, Akira; Jin, Ming; Emeline, Alexei V; Murakami, Taketoshi

    2006-12-21

    Dual function of self-cleaning and antireflection can be created in double-layered TiO2-SiO2 nanostructured films. The film were prepared by (1) layer-by-layer deposition of multilayered SiO2 nanoparticles with polydiallyldimethylammonium (PDDA) cations, (2) layer-by-layer deposition of multilayered titanate nanosheets with polications on PDDA/SiO2 multilayer films, and (3) burning out the polymer and converting titanate nanosheets into TiO2 by hearing at 500 degrees C. The as-prepared films, consisting of a porous SiO2 bottom layer and a dense TiO2 top layer, improved the transmittance of glass or quartz substrates, as demonstrated by transmission spectra collected at normal incidence. The photocatalytic properties of the films were studied by the change of the water contact angle together with the decay of the IR absorption of the hydrocarbon chain of octadecylphosphonic-acid-modified films under 2.6 mW cm-2 UV illumination. Both the antireflective and the photocatalytic properties of the films were dependent on the number of PDDA/nanosheet bilayers deposited. however, excellent surface wettability of the films for water was obtained, independent of the preparation conditions. The experimental findings are discussed in terms of the special structure of the double-layered nanostructured film.

  20. Radiation Effects in Nanostructures: Comparison of Proton Irradiation Induced Changes on Quantum Dots and Quantum Wells

    Science.gov (United States)

    Leon, R.; Swift, G.; Magness, B.; Taylor, W.; Tang, Y.; Wang, K.; Dowd, P.; Zhang, Y.

    2000-01-01

    Successful implementation of technology using self-forming semiconductor Quantum Dots (QDs) has already demonstrated that temperature independent Dirac-delta density of states can be exploited in low current threshold QD lasers and QD infrared photodetectors.

  1. Electrically stimulated high-frequency replicas of a resonant current in GaAs/AlAs resonant-tunneling double-barrier THz nanostructures

    Science.gov (United States)

    Aleksanyan, A. A.; Karuzskii, A. L.; Kazakov, I. P.; Mityagin, Yu. A.; Murzin, V. N.; Perestoronin, A. V.; Shmelev, S. S.; Tskhovrebov, A. M.

    2016-12-01

    The periodical-in-voltage features of the negative differential conductance (NDC) region in the current-voltage characteristics of a high-quality GaAs/AlAs terahertz resonant-tunneling diode have been detected. The found oscillations are considered taking account of the LO-phonon excitation stimulated by tunneling of electrons through the quantum active region in the resonance nanostructure where an undoped quantum well layer is sandwiched between two undoped barrier layers. Rearrangements in the I-V characteristics of the resonant-tunneling diode as a consequence of the topological transformation of a measurement circuit from the circuit with the series resistance Rs to the circuit with the shunt Rp have been experimentally studied and analyzed. The revealed substantial changes in the current-voltage characteristics of the resonant-tunneling diode are discussed schematically using Kirchhoff's voltage law.

  2. Light-trapping for room temperature Bose-Einstein condensation in InGaAs quantum wells.

    Science.gov (United States)

    Vasudev, Pranai; Jiang, Jian-Hua; John, Sajeev

    2016-06-27

    We demonstrate the possibility of room-temperature, thermal equilibrium Bose-Einstein condensation (BEC) of exciton-polaritons in a multiple quantum well (QW) system composed of InGaAs quantum wells surrounded by InP barriers, allowing for the emission of light near telecommunication wavelengths. The QWs are embedded in a cavity consisting of double slanted pore (SP2) photonic crystals composed of InP. We consider exciton-polaritons that result from the strong coupling between the multiple quantum well excitons and photons in the lowest planar guided mode within the photonic band gap (PBG) of the photonic crystal cavity. The collective coupling of three QWs results in a vacuum Rabi splitting of 3% of the bare exciton recombination energy. Due to the full three-dimensional PBG exhibited by the SP2 photonic crystal (16% gap to mid-gap frequency ratio), the radiative decay of polaritons is eliminated in all directions. Due to the short exciton-phonon scattering time in InGaAs quantum wells of 0.5 ps and the exciton non-radiative decay time of 200 ps at room temperature, polaritons can achieve thermal equilibrium with the host lattice to form an equilibrium BEC. Using a SP2 photonic crystal with a lattice constant of a = 516 nm, a unit cell height of 2a=730nm and a pore radius of 0.305a = 157 nm, light in the lowest planar guided mode is strongly localized in the central slab layer. The central slab layer consists of 3 nm InGaAs quantum wells with 7 nm InP barriers, in which excitons have a recombination energy of 0.944 eV, a binding energy of 7 meV and a Bohr radius of aB = 10 nm. We take the exciton recombination energy to be detuned 35 meV above the lowest guided photonic mode so that an exciton-polariton has a photonic fraction of approximately 97% per QW. This increases the energy range of small-effective-mass photonlike states and increases the critical temperature for the onset of a Bose-Einstein condensate. With three quantum wells in the central slab layer

  3. Blue InGaN light-emitting diodes with dip-shaped quantum wells

    Institute of Scientific and Technical Information of China (English)

    Lu Tai-Ping; Wang Hai-Long; Yang Xiao-Dong; LiShu-Ti; Zhang Kang; Liu Chao; Xiao Guo-Wei; Zhou Yu-Gang; ZhengShu-Wen; Yin Yi-An; Wu Le-Juan

    2011-01-01

    InGaN based light-emitting diodes (LEDs) with dip-shaped quantum wells and conventional rectangular quantum wells are numerically investigated by using the APSYS simulation software.It is found that the structure with dipshaped quantum wells shows improved light output power,lower current leakage and less efficiency droop.Based on numerical simulation and analysis,these improvements on the electrical and the optical characteristics are attributed mainly to the alleviation of the electrostatic field in dip-shaped InGaN/GaN multiple quantum wells (MQWs).

  4. Direct observation of free-exciton thermalization in quantum-well structures

    DEFF Research Database (Denmark)

    Umlauff, M.; Hoffmann, J.; Kalt, H.

    1998-01-01

    We report on a direct observation of free-exciton thermalization in quantum-well structures. A narrow energy distribution of free 1s excitons is created in ZnSe-based quantum wells by emission of one LO phonon after optical excitation of the continuum stales with picosecond laser pulses. The subs......We report on a direct observation of free-exciton thermalization in quantum-well structures. A narrow energy distribution of free 1s excitons is created in ZnSe-based quantum wells by emission of one LO phonon after optical excitation of the continuum stales with picosecond laser pulses...

  5. Structural and Optical Characteristics of GeSn Quantum Wells for Silicon-Based Mid-Infrared Optoelectronic Applications

    Science.gov (United States)

    Dou, Wei; Ghetmiri, Seyed Amir; Al-Kabi, Sattar; Mosleh, Aboozar; Zhou, Yiyin; Alharthi, Bader; Du, Wei; Margetis, Joe; Tolle, John; Kuchuk, Andrian; Benamara, Mourad; Li, Baohua; Naseem, Hameed A.; Mortazavi, Mansour; Yu, Shui-Qing

    2016-12-01

    This paper reports the study of Ge0.95Sn0.05/Ge0.91Sn0.09/Ge0.95Sn0.05 single quantum well (SQW) and double quantum wells (DQWs). The quantum well (QW) structures were grown on Ge buffered Si substrates using an industrial standard reduced-pressure chemical vapor deposition system. Pseudomorphically grown structures were observed using x-ray diffraction measurements. Defect-free interfaces between each layer were revealed using cross-sectional transmission electron microscopy. Atomic-scale high-resolution transmission electron microscopy and Fourier transform patterns exhibited the high crystalline quality of QWs. Temperature-dependent photoluminescence (PL) was performed, and the emission peaks attributed to the QW region were identified. The dominant optical transition changed from direct bandgap transition at 300 K to indirect bandgap transition at 10 K. Theoretical calculation showed the type-I band alignment for the QWs. Moreover, the Γ and L valley electron distributions and non-radiative lifetimes were evaluated, which further explained the PL characteristics of the QW samples.

  6. Effect of plasmonic losses on light emission enhancement in quantum-wells coupled to metallic gratings

    Science.gov (United States)

    Sadi, Toufik; Oksanen, Jani; Tulkki, Jukka

    2013-12-01

    Recent experimental work has shown significant luminescence enhancement from near-surface quantum-well (QW) structures using metallic grating to convert surface plasmon (SP) modes into radiative modes. This work introduces a detailed theoretical study of plasmonic losses and the role of SPs in improving light extraction from grated light-emitting QW structures, using the fluctuational electrodynamics method. The method explains experimental results demonstrating emission enhancement, light scattering, and plasmonic coupling in the structures. We study these effects in angle-resolved reflectometry and luminescence setups in InGaN QW structures with silver grating. In contrast to experiments, our model allows direct calculation of the optical losses. The model predicts that the plasmonic coupling and scattering increases light emission by a factor of up to three compared to a flat semiconductor structure. This corresponds to reducing the absorption losses from approximately 93% in the ungrated metallic structure to 75% in the grated structure. Lower losses are associated with a significant emission enhancement enabled by the SPs of silver/GaN interfaces, which are present in the blue/green wavelength range, and can be optimized by carefully nanostructuring the metal layer and by the positioning of the QW. In general, the enhancement results from the interplay of mode scattering, conversion of SP energy directly into light, and losses in the metallic grating. The reported losses are very high when compared to the losses present in modern light-emitting diodes (LEDs). Albeit, our work provides tools needed for further optimization of plasmonic light extraction, eventually leading to highly efficient LEDs.

  7. Crystal orientation effects on the piezoelectric field of strained zinc-blende quantum-well structures

    DEFF Research Database (Denmark)

    Duggen, Lars; Willatzen, Morten; Lassen, Benny

    2008-01-01

    A three-layered zinc-blende quantum-well structure is analyzed subject to both static and dynamic conditions for different crystal growth directions taking into account piezoelectric effects and lattice mismatch. It is found that the strain component Szz in the quantum-well region strongly depend...

  8. Biexciton binding energy in ZnSe quantum wells and quantum wires

    DEFF Research Database (Denmark)

    Wagner, Hans-Peter; Langbein, Wolfgang; Hvam, Jørn Märcher

    2002-01-01

    The biexciton binding energy E-XX is investigated in ZnSe/ZnMgSe quantum wells and quantum wires as a function of the lateral confinement by transient four-wave mixing. In the quantum wells one observes for decreasing well width a significant increase in the relative binding energy, saturating...

  9. Quantum confined Stark effect in Gaussian quantum wells: A tight-binding study

    Energy Technology Data Exchange (ETDEWEB)

    Ramírez-Morales, A.; Martínez-Orozco, J. C.; Rodríguez-Vargas, I. [Unidad Académica de Física, Universidad Autónoma de Zacatecas, Calzada Solidaridad Esquina Con Paseo La Bufa S/N, 98060 Zacatecas, Zac. (Mexico)

    2014-05-15

    The main characteristics of the quantum confined Stark effect (QCSE) are studied theoretically in quantum wells of Gaussian profile. The semi-empirical tight-binding model and the Green function formalism are applied in the numerical calculations. A comparison of the QCSE in quantum wells with different kinds of confining potential is presented.

  10. Monolithic integration of electroabsorption modulators and tunnel injection distributed feedback lasers using quantum well intermixing

    Science.gov (United States)

    Wang, Yang; Pan, Jiao-Qing; Zhao, Ling-Juan; Zhu, Hong-Liang; Wang, Wei

    2010-12-01

    Electroabsorption modulators combining Franz-Keldysh effect and quantum confined Stark effect have been monolithically integrated with tunnel-injection quantum-well distributed feedback lasers using a quantum well intermixing method. Superior characteristics such as extinction ratio and temperature insensitivity have been demonstrated at wide temperature ranges.

  11. Vertical excitation profile in diffusion injected multi-quantum well light emitting diode structure

    Science.gov (United States)

    Riuttanen, L.; Kivisaari, P.; Svensk, O.; Vasara, T.; Myllys, P.; Oksanen, J.; Suihkonen, S.

    2015-03-01

    Due to their potential to improve the performance of light-emitting diodes (LEDs), novel device structures based on nanowires, surface plasmons, and large-area high-power devices have received increasing amount of interest. These structures are almost exclusively based on the double hetero junction (DHJ) structure, that has remained essentially unchanged for decades. In this work we study a III-nitride diffusion injected light-emitting diode (DILED), in which the active region is located outside the pn-junction and the excitation of the active region is based on bipolar diffusion of charge carriers. This unorthodox approach removes the need of placing the active region in the conventional current path and thus enabling carrier injection in device structures, which would be challenging to realize with the conventional DHJ design. The structure studied in this work is has 3 indium gallium nitride / gallium nitride (InGaN/GaN) quantum wells (QWs) under a GaN pn-junction. The QWs are grown at diferent growth temperatures for obtaining distinctive luminescence peaks. This allows to obtain knowledge on the carrier diffusion in the structure. When the device is biased, all QWs emit light indicating a significant diffusion current into the QW stack.

  12. Optical Absorption, Emission, and Modulation in Iii-V Semiconductor Quantum Well Structures

    Science.gov (United States)

    Shank, Steven Marc

    An experimental study of topics relating to optical absorption, emission, and modulation in III-V semiconductor GaAs/AlGaAs quantum well structures is presented. Several novel quantum well structures are examined and evaluated for use in electrooptic modulators, laser diodes, and monolithically integrated laser diodes and passive waveguides. The design of the epitaxial structures, the molecular beam epitaxy growth, the optical characterization of the wafers, the fabrication of the wafers into basic optoelectronic devices (electrooptic waveguides, laser diodes, and segmented laser diodes), and the characterization of these devices are described. The quantum confined Stark effect and its influence on the electrooptic properties of quantum wells are described. In particular, electroabsorption and electrobirefringence in (111)B quantum wells are investigated. This quantum well system is chosen due to the larger heavy hole effective mass compared to standard (100) quantum wells. It is demonstrated that electroabsorption and electrobirefringence are enhanced in (111)B quantum wells, which agrees with theoretical predictions based on the heavy hole mass anisotropy. Computer simulations of the quantum confined Stark effect in asymmetric quantum well structures are described. It is demonstrated that asymmetric quantum wells can exhibit enhanced red shifts of the absorption edge, and blue shifts of the absorption edge under an applied reverse bias. An experimental investigation of laser diodes with asymmetric quantum well active regions is described. An evaluation of the blue shift effect on the interband absorption at the laser wavelength is made and related to the efficiency of these structures for monolithic integration with passive waveguides. The optical properties of n-type modulation doped quantum wells are described. It is shown that the interband absorption at the spontaneous emission peak can be greatly reduced compared to undoped quantum wells. N-type modulation

  13. Intervalley splitting and intersubband transitions in n -type Si/SiGe quantum wells: Pseudopotential vs. effective mass calculation

    Science.gov (United States)

    Valavanis, A.; Ikonić, Z.; Kelsall, R. W.

    2007-05-01

    Intervalley mixing between conduction-band states in low-dimensional Si/SiGe heterostructures induces splitting between nominally degenerate energy levels. The symmetric double-valley effective mass approximation and the empirical pseudopotential method are used to find the electronic states in different types of quantum wells. A reasonably good agreement between the two methods is found, with the former being much faster computationally. Aside from being an oscillatory function of well width, the splitting is found to be almost independent of in-plane wave vector, and an increasing function of the magnitude of interface gradient. While the model is defined for symmetric envelope potentials, it is shown to remain reasonably accurate for slightly asymmetric structures such as a double quantum well, making it acceptable for simulation of multilayer intersubband optical devices. Intersubband optical transitions are investigated under both approximations and it is shown that in most cases valley splitting causes linewidth broadening, although under extreme conditions, transition line doublets may result.

  14. Thomas-Fermi approximation in two p-type delta-doped quantum wells in GaAs an Si

    Energy Technology Data Exchange (ETDEWEB)

    Gaggero-Sager, L. M. [Universidad Autonoma de Zacatecas, Zacatecas (Mexico); M' Peko, J. C.; Perez Alvarez, R. [Universidad de La Habana, Ciudad Habana (Cuba)

    2001-04-01

    Thomas-Fermi calculations of the hole subband structure in two coupled p-type d-doped GaAs and Si quantum wells are carried out as a function of the impurity concentration and the distance l between them. A simple formula is obtained for the potential as a function of these two magnitudes by both types of systems. The numerical results for a double Be-{delta}-doped GaAs (double B-{delta}-doped Si) quantum well show that the energy levels degenerate for l{>=}300 A(l{>=}200 A) for an impurity concentration of 1 x 10{sup 1}3 cm{sup -2}. [Spanish] Presentamos calculos de la estructura de subbandas de huecos, utilizando la aproximacion de Thomas-Fermi para dos pozos cuanticos d-dopados tipo p en GaAs y Si, como funcion de la concentracion de impurezas y de la distancia l entre ambos para los dos tipos de sistemas. Los resultados numericos muestran que para un pozo doble de B-{delta}-dopado GaAs (pozo doble de B-{delta}-dopado Si) con una concentracion de 1 x 10{sup 1}3 cm{sup -2} los niveles estan degenerados para l{>=}300 A(l{>=}200 A).

  15. Anisotropic emission and photon-recycling in strain-balanced quantum well solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Cabrera, C. I.; Enciso, A.; Contreras-Solorio, D. A. [Academic Unit of Physics, Autonomous University of Zacatecas, Czda. Solidaridad y Paseo La Bufa S/N, 98060 Zacatecas, Zac. (Mexico); Rimada, J. C. [Solar Cell Laboratory, Institute of Materials Science and Technology (IMRE), University of Havana, Zapata y G, 10400 La Habana (Cuba); Hernandez, L., E-mail: luisman@fisica.uh.cu [Faculty of Physics, University of Havana, Colina Universitaria. 10400 La Habana (Cuba); Connolly, J. P. [Nanophotonics Technology Center, Universidad Politécnica de Valencia, 46022 Valencia (Spain)

    2014-04-28

    Strain-balanced quantum well solar cells (SB-QWSCs) extend the photon absorption edge beyond that of bulk GaAs by incorporation of quantum wells in the i-region of a p–i–n device. Anisotropy arises from a splitting of the valence band due to compressive strain in the quantum wells, suppressing a transition which contributes to emission from the edge of the quantum wells. We have studied both the emission light polarized in the plane perpendicular (TM) to the quantum well which couples exclusively to the light hole transition and the emission polarized in the plane of the quantum wells (TE) which couples mainly to the heavy hole transition. It was found that the spontaneous emission rates TM and TE increase when the quantum wells are deeper. The addition of a distributed Bragg reflector can substantially increase the photocurrent while decreasing the radiative recombination current. We have examined the impact of the photon recycling effect on SB-QWSC performance. We have optimized SB-QWSC design to achieve single junction efficiencies above 30%.

  16. On the binding energies of excitons in polar quantum well structures in a weak electric field

    Institute of Scientific and Technical Information of China (English)

    Wu Yun-Feng; Liang Xi-Xia; K. K. Bajaj

    2005-01-01

    The binding energies of excitons in quantum well structures subjected to an applied uniform electric field by taking into account the exciton longitudinal optical phonon interaction is calculated. The binding energies and corresponding Stark shifts for Ⅲ-Ⅴ and Ⅱ-Ⅵ compound semiconductor quantum well structures have been numerically computed.The results for GaAs/AlGaAs and ZnCdSe/ZnSe quantum wells are given and discussed. Theoretical results show that the exciton-phonon coupling reduces both the exciton binding energies and the Stark shifts by screening the Coulomb interaction. This effect is observable experimentally and cannot be neglected.

  17. Mid-infrared intersubband absorption from p-Ge quantum wells grown on Si substrates

    Energy Technology Data Exchange (ETDEWEB)

    Gallacher, K.; Millar, R. W.; Paul, D. J., E-mail: Douglas.Paul@glasgow.ac.uk [School of Engineering, University of Glasgow, Rankine Building, Oakfield Avenue, Glasgow G12 8LT (United Kingdom); Ballabio, A.; Frigerio, J.; Isella, G. [L-NESS, Dipartimento di Fisica del Politecnico di Milano, Polo Territoriale di Como, Via Anzani 42, Como I-22100 (Italy); Bashir, A.; MacLaren, I. [School of Physics and Astronomy, University of Glasgow, Kelvin Building, University Avenue, Glasgow G12 8QQ (United Kingdom); Ortolani, M. [Center for Life NanoScience@Sapienza, Istituto Italiano di Tecnologia, Viale Regina Elena 291, Rome I-00161 (Italy)

    2016-02-29

    Mid-infrared intersubband absorption from p-Ge quantum wells with Si{sub 0.5}Ge{sub 0.5} barriers grown on a Si substrate is demonstrated from 6 to 9 μm wavelength at room temperature and can be tuned by adjusting the quantum well thickness. Fourier transform infra-red transmission and photoluminescence measurements demonstrate clear absorption peaks corresponding to intersubband transitions among confined hole states. The work indicates an approach that will allow quantum well intersubband photodetectors to be realized on Si substrates in the important atmospheric transmission window of 8–13 μm.

  18. Inter-Well Coupling and Resonant Tunneling Modes of Multiple Graphene Quantum Wells

    Institute of Scientific and Technical Information of China (English)

    安丽萍; 王同标; 刘念华

    2011-01-01

    We investigate the inter-well coupling of multiple graphene quantum well structures consisting of graphene superlattices with different periodic potentials. The general form of the eigenlevel equation for the bound states of the quantum well is expressed in terms of the transfer matrix elements. It is found that the electronic transmission exhibits resonant tunneling peaks at the eigenlevels of the bound states and shifts to the higher energy with increasing the incident angle. If there are N coupled quantum wells, the resonant modes have N-fold splitting. The peaks of resonant tunneling can be controlled by modulating the graphene barriers.

  19. Simulation of quantum-well slipping effect on optical bandwidth in transistor laser

    Institute of Scientific and Technical Information of China (English)

    Hassan Kaatuzian; Seyed Iman Taghavi

    2009-01-01

    An optical bandwidth analysis of a quantum-well(16 nm)transistor laser with 150-μm cavity length using a charge control model is reported in order to modify the quantum-well location through the base region.At constant bias current,the simulation shows significant enhancement in optical bandwidth due to moving the quantum well in the direction of collector-base junction.No remarkable resonance peak,limiting factor in laser diodes,is observed during this modification in transistor laser structure.The method can be utilized for transistor laser structure design.

  20. Theoretical Study on Absorption of Magnetically Tunable Terahertz Quantum- Well Photodetectors

    Institute of Scientific and Technical Information of China (English)

    CHEN Yu-Ling; GUO Xu-Guang; CAO Jun-Cheng

    2006-01-01

    Because of the Zeeman splitting effect in diluted semiconductor (Zn,Cd,Mn)Se, the absorption spectrum of ZnSe/(Zn,Cd,Mn)Se quantum wells can be adjusted by magnetic field effectively. Within the effective-mass approximation, the conduction electronic structure and the absorption spectrum of ZnSe/(Zn,Cd,Mn)Se quantum wells subjected to in-plane magnetic Gelds are investigated. Our theoretical results show that it is possible to use the ZnSe/(Zn,Cd,Mn)Se quantum well as magnetically tunable terahertz photodetectors.

  1. A new switching characteristics of highly doped multi-quantum well

    CERN Document Server

    Song, C K

    1999-01-01

    A new type of hysteretic current-voltage characteristics, which switched from a low conductance off-state into a high conductance on-state at a threshold voltage and the high conductance state was sustained even when the bias voltage reduced below the threshold voltage, was experimentally observed for the highly doped multi-quantum well structure. The characteristics were attributed to confinement of electrons and impact ionization of the confined electrons out of the quantum wells. The test devices employing 10 periods of quantum wells were fabricated by using AlGaAs/GaAs semiconductor heterostructure and I-V characteristics were examined.

  2. Plasmon enhancement of Coulomb drag in double-quantum-well systems

    DEFF Research Database (Denmark)

    Flensberg, Karsten; Hu, Ben Yu-Kuang

    1995-01-01

    We derive an expression for the drag rate (i.e., interlayer momentum transfer rate) for carriers in two coupled two-dimensional gases to lowest nonvanishing order in the screened interlayer electron-electron interaction, valid for arbitrary intralayer scattering mechanisms, using the Boltzmann tr...

  3. Nanostructured photovoltaics

    Science.gov (United States)

    Fu, Lan; Tan, H. Hoe; Jagadish, Chennupati

    2013-01-01

    Energy and the environment are two of the most important global issues that we currently face. The development of clean and sustainable energy resources is essential to reduce greenhouse gas emission and meet our ever-increasing demand for energy. Over the last decade photovoltaics, as one of the leading technologies to meet these challenges, has seen a continuous increase in research, development and investment. Meanwhile, nanotechnology, which is considered to be the technology of the future, is gradually revolutionizing our everyday life through adaptation and incorporation into many traditional technologies, particularly energy-related technologies, such as photovoltaics. While the record for the highest efficiency is firmly held by multijunction III-V solar cells, there has never been a shortage of new research effort put into improving the efficiencies of all types of solar cells and making them more cost effective. In particular, there have been extensive and exciting developments in employing nanostructures; features with different low dimensionalities, such as quantum wells, nanowires, nanotubes, nanoparticles and quantum dots, have been incorporated into existing photovoltaic technologies to enhance their performance and/or reduce their cost. Investigations into light trapping using plasmonic nanostructures to effectively increase light absorption in various solar cells are also being rigorously pursued. In addition, nanotechnology provides researchers with great opportunities to explore the new ideas and physics offered by nanostructures to implement advanced solar cell concepts such as hot carrier, multi-exciton and intermediate band solar cells. This special issue of Journal of Physics D: Applied Physics contains selected papers on nanostructured photovoltaics written by researchers in their respective fields of expertise. These papers capture the current excitement, as well as addressing some open questions in the field, covering topics including the

  4. Electromagnetically induced transparency due to intervalence band coherence in a GaAs quantum well.

    Science.gov (United States)

    Phillips, Mark; Wang, Hailin

    2003-05-15

    We demonstrate electromagnetically induced transparency in the transient optical response in a GaAs quantum well by using the nonradiative coherence between the heavy-hole and the light-hole valence bands.

  5. Modelling and characterization of colliding-pulse mode-locked (CPM) quantum well lasers. [MPS1

    DEFF Research Database (Denmark)

    Bischoff, Svend; Brorson, S.D.; Franck, T.

    1996-01-01

    A theoretical and experimental study of passive colliding pulse mode-locked quantum well lasers is presented. The theoretical model for the gain dynamics is based on semi-classical density matrixequations. The gain dynamics are characterized exp...

  6. Spectrally-Tunable Infrared Camera Based on Highly-Sensitive Quantum Well Infrared Photodetectors Project

    Data.gov (United States)

    National Aeronautics and Space Administration — We propose to develop a SPECTRALLY-TUNABLE INFRARED CAMERA based on quantum well infrared photodetector (QWIP) focal plane array (FPA) technology. This will build on...

  7. Role of spatial dispersion of electromagnetic wave at its transmission through quantum well

    CERN Document Server

    Korovin, L I; Contreras-Solorio, D A; Pavlov, S T

    2001-01-01

    The theory on the light transmission through the quantum well, placed in the strong magnetic field, perpendicular to the well plane, wherein the interzone transitions take place, is developed. The light wave length is assumed to be comparable with the well width. The formulae for reflection, absorption and transmission wherein the spatial dispersion of the monochromatic light wave and the difference in the reflection indices of the quantum well and the barrier are accounted for, are obtained. It is shown that accounting for these factors effects the reflection most of all, because along with the reflection, caused by the interzonal transitions in the quantum well there appears the additional reflection from the well boundaries. The most radical changes in the reflection take place in the case, when the reverse radiation lifetime of the excited state in the quantum well is shorter as compared to the reverse non-radiation lifetime

  8. Ultrafast spectral interferometry of resonant secondary emmission from semiconductor quantum wells

    DEFF Research Database (Denmark)

    Birkedal, Dan; Shah, Jagdeep

    1999-01-01

    Recent investigations of secondary emission from quantum well excitons follwing resonant excitation have demonstrated an intricate interplay of coherent Rayleigh scattering and incoherent luminescence. We have very recently demonstrated that it is possible to isolate and time resolve the coherent...

  9. Partial screening of internal electric fields in strained piezoelectric quantum well lasers: Implications for optoelectronic integration

    Science.gov (United States)

    Pabla, A. S.; Woodhead, J.; Khoo, E. A.; Grey, R.; David, J. P. R.; Rees, G. J.

    1996-03-01

    The spectral electroluminescence characteristics of broad-area (Al)GaAs/In0.23Ga0.77As/(Al)GaAs single quantum well separate confinement heterostructure lasers grown on (111)B GaAs have been studied under forward biased current injection. A room-temperature threshold current density of 750 A/cm2 is measured for a 1000 μm laser. The subthreshold electroluminescence spectrum blue shifts with increasing current up to the point of lasing threshold. Our measurements reveal that lasing is achieved while there is a strong residual or ``unscreened'' electric field across the quantum well. Based on these observations we outline how piezoelectric quantum wells can be used to monolithically integrate a quantum well laser with a blue-shifting electroabsorption modulator.

  10. Modelling and characterization of colliding-pulse mode-locked (CPM) quantum well lasers. [MPS1

    DEFF Research Database (Denmark)

    Bischoff, Svend; Brorson, S.D.; Franck, T.;

    1996-01-01

    A theoretical and experimental study of passive colliding pulse mode-locked quantum well lasers is presented. The theoretical model for the gain dynamics is based on semi-classical density matrixequations. The gain dynamics are characterized exp...

  11. The over-barrier resonant states and multi-channel scattering by a quantum well

    Directory of Open Access Journals (Sweden)

    Alexander F. Polupanov

    2008-06-01

    Full Text Available We demonstrate an explicit numerical method for accurate calculation ofthe analytic continuation of the scattering matrix, describing the multichannelscattering by a quantum well, to the unphysical region of complexvalues of the energy. Results of calculations show that one or severalpoles of the S-matrix exist, corresponding to the over-barrier resonantstates that are critical for the effect of the absolute reflection at scatteringof the heavy hole by a quantum well in the energy range where only theheavy hole may propagate over barriers in a quantum-well structure.Light- and heavy-hole states are described by the Luttinger Hamiltonianmatrix. The qualitative behaviour of the over-barrier scattering andresonant states is the same at variation of the shape of the quantum-wellpotential, however lifetimes of resonant states depend drastically on theshape and depth of a quantum well.

  12. Handheld Longwave Infrared Camera Based on Highly-Sensitive Quantum Well Infrared Photodetectors Project

    Data.gov (United States)

    National Aeronautics and Space Administration — We propose to develop a compact handheld longwave infrared camera based on quantum well infrared photodetector (QWIP) focal plane array (FPA) technology. Based on...

  13. Optical Two-Dimensional Spectroscopy of Disordered Semiconductor Quantum Wells and Quantum Dots

    Energy Technology Data Exchange (ETDEWEB)

    Cundiff, Steven T. [Univ. of Colorado, Boulder, CO (United States)

    2016-05-03

    This final report describes the activities undertaken under grant "Optical Two-Dimensional Spectroscopy of Disordered Semiconductor Quantum Wells and Quantum Dots". The goal of this program was to implement optical 2-dimensional Fourier transform spectroscopy and apply it to electronic excitations, including excitons, in semiconductors. Specifically of interest are quantum wells that exhibit disorder due to well width fluctuations and quantum dots. In both cases, 2-D spectroscopy will provide information regarding coupling among excitonic localization sites.

  14. Dielectric coating and surface plasmon enhancement of multi-color quantum-well structures

    DEFF Research Database (Denmark)

    Fadil, Ahmed; Iida, Daisuke; Ou, Yiyu

    We fabricate a multi-colored quantum-well structure as a prototype towards monolithic white light-emitting diodes, and modify the emission intensities of different colors by introducing dielectric and Ag nanoparticle coating.......We fabricate a multi-colored quantum-well structure as a prototype towards monolithic white light-emitting diodes, and modify the emission intensities of different colors by introducing dielectric and Ag nanoparticle coating....

  15. Chirping of an optical transition by an ultrafast acoustic soliton train in a semiconductor quantum well.

    Science.gov (United States)

    Scherbakov, A V; van Capel, P J S; Akimov, A V; Dijkhuis, J I; Yakovlev, D R; Berstermann, T; Bayer, M

    2007-08-03

    Acoustic solitons formed during the propagation of a picosecond strain pulse in a GaAs crystal with a ZnSe/ZnMgSSe quantum well on top lead to exciton resonance energy shifts of up to 10 meV, and ultrafast frequency modulation, i.e., chirping, of the exciton transition. The effects are well described by a theoretical analysis based on the Korteweg-de Vries equation and accounting for the properties of the excitons in the quantum well.

  16. Transmission line model for strained quantum well lasers including carrier transport and carrier heating effects.

    Science.gov (United States)

    Xia, Mingjun; Ghafouri-Shiraz, H

    2016-03-01

    This paper reports a new model for strained quantum well lasers, which are based on the quantum well transmission line modeling method where effects of both carrier transport and carrier heating have been included. We have applied this new model and studied the effect of carrier transport on the output waveform of a strained quantum well laser both in time and frequency domains. It has been found that the carrier transport increases the turn-on, turn-off delay times and damping of the quantum well laser transient response. Also, analysis in the frequency domain indicates that the carrier transport causes the output spectrum of the quantum well laser in steady state to exhibit a redshift which has a narrower bandwidth and lower magnitude. The simulation results of turning-on transients obtained by the proposed model are compared with those obtained by the rate equation laser model. The new model has also been used to study the effects of pump current spikes on the laser output waveforms properties, and it was found that the presence of current spikes causes (i) wavelength blueshift, (ii) larger bandwidth, and (iii) reduces the magnitude and decreases the side-lobe suppression ratio of the laser output spectrum. Analysis in both frequency and time domains confirms that the new proposed model can accurately predict the temporal and spectral behaviors of strained quantum well lasers.

  17. Electrode-induced In-plane Strain Variation in Si Quantum Well

    Science.gov (United States)

    Park, Joonkyu; Ahn, Youngjun; Savage, Donald; Prance, Jonathan; Simmons, Christine; Lagally, Max; Coppersmith, Susan; Holt, Martin; Eriksson, Mark; Evans, Paul

    Silicon quantum devices are often formed in electrostatically defined quantum dots within Si/SiGe heterostructures incorporating a strained silicon quantum well. Structural variations within the quantum well arise from several sources, including the plastic relaxation of the SiGe substrate and stresses arising from electrodes. The residual stress in the electrode causes an elastic bending distortion of the quantum well that modifies the energy by which the two split-off conduction minima in the silicon quantum well are shifted by biaxial strain. We report a synchrotron hard x-ray nanobeam diffraction study of the quantum well distortion (i) near isolated Pd electrodes and (ii) within a complex quantum dot pattern. The strain difference between the two interfaces of the 10-nm-thick silicon quantum well has a magnitude of up to 10-5 in (i) while it is as large as 10-4 in (ii) which is far larger than the strain difference arising from the plastic relaxation of the SiGe substrate. Mechanical analysis using the edge-force model, shows that the residual stress in the Pd electrode was 350 MPa. We expect that similar effects will arise in all quantum electronic systems with metal-electrode-defined devices.

  18. Ultrafast all-optical switching and error-free 10 Gbit/s wavelength conversion in hybrid InP-silicon on insulator nanocavities using surface quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Bazin, Alexandre; Monnier, Paul; Beaudoin, Grégoire; Sagnes, Isabelle; Raj, Rama [Laboratoire de Photonique et de Nanostructures (CNRS UPR20), Route de Nozay, Marcoussis 91460 (France); Lenglé, Kevin; Gay, Mathilde; Bramerie, Laurent [Université Européenne de Bretagne (UEB), 5 Boulevard Laënnec, 35000 Rennes (France); CNRS-Foton Laboratory (UMR 6082), Enssat, BP 80518, 22305 Lannion Cedex (France); Braive, Rémy; Raineri, Fabrice, E-mail: fabrice.raineri@lpn.cnrs.fr [Laboratoire de Photonique et de Nanostructures (CNRS UPR20), Route de Nozay, Marcoussis 91460 (France); Université Paris Diderot, Sorbonne Paris Cité, 75207 Paris Cedex 13 (France)

    2014-01-06

    Ultrafast switching with low energies is demonstrated using InP photonic crystal nanocavities embedding InGaAs surface quantum wells heterogeneously integrated to a silicon on insulator waveguide circuitry. Thanks to the engineered enhancement of surface non radiative recombination of carriers, switching time is obtained to be as fast as 10 ps. These hybrid nanostructures are shown to be capable of achieving systems level performance by demonstrating error free wavelength conversion at 10 Gbit/s with 6 mW switching powers.

  19. Demonstration of periodic nanostructure formation with less ablation by double-pulse laser irradiation on titanium

    Science.gov (United States)

    Furukawa, Yuki; Sakata, Ryoichi; Konishi, Kazuki; Ono, Koki; Matsuoka, Shusaku; Watanabe, Kota; Inoue, Shunsuke; Hashida, Masaki; Sakabe, Shuji

    2016-06-01

    By pairing femtosecond laser pulses (duration ˜40 fs and central wavelength ˜810 nm) at an appropriate time interval, a laser-induced periodic surface structure (LIPSS) is formed with much less ablation than one formed with a single pulse. On a titanium plate, a pair of laser pulses with fluences of 70 and 140 mJ/cm2 and a rather large time interval (>10 ps) creates a LIPSS with an interspace of 600 nm, the same as that formed by a single pulse of 210 mJ/cm2, while the double pulse ablates only 4 nm, a quarter of the ablation depth of a single pulse.

  20. A high-sensitive ultraviolet photodetector composed of double-layered TiO{sub 2} nanostructure and Au nanoparticles film based on Schottky junction

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Huan; Qin, Pei [School of Chemical Engineering and Light Industry, Guangdong University of Technology, Guangzhou, 510006 (China); Yi, Guobin, E-mail: ygb702@163.com [School of Chemical Engineering and Light Industry, Guangdong University of Technology, Guangzhou, 510006 (China); Zu, Xihong [School of Chemical Engineering and Light Industry, Guangdong University of Technology, Guangzhou, 510006 (China); Zhang, Li, E-mail: zhangli2368@126.com [School of Materials and Energy, Guangdong University of Technology, Guangzhou, 510006 (China); Hong, Wei; Chen, Xudong [School of Chemistry and Chemical Engineering, Sun Yat-Sen (Zhongshan) University, Guangzhou, 510275 (China)

    2017-06-15

    In this study, a Schottky-type ultraviolet (UV) photodetector based on double-layered nanostructured TiO{sub 2}/Au films was fabricated. Double-layered titanium dioxide (TiO{sub 2}) nanostructures composed of one layer of TiO{sub 2} nano-flowers on one layer of TiO{sub 2} nanorods on fluorine-doped tin oxide (FTO) pre-coated glass substrates were synthesized via a convenient hydrothermal method using titanium butoxide and hydrochloric acid as the starting precursor, without involving the use of any other surfactants and catalysts. A granular-shaped thin-layer of Au film using vacuum sputter coating technique was subsequently deposited on TiO{sub 2} for the formation of Schottky-type photodetector. The as-fabricated Schottky device showed various photocurrent responses when irradiated with different wavelength of UV light. This suggests that the newly-developed photodetectors have promising potential for identifying different UV light wavelengths. - Highlights: • A novel double-layered TiO{sub 2} nanostructure was synthesized by a simple method. • An UV photodetector composed of TiO{sub 2} and Au was designed and fabricated. • The preparation method of TiO{sub 2}/Au UV photodetector was simple and convenient. • The UV photodetector based on TiO{sub 2}/Au showed excellent sensitivity to UV light.

  1. Electron spin relaxation in p-type GaAs quantum wells

    Science.gov (United States)

    Zhou, Y.; Jiang, J. H.; Wu, M. W.

    2009-11-01

    We investigate electron spin relaxation in p-type GaAs quantum wells from a fully microscopic kinetic spin Bloch equation approach, with all the relevant scatterings, such as electron-impurity, electron-phonon, electron-electron Coulomb, electron-hole Coulomb and electron-hole exchange (the Bir-Aronov-Pikus (BAP) mechanism) scatterings, explicitly included. Via this approach, we examine the relative importance of the D'yakonov-Perel' (DP) and BAP mechanisms in wide ranges of temperature, hole density, excitation density and impurity density, and present a phase-diagram-like picture showing the parameter regime where the DP or BAP mechanism is more important. It is discovered that in the impurity-free case the temperature regime where the BAP mechanism is more efficient than the DP one is around the hole Fermi temperature for high hole density, regardless of excitation density. However, in the high impurity density case with the impurity density identical to the hole density, this regime is roughly from the electron Fermi temperature to the hole Fermi temperature. Moreover, we predict that for the impurity-free case, in the regime where the DP mechanism dominates the spin relaxation at all temperatures, the temperature dependence of the spin relaxation time (SRT) presents a peak around the hole Fermi temperature, which originates from the electron-hole Coulomb scattering. We also predict that at low temperature, the hole-density dependence of the electron SRT exhibits a double-peak structure in the impurity-free case, whereas it shows first a peak and then a valley in the case of identical impurity and hole densities. These intriguing behaviors are due to the contribution from holes in high subbands.

  2. Electric field dependent Electroreflectance of GaAs/AlGaAs multiple quantum well Bragg structure at second quantum state

    Science.gov (United States)

    Nakarmi, Mim; Shakya, Naresh; Chaldyshev, Vladimir

    Electroreflectance Spectroscopy was employed to study the effect of electric field on the excitonic transitions in a GaAs/AlGaAs multiple quantum well (MQW) Bragg structure. The sample used in this experiment consists of 60 periods of quantum well structures with GaAs well layer (~13 nm) and AlGaAs barrier layer (~94 nm), grown by molecular beam expitaxy on a semi-insulating GaAs substrate. The sample structure was designed to coincide the Bragg resonance peak with the x(e2-hh2) exciton transitions. We observed a significant enhancement of excitonic feature around the x(e2-hh2) exciton transition due to the double resonance along with the sharp features of x(e1-hh1) and x(e1-lh1) ground state exciton transitions by tuning the angle of incidence of the light. We will present the results on electric field dependent electroreflectance measurements of this structure and discuss the effect of electric field on the first and second energy states.

  3. Phase transitions in two tunnel-coupled HgTe quantum wells: Bilayer graphene analogy and beyond

    Science.gov (United States)

    Krishtopenko, S. S.; Knap, W.; Teppe, F.

    2016-08-01

    HgTe quantum wells possess remarkable physical properties as for instance the quantum spin Hall state and the “single-valley” analog of graphene, depending on their layer thicknesses and barrier composition. However, double HgTe quantum wells yet contain more fascinating and still unrevealed features. Here we report on the study of the quantum phase transitions in tunnel-coupled HgTe layers separated by CdTe barrier. We demonstrate that this system has a 3/2 pseudo spin degree of freedom, which features a number of particular properties associated with the spin-dependent coupling between HgTe layers. We discover a specific metal phase arising in a wide range of HgTe and CdTe layer thicknesses, in which a gapless bulk and a pair of helical edge states coexist. This phase holds some properties of bilayer graphene such as an unconventional quantum Hall effect and an electrically-tunable band gap. In this “bilayer graphene” phase, electric field opens the band gap and drives the system into the quantum spin Hall state. Furthermore, we discover a new type of quantum phase transition arising from a mutual inversion between second electron- and hole-like subbands. This work paves the way towards novel materials based on multi-layered topological insulators.

  4. Correlation between the structural and cathodoluminescence properties in InGaN/GaN multiple quantum wells with large number of quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Jing; Zhao, Degang, E-mail: dgzhao@red.semi.ac.cn; Jiang, Desheng; Chen, Ping; Zhu, Jianjun; Liu, Zongshun; Le, Lingcong; He, Xiaoguang; Li, Xiaojing [State Key Laboratory on Integrated Optoelectronics, Institute of Semiconductors, Chinese Academy of Sciences, PO BOX 912, Beijing 100083 (China); Wang, Hui; Yang, Hui [Suzhou Institute of Nano-tech and Nano-bionics, Chinese Academy of Sciences, Suzhou 215123 (China); Jahn, Uwe [Paul-Drude-Institut für Festkörperelektronik, Hausvogteiplatz 5–7, 10117 Berlin (Germany)

    2014-09-01

    Cathodoluminescence (CL) characteristics on 30-period InGaN/GaN multiple quantum well (MQW) solar cell structures are investigated, revealing the relationship between optical and structural properties of the MQW structures with a large number of quantum wells. In the bottom MQW layers, a blueshift of CL peak along the growth direction is found and attributed to the decrease of indium content due to the compositional pulling effect. An obvious split of emission peak and a redshift of the main emission energy are found in the top MQW layers when the MQW grows above the critical layer thickness. They are attributed to the segregation of In-rich InGaN clusters rather than the increase of indium content in quantum well layer. The MQW structure is identified to consist of two regions: a strained one in the bottom, where the indium content is gradually decreased, and a partly relaxed one in the top with segregated In-rich InGaN clusters.

  5. Transport properties of silicon complementary-metal-oxide semiconductor quantum well field-effect transistors

    Science.gov (United States)

    Naquin, Clint Alan

    Introducing explicit quantum transport into silicon (Si) transistors in a manner compatible with industrial fabrication has proven challenging, yet has the potential to transform the performance horizons of large scale integrated Si devices and circuits. Explicit quantum transport as evidenced by negative differential transconductances (NDTCs) has been observed in a set of quantum well (QW) n-channel metal-oxide-semiconductor (NMOS) transistors fabricated using industrial silicon complementary MOS processing. The QW potential was formed via lateral ion implantation doping on a commercial 45 nm technology node process line, and measurements of the transfer characteristics show NDTCs up to room temperature. Detailed gate length and temperature dependence characteristics of the NDTCs in these devices have been measured. Gate length dependence of NDTCs shows a correlation of the interface channel length with the number of NDTCs formed as well as with the gate voltage (VG) spacing between NDTCs. The VG spacing between multiple NDTCs suggests a quasi-parabolic QW potential profile. The temperature dependence is consistent with partial freeze-out of carrier concentration against a degenerately doped background. A folding amplifier frequency multiplier circuit using a single QW NMOS transistor to generate a folded current-voltage transfer function via a NDTC was demonstrated. Time domain data shows frequency doubling in the kHz range at room temperature, and Fourier analysis confirms that the output is dominated by the second harmonic of the input. De-embedding the circuit response characteristics from parasitic cable and contact impedances suggests that in the absence of parasitics the doubling bandwidth could be as high as 10 GHz in a monolithic integrated circuit, limited by the transresistance magnitude of the QW NMOS. This is the first example of a QW device fabricated by mainstream Si CMOS technology being used in a circuit application and establishes the feasibility

  6. The Over-Barrier Resonant States and Multi-Channel Scattering in Multiple Quantum Wells

    Directory of Open Access Journals (Sweden)

    A Polupanov

    2016-09-01

    Full Text Available We demonstrate an explicit numerical method for accurate calculation of the scattering matrix and its poles, and apply this method to describe the multi-channel scattering in the multiple quantum-wells structures. The S-matrix is continued analytically to the unphysical region of complex energy values. Results of calculations show that there exist one or more S-matrix poles, corresponding to the over-barrier resonant states critical for the effect of the absolute reflection of holes in the energy range where only the heavy ones may propagate over barriers in a structure. Light- and heavy-hole states are described by the Luttinger Hamiltonian matrix. In contrast to the single quantum-well case, at some parameters of a multiple quantum-wells structure the number of S-matrix poles may exceed that of the absolute reflection peaks, and at different values of parameters the absolute reflection peak corresponds to different resonant states. The imaginary parts of the S-matrix poles and hence the lifetimes of resonant states as well as the widths of resonant peaks of absolute reflection depend drastically on the quantum-well potential depth. In the case of shallow quantum wells there is in fact a long-living over-barrier resonant hole state.

  7. THE QUANTUM-WELL STRUCTURES OF SELF ELECTROOPTIC-EFFECT DEVICES AND GALLIUM-ARSENIDE

    Directory of Open Access Journals (Sweden)

    Mustafa TEMİZ

    1996-02-01

    Full Text Available Multiple quantum-well (MQW electroabsorptive self electro optic-effect devices (SEEDs are being extensively studied for use in optical switching and computing. The self electro-optic-effect devices which has quantum-well structures is a new optoelectronic technology with capability to obtain both optical inputs and outputs for Gallium-Arsenide/Aluminum Gallium-Arsenide (GaAs/AlGaAs electronic circuits. The optical inputs and outputs are based on quantum-well absorptive properties. These quantum-well structures consist of many thin layers of semiconductors materials of GaAs/AlGaAs which have emerged some important directions recently. The most important advance in the physics of these materials since the early days has been invention of the heterojunction structures which is based at present on GaAs technology. GaAs/AlGaAs structures present some important advantages to relevant band gap and index of refraction which allow to form the quantum-well structures and also to make semiconductor lasers, dedectors and waveguide optical switches.

  8. Calculation of Excitonic Transitions in ZnO/MgZnO Quantum-Well Heterostructures

    Institute of Scientific and Technical Information of China (English)

    徐天宁; 吴惠桢; 邱东江; 陈乃波

    2003-01-01

    We calculate the excitonic transition energies and exciton binding energies in ZnO/MgxZn1-xO quantum-well heterostructures with Mg composition x varied from 0.08 to 0.36. The effect of the exciton-phonon interaction on the exciton binding energies is taken into account in the model. For the ZnO/Mg0.12Zn0.88O quantum-well structure, we compare the calculated result with the available experimental data at 5 K, and a good agreement is achieved. The excitonic transition energies at room temperature in ZnO/MgxZn1-xO quantum-well heterostructures are also calculated. The results show that when the well width exceeds 50 A, the quantum size effect is neglectable and the excitonic transition energies in ZnO/MgxZn1-xO (with x varied from 0.08 to 0.36)quantum-well heterostructures are close to the value of bulk ZnO. The maximum exciton binding energy as large as 121.1 meV is obtained for the well width of 12.5 A in the ZnO/Mg0.36Zn0.64O quantum-well heterostructures.

  9. Characteristics of InGaN multiple quantum well blue-violet laser diodes

    Institute of Scientific and Technical Information of China (English)

    LI Deyao; YANG Hui; LIANG Junwu; ZHANG Shuming; WANG Jianfeng; CHEN Jun; CHEN Lianghui; CHONG Ming; ZHU Jianjun; ZHAO Degang; LIU Zongshun

    2006-01-01

    Studies on InGaN multiple quantum well blue-violet laser diodes have been reported. Laser structures with long-period multiple quantum wells were grown by metal-organic chemical vapor deposition. Triple-axis X-ray diffraction (TAXRD) measurements show that the multiple quantum wells were high quality. Ridge waveguide laser diodes were fabricated with cleaved facet mirrors. The laser diodes lase at room temperature under a pulsed current. A threshold current density of 3.3 kA/cm2 and a characteristic temperature T0 of 145 K were observed for the laser diode.orted. Laser structures with long-period multiple quantum wells were grown by metal-organic chemical vapor deposition. Triple-axis X-ray diffraction (TAXRD) measurements show that the multiple quantum wells were high quality. Ridge waveguide laser diodes were fabricated with cleaved facet mirrors. The laser diodes lase at room temperature under a pulsed current. A threshold current density of 3.3 kA/cm2 and a characteristic temperature T0 of 145 K were observed for the laser diode.

  10. Optical Conductivity of Impurity-Doped Parabolic Quantum Wells in an Applied Electric Field

    Institute of Scientific and Technical Information of China (English)

    GUO Kang-Xian; CHEN Chuan-Yu

    2005-01-01

    The optical conductivity of impurity-doped parabolic quantum wells in an applied electric field is investigated with the memory-function approach, and the analytic expression for the optical conductivity is derived. With characteristic parameters pertaining to GaAs/Ga1-xAlxAs parabolic quantum wells, the numerical results are presented.It is shown that, the smaller the well width, the larger the peak intensity of the optical conductivity, and the more asymmetric the shape of the optical conductivity; the optical conductivity is more sensitive to the electric field, the electric field enhances the optical conductivity; when the dimension of the quantum well increases, the optical conductivity increases until it reaches a maximum value, and then decreases.

  11. InGaAs Quantum Well Grown on High-Index Surfaces for Superluminescent Diode Applications.

    Science.gov (United States)

    Li, Zhenhua; Wu, Jiang; Wang, Zhiming M; Fan, Dongsheng; Guo, Aqiang; Li, Shibing; Yu, Shui-Qing; Manasreh, Omar; Salamo, Gregory J

    2010-04-22

    The morphological and optical properties of In0.2Ga0.8As/GaAs quantum wells grown on various substrates are investigated for possible application to superluminescent diodes. The In0.2Ga0.8As/GaAs quantum wells are grown by molecular beam epitaxy on GaAs (100), (210), (311), and (731) substrates. A broad photoluminescence emission peak (~950 nm) with a full width at half maximum (FWHM) of 48 nm is obtained from the sample grown on (210) substrate at room temperature, which is over four times wider than the quantum well simultaneously grown on (100) substrate. On the other hand, a very narrow photoluminescence spectrum is observed from the sample grown on (311) with FWHM = 7.8 nm. The results presented in this article demonstrate the potential of high-index GaAs substrates for superluminescent diode applications.

  12. Controlling the Spontaneous Emission Rate of Quantum Wells in Rolled-Up Hyperbolic Metamaterials.

    Science.gov (United States)

    Schulz, K Marvin; Vu, Hoan; Schwaiger, Stephan; Rottler, Andreas; Korn, Tobias; Sonnenberg, David; Kipp, Tobias; Mendach, Stefan

    2016-08-19

    We experimentally demonstrate the enhancement of the spontaneous emission rate of GaAs quantum wells embedded in rolled-up metamaterials. We fabricate microtubes whose walls consist of alternating Ag and (In)(Al)GaAs layers with incorporated active GaAs quantum-well structures. By variation of the layer thickness ratio of the Ag and (In)(Al)GaAs layers we control the effective permittivity tensor of the metamaterial according to an effective medium approach. Thereby, we can design samples with elliptic or hyperbolic dispersion. Time-resolved low temperature photoluminescence spectroscopy supported by finite-difference time-domain simulations reveal a decrease of the quantum well's spontaneous emission lifetime in our metamaterials as a signature of the crossover from elliptic to hyperbolic dispersion.

  13. A gold hybrid structure as optical coupler for quantum well infrared photodetector

    Energy Technology Data Exchange (ETDEWEB)

    Ding, Jiayi; Li, Qian; Jing, Youliang [National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Sciences, 500 Yu Tian Road, Shanghai 200083 (China); Chen, Xiaoshuang, E-mail: xschen@mail.sitp.ac.cn; Li, Zhifeng; Li, Ning; Lu, Wei [National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Sciences, 500 Yu Tian Road, Shanghai 200083 (China); Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei, Anhui 230026 (China)

    2014-08-28

    A hybrid structure consisting of a square lattice of gold disk arrays and an overlaying gold film is proposed as an optical coupler for a backside-illuminated quantum well infrared photodetector (QWIP). Finite difference time-domain method is used to numerically simulate the reflection spectra and the field distributions of the hybrid structure combined with the QWIP device. The results show that the electric field component perpendicular to the quantum well is strongly enhanced when the plasmonic resonant wavelength of the hybrid structure coincides with the response one of the quantum well infrared photodetector regardless of the polarization of the incident light. The effect of the diameter and thickness of an individual gold disk on the resonant wavelength is also investigated, which indicates that the localized surface plasmon also plays a role in the light coupling with the hybrid structure. The coupling efficiency can exceed 50 if the structural parameters of the gold disk arrays are well optimized.

  14. The effects of strain on indirect absorption in Ge/SiGe quantum wells

    Science.gov (United States)

    Lever, L.; Ikonić, Z.; Kelsall, R. W.

    2012-06-01

    We calculate the conduction band electron scattering rates from the Γ-valley into the indirect valleys in germanium, and use this to determine the strength of the indirect absorption in Ge/SiGe quantum well heterostructures. This is done as a function of the in-plane compressive strain in the Ge quantum wells, which results from pseudomorphic growth on a SiGe virtual substrate. This compressive strain results in the Δ valleys becoming available as destination states for scattering, which leads to a reduction in the Γ-valley lifetime. We calculate the indirect absorption and lifetime broadening of excitonic peaks, and show that indirect absorption decreases as the Ge fraction in the virtual substrate increases. We conclude that the Ge fraction of the SiGe virtual substrate should be approximately 95% or larger for optimum electroabsorption performance of Ge/SiGe quantum wells.

  15. Controlling the Spontaneous Emission Rate of Quantum Wells in Rolled-Up Hyperbolic Metamaterials

    Science.gov (United States)

    Schulz, K. Marvin; Vu, Hoan; Schwaiger, Stephan; Rottler, Andreas; Korn, Tobias; Sonnenberg, David; Kipp, Tobias; Mendach, Stefan

    2016-08-01

    We experimentally demonstrate the enhancement of the spontaneous emission rate of GaAs quantum wells embedded in rolled-up metamaterials. We fabricate microtubes whose walls consist of alternating Ag and (In)(Al)GaAs layers with incorporated active GaAs quantum-well structures. By variation of the layer thickness ratio of the Ag and (In)(Al)GaAs layers we control the effective permittivity tensor of the metamaterial according to an effective medium approach. Thereby, we can design samples with elliptic or hyperbolic dispersion. Time-resolved low temperature photoluminescence spectroscopy supported by finite-difference time-domain simulations reveal a decrease of the quantum well's spontaneous emission lifetime in our metamaterials as a signature of the crossover from elliptic to hyperbolic dispersion.

  16. InGaAs Quantum Well Grown on High-Index Surfaces for Superluminescent Diode Applications

    Directory of Open Access Journals (Sweden)

    Wu Jiang

    2010-01-01

    Full Text Available Abstract The morphological and optical properties of In0.2Ga0.8As/GaAs quantum wells grown on various substrates are investigated for possible application to superluminescent diodes. The In0.2Ga0.8As/GaAs quantum wells are grown by molecular beam epitaxy on GaAs (100, (210, (311, and (731 substrates. A broad photoluminescence emission peak (~950 nm with a full width at half maximum (FWHM of 48 nm is obtained from the sample grown on (210 substrate at room temperature, which is over four times wider than the quantum well simultaneously grown on (100 substrate. On the other hand, a very narrow photoluminescence spectrum is observed from the sample grown on (311 with FWHM = 7.8 nm. The results presented in this article demonstrate the potential of high-index GaAs substrates for superluminescent diode applications.

  17. Confined optical-phonon-assisted cyclotron resonance in quantum wells via two-photon absorption process

    Science.gov (United States)

    Phuc, Huynh Vinh; Hien, Nguyen Dinh; Dinh, Le; Phong, Tran Cong

    2016-06-01

    The effect of confined phonons on the phonon-assisted cyclotron resonance (PACR) via both one and two photon absorption processes in a quantum well is theoretically studied. We consider cases when electrons are scattered by confined optical phonons described by the Fuchs-Kliewer slab, Ridley's guided, and Huang-Zhu models. The analytical expression of the magneto-optical absorption coefficient (MOAC) is obtained by relating it to the transition probability for the absorption of photons. It predicts resonant peaks caused by transitions between Landau levels and electric subband accompanied by confined phonons emission in the absorption spectrum. The MOAC and the full-width at half-maximum (FWHM) for the intra- and inter-subband transitions are given as functions of the magnetic field, temperature, and quantum well width. In narrow quantum wells, the phonon confinement becomes more important and should be taken into account in studying FWHM.

  18. Temperature-driven single-valley Dirac fermions in HgTe quantum wells

    Science.gov (United States)

    Marcinkiewicz, M.; Ruffenach, S.; Krishtopenko, S. S.; Kadykov, A. M.; Consejo, C.; But, D. B.; Desrat, W.; Knap, W.; Torres, J.; Ikonnikov, A. V.; Spirin, K. E.; Morozov, S. V.; Gavrilenko, V. I.; Mikhailov, N. N.; Dvoretskii, S. A.; Teppe, F.

    2017-07-01

    We report on the temperature-dependent magnetospectroscopy of two HgTe/CdHgTe quantum wells below and above the critical well thickness dc. Our results, obtained in magnetic fields up to 16 T and s temperature range from 2 to 150 K, clearly indicate a change in the band-gap energy with temperature. A quantum well wider than dc evidences a temperature-driven transition from topological insulator to semiconductor phases. At a critical temperature of 90 K, the merging of inter- and intraband transitions in weak magnetic fields clearly specifies the formation of a gapless state, revealing the appearance of single-valley massless Dirac fermions with a velocity of 5.6 ×105m s-1 . For both quantum wells, the energies extracted from the experimental data are in good agreement with calculations on the basis of the eight-band Kane Hamiltonian with temperature-dependent parameters.

  19. Reversible Carriers Tunnelling in Asymmetric Coupled InGaN/GaN Quantum Wells

    Institute of Scientific and Technical Information of China (English)

    PEI Xiao-Jiang; GUO Li-Wei; WANG Yang; WANG Xiao-Hui; JIA Hai-Qiang; CHEN Hong; ZHOU Jun-Ming; WANG Li; Tamai N

    2008-01-01

    Temperature-dependent photoluminescence (PL) and time resolved photoluminescence (TRPL) are performed to study the PL characteristics and carrier transfer mechanism in asymmetric coupled InGaN/GaN multiple quantum wells (AS-QWs). Our results reveal that abnormal carrier tunnelling from the wide quantum well (WQW) to the narrow quantum well (NQW) is observed at temperature higher than about lOOK, while a normal carrier tunnelling from the NQW to the WQW is observed at temperature lower than 100 K. The reversible carrier tunnelling between the two QWs makes it possible to explore new types of temperature sensitive emission devices.It is shown that PL internal quantum efficiency (IQE) of the NQW is enhanced to about 46% due to the assistant of the abnormal carrier tunnelling.

  20. International Workshop on "Intersubband Transitions in Quantum Wells : Physics and Applications"

    CERN Document Server

    Su, Yan-Kuin

    1998-01-01

    The International Workshop on "Intersubband Transitions in Quantum Wells:: Physics and Applications," was held at National Cheng Kung University, in Tainan, Taiwan, December 15-18, 1997. The objective of the Workshop is to facilitate the presentation and discussion of the recent results in theoretical, experimental, and applied aspects of intersubband transitions in quantum wells and dots. The program followed the tradition initiated at the 1991 conference in Cargese-France, the 1993 conference in Whistler, B. C. Canada, and the 1995 conference in Kibbutz Ginosar, Israel. Intersubband transitions in quantum wells and quantum dots have attracted considerable attention in recent years, mainly due to the promise of various applications in the mid- and far-infrared regions (2-30 J. lm). Over 40 invited and contributed papers were presented in this four-day workshop, with topics covered most aspects of the intersubband transition phenomena including: the basic intersubband transition processes, multiquantum well i...

  1. Optical and structural properties of MOVPE-grown GaInSb/GaSb quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Wagener, Viera, E-mail: viera.wagener@nmmu.ac.z [Physics Department, Nelson Mandela Metropolitan University, PO Box 77000, Port Elizabeth 6031 (South Africa); Olivier, E.J.; Botha, J.R. [Physics Department, Nelson Mandela Metropolitan University, PO Box 77000, Port Elizabeth 6031 (South Africa)

    2009-12-15

    This paper reports on the optical and structural properties of strained type-I Ga{sub 1-x}In{sub x}Sb quantum wells embedded in GaSb from a metal-organic vapour phase epitaxial growth perspective. Photoluminescence measurements and transmission electron microscopy were used to evaluate the effect of the growth temperature on the quality of Ga{sub 1-x}In{sub x}Sb strained layers with varied alloy compositions and thicknesses. Although the various factors contributing to the overall quality of the strained layers are difficult to separate, the quantum well characteristics are significantly altered by the growth temperature. Despite the high growth rates (approx2 nm/s), quantum wells grown at 607 deg. C display photoluminescence emissions with full-width at half-maximum of 3.5-5.0 meV for an indium solid content (x) up to 0.15.

  2. Time-resolved spectroscopy of biexciton luminescence in ZnxCd1-xSe-ZnSySe1-y multiple quantum wells

    OpenAIRE

    Yamada, Yoichi; Mishina, Tomobumi; Masumoto, Yasuaki; Kawakami, Yoichi; Yamaguchi, Shigeo; Ichino, Kunio; Fujita, Shizuo; Fujita, Shigeo; Taguchi, Tsunemasa

    1995-01-01

    The radiative lifetime of biexcitons in ZnxCd1-xSe-ZnSySe1-y multiple quantum wells has been studied by means of time-resolved luminescence spectroscopy under high-density excitation. It is shown that the rise of the biexciton luminescence becomes more rapid with increasing excitation energy density and that the biexciton luminescence decays with a double exponential form. It is found that the decay-time constant of the faster-decay component in the double-exponential decay corresponds to the...

  3. Quantum well saturable absorber mirror with electrical control of modulation depth

    DEFF Research Database (Denmark)

    Liu, Xiaomin; Rafailov, E.U.; Livshits, D.

    2010-01-01

    A saturable absorber mirror comprizing InGaAs/GaAs quantum wells incorporated into a p-i-n structure is demonstrated. Its modulation depth can be reduced from 4.25 % to 1.63 % by applying reverse bias voltage in the range 0–1 V.......A saturable absorber mirror comprizing InGaAs/GaAs quantum wells incorporated into a p-i-n structure is demonstrated. Its modulation depth can be reduced from 4.25 % to 1.63 % by applying reverse bias voltage in the range 0–1 V....

  4. Nonlinear excitation kinetics of biased quantum wells. Coherent dynamical screening effect

    DEFF Research Database (Denmark)

    Turchinovich, Dmitry; Jepsen, Peter Uhd

    2006-01-01

    In this paper we describe a strongly nonlinear process of ultrafast photoexcitation of a biased quantum well. This process is governed by coherent dynamical screening, where the instantaneously polarized photoexcited carriers screen initial bias field. This results in a dynamic modification...... of the bandstructure of the quantum well, which is totally coherent with the temporal intensity distribution of the excitation laser pulse. We developed a time-resolved theoretical model of coherent dynamical screening, which predicts interesting fundamental consequences, such as nonlinear absorption and ultra......-broadband THz emission. The results of our THz and optical experiments are in good agreement with the theoretical model....

  5. Feshbach shape resonance for high Tc pairing in superlattices of quantum stripes and quantum wells

    Directory of Open Access Journals (Sweden)

    A Bianconi

    2006-09-01

    Full Text Available   The Feshbach shape resonances in the interband pairing in superconducting superlattices of quantum wells or quantum stripes is shown to provide the mechanism for high Tc superconductivity. This mechanism provides the Tc amplification driven by the architecture of material: superlattices of quantum wells (intercalated graphite or diborides and superlattices of quantum stripes (doped high Tc cuprate perovskites where the chemical potential is tuned to a Van Hove-Lifshitz singularity (vHs in the electronic energy spectrum of the superlattice associated with the change of the Fermi surface dimensionality in one of the subbands.

  6. Binding Energy of Biexcitons in GaAs Quantum-Well Wires

    Institute of Scientific and Technical Information of China (English)

    LIU Jian-Jun; CHEN Xiao-Fang; LI Shu-Shen

    2004-01-01

    @@ The binding energy of a biexciton in GaAs quantum-well wires is calculated variationally by use ofa two-parameter trial wavefunction and a one-dimensional equivalent potential model. There is no artificial parameter added in our calculation. Our results agree fairly well with the previous results. It is found that the binding energies are closely correlative to the size of wire. The binding energy of biexcitons is smaller than that of neutral bound excitons in GaAs quantum-well wires when the dopant is located at the centre of the wires.

  7. Nonlinear photonic diode behavior in energy-graded core-shell quantum well semiconductor rod.

    Science.gov (United States)

    Ko, Suk-Min; Gong, Su-Hyun; Cho, Yong-Hoon

    2014-09-10

    Future technologies require faster data transfer and processing with lower loss. A photonic diode could be an attractive alternative to the present Si-based electronic diode for rapid optical signal processing and communication. Here, we report highly asymmetric photonic diode behavior with low scattering loss, from tapered core-shell quantum well semiconductor rods that were fabricated to have a large gradient in their bandgap energy along their growth direction. Local laser illumination of the core-shell quantum well rods yielded a huge contrast in light output intensities from opposite ends of the rod.

  8. Formulation of a self-consistent model for quantum well pin solar cells

    Science.gov (United States)

    Ramey, S.; Khoie, R.

    1997-04-01

    A self-consistent numerical simulation model for a pin single-cell solar cell is formulated. The solar cell device consists of a p-AlGaAs region, an intrinsic i-AlGaAs/GaAs region with several quantum wells, and a n-AlGaAs region. Our simulator solves a field-dependent Schrödinger equation self-consistently with Poisson and Drift-Diffusion equations. The emphasis is given to the study of the capture of electrons by the quantum wells, the escape of electrons from the quantum wells, and the absorption and recombination within the quantum wells. We believe this would be the first such comprehensive model ever reported. The field-dependent Schrödinger equation is solved using the transfer matrix method. The eigenfunctions and eigenenergies obtained are used to calculate the escape rate of electrons from the quantum wells, and the non-radiative recombination rates of electrons at the boundaries of the quantum wells. These rates together with the capture rates of electrons by the quantum wells are then used in a self-consistent numerical Poisson-Drift-Diffusion solver. The resulting field profiles are then used in the field-dependent Schrödinger solver, and the iteration process is repeated until convergence is reached. In a p-AlGaAs i-AlGaAs/GaAs n-AlGaAs cell with aluminum mole fraction of 0.3, with one 100 Å-wide 284 meV-deep quantum well, the eigenenergies with zero field are 36meV, 136meV, and 267meV, for the first, second and third subbands, respectively. With an electric field of 50 kV/cm, the eigenenergies are shifted to 58meV, 160meV, and 282meV, respectively. With these eigenenergies, the thermionic escape time of electrons from the GaAs Γ-valley, varies from 220 pS to 90 pS for electric fields ranging from 10 to 50 kV/cm. These preliminary results are in good agreement with those reported by other researchers.

  9. Experimental investigation of spin-orbit coupling in n-type PbTe quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Peres, M. L.; Monteiro, H. S.; Castro, S. de [Institute of Physics and Chemistry, Federal University of Itajubá, PB 50, 37500-903 Itajubá, MG (Brazil); Chitta, V. A.; Oliveira, N. F. [Institute of Physics, University of São Paulo, PB 66318, 05315-970 São Paulo, SP (Brazil); Mengui, U. A.; Rappl, P. H. O.; Abramof, E. [Laboratório Associado de Sensores e Materiais, Instituto Nacional de Pesquisas Espaciais, PB 515, 12201-970 São José dos Campos, SP (Brazil); Maude, D. K. [Grenoble High Magnetic Field Laboratory, CNRS, BP 166, 38042 Grenoble Cedex 9 (France)

    2014-03-07

    The spin-orbit coupling is studied experimentally in two PbTe quantum wells by means of weak antilocalization effect. Using the Hikami-Larkin-Nagaoka model through a computational global optimization procedure, we extracted the spin-orbit and inelastic scattering times and estimated the strength of the zero field spin-splitting energy Δ{sub so}. The values of Δ{sub so} are linearly dependent on the Fermi wave vector (k{sub F}) confirming theoretical predictions of the existence of large spin-orbit coupling in IV-VI quantum wells originated from pure Rashba effect.

  10. Electronic excitation induced structural and optical modifications in InGaN/GaN quantum well structures grown by MOCVD

    Science.gov (United States)

    Prabakaran, K.; Ramesh, R.; Jayasakthi, M.; Surender, S.; Pradeep, S.; Balaji, M.; Asokan, K.; Baskar, K.

    2017-03-01

    The present study focuses on the electronic excitation induced structural and optical properties of InGaN/GaN quantum well (QW) structures grown by metal organic chemical vapor deposition technique. These excitations were produced using Au7+ ion irradiation with 100 MeV energy. The X-ray rocking curves intensity and full width at half-maximum values corresponding to the planes of (0 0 0 2) and (1 0 -1 5) of the irradiated QW structures show the modifications in the screw and edge-type dislocation densities vary with the ion fluences. The structural characteristics using the reciprocal space mapping indicate the intermixing effects in InGaN/GaN QW structures. Atomic force microscopy images confirmed the presence of nanostructures and the surface modification due to heavy ion irradiation. The irradiated QW structures exhibited degraded photoluminescence intensity and a subsequent decrease in the yellow luminescence band intensity with the fluences of 1 × 1011 and 5 × 1012 ions/cm2 compared to the pristine QW structures.

  11. Influence of Plasmonic Array Geometry on Energy Transfer from a Quantum Well to a Quantum Dot Layer

    CERN Document Server

    Higgins, Luke J; Karanikolas, Vasilios D; Bell, Alan P; Gough, John J; Murphy, Graham P; Parbrook, Peter J; Bradley, A Louise

    2016-01-01

    A range of seven different Ag plasmonic arrays formed using nanostructures of varying shape, size and gap were fabricated using helium-ion lithography (HIL) on an InGaN/GaN quantum well (QW) substrate. The influence of the array geometry on plasmon-enhanced F\\"orster resonance energy transfer (FRET) from a single InGaN QW to a ~ 80 nm layer of CdSe/ZnS quantum dots (QDs) embedded in a poly(methyl methacrylate) (PMMA) matrix is investigated. It is shown that the energy transfer efficiency is strongly dependent on the array properties and an efficiency of ~ 51% is observed for a nanoring array. There were no signatures of FRET in the absence of the arrays. The QD acceptor layer emission is highly sensitive to the array geometry. A model was developed to confirm that the increase in the QD emission on the QW substrate compared with a GaN substrate can be attributed solely to plasmon-enhanced FRET. The individual contributions of direct enhancement of the QD layer emission by the array and the plasmon-enhanced FR...

  12. Influence of Mg-doped barriers on semipolar (202xAF1) multiple-quantum-well green light-emitting diodes

    Science.gov (United States)

    Huang, Chia-Yen; Yan, Qimin; Zhao, Yuji; Fujito, Kenji; Feezell, Daniel; Van de Walle, Chris G.; Speck, James S.; DenBaars, Steven P.; Nakamura, Shuji

    2011-10-01

    We report the effects of Mg doping in the barriers of semipolar (202¯1) multiple-quantum-well light-emitting diodes (LEDs) with long emission wavelengths (>500 nm). With moderate Mg doping concentrations (3 × 1018-5 × 1018 cm-3) in the barriers, the output power was enhanced compared to those with undoped barriers, which suggests that hole transport in the active region is a limiting factor for device performance. Improved hole injection due to Mg doping in the barriers is demonstrated by dichromatic LED experiments and band diagram simulations. With Mg-doped AlGaN barriers, double-quantum-well LEDs with orange to red emission (λ > 600 nm) were also demonstrated.

  13. Effects of bias and temperature on the intersubband absorption in very long wavelength GaAs/AlGaAs quantum well infrared photodetectors

    Energy Technology Data Exchange (ETDEWEB)

    Liu, X. H.; Zhou, X. H., E-mail: xhzhou@mail.sitp.ac.cn; Li, N.; Liao, K. S.; Huang, L.; Li, Q.; Li, Z. F.; Chen, P. P.; Lu, W. [National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Sciences, 500 Yu-Tian Road, Shanghai 200083 (China); Wang, L.; Sun, Q. L. [Institute of Physics, Chinese Academy of Sciences, Beijing 100080 (China)

    2014-03-28

    The temperature- and bias-dependent photocurrent spectra of very long wavelength GaAs/AlGaAs quantum well infrared photodetectors (QWIPs) are studied using spectroscopic measurements and corresponding theoretical calculations. It is found that the peak response wavelength will shift as the bias and temperature change. Aided by band structure calculations, we propose a model of the double excited states and explain the experimental observations very well. In addition, the working mechanisms of the quasi-bound state confined in the quantum well, including the processes of tunneling and thermionic emission, are also investigated in detail. We confirm that the first excited state, which belongs to the quasi-bound state, can be converted into a quasi-continuum state induced by bias and temperature. These obtained results provide a full understanding of the bound-to-quasi-bound state and the bound-to-quasi-continuum state transition, and thus allow for a better optimization of QWIPs performance.

  14. Significant internal quantum efficiency enhancement of GaN/AlGaN multiple quantum wells emitting at ~350 nm via step quantum well structure design

    KAUST Repository

    Wu, Feng

    2017-05-03

    Significant internal quantum efficiency (IQE) enhancement of GaN/AlGaN multiple quantum wells (MQWs) emitting at similar to 350 nm was achieved via a step quantum well (QW) structure design. The MQW structures were grown on AlGaN/AlN/sapphire templates by metal-organic chemical vapor deposition (MOCVD). High resolution x-ray diffraction (HR-XRD) and scanning transmission electron microscopy (STEM) were performed, showing sharp interface of the MQWs. Weak beam dark field imaging was conducted, indicating a similar dislocation density of the investigated MQWs samples. The IQE of GaN/AlGaN MQWs was estimated by temperature dependent photoluminescence (TDPL). An IQE enhancement of about two times was observed for the GaN/AlGaN step QW structure, compared with conventional QW structure. Based on the theoretical calculation, this IQE enhancement was attributed to the suppressed polarization-induced field, and thus the improved electron-hole wave-function overlap in the step QW.

  15. Significant internal quantum efficiency enhancement of GaN/AlGaN multiple quantum wells emitting at ~350 nm via step quantum well structure design

    Science.gov (United States)

    Wu, Feng; Sun, Haiding; AJia, Idris A.; Roqan, Iman S.; Zhang, Daliang; Dai, Jiangnan; Chen, Changqing; Feng, Zhe Chuan; Li, Xiaohang

    2017-06-01

    Significant internal quantum efficiency (IQE) enhancement of GaN/AlGaN multiple quantum wells (MQWs) emitting at ~350 nm was achieved via a step quantum well (QW) structure design. The MQW structures were grown on AlGaN/AlN/sapphire templates by metal-organic chemical vapor deposition (MOCVD). High resolution x-ray diffraction (HR-XRD) and scanning transmission electron microscopy (STEM) were performed, showing sharp interface of the MQWs. Weak beam dark field imaging was conducted, indicating a similar dislocation density of the investigated MQWs samples. The IQE of GaN/AlGaN MQWs was estimated by temperature dependent photoluminescence (TDPL). An IQE enhancement of about two times was observed for the GaN/AlGaN step QW structure, compared with conventional QW structure. Based on the theoretical calculation, this IQE enhancement was attributed to the suppressed polarization-induced field, and thus the improved electron-hole wave-function overlap in the step QW.

  16. Efficient method for calculating electronic bound states in arbitrary one-dimensional quantum wells

    Science.gov (United States)

    de Aquino, V. M.; Iwamoto, H.; Dias, I. F. L.; Laureto, E.; da Silva, M. A. T.; da Silva, E. C. F.; Quivy, A. A.

    2017-01-01

    In the present paper it is demonstrated that the bound electronic states of multiple quantum wells structures may be calculated very efficiently by expanding their eigenstates in terms of the eigenfunctions of a particle in a box. The bound states of single and multiple symmetric or nonsymmetric wells are calculated within the single-band effective mass approximation. A comparison is then made between the results obtained for simple cases with exact calculations. We also apply our approach to a GaAs/AlGaAs multiple quantum well structure composed of forty periods each one with seven quantum wells. The method may be very useful to design narrow band quantum cascade photodetectors to work without applied bias in a photovoltaic mode. With the presented method the effects of a electric field may also be easily included which is very important if one desires study quantum well structures for application to the development of quantum cascade lasers. The advantages of the method are also presented.

  17. Exciton localization and interface roughness in growth-interrupted GaAs/AlAs quantum wells

    DEFF Research Database (Denmark)

    Leosson, Kristjan; Jensen, Jacob Riis; Langbein, Wolfgang Werner

    2000-01-01

    We have used photoluminescence spectroscopy to investigate the influence of interface roughness in GaAs/ AlAs quantum wells on their optical properties over a wide continuous range of well thicknesses. In order to compare different correlation lengths of the in-plane disorder potential, the wells...

  18. InAlGaAs/AlGaAs quantum wells: line widths, transition energies and segregation

    DEFF Research Database (Denmark)

    Jensen, Jacob Riis; Hvam, Jørn Märcher; Langbein, Wolfgang

    2000-01-01

    We investigate the optical properties of InAlCaAs/AlGaAs quantum wells pseudomorphically grown on GaAs using molecular beam epitaxy (MBE). The transition energies, measured with photoluminescence (PL), are modelled solving the Schrodinger equation, and taking into account segregation in the group...

  19. Investigation of Transmission Resonances with Specific Properties in Rectangular Semiconductor Quantum Wells

    Science.gov (United States)

    Niketic, Nemanja; Milanovic, Vitomir; Radovanovic, Jelena

    2012-01-01

    In this paper we provide a detailed analysis of the energy position and type of transmission maxima in rectangular quantum wells (QWs), taking into consideration the difference of electron effective masses in the barrier and well layers. Particular attention is given to transmission maxima that are less than unity and the implications of effective…

  20. Intrinsic optical confinement for ultrathin InAsN quantum well superlattices

    Energy Technology Data Exchange (ETDEWEB)

    Sakri, A.; Robert, C.; Pedesseau, L.; Cornet, C.; Durand, O.; Even, J.; Jancu, J.-M. [Université Europeenne de Bretagne, INSA Rennes,France and CNRS, UMR 6082, Foton, 20 avenues des Buttes de Coësmes, 35708 Rennes (France)

    2013-12-04

    We study energy-band engineering with InAsN monolayer in GaAs/GaP quantum well structure. A tight-binding calculation indicates that both type I alignment along with direct band-gap behavior can be obtained. We show that the optical transitions are less sensitive to the position of the probe.

  1. Exciton dynamics in GaAs/AlxGa1-xAs quantum wells

    DEFF Research Database (Denmark)

    Litvinenko, K.; Birkedal, Dan; Lyssenko, V. G.

    1999-01-01

    The changes induced in the optical absorption spectrum of a GaAs/AlxGa1-xAs multiple quantum well due to a photoexcited carrier distribution are reexamined. We use a femtosecond pump-probe technique to excite excitons and free electron-hole pairs. We find that for densities up to 10(11) cm(-2...

  2. Localized excitons in quantum wells show spin relaxation without coherence loss

    DEFF Research Database (Denmark)

    Zimmermann, R.; Langbein, W.; Runge, E.;

    2001-01-01

    The coherence in the secondary emission from quantum well excitons is studied using the speckle method. Analysing the different polarization channels allows to conclude that (i) no coherence loss occurs in the cross-polarized emission, favouring spin beating instead of spin dephasing, and that (i...

  3. Interaction induced dephasing of excitons in wide ZnSe/ZnMgSe single quantum wells

    DEFF Research Database (Denmark)

    Wagner, Hans Peter; Schätz, A.; Maier, R.;

    1998-01-01

    The dephasing of excitons in wide ZnSe/Zn0.94Mg0.06Se single quantum wells (SQW) is investigated by spectrally resolved, time integrated four-wave mixing (FWM). Simultaneous excitation of Is center-of-mass quantized heavy-hole and light-hole excition states leads to pronounced quantum beats. Pola...

  4. Electric field effect on the second-order nonlinear optical properties in semiparabolic quantum wells

    Science.gov (United States)

    Yuan, Jian-Hui; Chen, Ni; Zhang, Yan; Mo, Hua; Zhang, Zhi-Hai

    2016-03-01

    Electric field effect on the second-order nonlinear optical properties in semiparabolic quantum wells are studied theoretically. Both the second-harmonic generation susceptibility and nonlinear optical rectification depend dramatically on the direction and the strength of the electric field. Numerical results show that both the second-harmonic generation susceptibility and nonlinear optical rectification are always weakened as the electric field increases where the direction of the electric field is along the growth direction of the quantum wells, which is in contrast to the conventional case. However, the second-harmonic generation susceptibility is weakened, but the nonlinear optical rectification is strengthened as the electric field increases where the direction of the electric field is against the growth direction of the quantum wells. Also it is the blue (or red) shift of the resonance that is induced by increasing of the electric field when the direction of the electric field is along (or against) the growth direction of the quantum wells. Finally, the resonant peak and its corresponding to the resonant energy are also taken into account.

  5. Improvement of light-current characteristic linearity in a quantum well laser with asymmetric barriers

    DEFF Research Database (Denmark)

    Zubov, F. I.; Zhukov, A. E.; Shernyakov, Yu M.;

    2014-01-01

    The effect of asymmetric barriers on the light-current characteristic (LCC) of a quantum well laser was studied theoretically and experimentally. It is shown that the utilization of asymmetric barriers in a waveguide prevents the nonlinearity of LCC and, consequently, allows rising of the maximum...

  6. Energy Spectrum of a Positronium Negative Ion in a Parabolic Quantum Well

    Institute of Scientific and Technical Information of China (English)

    XIEWen-Fang

    2002-01-01

    The method of few-body physics is applied to calculating the energy levels of low-lying states of a positronium negative ion in a parabolic quantum well.The results show that the energy levels of a positronium negative ion in two-dimensional case are lower than those in three-dimensional case.

  7. Energy Spectrum of a Positronium Negative Ion in a Parabolic Quantum Well

    Institute of Scientific and Technical Information of China (English)

    XIE Wen-Fang

    2002-01-01

    The method of few-body physics is applied to calculating the energy levels of low-lying states ofa positro-nium negative ion in a parabolic quantum well. The results show that the energy levels of a positronium negativeion intwo-dimensional case are lower than those in three-dimensional case.

  8. Spin injection from Co2MnGa into an InGaAs quantum well

    DEFF Research Database (Denmark)

    Hickey, M. C.; Damsgaard, Christian Danvad; Holmes, S. N.;

    2008-01-01

    We have demonstrated spin injection from a full Heusler alloy Co2MnGa thin film into a (100) InGaAs quantum well in a semiconductor light-emitting diode structure at a temperature of 5 K. The detection is performed in the oblique Hanle geometry, allowing quantification of the effective spin...

  9. Multi-quantum-well nanowire heterostructures for wavelength-controlled lasers

    Science.gov (United States)

    Qian, Fang; Li, Yat; Gradečak, Silvija; Park, Hong-Gyu; Dong, Yajie; Ding, Yong; Wang, Zhong Lin; Lieber, Charles M.

    2008-09-01

    Rational design and synthesis of nanowires with increasingly complex structures can yield enhanced and/or novel electronic and photonic functions. For example, Ge/Si core/shell nanowires have exhibited substantially higher performance as field-effect transistors and low-temperature quantum devices compared with homogeneous materials, and nano-roughened Si nanowires were recently shown to have an unusually high thermoelectric figure of merit. Here, we report the first multi-quantum-well (MQW) core/shell nanowire heterostructures based on well-defined III-nitride materials that enable lasing over a broad range of wavelengths at room temperature. Transmission electron microscopy studies show that the triangular GaN nanowire cores enable epitaxial and dislocation-free growth of highly uniform (InGaN/GaN)n quantum wells with n=3, 13 and 26 and InGaN well thicknesses of 1-3nm. Optical excitation of individual MQW nanowire structures yielded lasing with InGaN quantum-well composition-dependent emission from 365 to 494nm, and threshold dependent on quantum well number, n. Our work demonstrates a new level of complexity in nanowire structures, which potentially can yield free-standing injection nanolasers.

  10. Interaction-induced effects in the nonlinear coherent response of quantum-well excitons

    DEFF Research Database (Denmark)

    Wagner, Hans Peter; Schätz, A.; Langbein, Wolfgang Werner;

    1999-01-01

    Interaction-induced processes are studied using the third-order nonlinear polarization created in polarization-dependent four-wave-mixing experiments (FWM) on a ZnSe single quantum well. We discuss their influence by a comparison of the experimental FWM with calculations based on extended optical...

  11. Thermalization of Hot Free Excitons in ZnSe-Based Quantum Wells

    DEFF Research Database (Denmark)

    Hoffmann, J.; Umlauff, M.; Kalt, H.

    1997-01-01

    Thermalization of hot-exciton populations in ZnSe quantum wells occurs on a time scale of 100 ps. Strong exciton-phonon coupling in II-VI semiconductors leads to a direct access to the thermalization dynamics via time-resolved spectroscopy of phonon-assisted luminescence. The experimental spectra...

  12. On the cascade capture of electrons at donors in GaAs quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Aleshkin, V. Ya., E-mail: aleshkin@ipmras.ru [Russian Academy of Sciences, Institute for Physics of Microstructures (Russian Federation)

    2015-09-15

    The impact parameter for the cascade capture of electrons at a charged donor in a GaAs quantum well is calculated. A simple approximate analytical expression for the impact parameter is suggested. The temperature dependence of the impact parameter for the case of electron scattering by the piezoelectric potential of acoustic phonons is determined.

  13. Impurity-free quantum well intermixing for large optical cavity high-power laser diode structures

    Science.gov (United States)

    Kahraman, Abdullah; Gür, Emre; Aydınlı, Atilla

    2016-08-01

    We report on the correlation of atomic concentration profiles of diffusing species with the blueshift of the quantum well luminescence from both as-grown and impurity free quantum wells intermixed on actual large optical cavity high power laser diode structures. Because it is critical to suppress catastrophic optical mirror damage, sputtered SiO2 and thermally evaporated SrF2 were used both to enhance and suppress quantum well intermixing, respectively, in these (Al)GaAs large optical cavity structures. A luminescence blueshift of 55 nm (130 meV) was obtained for samples with 400 nm thick sputtered SiO2. These layers were used to generate point defects by annealing the samples at 950 °C for 3 min. The ensuing Ga diffusion observed as a shifting front towards the surface at the interface of the GaAs cap and AlGaAs cladding, as well as Al diffusion into the GaAs cap layer, correlates well with the observed luminescence blue shift, as determined by x-ray photoelectron spectroscopy. Although this technique is well-known, the correlation between the photoluminescence peak blue shift and diffusion of Ga and Al during impurity free quantum well intermixing on actual large optical cavity laser diode structures was demonstrated with both x ray photoelectron and photoluminescence spectroscopy, for the first time.

  14. Many-Body Effect in Spin Dephasing in n-Type GaAs Quantum Wells

    Institute of Scientific and Technical Information of China (English)

    WENG Ming-Qi; WU Ming-Wei

    2005-01-01

    @@ By constructing and numerically solving the kinetic Bloch equations we perform a many-body study of the spin dephasing due to the D'yakonov-Perel' effect in n-type GaAs (100) quantum wells for high temperatures.

  15. Modeling of dilute nitride cascaded quantum well solar cells for high efficiency photovoltaics

    Science.gov (United States)

    Vijaya, G.; Alemu, A.; Freundlich, A.

    2013-03-01

    III-V Dilute Nitride multi-quantum well structures are currently promising candidates to achieve 1 sun efficiencies of cell in a 4 junction configuration could yield 1 sun efficiencies greater than 40%. However for a conventional deep well design the characteristic carrier escape times could exceed that of radiative recombination hence limiting the current output of the cell, as has been indicated by prior experiments. In order to increase the current extraction here we evaluate the performance of a cascaded quantum well design whereby a thermally assisted resonant tunneling process is used to accelerate the carrier escape process (efficiency. The quantum efficiency of a p-i-n subcell where a periodic sequence of quantum wells with well and barrier thicknesses adjusted for the sequential extraction operation is calculated using a 2D drift diffusion model and taking into account absorption properties of resulting MQWs. The calculation also accounts for the E-field induced modifications of absorption properties and quantization in quantum wells. The results are then accounted for to calculate efficiencies for the proposed 4 junction design, and indicate potential for reaching efficiencies in excess of this structure is above 42% (1 sun) and above 50% (500 sun) AM1.5.

  16. Exciton dynamics in near-surface InGaN quantum wells coupled to colloidal nanocrystals

    DEFF Research Database (Denmark)

    Kopylov, Oleksii; Shirazi, Roza; Yvind, Kresten;

    2013-01-01

    We study non-radiative energy transfer between InGaN quantum wells and colloidal InP nanocrystals separated by sub-10nm distance. A significant non-radiative energy transfer between the two layers is accompanied by reduced surface recombination in InGaN....

  17. Quantum well saturable absorber mirror with electrical control of modulation depth

    DEFF Research Database (Denmark)

    Liu, Xiaomin; Rafailov, Edik U.; Livshits, Daniil

    2010-01-01

    We demonstrate a quantum well QW semiconductor saturable absorber mirror SESAM comprising low-temperature grown InGaAs/GaAs QWs incorporated into a p-i-n structure. By applying the reverse bias voltage in the range 0–2 V to the p-i-n structure, we were able to change the SESAM modulation depth...

  18. Efficiency studies on semipolar GaInN-GaN quantum well structures

    Energy Technology Data Exchange (ETDEWEB)

    Scholz, Ferdinand; Meisch, Tobias; Elkhouly, Karim [Institute of Optoelectronics, Ulm University (Germany)

    2016-12-15

    In order to clarify the reasons for the fairly poor electroluminescence (EL) performance of semipolar LED structures grown on patterned sapphire wafers, we have analyzed both, pure photoluminescence (PL) test structures without doping only containing 5 GaInN quantum wells and full EL test structures, all emitting at a wavelength of about 510 nm. Evaluating the PL intensity over a wide range of temperatures and excitation powers, we conclude that such quantum wells possess a fairly large internal quantum efficiency of about 20%. However, on EL test structures containing nominally the same quantum wells, we obtained an optical output power of only about 150μW at an applied current of 20 mA. This may be due partly to some thermal destruction of the quantum wells by the overgrowth with p-GaN. Even more important seems to be the not yet finally optimized p-doping of these structures. (copyright 2016 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  19. Room-temperature near-field reflection spectroscopy of single quantum wells

    DEFF Research Database (Denmark)

    Langbein, Wolfgang Werner; Hvam, Jørn Marcher; Madsen, Steen;

    1997-01-01

    . This technique suppresses efficiently the otherwise dominating far-field background and reduces topographic artifacts. We demonstrate its performance on a thin, strained near-surface CdS/ZnS single quantum well at room temperature. The optical structure of these topographically flat samples is due to Cd...

  20. Two-Dimensional GaAs/AlGaAs Multiple Quantum Well Spatial Light Modulators

    Institute of Scientific and Technical Information of China (English)

    Qin Wang; Jan Borglind; Smilja Becanovic; Stéphane Junique; Daniel (A)gren; Bertrand Noharet; Linda H(o)glund; Olof (O)berg; Erik Petrini; Jan Y. Andersson; Hedda Malm

    2003-01-01

    Multiple quantum well spatial light modulators with 128x128 array in 38μm pitch are fabricated using two pproaches, one with an attachment of an optical substrate and another one without. These two fabrication processes are described and compared.

  1. Properties of Excitons Bound to Neutral Donors in GaAs Quantum-Well Wires

    Institute of Scientific and Technical Information of China (English)

    LIU Jian-Jun; WANG Xue-Feng

    2005-01-01

    @@ In the effective mass approximation, the binding energy of an exciton bound to a neutral donor (D0, X) is calcu-lated variationally for rectangular GaAs quantum-well wires (QWWs) by using a three-parameter wavefunction.

  2. Ultrafast carrier dynamics in InGaN/GaN multiple quantum wells

    DEFF Research Database (Denmark)

    Porte, Henrik; Turchinovich, Dmitry; Cooke, David

    We studied the THz conductivity of InGaN/GaN multiple quantum wells (MQWs)by time-resolved terahertz spectroscopy. A nonexponential carrier density decay is observed due to the restoration of a built-in piezoelectric field. Terahertz conductivity spectra show a nonmetallic behavior of the carriers....

  3. Terahertz study of ultrafast carrier dynamics in InGa/GaN multiple quantum wells

    DEFF Research Database (Denmark)

    Porte, Henrik; Turchinovich, Dmitry; Cooke, David

    2009-01-01

    Ultrafast carrier dynamics in InGaN/GaN multiple quantum wells is measured by time-resolved terahertz spectroscopy. The built-in piezoelectric field is initially screened by photoexcited, polarized carriers, and is gradullay restored as the carriers recombine. We observe a nonexponential decay...

  4. Optical properties of InAlGaAs quantum wells: Influence of segregation and band bowing

    DEFF Research Database (Denmark)

    Jensen, Jacob Riis; Hvam, Jørn Märcher; Langbein, Wolfgang

    1999-01-01

    Knowledge of the quaternary InAlGaAs material system is very limited for the composition range relevant for growth on GaAs substrates. We report on the characterization and modeling of InAlGaAs quantum wells with AlGaAs barriers, grown pseudomorphically on a GaAs substrate with molecular beam...

  5. Localization landscape theory of disorder in semiconductors. II. Urbach tails of disordered quantum well layers

    Science.gov (United States)

    Piccardo, Marco; Li, Chi-Kang; Wu, Yuh-Renn; Speck, James S.; Bonef, Bastien; Farrell, Robert M.; Filoche, Marcel; Martinelli, Lucio; Peretti, Jacques; Weisbuch, Claude

    2017-04-01

    Urbach tails in semiconductors are often associated to effects of compositional disorder. The Urbach tail observed in InGaN alloy quantum wells of solar cells and LEDs by biased photocurrent spectroscopy is shown to be characteristic of the ternary alloy disorder. The broadening of the absorption edge observed for quantum wells emitting from violet to green (indium content ranging from 0% to 28%) corresponds to a typical Urbach energy of 20 meV. A three-dimensional absorption model is developed based on a recent theory of disorder-induced localization which provides the effective potential seen by the localized carriers without having to resort to the solution of the Schrödinger equation in a disordered potential. This model incorporating compositional disorder accounts well for the experimental broadening of the Urbach tail of the absorption edge. For energies below the Urbach tail of the InGaN quantum wells, type-II well-to-barrier transitions are observed and modeled. This contribution to the below-band-gap absorption is particularly efficient in near-ultraviolet emitting quantum wells. When reverse biasing the device, the well-to-barrier below-band-gap absorption exhibits a red-shift, while the Urbach tail corresponding to the absorption within the quantum wells is blue-shifted, due to the partial compensation of the internal piezoelectric fields by the external bias. The good agreement between the measured Urbach tail and its modeling by the localization theory demonstrates the applicability of the latter to compositional disorder effects in nitride semiconductors.

  6. Using tunnel junctions to grow monolithically integrated optically pumped semipolar III-nitride yellow quantum wells on top of electrically injected blue quantum wells.

    Science.gov (United States)

    Kowsz, Stacy J; Young, Erin C; Yonkee, Benjamin P; Pynn, Christopher D; Farrell, Robert M; Speck, James S; DenBaars, Steven P; Nakamura, Shuji

    2017-02-20

    We report a device that monolithically integrates optically pumped (20-21) III-nitride quantum wells (QWs) with 560 nm emission on top of electrically injected QWs with 450 nm emission. The higher temperature growth of the blue light-emitting diode (LED) was performed first, which prevented thermal damage to the higher indium content InGaN of the optically pumped QWs. A tunnel junction (TJ) was incorporated between the optically pumped and electrically injected QWs; this TJ enabled current spreading in the buried LED. Metalorganic chemical vapor deposition enabled the growth of InGaN QWs with high radiative efficiency, while molecular beam epitaxy was leveraged to achieve activated buried p-type GaN and the TJ. This initial device exhibited dichromatic optically polarized emission with a polarization ratio of 0.28. Future improvements in spectral distribution should enable phosphor-free polarized white light emission.

  7. Double-sided brush-shaped TiO2 nanostructure assemblies with highly ordered nanowires for dye-sensitized solar cells.

    Science.gov (United States)

    Zha, Chenyang; Shen, Liming; Zhang, Xiaoyan; Wang, Yifeng; Korgel, Brian A; Gupta, Arunava; Bao, Ningzhong

    2014-01-08

    We describe a seeded hydrothermal process for the growth of unique double-sided brush-shaped (DSBS) TiO2 nanostructure assemblies consisting of highly ordered rutile nanowires vertically aligned around an annealed TiO2 nanoparticle layer. The annealed TiO2 nanoparticle layer seeds the nanowire growth and also supports the DSBS structure. The morphology of the DSBS TiO2 nanostructure depends on the hydrothermal reaction time. The diameter of the nanowires is about 6.6 nm, and with increasing reaction time from 1 to 8 h the nanowire length increases from 0.6 to 6.2 μm, whereas the thickness of the nanoparticle layer decreases from 4.3 to 2.8 μm. These free-standing nanowire arrays provide large internal surface area, which is essential for minimizing carrier recombination in high performance photovoltaic devices. Furthermore, the nanowire architecture can help increase the rate of charge transport as compared to particulate films because of lower concentration of grain boundaries. The power conversion efficiency of backside (DSBS TiO2/FTO photoanode) illuminated dye-sensitized solar cells fabricated using the DSBS TiO2 nanostructure assembly is found to be depended on the nanowire length. A cell fabricated using 15.2 μm thick nanostructures sensitized by N719 has a short-circuit current density of 12.18 mA cm(-2), 0.78 V open circuit potential, and a 0.59 filling factor, yielding a maximum power conversion efficiency of 5.61% under AM 1.5 illumination.

  8. Quantum mechanical effects analysis of nanostructured solar cell models

    Directory of Open Access Journals (Sweden)

    Badea Andrei

    2016-01-01

    Full Text Available The quantum mechanical effects resulted from the inclusion of nanostructures, represented by quantum wells and quantum dots, in the i-layer of an intermediate band solar cell will be analyzed. We will discuss the role of these specific nanostructures in the increasing of the solar cells efficiency. InAs quantum wells being placed in the i-layer of a gallium arsenide (GaAs p-i-n cell, we will analyze the quantum confined regions and determine the properties of the eigenstates located therein. Also, we simulate the electroluminescence that occurs due to the nanostructured regions.

  9. Influence of free carriers on exciton ground states in quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Klochikhin, A.A. [Ioffe Physical Technical Institute, 194021 St. Petersburg (Russian Federation); Nuclear Physics Institute, 350000 St. Petersburg (Russian Federation); Kochereshko, V.P., E-mail: vladimir.kochereshko@mail.ioffe.ru [Ioffe Physical Technical Institute, 194021 St. Petersburg (Russian Federation); Spin Optics Laboratory, St. Petersburg State University, 198904 St. Petersburg (Russian Federation); Tatarenko, S. [CEA-CNRS Group “Nanophysique et Semiconducteurs”, Institut Néel, CNRS and Universite Joseph Fourier, 25 Avenue des Martyrs, 38042 Grenoble (France)

    2014-10-15

    The influence of free carriers on the ground state of the exciton at zero magnetic field in a quasi-two-dimensional quantum well that contains a gas of free electrons is considered in the framework of the random phase approximation. The effects of the exciton–charge-density interaction and the inelastic scattering processes due to the electron–electron exchange interaction are taken into account. The effect of phase-space filling is considered using an approximate approach. The results of the calculation are compared with the experimental data. - Highlights: • We discussed the effect of free carriers on the exciton ground state in quantum wells. • The processes of exciton–electron scattering become the most important for excitons in doped QWs. • The direct Coulomb scattering can be neglected. • The most important becomes the exchange inelastic exciton–electron scattering.

  10. Bound states in optical absorption of semiconductor quantum wells containing a two-dimensional electron Gas

    Science.gov (United States)

    Huard; Cox; Saminadayar; Arnoult; Tatarenko

    2000-01-01

    The dependence of the optical absorption spectrum of a semiconductor quantum well on two-dimensional electron concentration n(e) is studied using CdTe samples. The trion peak (X-) seen at low n(e) evolves smoothly into the Fermi edge singularity at high n(e). The exciton peak (X) moves off to high energy, weakens, and disappears. The X,X- splitting is linear in n(e) and closely equal to the Fermi energy plus the trion binding energy. For Cd0.998Mn0.002Te quantum wells in a magnetic field, the X,X- splitting reflects unequal Fermi energies for M = +/-1/2 electrons. The data are explained by Hawrylak's theory of the many-body optical response including spin effects.

  11. Limits to mobility in InAs quantum wells with nearly lattice-matched barriers

    Science.gov (United States)

    Shojaei, B.; Drachmann, A. C. C.; Pendharkar, M.; Pennachio, D. J.; Echlin, M. P.; Callahan, P. G.; Kraemer, S.; Pollock, T. M.; Marcus, C. M.; Palmstrøm, C. J.

    2016-12-01

    The growth and density dependence of the low temperature mobility of a series of two-dimensional electron systems confined to unintentionally doped, low extended defect density InAs quantum wells with A l1 -xG axSb barriers are reported. The electron-mobility-limiting scattering mechanisms were determined by utilizing dual-gated devices to study the dependence of mobility on carrier density and electric field independently. Analysis of possible scattering mechanisms indicate the mobility was limited primarily by rough interfaces in narrow quantum wells and a combination of alloy disorder and interface roughness in wide wells at high carrier density within the first occupied electronic subband. At low carrier density, the functional dependence of mobility on carrier density provided evidence of Coulombic scattering from charged defects. A gate-tuned electron mobility exceeding 750 000 c m2V-1s-1 was achieved at a sample temperature of 2 K.

  12. Tuneable frequency up-conversion based on biased asymmetric coupled quantum well structure

    Energy Technology Data Exchange (ETDEWEB)

    Hu Zhenhua [Department of Physics, Science College, Wuhan University of Technology, 430063, Wuhan, Hubei (China); Huang Dexiu, E-mail: hzh267@sohu.com [Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, 430074, Wuhan, Hubei (China)

    2011-02-01

    The behaviours of the optical nonlinear susceptibility {chi}{sup (3)} responsible for the phase-conjugate beam of frequency conversion in non-degenerate four-wave mixing (NDFWM) are studied for a biased asymmetric coupled quantum well (ACQW) structure. It is shown that the frequency up-conversion peak position determined by {chi}{sup (3)} is very sensitive to the external inverse electric field strength applied among the grown direction of quantum well but its value is insensitive to that. In other words, the frequency up-conversion peak has a large shift but its value maintains a constant when the electric field strength increases in a small bias range. The characteristics of the tuneable-frequency and the power balance of the ACQW structure may provide the high-efficient wavelength conversion in the optical communication system.

  13. Investigation of temperature-dependent photoluminescence in multi-quantum wells.

    Science.gov (United States)

    Fang, Yutao; Wang, Lu; Sun, Qingling; Lu, Taiping; Deng, Zhen; Ma, Ziguang; Jiang, Yang; Jia, Haiqiang; Wang, Wenxin; Zhou, Junming; Chen, Hong

    2015-07-31

    Photoluminescence (PL) is a nondestructive and powerful method to investigate carrier recombination and transport characteristics in semiconductor materials. In this study, the temperature dependences of photoluminescence of GaAs-AlxGa1-xAs multi-quantum wells samples with and without p-n junction were measured under both resonant and non-resonant excitation modes. An obvious increase of photoluminescence(PL) intensity as the rising of temperature in low temperature range (T photoluminescence characters from the temperature dependence of integrated PL intensity unavailable. For resonant excitation, carriers are generated only in the wells and the temperature dependence of integrated PL intensity is very suitable to analysis the photoluminescence characters of quantum wells.

  14. Spin-related transport phenomena in HgTe-based quantum well structures

    Energy Technology Data Exchange (ETDEWEB)

    Koenig, Markus

    2007-12-15

    Within the scope of this thesis, spin related transport phenomena have been investigated in HgTe/Hg{sub 0.3}Cd{sub 0.7}Te quantum well structures. In our experiments, the existence of the quantum spin Hall (QSH) state was successfully demonstrated for the first time and the presented results provide clear evidence for the charge transport properties of the QSH state. Our experiments provide the first direct observation of the Aharonov-Casher (AC) effect in semiconductor structures. In conclusion, HgTe quantum well structures have proven to be an excellent template for studying spin-related transport phenomena: The QSH relies on the peculiar band structure of the material and the existence of both the spin Hall effect and the AC effect is a consequence of the substantial spin-orbit interaction. (orig.)

  15. Spinor-electron wave guided modes in coupled quantum wells structures by solving the Dirac equation

    Energy Technology Data Exchange (ETDEWEB)

    Linares, Jesus [Area de Optica, Departamento de Fisica Aplicada, Facultade de Fisica, Escola Universitaria de Optica e Optometria, Universidade de Santiago de Compostela, E-15782 Santiago de Compostela, Galicia (Spain)], E-mail: suso.linares.beiras@usc.es; Nistal, Maria C. [Area de Optica, Departamento de Fisica Aplicada, Facultade de Fisica, Escola Universitaria de Optica e Optometria, Universidade de Santiago de Compostela, E-15782 Santiago de Compostela, Galicia (Spain)

    2009-05-04

    A quantum analysis based on the Dirac equation of the propagation of spinor-electron waves in coupled quantum wells, or equivalently coupled electron waveguides, is presented. The complete optical wave equations for Spin-Up (SU) and Spin-Down (SD) spinor-electron waves in these electron guides couplers are derived from the Dirac equation. The relativistic amplitudes and dispersion equations of the spinor-electron wave-guided modes in a planar quantum coupler formed by two coupled quantum wells, or equivalently by two coupled slab electron waveguides, are exactly derived. The main outcomes related to the spinor modal structure, such as the breaking of the non-relativistic degenerate spin states, the appearance of phase shifts associated with the spin polarization and so on, are shown.

  16. Effect of the quantum well thickness on the performance of InGaN photovoltaic cells

    Energy Technology Data Exchange (ETDEWEB)

    Redaelli, L.; Mukhtarova, A.; Valdueza-Felip, S.; Ajay, A.; Durand, C.; Eymery, J.; Monroy, E. [Université Grenoble Alpes, 38000 Grenoble (France); CEA-CNRS Group «Nanophysique et semiconducteurs», CEA-Grenoble, INAC/SP2M, 17 avenue des Martyrs, 38054 Grenoble cedex 9 (France); Bougerol, C.; Himwas, C. [Université Grenoble Alpes, 38000 Grenoble (France); CEA-CNRS Group «Nanophysique et semiconducteurs», Institut Néel-CNRS, 25 avenue des Martyrs, 38042 Grenoble cedex 9 (France); Faure-Vincent, J. [Université Grenoble Alpes, 38000 Grenoble (France); CNRS, INAC-SPRAM, F-38000 Grenoble (France); CEA, INAC-SPRAM, F-38000 Grenoble (France)

    2014-09-29

    We report on the influence of the quantum well thickness on the effective band gap and conversion efficiency of In{sub 0.12}Ga{sub 0.88}N/GaN multiple quantum well solar cells. The band-to-band transition can be redshifted from 395 to 474 nm by increasing the well thickness from 1.3 to 5.4 nm, as demonstrated by cathodoluminescence measurements. However, the redshift of the absorption edge is much less pronounced in absorption: in thicker wells, transitions to higher energy levels dominate. Besides, partial strain relaxation in thicker wells leads to the formation of defects, hence degrading the overall solar cell performance.

  17. Strain Compensation in Single ZnSe/CdSe Quantum Wells: Analytical Model and Experimental Evidence.

    Science.gov (United States)

    Rieger, Torsten; Riedl, Thomas; Neumann, Elmar; Grützmacher, Detlev; Lindner, Jörg K N; Pawlis, Alexander

    2017-03-08

    The lattice mismatch between CdSe and ZnSe is known to limit the thickness of ZnSe/CdSe quantum wells on GaAs (001) substrates to about 2-3 monolayers. We demonstrate that this thickness can be enhanced significantly by using In0.12Ga0.88As pseudo substrates, which generate alternating tensile and compressive strains in the ZnSe/CdSe/ZnSe layers resulting in an efficient strain compensation. This method enables to design CdSe/ZnSe quantum wells with CdSe thicknesses ranging from 1 to 6 monolayers, covering the whole visible spectrum. The strain compensation effect is investigated by high resolution transmission electron microscopy and supported by molecular statics simulations. The model approach with the supporting experimental measurements is sufficiently general to be also applied to other highly mismatched material combinations for the design of advanced strained heterostructures.

  18. Coulomb-interaction induced coupling of Landau levels in intrinsic and modulation-doped quantum wells

    Science.gov (United States)

    Paul, J.; Stevens, C. E.; Zhang, H.; Dey, P.; McGinty, D.; McGill, S. A.; Smith, R. P.; Reno, J. L.; Turkowski, V.; Perakis, I. E.; Hilton, D. J.; Karaiskaj, D.

    2017-06-01

    We have performed two-dimensional Fourier transform spectroscopy on intrinsic and modulation doped quantum wells in external magnetic fields up to 10 T. In the undoped sample, the strong Coulomb interactions and the increasing separations of the electron and hole charge distributions with increasing magnetic fields lead to a nontrivial in-plane dispersion of the magneto-excitons. Thus, the discrete and degenerate Landau levels are coupled to a continuum. The signature of this continuum is the emergence of elongated spectral line shapes at the Landau level energies, which are exposed by the multidimensional nature of our technique. Surprisingly, the elongation of the peaks is completely absent in the lowest Landau level spectra obtained from the modulation doped quantum well at high fields.

  19. Coherent Interband and Intersubband Dynamics in Terahertz-Driven GaAs Quantum Wells

    Institute of Scientific and Technical Information of China (English)

    2005-01-01

    We theoretically investigate the optical absorption spectra and charge density by subjecting a GaAs quantum well to both an intense terahertz (THz)-frequency driving field and an optical pulse within the theory of density matrix. In presence of a strong THz field, the optical transitions in quantum well subbands are altered by the THz field. The alteration has a direct impact on the optical absorption and the charge density. The excitonic peak splitting and THz optical sideband in the absorption spectra show up when changing the THz field intensity and/or frequency. The Autler-Towns splitting is a result from the THz nonlinear dynamics of confined excitons. On the other hand, the carrier charge density is created as wave packets formed by coherent superposition of several eigenstates. The charge density exhibitsquantum beats for short pulses and/or wider wells and is modulated by the THz field.

  20. Mid/far-infrared photo-detectors based on graphene asymmetric quantum wells

    Science.gov (United States)

    Ben Salem, E.; Chaabani, R.; Jaziri, S.

    2016-09-01

    We conducted a theoretical study on the electronic properties of a single-layer graphene asymmetric quantum well. Quantification of energy levels is limited by electron-hole conversion at the barrier interfaces and free-electron continuum. Electron-hole conversion at the barrier interfaces can be controlled by introducing an asymmetry between barriers and taking into account the effect of the interactions of the graphene sheet with the substrate. The interaction with the substrate induces an effective mass to carriers, allowing observation of Fabry-Pérot resonances under normal incidence and extinction of Klein tunneling. The asymmetry, between barriers creates a transmission gap between confined states and free-electron continuum, allowing the large graphene asymmetric quantum well to be exploited as a photo-detector operating at mid- and far-infrared frequency regimes.

  1. Lateral charge carrier diffusion in InGaN quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Danhof, J.; Solowan, H.M.; Schwarz, U.T. [Albert-Ludwigs-Universitaet Freiburg, IMTEK, Georges-Koehler-Allee 106, 79110 Freiburg (Germany); Fraunhofer Institute for Applied Solid State Physics IAF, Tullastrasse 72, 79108 Freiburg (Germany); Kaneta, A.; Kawakami, Y. [Kyoto University, Katsura Campus, Nishikyo-ku, Kyoto 615-2312 (Japan); Schiavon, D.; Meyer, T.; Peter, M. [Osram Opto Semiconductors GmbH, Leibnizstrasse 4, 93055 Regensburg (Germany)

    2012-03-15

    We investigated lateral charge carrier transport in indium gallium nitride InGaN/GaN multi-quantum wells for two different samples, one sample emitting green light at about 510 nm and the other emitting cyan light at about 470 nm. For the cyan light emitting sample we found a diffusion constant of 1.2 cm{sup 2}/s and for the green light emitting sample 0.25 cm{sup 2}/s. The large difference in diffusion constant is due to a higher point defect density in the green light emitting quantum wells (QWs) as high indium incorporation tends to reduce material quality. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  2. Polarons with Spatially Dependent Mass in a Finite Parabolic Quantum Well

    Institute of Scientific and Technical Information of China (English)

    赵凤岐; 梁希侠

    2002-01-01

    We study the energy levels of an electron (or hole) polaron in a parabolic quantum well structure, includingthe spatial dependence of the effective mass. We also consider the two-mode behaviour of longitudinal opticalphonon modes of the ternary mixed crystals in the structure, in the calculation of the effect of the electron-phonon interaction. We calculate the ground state, the first excited state and the transition energy ofan electron(or hole) in the GaAs/Alx Ga1-xAs parabolic quantum well structure. The numerical results show that theelectron-phonon interaction obviously affects the energy levels of the electron (or hole), which are in agreementwith experimental results.

  3. Variational Calculations of Neutral Bound Excitons in GaAs Quantum-Well Wires

    Institute of Scientific and Technical Information of China (English)

    LIU Jian-Jun; DI Bing; YANG Guo-Chen; LI Shu-Shen

    2004-01-01

    @@ The binding energy of an exciton bound to a neutral donor (D0, X) in GaAs quantum-well wires is calculated variationally as a function of the wire width for different positions of the impurity inside the wire by using a two-parameter wavefunction. There is no artificial parameter added in our calculation. The results we have obtained show that the binding energies are closely correlated to the sizes of the wire, the impurity position, and also that their magnitudes are greater than those in the two-dimensional quantum wells compared. In addition,we also calculate the average interparticle distance as a function of the wire width. The results are discussed in detail.

  4. Pressure- and temperature-driven phase transitions in HgTe quantum wells

    Science.gov (United States)

    Krishtopenko, S. S.; Yahniuk, I.; But, D. B.; Gavrilenko, V. I.; Knap, W.; Teppe, F.

    2016-12-01

    We present theoretical investigations of pressure- and temperature-driven phase transitions in HgTe quantum wells grown on a CdTe buffer. Using the eight-band k .p Hamiltonian we calculate evolution of energy-band structure at different quantum well widths with hydrostatic pressure up to 20 kbars and temperature ranging up to 300 K. In particular, we show that, in addition to temperature, tuning of hydrostatic pressure allows us to drive transitions between semimetal, band insulator, and topological insulator phases. Our realistic band-structure calculations reveal that the band inversion under hydrostatic pressure and temperature may be accompanied by nonlocal overlapping between conduction and valence bands. The pressure and temperature phase diagrams are presented.

  5. Temperature dependence of excitonic transition in ZnSe/ZnCdSe quantum wells

    Institute of Scientific and Technical Information of China (English)

    GUO Zi-zheng; LIANG Xi-xia; BAN Shi-liang

    2005-01-01

    A theoretical calculation for the temperature dependence of the excitonic transition in ZnSe/ZnCdSe quantum wells is performed. The exciton binding energy is calculated with a variational technique by considering the temperature-dependence parameters. Our results show that the exciton binding energy reduces linearly with temperature increasing. We find that the strain due to lattice mismatch and differential thermal expansion decreases with the temperature increasing.

  6. Quantum Well Infrared Photodetectors:the Basic Design and New Research Directions

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    The basic design principles and parameters of GaAs/AlGaAs quantum well infrared photodetectors (QWIP) are reviewed.Furthermore new research directions,devices and applications suited for QWIPs are discussed.These include monolithic integration of QWIPs with GaAs based electronic and optoelectronic devices,high frequency and high speed QWIPs and applications,multicolor and multispectral detectors,and p-type QWIPs.

  7. Carrier localization mechanisms in InGaN/GaN quantum wells

    OpenAIRE

    Watson-Parris, D.; Godfrey, M. J.; Dawson, P.; Oliver, R. A.; Galtrey, M. J.; Kappers, M. J.; Humphreys, C J

    2010-01-01

    Localization lengths of the electrons and holes in InGaN/GaN quantum wells have been calculated using numerical solutions of the effective mass Schr\\"odinger equation. We have treated the distribution of indium atoms as random and found that the resultant fluctuations in alloy concentration can localize the carriers. By using a locally varying indium concentration function we have calculated the contribution to the potential energy of the carriers from band gap fluctuations, the deformation p...

  8. Field-effect transistor self-electrooptic effect device integrated photodiode, quantum well modulator and transistor

    Energy Technology Data Exchange (ETDEWEB)

    Miller, D.A.B.; Feuer, M.D.; Chang, T.Y.; Shunk, S.C.; Henry, J.E.; Burrows, D.J.; Chemla, D.S.

    1989-03-01

    The authors propose and demonstrate the integration of a photodiode, a quantum-confined Stark effect quantum well optical modulator and a metal-semiconductor field-effect transistor (MESFET), to make a field-effect transistor self-electrooptic effect device. This integration allows optical inputs and outputs on the surface of a GaAs-integrated circuit chip, compatible with standard MESFET processing. As an illustration of feasibility, the authors demonstrate optical signal amplification with a single MESFET.

  9. On the Matsubara-Toyozawa Formalism to Treat Impurity Bands in δ-DOPED Quantum Wells

    Science.gov (United States)

    da Cunha Lima, I. C.; da Silva, A. Ferreira

    We obtain the density of the ground and excited states for electrons bound to shallow donors in a δ-dopping of a quantum well. We use the Matsubara-Toyozawa technique to treat disorder. The impurity bands are calculated for a concentration of 9.4×109 cm-2. We show that for this concentration of interest the excited bands do not overlap the ground state.

  10. Handheld deep ultraviolet emission device based on aluminum nitride quantum wells and graphene nanoneedle field emitters.

    Science.gov (United States)

    Matsumoto, Takahiro; Iwayama, Sho; Saito, Takao; Kawakami, Yasuyuki; Kubo, Fumio; Amano, Hiroshi

    2012-10-22

    We report the successful fabrication of a compact deep ultraviolet emission device via a marriage of AlGaN quantum wells and graphene nanoneedle field electron emitters. The device demonstrated a 20-mW deep ultraviolet output power and an approximately 4% power efficiency. The performance of this device may lead toward the realization of an environmentally friendly, convenient and practical deep ultraviolet light source.

  11. Simulation of the dark current of quantum-well infrared photodetectors

    Science.gov (United States)

    Claro, M. S.; Fernandes, F. M.; da Silva, E. C. F.; Quivy, A. A.

    2017-04-01

    We developed a method to calculate the dark current of quantum-well infrared photodetectors without the need to fit any experimental data or to perform extra transport measurements on other samples. The temperature range of the calculations was extended below 30 K by combining a thermionic model valid at high temperature and a miniband-transport model valid at low temperature whenever any superlattice characteristics were relevant in the device.

  12. Long Wavelength 256 X 256 Quantum Well Infrared Photodetector Portable Camera

    Science.gov (United States)

    Gunapala, S. D.; Liu, J. K.; Shott, C. A.; Hoelter, T.; Sundaram, M.; Park, J. S.; Laband, S.; James, J.

    1996-01-01

    In this paper, we discuss the development of very sensitive long wavelength infrared (LWIR) GaAs/AlGal-xAs Quantum well infrared photodetectors (QWIPS), fabrication of random reflectors for efficient light coupling, and the demonstration of a LWIR 256 X 256 focal plane array imaging camera. Excellent imagery, with a noise equivalent differential temperature (NE-delta-T) of 25 mK has been achieved.

  13. Terahertz-Induced Changes of Optical Spectra in GaAs Quantum Wells

    Institute of Scientific and Technical Information of China (English)

    MI Xian-Wu; CAO Jun-Cheng

    2004-01-01

    @@ We have theoretically investigated optical absorption spectra in GaAs quantum well (QW) driven by both a strong terahertz (THz) field and a near-infrared field within the theory of density matrix. In presence of a strong THz field, the optical transitions in the QW subbands are altered by the THz field. The alteration has a direct impact on the optical absorption and results in the Autler-Townes splitting and the sidebands generation, which is in agreement with the experiments.

  14. Intrinsic Hall effect and separation of Rashba and Dresselhaus spin splittings in semiconductor quantum wells

    Institute of Scientific and Technical Information of China (English)

    Song Hong-Zhou; Zhang Ping; Duan Su-Qing; Zhao Xian-Geng

    2006-01-01

    We have proposed a method to separate Rashba and Dresselhaus spin splittings in semiconductor quantum wells by using the intrinsic Hall effect. It is shown that the interference between Rashba and Dresselhaus terms can deflect the electrons in opposite transverse directions with a change of sign in the macroscopic Hall current, thus providing an alternative way to determine the different contributions to the spin-orbit coupling.

  15. Numerical analysis of AlGaAs/GaAs multi-quantum well superluminescent diodes

    Science.gov (United States)

    Navaeipour, Parvin; Asgari, Asghar

    2014-09-01

    In this paper, we have investigated numerically AlGaAs/GaAs multi-quantum well superluminescent diodes. In these devices the dependence of optical gain, output power on the cavity length and the density states have been analyzed. It is observed that the optical gain and its FWHM bandwidth increase with the increasing density state. Furthermore, the output power increases with the increasing cavity length, whereas the FWHM bandwidth decreases.

  16. Selection of the lasing frequency and heating the quantum-well heterostructure laser diodes

    OpenAIRE

    Kononenko, V.K.; Kuntsevich, B. F.

    2011-01-01

    Numerical simulation of controlling the lasing frequency for the 1.5 μm-range quantum-well heterostructure laser diodes is developed with taking into account increasing the active region temperature under pump current modulation. Peculiarities of the amplitude-frequency characteristics are analyzed at selection of the lasing frequency. General description of the heating of the laser active region during the current modulation is given and selection conditions of the lasing frequency tha...

  17. A 980 nm pseudomorphic single quantum well laser for pumping erbium-doped optical fiber amplifiers

    Science.gov (United States)

    Larsson, A.; Forouhar, S.; Cody, J.; Lang, R. J.; Andrekson, P. A.

    1990-01-01

    The authors have fabricated ridge waveguide pseudomorphic InGaAs/GaAs/AlGaAs GRIN-SCH SQW (graded-index separate-confinement-heterostructure single-quantum-well) lasers, emitting at 980 nm, with a maximum output power of 240 mW from one facet and a 22 percent coupling efficiency into a 1.55-micron single-mode optical fiber. These lasers satisfy the requirements on efficient and compact pump sources for Er3+-doped fiber amplifiers.

  18. Energy spectrum of an electron confined in the hexagon-shaped quantum well

    Institute of Scientific and Technical Information of China (English)

    Yu.; V.; VOROBIEV; V.; R.; VIEIRA; P.; P.; HORLEY; P.; N.; GORLEY; J.; GONZLEZ-HERNNDEZ

    2009-01-01

    Considering the hexagonal-shaped quantum-scale formations on the surface of thin semiconductor films, a methodology was developed to obtain the analytical solution of the Schrdinger equation when impenetrable walls of a quantum well are treated as mirrors. The results obtained allowed the calculation of the space probability distributions and the energy spectrum of the particle confined in a hex-agonal-shaped well.

  19. Guided-wave photodiode using through-absorber quantum-well-intermixing and methods thereof

    Energy Technology Data Exchange (ETDEWEB)

    Skogen, Erik J.

    2016-10-25

    The present invention includes a high-speed, high-saturation power detector (e.g., a photodiode) compatible with a relatively simple monolithic integration process. In particular embodiments, the photodiode includes an intrinsic bulk absorption region, which is grown above a main waveguide core including a number of quantum wells (QWs) that are used as the active region of a phase modulator. The invention also includes methods of fabricating integrated photodiode and waveguide assemblies using a monolithic, simplified process.

  20. Variational Method for the Three-Dimensional Many-Electron Dynamics of Semiconductor Quantum Wells

    CERN Document Server

    Haas, F

    2015-01-01

    The three-dimensional nonlinear dynamics of an electron gas in a semiconductor quantum well is analyzed in terms of a self-consistent fluid formulation and a variational approach. Assuming a time-dependent localized profile for the fluid density and appropriated spatial dependences of the scalar potential and fluid velocity, a set of ordinary differential equations is derived. In the radially symmetric case, the prominent features of the associated breathing mode are characterized.

  1. Effects of impurity location on the impurity bands and their spectral densities in quantum wells

    Science.gov (United States)

    Gold, A.; Ghazali, A.; Serre, J.

    1989-09-01

    The electronic density of states and the spectral density of quantum wells are calculated as functions of the impurity position zi. A multiple-scattering method which accounts for the formation of impurity bands is used. The study of the spectral densities provides us with the behavior of the averaged wave functions of the ground- and excited-state impurity bands in the k space. We demonstrate that our approach can be used to study hybridization effects between different bands.

  2. Energy spectrum of an electron confined in the hexagon-shaped quantum well

    Institute of Scientific and Technical Information of China (English)

    Yu.V.VOROBIEV; V.R.VlEIRA; P.P.HORLEY; P.N.GORLEY; J.GONZ(A)LEZ-HERN(A)NDEZ

    2009-01-01

    Considering the hexagonal-shaped quantum-scale formations on the surface of thin semiconductor films, a methodology was developed to obtain the analytical solution of the Schr(o)dinger equation when impenetrable walls of a quantum well are treated as mirrors. The results obtained allowed the calcula-tion of the space probability distributions and the energy spectrum of the particle confined in a hex-agonal-shaped well.

  3. Temperature transformations of optical spectra in semiconductor flat heterostructures with quantum wells.

    Science.gov (United States)

    Kondryuk, D V; Derevyanchuk, A V; Kramar, V M

    2016-04-20

    The results of theoretical study of the temperature dependence of a long-wave range fundamental absorption edge in flat nanoheterostructures with a single quantum well (nanofilms) are adduced. The quantum well is assumed to be rectangular, of finite depth, and with unstrained heterojunctions as the nanofilm surface. Energies of electrons, holes, and excitons have been calculated within the framework of the effective mass model using the Green functions techniques, with account of their interaction with polar optical phonons confined within a quantum well. Numerical calculations are performed for nanofilms β-CdS/β-HgS/β-CdS and Al0.3Ga0.7As/GaAs/Al0.3Ga0.7As. It is shown that interaction with optical phonons causes a long-wave shift of the threshold frequency of the fundamental absorption band and a shift of exciton peaks by hundreds of Å for the first mentioned nanofilm and by dozens of Å for the second one, which is characterized by lower magnitudes of the constants of the electron-phonon coupling. The shift magnitude, as well as the height and half-width of the exciton absorption band, changes when the temperature exceeds 80 and 100 K, respectively.

  4. Enhanced luminescence of near-surface quantum wells passivated in situ by InP

    Energy Technology Data Exchange (ETDEWEB)

    Lipsanen, H.; Sopanen, M.; Taskinen, M.; Tulkki, J. [Helsinki Univ. of Technology, Espoo (Finland). Optoelectronics Lab.; Ahopelto, J. [VTT Electronics, Espoo (Finland)

    1996-12-31

    The authors have studied the optical properties of MOVPE grown Al{sub x}Ga{sub 1{minus}x}As/GaAs structures passivated by in situ deposition of InP on the surface. One monolayer of InP was used for the passivation. The surface recombination was studied by photoluminescence measurements of near-surface Al{sub 0.22}Ga{sub 0.78}As/GaAs quantum wells. The luminescence intensity of the passivated samples increased by about five orders of magnitude for quantum wells located at less than 5 nm from the surface as compared to unpassivated samples. Furthermore, the authors observed a blueshift of 15 meV for a passivated surface quantum well. The effect of the thin InP layer on the Fermi level pinning on the surface was studied by photoreflectance of a surface-i-n{sup +} sample. The pinning position was reduced by 0.3 eV from the mid-bandgap value.

  5. Scattering mechanisms in shallow undoped Si/SiGe quantum wells

    Directory of Open Access Journals (Sweden)

    D. Laroche

    2015-10-01

    Full Text Available We report the magneto-transport study and scattering mechanism analysis of a series of increasingly shallow Si/SiGe quantum wells with depth ranging from ∼ 100 nm to ∼ 10 nm away from the heterostructure surface. The peak mobility increases with depth, suggesting that charge centers near the oxide/semiconductor interface are the dominant scattering source. The power-law exponent of the electron mobility versus density curve, μ ∝ nα, is extracted as a function of the depth of the Si quantum well. At intermediate densities, the power-law dependence is characterized by α ∼ 2.3. At the highest achievable densities in the quantum wells buried at intermediate depth, an exponent α ∼ 5 is observed. We propose and show by simulations that this increase in the mobility dependence on the density can be explained by a non-equilibrium model where trapped electrons smooth out the potential landscape seen by the two-dimensional electron gas.

  6. Influence of metalorganic precursors flow interruption timing on green InGaN multiple quantum wells

    Science.gov (United States)

    Dmukauskas, M.; Kadys, A.; Malinauskas, T.; Grinys, T.; Reklaitis, I.; Badokas, K.; Skapas, M.; Tomašiūnas, R.; Dobrovolskas, D.; Stanionytė, S.; Pietzonka, I.; Strassburg, M.; Lugauer, H.-J.

    2016-12-01

    The paper reports on fully strained green light emitting InGaN/GaN multiple quantum wells, grown by metalorganic vapor phase epitaxy, using metal precursor multiple flow interruptions during InGaN quantum well growth. Optimization of the interruption timing (pulse t 1  =  20 s, pause t 2  =  12 s) lets us reach the integrated photoluminescence enhancement for the growth at temperature 780 ºC. The enhancement, as a function of pause duration, appeared to be pulse duration dependent: a lower enhancement can be achieved using shorter pulses with optimized relatively shorter pauses. Indium evaporation during the interruption time was interpreted as the main issue to keep the layers intact. Quantum wells revealing the highest photoluminescence enhancement were inspected for interface quality, layer thickness, growth speed, strain, surface morphology and roughness by TEM, XRD and AFM techniques, and compared with the one grown in the conventional mode.

  7. Enhanced UV luminescence from InAlN quantum well structures using two temperature growth

    Energy Technology Data Exchange (ETDEWEB)

    Zubialevich, Vitaly Z., E-mail: vitaly.zubialevich@tyndall.ie [Tyndall National Institute, University College Cork, Lee Maltings, Dyke Parade, Cork (Ireland); Sadler, Thomas C.; Dinh, Duc V. [Tyndall National Institute, University College Cork, Lee Maltings, Dyke Parade, Cork (Ireland); Alam, Shahab N.; Li, Haoning; Pampili, Pietro [Tyndall National Institute, University College Cork, Lee Maltings, Dyke Parade, Cork (Ireland); School of Engineering, University College Cork, Cork (Ireland); Parbrook, Peter J., E-mail: peter.parbrook@tyndall.ie [Tyndall National Institute, University College Cork, Lee Maltings, Dyke Parade, Cork (Ireland); School of Engineering, University College Cork, Cork (Ireland)

    2014-11-15

    InAlN/AlGaN multiple quantum wells (MQWs) emitting between 300 and 350 nm have been prepared by metalorganic chemical vapor deposition on planar AlN templates. To obtain strong room temperature luminescence from InAlN QWs a two temperature approach was required. The intensity decayed weakly as the temperature was increased to 300 K, with ratios I{sub PL}(300 K)/I{sub PL}(T){sub max} up to 70%. This high apparent internal quantum efficiency is attributed to the exceptionally strong carrier localization in this material, which is also manifested by a high Stokes shift (0.52 eV) of the luminescence. Based on these results InAlN is proposed as a robust alternative to AlGaN for ultraviolet emitting devices. - Highlights: • InAlN quantum wells with AlGaN barriers emitting in near UV successfully grown using quasi-2T approach. • 1 nm AlGaN capping of InAlN quantum wells used to avoid In desorption during temperature ramp to barrier growth conditions. • Strong, thermally resilient luminescence obtained as a result of growth optimization. • Promise of InAlN as an alternative active region for UV emitters demonstrated.

  8. Magnetic field effects on the electron Raman scattering in coaxial cylindrical quantum well wires

    Energy Technology Data Exchange (ETDEWEB)

    Rezaei, G., E-mail: grezaei2001@gmail.com [Department of Physics, College of Sciences, Yasouj University, Yasouj 75914-353 (Iran, Islamic Republic of); Karimi, M.J.; Pakarzadeh, H. [Department of Physics, College of Sciences, Shiraz University of Technology, Shiraz 71555-313 (Iran, Islamic Republic of)

    2013-11-15

    Based on the effective mass and parabolic one band approximations, the influence of an external magnetic field on the differential cross-section for the intersubband electron Raman scattering process in coaxial cylindrical quantum well wires is investigated. The dependence of differential cross-section on magnetic field strength and structural parameters of the coaxial cylindrical quantum well wire is studied. It is found that the magnetic field strength and the geometrical size of the system have a great influence on the position of the singularities in the emission spectra. Moreover, one can control the frequency shift in the Raman spectrum by varying the magnetic field strength and the size of the coaxial cylindrical quantum well wire. -- Highlights: • Magnetic field effects on ERS in CCQWWs are investigated. • Light polarization vectors and geometrical size effects on the ERS are also studied. • Number, position and magnitude of the peaks depend on the magnetic field strength. • The light polarization vectors have a great influence on the magnitude of the peaks. • An increase in the size leads to the considerable changes in the emission spectra.

  9. Progress in design and fabrication of resonator quantum well infrared photodetectors (R-QWIP) (Conference Presentation)

    Science.gov (United States)

    Sun, Jason N.; Choi, Kwong-Kit; Olver, Kimberley A.; Fu, Richard X.

    2017-05-01

    Resonator-Quantum Well Infrared Photo detectors (R-QWIPs) are the next generation of QWIP detectors that use resonances to increase the quantum efficiency (QE). Recently, we are exploring R-QWIPs for broadband long wavelength applications. To achieve the expected performance, two optimized inductively coupled plasma (ICP) etching processes (selective and non-selective) are developed. Our selective ICP etching process has a nearly infinite selectivity of etching GaAs over Ga1-xAlxAs. By using the etching processes, two format (1Kx1K and 40x40) detectors with 25 μm pixel pitch were fabricated successfully. In despite of a moderate doping of 0.5 × 1018 cm-3 and a thin active layer thickness of 0.6 or 1.3 μm, we achieved a quantum efficiency 35% and 37% for 8 quantum wells and 19 quantum wells respectively. The temperature at which photocurrent equals dark current is about 66 K under F/2 optics for a cutoff wavelength up to 11 μm. The NEΔT of the FPAs is estimated to be 22 mK at 2 ms integration time and 60 K operating temperature. This good result thus exemplifies the advantages of R-QWIP.

  10. Raman gain in a Boron based Group-III nitride quantum well

    Science.gov (United States)

    Narayana Moorthy, N.; John Peter, A.; Lee, Chang Woo

    2014-06-01

    Electron Raman scattering of a hydrogenic impurity is studied using exact diagonalization method in a BxGa1-xN/BN coupled quantum well. Intersubband scattering rates, in a Boron based wide band gap GaN, are considered. BxGa1-xN semiconductor is taken as inner quantum well and BN material is taken as barrier material. The effect of quantum confinement on the differential cross section of Raman scattering, with and without the impurity, is obtained. The built-in internal electric field is included throughout the calculations. The third order susceptibility with the incident photon energy is calculated with and without doping impurity. The donor hydrogenic binding energy and its low lying excited states are computed taking into account the geometrical confinement. The binding energy is obtained for various impurity position and the Boron alloy content in BxGa1-xN quantum well. It is brought out that the geometrical confinement and built-in internal electric fields have great influence on the optical properties of the semiconductor.

  11. Controlled finite momentum pairing and spatially varying order parameter in proximitized HgTe quantum wells

    Science.gov (United States)

    Hart, Sean; Ren, Hechen; Kosowsky, Michael; Ben-Shach, Gilad; Leubner, Philipp; Brüne, Christoph; Buhmann, Hartmut; Molenkamp, Laurens W.; Halperin, Bertrand I.; Yacoby, Amir

    2017-01-01

    Conventional s-wave superconductivity arises from singlet pairing of electrons with opposite Fermi momenta, forming Cooper pairs with zero net momentum. Recent studies have focused on coupling s-wave superconductors to systems with an unusual configuration of electronic spin and momentum at the Fermi surface, where the nature of the paired state can be modified and the system may even undergo a topological phase transition. Here we present measurements and theoretical calculations of HgTe quantum wells coupled to aluminium or niobium superconductors and subject to a magnetic field in the plane of the quantum well. We find that this magnetic field tunes the momentum of Cooper pairs in the quantum well, directly reflecting the response of the spin-dependent Fermi surfaces. In the high electron density regime, the induced superconductivity evolves with electron density in agreement with our model based on the Hamiltonian of Bernevig, Hughes and Zhang. This agreement provides a quantitative value for g ˜/vF, where g ˜ is the effective g-factor and vF is the Fermi velocity. Our new understanding of the interplay between spin physics and superconductivity introduces a way to spatially engineer the order parameter from singlet to triplet pairing, and in general allows investigation of electronic spin texture at the Fermi surface of materials.

  12. Quantum anomalous Hall effect in magnetically doped InAs/GaSb quantum wells.

    Science.gov (United States)

    Wang, Qing-Ze; Liu, Xin; Zhang, Hai-Jun; Samarth, Nitin; Zhang, Shou-Cheng; Liu, Chao-Xing

    2014-10-03

    The quantum anomalous Hall effect has recently been observed experimentally in thin films of Cr-doped (Bi,Sb)(2)Te(3) at a low temperature (∼ 30 mK). In this work, we propose realizing the quantum anomalous Hall effect in more conventional diluted magnetic semiconductors with magnetically doped InAs/GaSb type-II quantum wells. Based on a four-band model, we find an enhancement of the Curie temperature of ferromagnetism due to band edge singularities in the inverted regime of InAs/GaSb quantum wells. Below the Curie temperature, the quantum anomalous Hall effect is confirmed by the direct calculation of Hall conductance. The parameter regime for the quantum anomalous Hall phase is identified based on the eight-band Kane model. The high sample quality and strong exchange coupling make magnetically doped InAs/GaSb quantum wells good candidates for realizing the quantum anomalous Hall insulator at a high temperature.

  13. Optical spectroscopy of GaAs/AlGaAs V-groove quantum wires Quantum wells

    CERN Document Server

    Roshan, R

    2001-01-01

    In this thesis we report on optical spectroscopy of GaAs/AIGaAs quantum wires (QWRs), grown on pre-patterned semi-insulating GaAs (100) substrates by low-pressure metal organic vapour phase epitaxy (LP-MOVPE). Crescent-shaped quantum wires develop at the bottom of the grooves by self-organisation when a GaAs quantum well embedded in Al sub 0 sub . sub 3 Ga sub 0 sub . sub 7 As barriers was overgrown on the patterned surface. The overgrowth also resulted in the formation of vertical quantum wells (VQWs) in the AIGaAs barriers and sidewall quantum wells (SQWs) on the (111) surfaces that define the grooves. A narrow constriction (pinch-off) separates the QWRs from the side walls and provides two-dimensional confinement in them. Several types of wire arrangements are investigated in detail which includes single QWR, vertical stacked QWRs, lateral arrays of wires with sub-mu m pitch and gated QWRs. Both conventional far-field and near-field spectroscopic techniques are used to study these wires. A low-temperature ...

  14. Magnetoconductance in InN/GaN quantum wells in topological insulator phase

    Science.gov (United States)

    Bardyszewski, W.; Rodak, D.; Łepkowski, S. P.

    2017-04-01

    We present a theoretical study of the magnetic-field effect on the electronic properties of the two-dimensional, hypothetical topological insulator based on the InN/GaN quantum well system. Using the effective two-dimensional Hamiltonian, we have modelled magneto-transport in mesoscopic, symmetric samples of such materials. It turns out that, as in the case of the other two-dimensional topological insulators, the magnetoconductance in such samples is quantized due to the presence of helical edge states for magnetic fields below a certain critical value and for fairly small disorder strength. However, in our case the helical edge transport is much more prone to the disorder than, for example, in the case of topological insulators based on the HgTe/CdTe quantum wells. At low enough level of disorder and for the Fermi energy located in the energy gap of an infinite planar quantum well, we may expect an interesting phenomenon of non-monotonic dependence of the conductance on the magnetic field caused by the complicated interplay of couplings between the heavy hole, light hole and conduction subbands.

  15. High-resolution x-ray diffraction investigations of highly mismatched II-VI quantum wells

    Science.gov (United States)

    Passow, T.; Leonardi, K.; Stockmann, A.; Selke, H.; Heinke, H.; Hommel, D.

    1999-05-01

    High-resolution x-ray diffraction (HRXRD) was used to systematically investigate CdSe and ZnTe quantum wells one to three monolayers thick sandwiched between a ZnSe buffer and cap layer grown at different substrate temperatures. For comparison high-resolution transmission electron microscopy (HRTEM) measurements were performed which were evaluated by digital analysis of lattice images. The x-ray diffraction profiles show typically two main layer peaks. Their intensity ratio depends critically on the quantum well thickness and varies only weakly with the thickness of the ZnSe layers. The total Cd or Te content determined from comparisons of experimental and simulated (004) icons/Journals/Common/omega" ALT="omega" ALIGN="TOP"/>-2icons/Journals/Common/theta" ALT="theta" ALIGN="TOP"/> scans is well confirmed by the results from digital analysis of HRTEM lattice images. For quantum well thicknesses larger than 1.5 (ZnTe) or 2.0 (CdSe) monolayers, no simulation parameters could be found to achieve good agreement between theoretical and measured diffraction profiles. This transition is more clearly visible in diffraction profiles of asymmetrical reflections. By HRTEM measurements, this could be correlated to the occurrence of stacking faults at these thicknesses. The formation of quantum islands detected by HRTEM was not reflected in the HRXRD icons/Journals/Common/omega" ALT="omega" ALIGN="TOP"/>-2icons/Journals/Common/theta" ALT="theta" ALIGN="TOP"/> scans.

  16. Temperature and current dependent electroluminescence measurements on colour-coded multiple quantum well light emitting diodes

    Energy Technology Data Exchange (ETDEWEB)

    Bergbauer, Werner [OSRAM Opto Semiconductors GmbH, Regensburg (Germany); FH Deggendorf (Germany); Laubsch, Ansgar; Peter, Matthias; Mayer, Tobias; Bader, Stefan; Oberschmid, Raimund; Hahn, Berthold [OSRAM Opto Semiconductors GmbH, Regensburg (Germany); Benstetter, Guenther [FH Deggendorf (Germany)

    2008-07-01

    As the efficiency and the luminous flux have been increased enormously in the last few years, today Light Emitting Diodes (LEDs) are even pushed to applications like general lighting and Home Cinema Projection. Still, InGaN/GaN heterostructure based LEDs suffer from loss-mechanisms like non-radiative defect and Auger recombination, carrier leakage and piezo-field induced carrier separation. To optimize the high current efficiency we evaluated the benefit of Multiple Quantum Well (MQW) compared to Single Quantum Well (SQW) LEDs. Temperature dependent electroluminescence of colour-coded structures with different Indium content in certain Quantum Wells was measured. The experiments demonstrated a strong temperature and current dependence of the MQW operation. The comparison between different LED structures showed effectively the increased LED performance of those structures which operate with a well adjusted MQW active area. Due to the enhanced carrier distribution in the high current range, these LEDs show a higher light output and additionally a reduced wavelength shift.

  17. Electronic excitation induced structural and optical modifications in InGaN/GaN quantum well structures grown by MOCVD

    Energy Technology Data Exchange (ETDEWEB)

    Prabakaran, K.; Ramesh, R.; Jayasakthi, M.; Surender, S.; Pradeep, S. [Crystal Growth Centre, Anna University, Chennai (India); Balaji, M. [National Centre for Nanoscience and Nanotechnology, University of Madras, Guindy Campus, Chennai (India); Asokan, K. [Inter-University Accelerator Centre, New Delhi (India); Baskar, K., E-mail: drbaskar2009@gmail.com [Crystal Growth Centre, Anna University, Chennai (India); Manonmaniam Sundaranar University, Tirunelveli (India)

    2017-03-01

    Highlights: • Effects on InGaN/GaN QW structures by Au{sup 7+} (100 MeV) ion have been investigated. • Structural defects of the irradiated InGaN/GaN QW structures are determined. • The intermixing effect in irradiated InGaN/GaN QW structures were understood. • Modified luminescence was observed in the PL spectra due to heavy ion irradiation. • Surface modification was observed due to the heavy ion irradiation. - Abstract: The present study focuses on the electronic excitation induced structural and optical properties of InGaN/GaN quantum well (QW) structures grown by metal organic chemical vapor deposition technique. These excitations were produced using Au{sup 7+} ion irradiation with 100 MeV energy. The X-ray rocking curves intensity and full width at half-maximum values corresponding to the planes of (0 0 0 2) and (1 0 −1 5) of the irradiated QW structures show the modifications in the screw and edge-type dislocation densities vary with the ion fluences. The structural characteristics using the reciprocal space mapping indicate the intermixing effects in InGaN/GaN QW structures. Atomic force microscopy images confirmed the presence of nanostructures and the surface modification due to heavy ion irradiation. The irradiated QW structures exhibited degraded photoluminescence intensity and a subsequent decrease in the yellow luminescence band intensity with the fluences of 1 × 10{sup 11} and 5 × 10{sup 12} ions/cm{sup 2} compared to the pristine QW structures.

  18. Novel InN/InGaN multiple quantum well structures for slow-light generation at telecommunication wavelengths

    Energy Technology Data Exchange (ETDEWEB)

    Naranjo, F.B.; Valdueza-Felip, S.; Gonzalez-Herraez, M. [Grupo de Ingenieria Fotonica, Departamento de Electronica, Escuela Politecnica Superior, Universidad de Alcala Campus Universitario, 28871 Alcala de Henares, Madrid (Spain); Kandaswamy, P.K.; Lahourcade, L.; Calvo, V.; Monroy, E. [CEA-Grenoble, INAC/SP2M, 17 rue des Martyrs, 38054 Grenoble cedex 9 (France); Martin-Lopez, S.; Corredera, P. [Departamento de Metrologia, Instituto de Fisica Aplicada (CSIC), 28006 Madrid (Spain)

    2010-01-15

    The third order susceptibility is responsible for a variety of optical non-linear phenomena - like self focusing, phase conjugation and four-wave mixing - with applications in coherent control of optical communication. InN is particularly attractive due to its near-IR bandgap and predicted high nonlinear effects. Moreover, the synthesis of InN nanostructures makes possible to taylor the absorption edge in the telecomunication spectral range and enhance nonlinear parameters thanks to carrier confinement. In this work, we assess the nonlinear optical behavior of InN/In{sub x}Ga{sub (1-x)}N (0.9 > x > 0.7) multiple-quantum-well (MQW) structures grown by plasma-assisted MBE on GaN-on-sapphire templates. Low-temperature (5 K) photoluminescence measurements show near-IR emission whose intensity increases with the In content in the barriers, which is explained in terms of the existence of piezoelectric fields in the structures. The nonlinear optical absorption coefficient, {alpha}{sub 2}, were measured at 1.55 {mu}m using the Z-scan method. We observe a strong dependence of the nonlinear absorption coefficient on the In content in the barriers. Saturable absorption is observed for the sample with x = 0.9, with {alpha}{sub 2} {proportional_to} -9 x 10{sub 3} cm/GW. For this sample, an optically controlled reduction of the speed of light by a factor S {proportional_to} 80 is obtained at 1.55 {mu}m (copyright 2010 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  19. Formation and characteristics of AlGaN-based three-dimensional hexagonal nanopyramid semi-polar multiple quantum wells

    Science.gov (United States)

    Tian, Yingdong; Yan, Jianchang; Zhang, Yun; Zhang, Yonghui; Chen, Xiang; Guo, Yanan; Wang, Junxi; Li, Jinmin

    2016-05-01

    We demonstrated for the first time the formation and study of semi-polar AlGaN multiple-quantum-wells (MQWs) grown on highly regular hexagonal AlN nanopyramids. The AlN nanopyramids were obtained by a metal-organic chemical vapor phase deposition regrowth method on a well-ordered AlN nanorod array prepared by a top-down etching process. The growth mechanism of the AlN nanopyramids was ascribed to the slow growth of the (101&cmb.macr;1) semi-polar plane, which resulted from hydrogen passivation. Beneath the semi-polar facets, air voids were formed. This was attributed to the insufficient delivery of gas reactants to the bottom of the nanorods during the growth process. The polarization effect in semi-polar AlGaN MQWs was numerically calculated. The results showed that the internal electric field (IEF) in the semi-polar MQWs was remarkably reduced by 80% in comparison with c-plane MQWs. Power dependent photoluminescence indicated that the semi-polar AlGaN MQWs had negligible wavelength shifts that resulted from the reduced IEF, which was in accordance with theoretical predictions. In addition, epitaxial strain was greatly relieved in the AlN regrowth layer, which was revealed from the peak shift of the E2(high) phonon using micro-Raman spectroscopy. The advantages of AlGaN-based hexagonal nanopyramid semi-polar three dimensional nanostructures would lead to a large improvement of output power in UV-LEDs.

  20. Influence of plasmonic array geometry on energy transfer from a quantum well to a quantum dot layer.

    Science.gov (United States)

    Higgins, Luke J; Marocico, Cristian A; Karanikolas, Vasilios D; Bell, Alan P; Gough, John J; Murphy, Graham P; Parbrook, Peter J; Bradley, A Louise

    2016-10-27

    A range of seven different Ag plasmonic arrays formed using nanostructures of varying shape, size and gap were fabricated using helium-ion lithography (HIL) on an InGaN/GaN quantum well (QW) substrate. The influence of the array geometry on plasmon-enhanced Förster resonance energy transfer (FRET) from a single InGaN QW to a ∼80 nm layer of CdSe/ZnS quantum dots (QDs) embedded in a poly(methyl methacrylate) (PMMA) matrix is investigated. It is shown that the energy transfer efficiency is strongly dependent on the array properties and an efficiency of ∼51% is observed for a nanoring array. There were no signatures of FRET in the absence of the arrays. The QD acceptor layer emission is highly sensitive to the array geometry. A model was developed to confirm that the increase in the QD emission on the QW substrate compared with a GaN substrate can be attributed solely to plasmon-enhanced FRET. The individual contributions of direct enhancement of the QD layer emission by the array and the plasmon-enhanced FRET are separated out, with the QD emission described by the product of an array emission factor and an energy transfer factor. It is shown that while the nanoring geometry results in an energy transfer factor of ∼1.7 the competing quenching by the array, with an array emission factor of ∼0.7, results in only an overall gain of ∼14% in the QD emission. The QD emission was enhanced by ∼71% for a nanobox array, resulting from the combination of a more modest energy transfer factor of 1.2 coupled with an array emission factor of ∼1.4.

  1. Refractive index modulation based on excitonic effects in GaInAs-InP coupled asymmetric quantum wells

    DEFF Research Database (Denmark)

    Thirstrup, Carsten

    1995-01-01

    The effect of excitons in GaInAs-InP coupled asymmetric quantum wells on the refractive index modulation, is analyzed numerically using a model based on the effective mass approximation. It is shown that two coupled quantum wells brought in resonance by an applied electric field will, due...

  2. InAsP-based quantum wells as infrared pressure gauges for use in a diamond anvil cell

    Science.gov (United States)

    Trushkin, S.; Kamińska, A.; Trzeciakowski, W.; Hopkinson, M.; Suchocki, A.

    2012-10-01

    The results of high-pressure, low-temperature luminescence measurements of three InAsP-based multiple quantum well structures are reported for application as pressure sensors for diamond anvil cells working in the near-infrared spectral range. The multiple quantum well structures exhibit a much higher pressure shift of the luminescence lines as compared with ruby, typically used as the pressure sensor for diamond anvil cell. However, the full width at half maximum of the quantum wells is much higher than that for ruby. This reduces the available sensitivity gain exhibited by the InAsP-based quantum wells, but the improvement is still 2-3 times higher than that of ruby. Three InAsP multiple quantum well samples were examined, which exhibited luminescence at various wavelengths. The wavelength shift of these samples could be calibrated using similar parameters.

  3. Wavelength-dependent femtosecond pulse amplification in wideband tapered-waveguide quantum well semiconductor optical amplifiers.

    Science.gov (United States)

    Xia, Mingjun; Ghafouri-Shiraz, H

    2015-12-10

    In this paper, we study the wavelength-dependent amplification in three different wideband quantum well semiconductor optical amplifiers (QWAs) having conventional, exponentially tapered, and linearly tapered active region waveguide structures. A new theoretical model for tapered-waveguide QWAs considering the effect of lateral carrier density distribution and the strain effect in the quantum well is established based on a quantum well transmission line modeling method. The temporal and spectral characteristics of amplified femtosecond pulse are analyzed for each structure. It was found that, for the amplification of a single femtosecond pulse, the tapered-waveguide QWA provides higher saturation gain, and the output spectra of the amplified pulse in all three structures exhibit an apparent redshift and bandwidth narrowing due to the reduction of carrier density; however, the output spectrum in the tapered-waveguide amplifier is less distorted and exhibits smaller bandwidth narrowing. For the simultaneous amplification of two femtosecond pulses with different central frequencies, in all the three structures, two peaks appear in the output spectra while the peak at the frequency closer to the peak frequency of the QWA gain spectrum receives higher amplification due to the frequency (wavelength) dependence of the QWA gain. At a low peak power level of the input pulse, the bandwidth of each window in the tapered structure is larger than that of the conventional waveguide structure, which aggravates the spectrum alias in the amplification of femtosecond pulses with different central frequencies. As the peak powers of the two pulses increase, the spectrum alias in the conventional waveguide becomes more serious while there are small changes in the tapered structures. Also, we have found that in the amplification of a femtosecond pulse train, the linear-tapered QWAs exhibit the fastest gain recovery as compared with the conventional and exponentially tapered QWAs.

  4. Temperature dependence of active photonic band gap in bragg-spaced quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Hu Zhiqiang; Wang Tao; Yu Chunchao; Xu Wei, E-mail: huzhiqianghzq@163.com [Wuhan National Laboratory for Optoelectronics, College of Optoelectronic Science and Engineering, Huazhong University of Science and Technology, Wuhan 430074, Hubei (China)

    2011-02-01

    A novel all-optical polarization switch of active photonic band gap structure based on non-resonant optical Stark effect bragg-spaced quantum wells was investigated and it could be compatible with the optical communication system. The theory is based on InGaAsP/InP Bragg-spaced quantum wells (BSQWs). Mainly through the design of the InGaAsP well layer component and InP barrier thickness to make the quantum-period cycle meet the bragg condition and the bragg frequency is equal to re-hole exciton resonance frequency. When a spectrally narrow control pulse is tuned within the forbidden gap, such BSQWs have been shown to exhibit large optical nonlinearities and ps recovery times, which can form T hz switch. However, the exciton binding energy of InGaAsP will be automatically separate at room temperature, so the effect of all-optical polarization switching of active photonic band gap bragg structure quantum wells can only be studied at low temperature. By a large number of experiments, we tested part of the material parameters of BSQWs in the temperature range 10-300K. On this basis, the InGaAsP and InP refractive index changes with wavelength, InP thermal expansion coefficient are studied and a relationship equation is established. Experimental results show that the bragg reflection spectra with temperature mainly is effected by InP refractive index changes with temperature. Our theoretical study and experiment are an instruction as a reference in the designs and experiments of future practical optical switches.

  5. Thermoelectric properties of Mg2X (X = Si, Ge) based bulk and quantum well systems

    Science.gov (United States)

    Yelgel, Övgü Ceyda

    2017-01-01

    Mg2X (X = Si, Ge) compounds are promising thermoelectric materials for middle temperature applications due to good thermoelectric properties, nontoxicity, and abundantly available constituent elements. So far, these materials used in applications have all been in bulk form. Herein we report a full theory of thermoelectric transport properties of 3D bulk and 2D quantum well systems. The main aim of this present work is to show the effect of quantum confinement on the enhancement of the thermoelectric figure of merit theoretically. Results are given for n-type Mg2 Si0.5 Ge0.5 solid solutions and n-type Mg2Si/Mg2Ge/Mg2Si quantum well systems where the values of well widths are taken as 10 nm, 15 nm, and 20 nm, respectively. The n-type doping is made by using Sb- and La-elements as dopants. Experimental results for solid solutions are included to provide demonstration of proof of principle for the theoretical model applied for 3D bulk structures. The maximum thermoelectric figure of merits of Lax Mg2 -x Si0.49 Ge0.5 Sb0.01 solid solutions are obtained to be 0.64 and 0.56 at 800 K for x = 0 and x = 0.01 sample, respectively. While, at the same temperature, due to the relatively low phonon thermal conductivity the state-of-the-art ZT values of 2.41 and 2.26 have been attained in the Mg2Si/Mg2Ge/Mg2Si quantum well samples with 0.01 wt. % Sb-doped and 0.01 wt. % Sb- and 0.01 wt. % La-doped, respectively.

  6. Temperature Dependence of the Polariton Linewidth in a GaAs Quantum Well Microcavity

    DEFF Research Database (Denmark)

    Borri, P.; Jensen, Jacob Riis; Langbein, W.;

    2000-01-01

    The temperature dependent linewidths of the polariton resonances in a GaAs/AlGaAs single quantum well microcavity are measured. Due to the dominant homogeneous broadening of the investigated resonances, a direct linewidth analysis of the reflectivity spectra allows us to investigate the role...... of scattering mechanisms in the lower polariton branch compared to the middle and upper polaritons. We find that the lower polariton linewidth is smaller than the middle and upper polariton linewidths at all investigated temperatures from 11 to 100 K, in agreement with expectations in literature....

  7. Temperature dependence of the lowest excitonic transition for an InAs ultrathin quantum well

    Science.gov (United States)

    Singh, S. D.; Porwal, S.; Sharma, T. K.; Rustagi, K. C.

    2006-03-01

    Temperature dependent photoluminescence and photoreflectance techniques are used to investigate the lowest excitonic transition of InAs ultrathin quantum well. It is shown that the temperature dependence of the lowest energy transition follows the band gap variation of GaAs barrier, which is well reproduced by calculated results based on the envelope function approximation with significant corrections due to strain and temperature dependences of the confinement potential. A redshift in photoluminescence peak energy compared to photoreflectance is observed at low temperatures. This is interpreted to show that the photoluminescence signal originates from the recombination of carriers occupying the band-tail states below the lowest critical point.

  8. GaAs/AlGaAs quantum well infrared photodetector with low noise

    Institute of Scientific and Technical Information of China (English)

    DENG Jun; WANG Bin; HAN Jun; LI Jian-jun; SHEN Guang-di

    2005-01-01

    A novel kind of multi-quantum well infrared photodetector(QWIP) is presented.In the new structure device,a p-type contact layer has been grown on the top of the conventional structure of QWIP,then a small tunneling current is instead of the large compensatory current,which made the device low dark current and low noise characteristics.The measured result of dark current is consistent with the calculated result,and the noise of the new structure QWIP is decreased to one third of the conventional QWIP.

  9. Magneto optical rotation in a GaAs Quantum Well Waveguide

    CERN Document Server

    Mortezapour, Ali; Mahmoudi, Mohammad

    2016-01-01

    The interaction of two orthogonally polarized beams and a four-level GaAs quantum well (QW) waveguide is investigated. It is shown that, by applying a static magnetic field normal to the propagation direction of the driving beams, the birefringence can be induced in the QW waveguide. Moreover, it is demonstrated that the dephasing rate between two ground states of the QW waveguide makes it a dichromatic medium and can also diminish the induced birefringence. Our results show how a large and complete magneto-optical rotation in the QW waveguide can be obtained via adjusting the intensity of the magnetic field and also the length of the QW waveguide.

  10. Confinement effect in a quantum well dot induced by an InP stressor

    Science.gov (United States)

    Tulkki, J.; Heinämäki, A.

    1995-09-01

    We have calculated the confinement effect in an In1-xGaxAs/GaAs quantum well dot induced by a dislocation-free InP stressor island. The energy levels were calculated by including the strain interaction and the band-edge confinement in the Luttinger-Kohn Hamiltonian. The maximum level spacing for the dipole-allowed interband E1-->HH1 line spectrum was 20 meV. Our calculation also gives excellent agreement with recent measurements [H. Lipsanen, M. Sopanen, and J. Ahopelto, Phys. Rev. B 51, 13 868 (1995)] and provides indirect evidence of screened Coulomb interaction, tentatively addressed to slow carrier relaxation.

  11. Magnetization dynamics down to a zero field in dilute (Cd,Mn)Te quantum wells.

    Science.gov (United States)

    Goryca, M; Ferrand, D; Kossacki, P; Nawrocki, M; Pacuski, W; Maślana, W; Gaj, J A; Tatarenko, S; Cibert, J; Wojtowicz, T; Karczewski, G

    2009-01-30

    The evolution of the magnetization in (Cd,Mn)Te quantum wells after a short pulse of magnetic field was determined from the giant Zeeman shift of spectroscopic lines. The dynamics in the absence of a static magnetic field was found to be up to 3 orders of magnitude faster than that at 1 T. Hyperfine interaction and strain are mainly responsible for the fast decay. The influence of a hole gas is clearly visible: at zero field anisotropic holes stabilize the system of Mn ions, while in a magnetic field of 1 T they are known to speed up the decay by opening an additional relaxation channel.

  12. Influence of carriers on magnetization relaxation in (Cd,Mn)Te quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Goryca, M.; Nawrocki, M. [Institute of Experimental Physics, Warsaw University, Hoza 69, 00-681 Warsaw (Poland); Ferrand, D.; Tatarenko, S. [Joined group ' ' Nanophysique et Semiconducteurs' ' , CNRS, CEA, Universite Joseph Fourier-Grenoble, Laboratoire de Spectrometrie Physique, BP 87, 38402 Saint Martin d' Heres cedex (France); Kossacki, P.; Pacuski, W.; Maslana, W. [Institute of Experimental Physics, Warsaw University, Hoza 69, 00-681 Warsaw (Poland); Joined group ' ' Nanophysique et Semiconducteurs' ' , CNRS, CEA, Universite Joseph Fourier-Grenoble, Laboratoire de Spectrometrie Physique, BP 87, 38402 Saint Martin d' Heres cedex (France); Wojtowicz, T.; Karczewski, G. [Institute of Physics, Polish Academy of Sciences, al. Lotnikow 32/46, 02-668 Warsaw (Poland); Cibert, J. [Laboratoire Louis Neel, CNRS, BP166, 38042 Grenoble cedex 9 (France)

    2007-07-01

    The relaxation of the magnetization after a short pulse of magnetic field in n-doped and p-doped (Cd,Mn)Te quantum wells is determined from the giant Zeeman shift of the photoluminescence and transmission lines. This technique allows us to investigate the magnetization dynamics in zero field. In n-doped samples the magnetization relaxation is found to be faster than 20 ns. In case of p-doped samples two components of relaxation are observed. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  13. Anisotropy dependent magnetization relaxation in (Cd,Mn)Te quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Goryca, M.; Nawrocki, M. [Institute of Experimental Physics, Warsaw University, Hoza 69, 00-681 Warsaw (Poland); Kossacki, P.; Pacuski, W.; Maslana, W. [Institute of Experimental Physics, Warsaw University, Hoza 69, 00-681 Warsaw (Poland); Joined Group Nanophysique et Semiconducteurs, CNRS/CEA/ Universite Joseph Fourier Grenoble, BP 87, 38402 Saint Martin d' Heres cedex (France); Ferrand, D.; Tatarenko, S. [Joined Group Nanophysique et Semiconducteurs, CNRS/CEA/ Universite Joseph Fourier Grenoble, BP 87, 38402 Saint Martin d' Heres cedex (France); Cibert, J. [Laboratoire Louis Neel, CNRS, BP166, 38042 Grenoble cedex 9 (France)

    2006-07-01

    An optical study of magnetization relaxation is presented for p-doped quantum wells with magnetic ions. The magnetic anisotropy of the system is controlled by the heavy-light hole splitting, tuned by uniaxial strain. We show that a suppression of the magnetic anisotropy results in an enhancement of the observed relaxation rate by a factor of at least 20. This is explained by the fact that the decrease of the anisotropy results in the lowering of the energy barrier for the domain magnetization flip process. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  14. RT CW operation of InGaN multi-quantum-well structure laser diodes

    OpenAIRE

    Shuji Nakamura

    1998-01-01

    Gallium nitride and other III–Vnitride-based semiconductors have a direct band gap that is suitable for blue light-emitting devices. The band gap energy of aluminium gallium indium nitride (AIInGaN) varies between 6.2 and 2.0 eV, depending on its composition at room temperature. Thus, using these semiconductors, red to UV emitting devices are fabricated. High efficient UV, blue and green InGaN single-quantum-well (SQW) structure light-emitting diodes (LEDs) have been fabricated with the exter...

  15. InGaAs/GaAs quantum-dot-quantum-well heterostructure formed by submonolayer deposition

    DEFF Research Database (Denmark)

    Xu, Zhangcheng; Leosson, K.; Birkedal, Dan;

    2003-01-01

    -dot-quantum-well (QDQW) structure, by using high power PL and selective PL with excitation energies below the band gap of the GaAs barriers and temperature dependent PL. As the temperature is increased from 10 to 300 K, a narrowing of the full width at half-maximum at intermediate temperatures and a sigmoidal behaviour...... of the peak energy of PL band of the SML QD ensemble are observed and attributed to thermally activated carrier transfer between QDs via QW states....

  16. The second harmonic generation in symmetrical and asymmetrical Gaussian potential quantum wells with applied electric field

    Science.gov (United States)

    Yuan, Jian-Hui; Chen, Ni; Mo, Hua; Zhang, Yan; Zhang, Zhi-Hai

    2015-12-01

    A detailed investigation of the second harmonic generation in symmetrical and asymmetrical Gaussian potential quantum wells under the influence of applied electric field by using the compact-density-matrix approach and the finite difference method. The results show that the second-harmonic generation susceptibility obtained in two cases can reach the magnitude of 10-4 m/V, which depend dramatically on the applied electric field and the structural parameters. Finally, the resonant peak and its corresponding to the resonant energy are also taken into account.

  17. Ground state of excitons in quantum-dot quantum-well nanoparticles:stochastic variational method

    Institute of Scientific and Technical Information of China (English)

    Zhang Heng; Shi Jun-Jie

    2004-01-01

    Within the framework of effective mass approximation, the ground state of excitons confined in spherical core-shell quantum-dot quantum-well (QDQW) nanoparticles is solved by using the stochastic variational method, in which the finite band offset and the heavy (light) hole exciton states are considered. The calculated lse-lsh transition energies for the chosen CdS/HgS/CdS QDQW samples are in good agreement with the experimental measurements. Moreover,some previous theoretical results are improved.

  18. Intrinsic Spin Hall Effect Induced by Quantum Phase Transition in HgCdTe Quantum Wells

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Wen; Chang, Kai; /Beijing, Inst. Semiconductors; Zhang, Shou-Cheng; /Stanford U., Phys. Dept.

    2010-03-19

    Spin Hall effect can be induced both by the extrinsic impurity scattering and by the intrinsic spin-orbit coupling in the electronic structure. The HgTe/CdTe quantum well has a quantum phase transition where the electronic structure changes from normal to inverted. We show that the intrinsic spin Hall effect of the conduction band vanishes on the normal side, while it is finite on the inverted side. This difference gives a direct mechanism to experimentally distinguish the intrinsic spin Hall effect from the extrinsic one.

  19. Optical Tamm state polaritons in a quantum well microcavity with gold layers

    Institute of Scientific and Technical Information of China (English)

    Zhang Wei-Li; Rao Yun-Jiang

    2012-01-01

    A new type of cavity polariton,the optical Tamm state(OTS)polariton,is proposed to be realized by sandwiching a quantum well(QW)between a gold layer and a distributed Bragg reflector(DBR).It is shown that OTS polaritons can be generated from the strong couplings between the QW excitons and the free OTSs.In addition,ff a second gold layer is introduced into the bottom of the DBR,two independent free OTSs can interact strongly with the Q W excitons to produce extra OTS polaritons.

  20. Intersubband carrier scattering in n - and p-Si/SiGe quantum wells with diffuse interfaces

    Science.gov (United States)

    Valavanis, A.; Ikonić, Z.; Kelsall, R. W.

    2008-02-01

    Scattering rate calculations in two-dimensional Si/Si1-xGex systems have typically been restricted to rectangular Ge profiles at interfaces between layers. Real interfaces, however, may exhibit diffuse Ge profiles either by design or as a limitation of the growth process. It is shown here that alloy disorder scattering dramatically increases with Ge interdiffusion in (100) and (111) n -type quantum wells, but remains almost constant in (100) p -type heterostructures. It is also shown that smoothing of the confining potential leads to large changes in subband energies and scattering rates, and a method is presented for calculating growth process tolerances.

  1. Circularly polarized lasing in chiral modulated semiconductor microcavity with GaAs quantum wells

    CERN Document Server

    Demenev, A A; Schneider, C; Brodbeck, S; Kamp, M; Höfling, S; Lobanov, S V; Weiss, T; Gippius, N A; Tikhodeev, S G

    2016-01-01

    We report the elliptically, close to circularly polarized lasing at $\\hbar\\omega = 1.473$ and 1.522 eV from an AlAs/AlGaAs Bragg microcavity with 12 GaAs quantum wells in the active region and chiral-etched upper distributed Bragg refractor under optical pump at room temperature. The advantage of using the chiral photonic crystal with a large contrast of dielectric permittivities is its giant optical activity, allowing to fabricate a very thin half-wave plate, with a thickness of the order of the emitted light wavelength, and to realize the monolithic control of circular polarization.

  2. Long-wavelength quantum well infrared photodetector (QWIP) research at Jet Propulsion Laboratory

    Science.gov (United States)

    Gunapala, Sarath D.; Liu, John K.; Sundaram, Mani; Bandara, Sumith V.; Shott, C. A.; Hoelter, Theodore R.; Maker, Paul D.; Muller, Richard E.

    1996-06-01

    One of the simplest device realizations of the classic particle-in-a-box problem of basic quantum mechanics is the quantum well infrared photodetector (QWIP). Optimization of the detector design and material growth and processing have culminated in the realization of a 15 micrometer cutoff 128 by 128 focal plane array camera and a camera with large (256 by 256 pixel) focal plane array of QWIPs which can see at 8.5 micrometer, holding forth great promise for a variety of applications in the 6 - 25 micrometer wavelength range. This paper discusses the physics of the QWIP and QWIP technology development at Jet Propulsion Laboratory.

  3. Stability Diagrams of a Bose-Einstein Condensate in a Periodic Array of Quantum Wells

    Institute of Scientific and Technical Information of China (English)

    XUE Rui; LIANG Zhao-Xin; LI Wei-Dong

    2009-01-01

    With the help of a set of exact closed-form solutions to the stationary Gross-Pitaevskii equation, we compre-hensively investigate Landau and dynamical instabilities of a Bose-Einstein condensate in a periodic array of quantum wells. In the tight-binding limit, the analytical expressions for both Landau and dynamical instabilities are obtained in terms of the compressibility and effective mass of the BEC system. Then the stability phase diagrams are shown to be similar to the one in the case of the sinusoidal optical lattice.

  4. Energy Transfer of Excitons Between Quantum Wells Separated by a Wide Barrier

    Energy Technology Data Exchange (ETDEWEB)

    LYO,SUNGKWUN K.

    1999-12-06

    We present a microscopic theory of the excitonic Stokes and anti-Stokes energy transfer mechanisms between two widely separated unequal quantum wells with a large energy mismatch ({Delta}) at low temperatures (T). Exciton transfer through dipolar coupling, photon-exchange coupling and over-barrier ionization of the excitons through exciton-exciton Auger processes are examined. The energy transfer rate is calculated as a function of T and the center-to-center distance d between the two wells. The rates depend sensitively on T for plane-wave excitons. For located excitons, the rates depend on T only through the T-dependence of the localization radius.

  5. Phosphor-free white light-emitting diode with laterally distributed multiple quantum wells

    Science.gov (United States)

    Park, Il-Kyu; Kim, Ja-Yeon; Kwon, Min-Ki; Cho, Chu-Young; Lim, Jae-Hong; Park, Seong-Ju

    2008-03-01

    A phosphor-free white light-emitting diode (LED) was fabricated with laterally distributed blue and green InGaN /GaN multiple quantum wells (MQWs) grown by a selective area growth method. Photoluminescence and electroluminescence (EL) spectra of the LED showed emission peaks corresponding to the individual blue and green MQWs. The integrated EL intensity ratio of green to blue emission varied from 2.5 to 6.5 with the injection current below 300mA, but remained constant at high injection currents above 300mA. The stability of the emission color at high currents is attributed to parallel carrier injection into both MQWs.

  6. Room temperature ballistic transport in InSb quantum well nanodevices.

    Science.gov (United States)

    Gilbertson, A M; Kormányos, A; Buckle, P D; Fearn, M; Ashley, T; Lambert, C J; Solin, S A; Cohen, L F

    2011-12-12

    We report the room temperature observation of significant ballistic electron transport in shallow etched four-terminal mesoscopic devices fabricated on an InSb/AlInSb quantum well (QW) heterostructure with a crucial partitioned growth-buffer scheme. Ballistic electron transport is evidenced by a negative bend resistance signature which is quite clearly observed at 295 K and at current densities in excess of 10(6) A/cm(2). This demonstrates unequivocally that by using effective growth and processing strategies, room temperature ballistic effects can be exploited in InSb/AlInSb QWs at practical device dimensions.

  7. Resonant Rayleigh scattering of exciton-polaritons in multiple quantum wells

    DEFF Research Database (Denmark)

    Malpuech, Guillaume; Kavokin, Alexey; Langbein, Wolfgang Werner;

    2000-01-01

    A theoretical concept of resonant Rayleigh scattering (RRS) of exciton-polaritons in multiple quantum wells (QWs) is presented. The optical coupling between excitons in different QWs can strongly affect the RRS dynamics, giving rise to characteristic temporal oscillations on a picosecond scale....... Bragg and anti-Bragg arranged QW structures with the same excitonic parameters are predicted to have drastically different RRS spectra. Experimental data on the RRS from multiple QWs show the predicted strong temporal oscillations at small scattering angles, which are well explained by the presented...

  8. Low-temperature illumination and annealing of ultrahigh quality quantum wells

    Science.gov (United States)

    Samani, M.; Rossokhaty, A. V.; Sajadi, E.; Lüscher, S.; Folk, J. A.; Watson, J. D.; Gardner, G. C.; Manfra, M. J.

    2014-09-01

    The effects of low-temperature illumination and annealing on fractional quantum Hall (FQH) characteristics of a GaAs/AlGaAs quantum well are investigated. Illumination alone, below 1 K, decreases the density of the two-dimensional electron gas (2DEG) electrons by more than an order of magnitude and resets the sample to a repeatable initial state. Subsequent thermal annealing at a few Kelvin restores the original density and dramatically improves FQH characteristics. A reliable illumination and annealing recipe is developed that yields an energy gap of 600 mK for the 5/2 state.

  9. Polarised two-photon excitation of quantum well excitons for manipulation of optically pumped terahertz lasers

    Energy Technology Data Exchange (ETDEWEB)

    Slavcheva, G., E-mail: gsk23@bath.ac.uk [Blackett Laboratory, Imperial College London, Prince Consort Road, London SW7 2AZ (United Kingdom); Kavokin, A.V., E-mail: A.Kavokin@soton.ac.uk [School of Physics and Astronomy, University of Southampton, Highfield, Southampton SO17 1BJ (United Kingdom); Spin Optics Laboratory, St. Petersburg State University, 1, Ulyanovskaya 198504 (Russian Federation)

    2014-11-15

    Optical pumping of excited exciton states in a semiconductor quantum well embedded in a microcavity is a tool for realisation of ultra-compact terahertz (THz) lasers based on stimulated optical transition between excited (2p) and ground (1s) exciton state. We show that the probability of two-photon absorption by a 2p-exciton is strongly dependent on the polarisation of both pumping photons. Five-fold variation of the threshold power for terahertz lasing by switching from circular to co-linear pumping is predicted. We identify photon polarisation configurations for achieving maximum THz photon generation quantum efficiency.

  10. Characterization of optical anisotropy in quantum wells under compressive anisotropic in-plane strain

    Science.gov (United States)

    Biermann, Mark L.; Walters, Matthew; Diaz-Barriga, James; Rabinovich, W. S.

    2003-10-01

    Anisotropic in-plane strain in quantum wells leads to an optical polarization anisotropy that can be exploited for device applications. We have determined that for many anisotropic compressive strain cases, the dependence of the optical anisotropy is linear in the strain anisotropy. This result holds for a variety of well and barrier materials and widths and for various overall strain conditions. Further, the polarization anisotropy per strain anisotropy varies as the reciprocal of the energy separation of the relevant hole sub-bands. Hence, a general result for the polarization anisotropy per strain anisotropy is avialable for cases of compressive anisotropic in-plane strain.

  11. Characterization of optical anisotropy in quantum wells under compressive anisotropic in-plane strain

    Energy Technology Data Exchange (ETDEWEB)

    Biermann, Mark L [Physics Department, 566 Brownson Rd., U.S. Naval Academy, Annapolis, MD 21402 (United States); Walters, Matthew [Physics Department, 566 Brownson Rd., U.S. Naval Academy, Annapolis, MD 21402 (United States); Diaz-Barriga, James [Physics Department, 566 Brownson Rd., U.S. Naval Academy, Annapolis, MD 21402 (United States); Rabinovich, W S [Naval Research Laboratory, Code 5652, 4555 Overlook Ave. SW, Washington, DC 20375-5320 (United States)

    2003-10-21

    Anisotropic in-plane strain in quantum wells leads to an optical polarization anisotropy that can be exploited for device applications. We have determined that for many anisotropic compressive strain cases, the dependence of the optical anisotropy is linear in the strain anisotropy. This result holds for a variety of well and barrier materials and widths and for various overall strain conditions. Further, the polarization anisotropy per strain anisotropy varies as the reciprocal of the energy separation of the relevant hole sub-bands. Hence, a general result for the polarization anisotropy per strain anisotropy is available for cases of compressive anisotropic in-plane strain.

  12. Deep levels, transport and THz emission properties of SiGe/Si quantum-well structures

    Institute of Scientific and Technical Information of China (English)

    I.; V.; ANTONOVA; M.; S.; KAGAN; E.; P.; NEUSTROEV; S.; A.; SMAGULOVA

    2009-01-01

    Recharging of quantum confinement levels in SiGe quantum wells (QW) was studied by charge deep-level transient spectroscopy (Q-DLTS) for Si/SiGe/Si structures with different Ge contents in the SiGe layer. A peak with activation energy varying in the range from 0 to 100 meV in different tempera-ture intervals was observed in Q-DLTS spectra. Activation energies extracted from Q-DLTS measure-mens are in good agreement with energies of quantum confinement levels in the QW.

  13. Can Hall drag be observed in Coulomb coupled quantum wells in a magnetic field?

    DEFF Research Database (Denmark)

    Hu, Ben Yu-Kuang

    1997-01-01

    We study the transresistivity rho(21) (or equivalently, the drag rate) of two Coulomb-coupled quantum wells in the presence of a perpendicular magnetic field, using semi-classical transport theory. Elementary arguments seem to preclude any possibility of observation of ''Hall drag'' (i.e., a non......-zero off-diagonal component in rho(21)). We show that these arguments are specious, and in fact Hall drag can be observed at sufficiently high temperatures when the intralayer transport time tau has significant energy-dependence around the Fermi energy epsilon(F). The ratio of the Hall to longitudinal...

  14. Effects of Mg doping on optical and electrical properties of GaNAs multiple quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Shiraga, Masahiro; Nakai, Yuko; Hirashima, Tomohiko; Kittaka, Akinobu; Ebisu, Mari; Tsurumachi, Noriaki; Nakanishi, Shunsuke; Miyagawa, Hayato; Itoh, Hiroshi; Koshiba, Shyun [Faculty of Engineering, Kagawa University, 2217-20 Hayashi-cho, Takamatsu, Kagawa 761-0396 (Japan); Takahashi, Naoshi [Faculty of Education, Kagawa University, 1-1 Saiwai-cho, Takamatsu, Kagawa 760-8521 (Japan); Noda, Takeshi [National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047 (Japan); Ohmori, Masato [Toyota Technological Institute, 2-12-1 Hisakata, Tempaku-ku, Nagoya 468-8511 (Japan); Akiyama, Hidefumi [Institute for Solid State Physics, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8581 (Japan)

    2011-02-15

    We have evaluated the effects of Mg doping on the optical and the electrical property of GaNAs/GaAs multiple quantum wells (MQWs) with high N composition (11{proportional_to}17%) grown by radio-frequency molecular beam epitaxy (RF-MBE). The results of Van der Pauw measurements revealed strong n-type conduction by Mg doping. The blue-shifts and enhanced intensities in photoluminescence by Mg doping suggest the type-II band structure of GaNAs/GaAs MQWs and carrier generation by interstitial Mg atoms. (copyright 2011 EILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  15. Fermi surface and quantum well states of V(110) films on W(110)

    Energy Technology Data Exchange (ETDEWEB)

    Krupin, Oleg [MS 6-2100, Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA 94720 (United States); Rotenberg, Eli [MS 6-2100, Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA 94720 (United States); Kevan, S D [Department of Physics, University of Oregon, Eugene, OR 97403 (United States)

    2007-09-05

    Using angle-resolved photoemission spectroscopy, we have measured the Fermi surface of V(110) films epitaxially grown on a W(110) substrate. We compare our results for thicker films to existing calculations and measurements for bulk vanadium and find generally very good agreement. For thinner films, we observe and analyse a diverse array of quantum well states that split and distort the Fermi surface segments. We have searched unsuccessfully for a thickness-induced topological transition associated with contact between the zone-centre jungle gym and zone-boundary hole ellipsoid Fermi surface segments. We also find no evidence for ferromagnetic splitting of any bands on this surface.

  16. Pseudo-square AlGaN/GaN quantum wells for terahertz absorption

    Science.gov (United States)

    Beeler, M.; Bougerol, C.; Bellet-Amalric, E.; Monroy, E.

    2014-09-01

    THz intersubband transitions are reported down to 160 μm within AlGaN/GaN heterostructures following a 4-layer quantum well design. In such a geometry, the compensation of the polarization-induced internal electric field is obtained through creating a gradual increase in polarization field throughout the quantum "trough" generated by three low-Al-content layers. The intersubband transitions show tunable absorption with respect to doping level as well as geometrical variations which can be regulated from 53 to 160 μm. They also exhibit tunnel-friendly designs which can be easily integrated into existing intersubband device architectures.

  17. Voltage-controlled sub-terahertz radiation transmission through GaN quantum well structure

    Science.gov (United States)

    Laurent, T.; Sharma, R.; Torres, J.; Nouvel, P.; Blin, S.; Varani, L.; Cordier, Y.; Chmielowska, M.; Chenot, S.; Faurie, J.-P.; Beaumont, B.; Shiktorov, P.; Starikov, E.; Gruzinskis, V.; Korotyeyev, V. V.; Kochelap, V. A.

    2011-08-01

    We report on measurements of radiation transmission in the 0.220-0.325 THz frequency range through GaN quantum wells grown on sapphire substrates at nitrogen and room temperatures. Significant enhancement of the transmitted beam intensity with applied voltage is found at nitrogen temperature. This effect is explained by changes in the mobility of two-dimensional electrons under electric bias. We have clarified which physical mechanism modifies the electron mobility and we suggest that the effect of voltage-controlled sub-terahertz transmission can be used for the development of electro-optic modulators operating in the sub-THz frequency range.

  18. Terahertz study of ultrafast carrier dynamics in InGaN/GaN multiple quantum wells

    Science.gov (United States)

    Porte, H. P.; Turchinovich, D.; Cooke, D. G.; Jepsen, P. Uhd

    2009-11-01

    Ultrafast carrier dynamics in InGaN/GaN multiple quantum wells is measured by time-resolved terahertz spectroscopy. The built-in piezoelectric field is initially screened by photoexcited, polarized carriers, and is gradullay restored as the carriers recombine. We observe a nonexponential decay of the carrier density. Time-integrated photoluminescence spectra have shown a complete screening of the built-in piezoelectric field at high excitation fluences. We also observe that the terahertz conductivity spectra differs from simple Drude conductivity, describing the response of free carriers, and are well fitted by the Drude-Smith model.

  19. Pseudo-square AlGaN/GaN quantum wells for terahertz absorption

    Energy Technology Data Exchange (ETDEWEB)

    Beeler, M.; Bellet-Amalric, E.; Monroy, E. [Université Grenoble Alpes, 38000 Grenoble (France); CEA-Grenoble, INAC/SP2M/NPSC, 17 avenue des Martyrs, 38054 Grenoble (France); Bougerol, C. [Université Grenoble Alpes, 38000 Grenoble (France); Institut Néel-CNRS, 25 avenue des Martyrs, 38042 Grenoble Cedex 9 (France)

    2014-09-29

    THz intersubband transitions are reported down to 160 μm within AlGaN/GaN heterostructures following a 4-layer quantum well design. In such a geometry, the compensation of the polarization-induced internal electric field is obtained through creating a gradual increase in polarization field throughout the quantum “trough” generated by three low-Al-content layers. The intersubband transitions show tunable absorption with respect to doping level as well as geometrical variations which can be regulated from 53 to 160 μm. They also exhibit tunnel-friendly designs which can be easily integrated into existing intersubband device architectures.

  20. Terahertz study of ultrafast carrier dynamics in InGaN/GaN multiple quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Porte, H P; Turchinovich, D; Cooke, D G; Jepsen, P Uhd, E-mail: hpor@fotonik.dtu.d [DTU Fotonik, Department of Photonics Engineering, Technical University of Denmark, Oersteds Plads 343, DK 2800 Kongens Lyngby (Denmark)

    2009-11-15

    Ultrafast carrier dynamics in InGaN/GaN multiple quantum wells is measured by time-resolved terahertz spectroscopy. The built-in piezoelectric field is initially screened by photoexcited, polarized carriers, and is gradullay restored as the carriers recombine. We observe a nonexponential decay of the carrier density. Time-integrated photoluminescence spectra have shown a complete screening of the built-in piezoelectric field at high excitation fluences. We also observe that the terahertz conductivity spectra differs from simple Drude conductivity, describing the response of free carriers, and are well fitted by the Drude-Smith model.

  1. Anomalous Hall effect of heavy holes in Ⅲ-Ⅴ semiconductor quantum wells

    Institute of Scientific and Technical Information of China (English)

    Wang Zhi-Gang; Zhang Ping

    2007-01-01

    The anomalous Hall effect of heavy holes in semiconductor quantum wells is studied in the intrinsic transport regime, where the Berry curvature governs the Hall current properties. Based on the first-order perturbation of wave function the expression of the Hall conductivity the same as that from the semiclassical equation of motion of the Bloch particles is derived. The dependence of Hall conductivity on the system parameters is shown. The amplitude of Hall conductivity is found to be balanced by a competition between the Zeeman splitting and the spin-orbit splitting.

  2. Reduced threshold all-optical bistability in etched quantum well microresonators

    Science.gov (United States)

    Rivera, T.; Ladan, F. R.; Izrael, A.; Azoulay, R.; Kuszelewicz, R.; Oudar, J. L.

    1994-02-01

    Etched vertical microresonators made of GaAs/AlGaAs multiple quantum wells produced by reactive ion etching was investigated to study the optical bistability phenomena. Reactive ion etching was preferred because of smooth vertical and minimization of density of surface recombination centers. A high cavity finesse was observed in the microresonators producing an optical bistability with wide hysteresis loops. A low threshold power of 70 microwatts was measured due to carrier confinement and vertical walls. The low bistability threshold power was attributed to self passivation happening during etching process, which produced a small surface recombination rate.

  3. Efficiency dip observed with InGaN-based multiple quantum well solar cells

    KAUST Repository

    Lai, Kunyu

    2014-01-01

    The dip of external quantum efficiency (EQE) is observed on In0.15Ga0.85N/GaN multiple quantum well (MQW) solar cells upon the increase of incident optical power density. With indium composition increased to 25%, the EQE dip becomes much less noticeable. The composition dependence of EQE dip is ascribed to the competition between radiative recombination and photocurrent generation in the active region, which are dictated by quantum-confined Stark effect (QCSE) and composition fluctuation in the MQWs.

  4. Compositional dependence of the band gap in Ga(NAsP) quantum well heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Jandieri, K., E-mail: kakhaber.jandieri@physik.uni-marburg.de; Ludewig, P.; Wegele, T.; Beyer, A.; Kunert, B.; Springer, P.; Baranovskii, S. D.; Koch, S. W.; Volz, K.; Stolz, W. [Materials Science Center and Faculty of Physics, Philipps-University Marburg, Marburg (Germany)

    2015-08-14

    We present experimental and theoretical studies of the composition dependence of the direct band gap energy in Ga(NAsP)/GaP quantum well heterostructures grown on either (001) GaP- or Si-substrates. The theoretical description takes into account the band anti-crossing model for the conduction band as well as the modification of the valence subband structure due to the strain resulting from the pseudomorphic epitaxial growth on the respective substrate. The composition dependence of the direct band gap of Ga(NAsP) is obtained for a wide range of nitrogen and phosphorus contents relevant for laser applications on Si-substrate.

  5. High contrast ratio, high uniformity multiple quantum well spatial light modulators

    Energy Technology Data Exchange (ETDEWEB)

    Huang Yuyang; Yang Chen; Yang Hui [Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083 (China); Liu, H C; Cui Guoxin; Bian Lifeng; Zhang Yaohui [Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences, Suzhou 215125 (China); Wasilewski, Z R; Buchanan, M; Laframboise, S R, E-mail: yhzhang2006@sinano.ac.c [Institute for Microstructural Sciences, National Research Council, Ottawa K1A 0R6 (Canada)

    2010-03-15

    Our latest research results on GaAs-AlGaAs multiple quantum well spatial light modulators are presented. The thickness uniformity of the epitaxial layers across the 3-inch wafer grown by our molecular beam epitaxy is better than 0.1% and the variation of cavity resonance wavelength within the wafer is only 0.9 nm. A contrast ratio (CR) of 102 by varying bias voltage from 0 to 6.7 V is achieved after fine tuning the cavity by etching an adjust layer. Both theoretical and experimental results demonstrate that incorporating an adjust layer is an effective tuning method for obtaining high CR. (semiconductor integrated circuits)

  6. Optical spectroscopy of single beryllium acceptors in GaAs/AlGaAs quantum well

    Science.gov (United States)

    Petrov, P. V.; Kokurin, I. A.; Klimko, G. V.; Ivanov, S. V.; Ivánov, Yu. L.; Koenraad, P. M.; Silov, A. Yu.; Averkiev, N. S.

    2016-09-01

    We carry out microphotoluminescence measurements of an acceptor-bound exciton (A0X ) recombination in the applied magnetic field with a single impurity resolution. In order to describe the obtained spectra we develop a theoretical model taking into account a quantum well (QW) confinement, an electron-hole and hole-hole exchange interaction. By means of fitting the measured data with the model we are able to study the fine structure of individual acceptors inside the QW. The good agreement between our experiments and the model indicates that we observe single acceptors in a pure two-dimensional environment whose states are unstrained in the QW plain.

  7. SEMICONDUCTOR PHYSICS: Phonon-induced magnetoresistance oscillations in a high-mobility quantum well

    Science.gov (United States)

    Qisheng, Zhou; Juncheng, Cao; Ming, Qi; Xiaolin, Lei

    2010-09-01

    We examine the temperature dependence of acoustic-phonon-induced magnetoresistance oscillations in a high-mobility GaAs-based quantum well with conventional transverse and longitudinal phonon modes, using a model in which the temperature increase of the Landau level broadening or the single-particle scattering rate 1/τs is attributed to the enhancement of electron-phonon scattering with rising temperature. The non-monotonic temperature behavior, showing an optimal temperature at which a given order of oscillation amplitude exhibits a maximum and the shift of the main resistance peak to higher magnetic field with rising temperature, is produced, in agreement with recent experimental findings.

  8. Strained InGaAs/InAlAs Quantum Wells for Complementary III-V Transistors

    Science.gov (United States)

    2014-01-01

    optic systems, radar, radio astronomy, and satellite communications. Quantum wells of InGaAs/InAlAs have a sufficient valence band offset for hole...n- and p-channels is also an attractive possibility since these materials have excellent electronic properties . This combination may enable the use...layers except the Al0.8Ga0.2Sb/Al0.8Ga0.2As superlattice. This resulted in differing thicknesses of AlGaSb and AlGaAs and different anion mole fractions

  9. Carrier-carrier relaxation kinetics in quantum well semiconductor structures with nonparabolic energy bands

    DEFF Research Database (Denmark)

    Dery, H.; Tromborg, Bjarne; Eisenstein, G.

    2003-01-01

    We describe carrier-carrier scattering dynamics in an inverted quantum well structure including the nonparabolic nature of the valance band. A solution of the semiconductor Bloch equations yields strong evidence to a large change in the temporal evolution of the carrier distributions compared...... to the case of parabolic bands. The nonparabolic bands and the consequent change in the density of states reduce considerably the degree of gain saturation while decreasing the time constant governing the relaxation. This results in a measurable reduction of the role played by carrier-carrier scattering...

  10. Asymmetric quantum-well structures for AlGaN/GaN/AlGaN resonant tunneling diodes

    Science.gov (United States)

    Yang, Lin'an; Li, Yue; Wang, Ying; Xu, Shengrui; Hao, Yue

    2016-04-01

    Asymmetric quantum-well (QW) structures including the asymmetric potential-barrier and the asymmetric potential-well are proposed for AlGaN/GaN/AlGaN resonant tunneling diodes (RTDs). Theoretical investigation gives that an appropriate decrease in Al composition and thickness for emitter barrier as well as an appropriate increase of both for collector barrier can evidently improve the negative-differential-resistance characteristic of RTD. Numerical simulation shows that RTD with a 1.5-nm-thick GaN well sandwiched by a 1.3-nm-thick Al0.15Ga0.85N emitter barrier and a 1.7-nm-thick Al0.25Ga0.75N collector barrier can yield the I-V characteristic having the peak current (Ip) and the peak-to-valley current ratio (PVCR) of 0.39 A and 3.6, respectively, about double that of RTD with a 1.5-nm-thick Al0.2Ga0.8N for both barriers. It is also found that an introduction of InGaN sub-QW into the diode can change the tunneling mode and achieve higher transmission coefficient of electron. The simulation demonstrates that RTD with a 2.8-nm-thick In0.03Ga0.97N sub-well in front of a 2.0-nm-thick GaN main-well can exhibit the I-V characteristic having Ip and PVCR of 0.07 A and 11.6, about 7 times and double the value of RTD without sub-QW, respectively. The purpose of improving the structure of GaN-based QW is to solve apparent contradiction between the device structure and the device manufacturability of new generation RTDs for sub-millimeter and terahertz applications.

  11. Hybrid phonons in nanostructures

    CERN Document Server

    Ridley, Brian K

    2017-01-01

    Crystalline semiconductor nanostructures have special properties associated with electrons and lattice vibrations and their interaction, and this is the topic of the book. The result of spatial confinement of electrons is indicated in the nomenclature of nonostructures: quantum wells, quantum wires, and quantum dots. Confinement also has a profound effect on lattice vibrations and an account of this is the prime focus. The documentation of the confinement of acoustic modes goes back to Lord Rayleigh’s work in the late nineteenth century, but no such documentation exists for optical modes. Indeed, it is only comparatively recently that any theory of the elastic properties of optical modes exists, and the account given in the book is comprehensive. A model of the lattice dynamics of the diamond lattice is given that reveals the quantitative distinction between acoustic and optical modes and the difference of connection rules that must apply at an interface. The presence of interfaces in nanostructures forces ...

  12. The electron-phonon interaction in GaAs/(AlGa)As quantum wells

    CERN Document Server

    Cross, A J

    2001-01-01

    detected phonon emission energy spectra. This thesis presents a study of the electron-phonon interaction in two dimensional electron gases (2DEGs), by measuring of the acoustic phonon emission from a sequence of n-type doped GaAs/(AIGa)As quantum wells. Previous studies of emission from 2DEGs confined in GaAs heterojunctions (Chin et al., 1984) have shown a surprising absence of longitudinal acoustic (LA) mode phonon emission, in contrast with theoretical studies (Vass, 1987) which predict that deformation potential coupled LA mode emission should dominate the energy relaxation processes. This may be attributed to the finite width of the quasi-2D sheet, which imposes a restriction on the maximum emitted phonon wavevector component perpendicular to the 2DEG, leading to a suppression of the emission (the '1/a sub 0 cutoff') at smaller phonon wavevectors than predicted by the earlier theory. By using the quantum well width w as a means of modulating the thickness of the 2DEG, the dependence of the 1/a sub 0 cuto...

  13. Toward 17µm pitch heterogeneously integrated Si/SiGe quantum well bolometer focal plane arrays

    Science.gov (United States)

    Ericsson, Per; Fischer, Andreas C.; Forsberg, Fredrik; Roxhed, Niclas; Samel, Björn; Savage, Susan; Stemme, Göran; Wissmar, Stanley; Öberg, Olof; Niklaus, Frank

    2011-06-01

    Most of today's commercial solutions for un-cooled IR imaging sensors are based on resistive bolometers using either Vanadium oxide (VOx) or amorphous Silicon (a-Si) as the thermistor material. Despite the long history for both concepts, market penetration outside high-end applications is still limited. By allowing actors in adjacent fields, such as those from the MEMS industry, to enter the market, this situation could change. This requires, however, that technologies fitting their tools and processes are developed. Heterogeneous integration of Si/SiGe quantum well bolometers on standard CMOS read out circuits is one approach that could easily be adopted by the MEMS industry. Due to its mono crystalline nature, the Si/SiGe thermistor material has excellent noise properties that result in a state-ofthe- art signal-to-noise ratio. The material is also stable at temperatures well above 450°C which offers great flexibility for both sensor integration and novel vacuum packaging concepts. We have previously reported on heterogeneous integration of Si/SiGe quantum well bolometers with pitches of 40μm x 40μm and 25μm x 25μm. The technology scales well to smaller pixel pitches and in this paper, we will report on our work on developing heterogeneous integration for Si/SiGe QW bolometers with a pixel pitch of 17μm x 17μm.

  14. Second harmonic generation from metamaterials strongly coupled to intersubband transitions in quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Campione, Salvatore, E-mail: sncampi@sandia.gov [Sandia National Laboratories, Albuquerque, New Mexico 87185 (United States); Center for Integrated Nanotechnologies (CINT), Sandia National Laboratories, Albuquerque, New Mexico 87185 (United States); Department of Electrical Engineering and Computer Science, University of California Irvine, Irvine, California 92697 (United States); Benz, Alexander; Brener, Igal, E-mail: ibrener@sandia.gov [Sandia National Laboratories, Albuquerque, New Mexico 87185 (United States); Center for Integrated Nanotechnologies (CINT), Sandia National Laboratories, Albuquerque, New Mexico 87185 (United States); Sinclair, Michael B. [Sandia National Laboratories, Albuquerque, New Mexico 87185 (United States); Capolino, Filippo [Department of Electrical Engineering and Computer Science, University of California Irvine, Irvine, California 92697 (United States)

    2014-03-31

    We theoretically analyze the second harmonic generation capacity of two-dimensional periodic metamaterials comprising sub-wavelength resonators strongly coupled to intersubband transitions in quantum wells (QWs) at mid-infrared frequencies. The metamaterial is designed to support a fundamental resonance at ∼30 THz and an orthogonally polarized resonance at the second harmonic frequency (∼60 THz), while the asymmetric quantum well structure is designed to provide a large second order susceptibility. Upon continuous wave illumination at the fundamental frequency we observe second harmonic signals in both the forward and backward directions, with the forward efficiency being larger. We calculate the overall second harmonic conversion efficiency of the forward wave to be ∼1.3 × 10{sup −2} W/W{sup 2}—a remarkably large value, given the deep sub-wavelength dimensions of the QW structure (about 1/15th of the free space wavelength of 10 μm). The results shown in this Letter provide a strategy for designing easily fabricated sources across the entire infrared spectrum through proper choice of QW and resonator designs.

  15. Enhancement of Two-photon Absorption in Quantum Wells for Extremely Nondegenerate Photon Pairs

    CERN Document Server

    Pattanaik, Himansu S; Khurgin, Jacob B; Hagan, David J; Van Stryland, Eric W

    2015-01-01

    We recently demonstrated orders of magnitude enhancement of two-photon absorption (2PA) in direct gap semiconductors due to intermediate state resonance enhancement for photons of very different energies. It can be expected that further enhancement of nondegenerate 2PA will be observed in quantum wells (QWs) since the intraband matrix elements do not vanish near the band center as they do in the bulk, and the density of states in QWs is larger near the band edge. Here we present a perturbation-theory based theoretical description of nondegenerate 2PA in semiconductor QWs, where both frequency and polarization of two incident waves can vary independently. Analytical expressions for all possible permutations of frequencies and polarizations have been obtained, and the results are compared with degenerate 2PA in quantum wells along with degenerate and nondegenerate 2PA in bulk semiconductors. We show that using QWs in place of bulk semiconductors with both beams in the TM-polarized mode leads to an additional or...

  16. Pumping dynamics of nuclear spins in GaAs quantum wells

    CERN Document Server

    Mocek, Raphael W; Cascio, Giovanni; Suter, Dieter

    2016-01-01

    Irradiating a semiconductor with circularly polarized light creates spin-polarized charge carriers. If the material contains atoms with non-zero nuclear spin, they interact with the electron spins via the hyperfine coupling. Here, we consider GaAs/AlGaAs quantum wells, where the conduction-band electron spins interact with three different types of nuclear spins. The hyperfine interaction drives a transfer of spin polarization to the nuclear spins, which therefore acquire a polarization that is comparable to that of the electron spins. In this paper, we analyze the dynamics of the optical pumping process in the presence of an external magnetic field while irradiating a single quantum well with a circularly polarized laser. We measure the time dependence of the photoluminescence polarization to monitor the buildup of the nuclear spin polarization and thus the average hyperfine interaction acting on the electron spins. We present a simple model that adequately describes the dynamics of this process and is in goo...

  17. Time-Resolved Photoluminescence Studies of InGaN/AlGaN Multiple Quantum Wells

    Science.gov (United States)

    Zeng, K. C.; Smith, M.; Lin, J. Y.; Jiang, H. X.; Robert, J. C.; Piner, E. L.; McIntosh, F. G.; Bahbahani, M.; Bedair, S. M.; Zavada, J.

    1997-03-01

    Picosecond time-resolved photoluminescence (PL) spectroscopy has been employed to study the dynamic processes of optical transitions in InGaN/AlGaN multiple quantum wells (MQW) grown by metal-organic chemical vapor deposition (MOCVD). The dynamical behavior of the PL emission reveals that the main emission line in these MQW is the combination of the localized exciton and a band-to-impurity emission lines. The spectral lineshape and the recombination dynamics of the localized exciton and of the band-to-impurity transitions have been systematically investigated at different temperatures and excitation intensities and for MQW with different structures and growth conditions. From these studies, important parameters, including the localization energy and the recombination lifetimes of the localized excitons in InGaN/AlGaN quantum wells, the well width fluctuation, alloy compositions in the well and the barrier materials, and the band offset between InGaN and AlGaN can be deduced. Comparing with time-resolved PL results of InGaN/GaN and GaN/AlGaN MQW, important effects of interface on the optical properties of the III-nitride MQW have been evaluated. Implications of our results to device applications will be discussed.

  18. Modeling the band gap of CdS quantum well structures

    Science.gov (United States)

    Harris, R. A.; Terblans, J. J.

    2016-10-01

    Within the framework of the effective mass approximation, an excited electron is studied in a cadmium sulfide (CdS) quantum well with varying well widths. The envelope function approximation is employed involving a three parameter variational calculation wherein one of these parameters is the distance between the electron and the hole. The relative change in the electron's energy (relative to its energy when it is in the valence band; in the hole) is investigated as a function of the electron-hole distance. Results from numerical calculations are presented and the non-linear behavior of different sized CdS quantum wells are discussed. Comparisons between experimentally measured CdS band gap energies (as a function of well-width) and the simulation data are made. A good agreement between the current model and experimental data exists. Density functional theory (DFT) calculations are done on crystallites of extremely small sizes to compare the current model's bandgap energies to DFT-predicted bandgap values at these extremes.

  19. High Efficiency Quantum Well Waveguide Solar Cells and Methods for Constructing the Same

    Science.gov (United States)

    Welser, Roger E. (Inventor); Sood, Ashok K. (Inventor)

    2014-01-01

    Photon absorption, and thus current generation, is hindered in conventional thin-film solar cell designs, including quantum well structures, by the limited path length of incident light passing vertically through the device. Optical scattering into lateral waveguide structures provides a physical mechanism to increase photocurrent generation through in-plane light trapping. However, the insertion of wells of high refractive index material with lower energy gap into the device structure often results in lower voltage operation, and hence lower photovoltaic power conversion efficiency. The voltage output of an InGaAs quantum well waveguide photovoltaic device can be increased by employing a III-V material structure with an extended wide band gap emitter heterojunction. Analysis of the light IV characteristics reveals that non-radiative recombination components of the underlying dark diode current have been reduced, exposing the limiting radiative recombination component and providing a pathway for realizing solar-electric conversion efficiency of 30% or more in single junction cells.

  20. Optical gain in GaAsBi/GaAs quantum well diode lasers

    Science.gov (United States)

    Marko, Igor P.; Broderick, Christopher A.; Jin, Shirong; Ludewig, Peter; Stolz, Wolfgang; Volz, Kerstin; Rorison, Judy M.; O'Reilly, Eoin P.; Sweeney, Stephen J.

    2016-07-01

    Electrically pumped GaAsBi/GaAs quantum well lasers are a promising new class of near-infrared devices where, by use of the unusual band structure properties of GaAsBi alloys, it is possible to suppress the dominant energy-consuming Auger recombination and inter-valence band absorption loss mechanisms, which greatly impact upon the device performance. Suppression of these loss mechanisms promises to lead to highly efficient, uncooled operation of telecommunications lasers, making GaAsBi system a strong candidate for the development of next-generation semiconductor lasers. In this report we present the first experimentally measured optical gain, absorption and spontaneous emission spectra for GaAsBi-based quantum well laser structures. We determine internal optical losses of 10-15 cm-1 and a peak modal gain of 24 cm-1, corresponding to a material gain of approximately 1500 cm-1 at a current density of 2 kA cm-2. To complement the experimental studies, a theoretical analysis of the spontaneous emission and optical gain spectra is presented, using a model based upon a 12-band k.p Hamiltonian for GaAsBi alloys. The results of our theoretical calculations are in excellent quantitative agreement with the experimental data, and together provide a powerful predictive capability for use in the design and optimisation of high efficiency lasers in the infrared.

  1. Hole weak anti-localization in a strained-Ge surface quantum well

    Science.gov (United States)

    Mizokuchi, R.; Torresani, P.; Maurand, R.; Zeng, Z.; Niquet, Y.-M.; Myronov, M.; De Franceschi, S.

    2017-08-01

    We report a magneto-transport study of a two-dimensional hole gas confined to a strained Ge quantum well grown on a relaxed Si0.2Ge0.8 virtual substrate. The conductivity of the hole gas measured as a function of a perpendicular magnetic field exhibits a zero-field peak resulting from weak anti-localization. The peak develops and becomes stronger upon increasing the hole density by means of a top gate electrode. This behavior is consistent with a Rashba-type spin-orbit coupling whose strength is proportional to the perpendicular electric field and hence to the carrier density. In the low-density, the single-subband regime, by fitting the weak anti-localization peak to an analytic model, we extract the characteristic transport time scales and a spin splitting energy ΔSO˜ 1 meV. Tight-binding calculations show that ΔSO is dominated by a cubic term in the in-plane wave vector. Finally, we observe a weak anti-localization peak also for magnetic fields parallel to the quantum well and associate this finding to an effect of intersubband scattering induced by interface defects.

  2. Theoretical model of optical fiber secure communication system with chaotic multiple-quantum-well lasers

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    Chaotic synchronization of injected multiple-quantum-well lasers of optical fiber system and a theoretical model of optical fiber chaotic secure communication system are presented by coupling a chaotic multiple-quantum-well laser synchronization system and a fiber channel. A new chaotic encoding method of chaos phase shift keying On/Off is proposed for optical fiber secure communications. Chaotic synchronization is achieved numerically in long-haul fiber system at wavelength 1.55μm. The effect of the nonlinear-phase of fiber is analyzed on chaotic signal and synchronization. A sinusoidal signal of 0.2 GHz frequency is simulated numerically with chaos masking in long-haul fiber analog communication at wavelength 1.55μm while a digital signal of 0.5 Gbit/s bit rate is simulated numerically with c1 haos masking and a rate of 0.05 Gbit/s are also simulated numerically with chaos shift keying and chaos phase shift keying On/Off in long-haul fiber digital communications at wavelength 1.55μm

  3. Development and application of InAsP/InP quantum well infrared detector

    Science.gov (United States)

    Geetanjali, Porwal, S.; Kumar, R.; Dixit, V. K.; Sharma, T. K.; Oak, S. M.

    2016-05-01

    InAsxP1-x/InP quantum wells grown using metal organic vapor phase epitaxy are investigated for infrared detector applications. The structural parameters of the QWs are evaluated from high resolution x-ray diffraction. The electronic transition energies measured from surface photo voltage and photoconductivity confirms that these QWs can be used for fabricating IR detectors in the wide wavelength range, i.e. 0.9-1.46 µm by inter-band transitions and 7-18 µm by inter-sub-band transitions. Subsequently the functionality of one such fabricated InAsxP1-x/InPQW detector is verified by measuring the photoluminescence of suitable semiconductor quantum well structure. At the request of all authors of the paper, and with the agreement of the Proceedings Editor, an updated version of this article was published on 24 June 2016. The original version supplied to AIP Publishing contained an error in the Figures 1 and 2 where the right side of the images were cutoff. The error has been corrected in the updated and re-published article.

  4. Transport of dipolar excitons in (Al,Ga)N/GaN quantum wells

    Science.gov (United States)

    Fedichkin, F.; Andreakou, P.; Jouault, B.; Vladimirova, M.; Guillet, T.; Brimont, C.; Valvin, P.; Bretagnon, T.; Dussaigne, A.; Grandjean, N.; Lefebvre, P.

    2015-05-01

    We investigate the transport of dipolar indirect excitons along the growth plane of polar (Al,Ga)N/GaN quantum well structures by means of spatially and time-resolved photoluminescence spectroscopy. The transport in these strongly disordered quantum wells is activated by dipole-dipole repulsion. The latter induces an emission blue shift that increases linearly with exciton density, whereas the radiative recombination rate increases exponentially. Under continuous, localized excitation, we observe continuously decreasing emission energy, as excitons propagate away from the excitation spot. This corresponds to a steady-state gradient of exciton density, measured over several tens of micrometers. Time-resolved microphotoluminescence experiments provide information on the dynamics of recombination and transport of dipolar excitons. We account for the ensemble of experimental results by solving the nonlinear drift-diffusion equation. Quantitative analysis suggests that in such structures, exciton propagation on the scale of 10 to 20 μ m is mainly driven by diffusion, rather than by drift, due to the strong disorder and the presence of nonradiative defects. Secondary exciton creation, most probably by the intense higher-energy luminescence, guided along the sample plane, is shown to contribute to the exciton emission pattern on the scale up to 100 μ m . The exciton propagation length is strongly temperature dependent, the emission being quenched beyond a critical distance governed by nonradiative recombination.

  5. Study of intersubband transitions in GaN-ZnGeN2 coupled quantum wells

    Science.gov (United States)

    Han, Lu; Lieberman, Colin; Zhao, Hongping

    2017-03-01

    In this work, we design and analyze a closely lattice-matched wide bandgap GaN-ZnGeN2 coupled quantum well (QW) structure targeting for near-infrared (IR) (λ ≤ 3 um) intersubband transition for quantum cascade laser applications. The coupled quantum well structure comprised two GaN wells separated by a thin ZnGeN2 barrier layer. The QW active region is surrounded by thick ZnGeN2 layers as barriers. The computations of the electron-phonon and electron-photon scattering rates are carried out by employing the Fermi's golden rule for transitions. The calculation takes into consideration the conservation of energy and momentum in scattering processes. The coupled QW structure is optimized through tuning the confined subband energy levels in the conduction band to achieve (1) electron-LO phonon resonant scattering when the energy separation between the first and second conduction subband levels matches the phonon energy of GaN (92 meV); and (2) dominant electron-photon transition in near-IR between the third and second conduction subband levels.

  6. Terahertz intersubband transition in GaN/AlGaN step quantum well

    Science.gov (United States)

    Wu, F.; Tian, W.; Yan, W. Y.; Zhang, J.; Sun, S. C.; Dai, J. N.; Fang, Y. Y.; Wu, Z. H.; Chen, C. Q.

    2013-04-01

    The influences of polarization and structure parameters on the intersubband transition frequency within terahertz (THz) range and oscillator strength in GaN/AlGaN step quantum well have been investigated by solving Schrödinger and Poisson equations self-consistently. The results show that the Al mole compositions of step quantum well and space barrier have a significant effect on the THz intersubband transition frequency. A specific phenomenon is found that the minimum energy spacing between the ground state and first excited state can be achieved as the Al mole composition of space barrier is about twice of that of step well. In particular, an intersubband transition with energy of 19.8 meV (4.83 THz) can be obtained with specifically designed parameters. This specific phenomenon still exists in a wide range of step well width and a narrow range of well width with less than 3% fluctuation of the Al mole composition of barrier. In addition, oscillator strength and dipole matrix element versus the widths of well and step well, the influences of doping location and concentration on the absorption coefficient, are also investigated in detail in this study. The results should be of benefit to the design of devices operating in the THz frequency range.

  7. Effect of III-V on insulator structure on quantum well intermixing

    Science.gov (United States)

    Takashima, Seiya; Ikku, Yuki; Takenaka, Mitsuru; Takagi, Shinichi

    2016-04-01

    To achieve the monolithic active/passive integration on the III-V CMOS photonics platform, quantum well intermixing (QWI) on III-V on insulator (III-V-OI) is studied for fabricating multi-bandgap III-V-OI wafers. By optimizing the QWI condition for a 250-nm-thick III-V layer, which contains a five-layer InGaAsP-based multi-quantum well (MQW) with 80-nm-thick indium phosphide (InP) cladding layers, we have successfully achieved a photoluminescence (PL) peak shift of over 100 nm on the III-V-OI wafer. We have also found that the progress of QWI on the III-V-OI wafer is slower than that on the InP bulk wafer regardless of the buried oxide (BOX) thickness, bonding interface materials, and handle wafers. We have also found that the progress of QWI on the III-V-OI wafer is slower than that on the InP bulk wafer regardless of the buried oxide (BOX) thickness, bonding interface materials, and bulk support wafers on which the III-V-OI structure is formed (handle wafers). By comparing between the measured PL shift and simulated diffusions of phosphorus vacancies and interstitials during QWI, we have found that the slow QWI progress in the III-V-OI wafer is probably attributed to the enhanced recombination of vacancies and interstitials by the diffusion blocking of vacancies and interstitials at the BOX interface.

  8. Excitonic field screening and bleaching in InGaN/GaN multiple quantum wells

    Science.gov (United States)

    Chen, Fei; Kirkey, W. D.; Furis, M.; Cheung, M. C.; Cartwright, A. N.

    2003-03-01

    Photoinduced carrier dynamics in a sequence of InGaN/GaN multiple quantum wells (MQWs) are studied by employing steady state and ultrafast spectroscopy at room temperature. Time-resolved photoluminescence (PL) measured short carrier lifetimes of ˜140 ps at room temperature. Steady state differential transmission was used to measure the in-well field screening due to the photoinjected carriers. The observed offset in emission energy from excitonic screening energies is consistent with the emission of carriers through localized states slightly below the excitonic resonance energy. Furthermore, time-resolved differential transmission with amplified pulses, where significant carrier densities can be optically generated, provides evidence of both excitonic bleaching and field screening in these InGaN quantum wells (QWs). The comparison of the time-resolved differential absorption spectra at various carrier densities allows us to identify different carrier recombination dynamics in the InGaN well and to separate the field screening from the bleaching effects. Finally, the extreme prolongation of the carrier recombination lifetime up to ˜4 μs suggests the spatial separation between electrons and holes under the large in-well fields.

  9. A real-time spectrum acquisition system design based on quantum dots-quantum well detector

    Science.gov (United States)

    Zhang, S. H.; Guo, F. M.

    2016-01-01

    In this paper, we studied the structure characteristics of quantum dots-quantum well photodetector with response wavelength range from 400 nm to 1000 nm. It has the characteristics of high sensitivity, low dark current and the high conductance gain. According to the properties of the quantum dots-quantum well photodetectors, we designed a new type of capacitive transimpedence amplifier (CTIA) readout circuit structure with the advantages of adjustable gain, wide bandwidth and high driving ability. We have implemented the chip packaging between CTIA-CDS structure readout circuit and quantum dots detector and tested the readout response characteristics. According to the timing signals requirements of our readout circuit, we designed a real-time spectral data acquisition system based on FPGA and ARM. Parallel processing mode of programmable devices makes the system has high sensitivity and high transmission rate. In addition, we realized blind pixel compensation and smoothing filter algorithm processing to the real time spectrum data by using C++. Through the fluorescence spectrum measurement of carbon quantum dots and the signal acquisition system and computer software system to realize the collection of the spectrum signal processing and analysis, we verified the excellent characteristics of detector. It meets the design requirements of quantum dot spectrum acquisition system with the characteristics of short integration time, real-time and portability.

  10. Improved interface quality and luminescence capability of InGaN/GaN quantum wells with Mg pretreatment

    Energy Technology Data Exchange (ETDEWEB)

    Wu, Zhengyuan; Shen, Xiyang; Xiong, Huan; Li, Qingfei; Kang, Junyong; Fang, Zhilai [Xiamen University, Collaborative Innovation Center for Optoelectronic Semiconductors and Efficient Devices, Department of Physics, Xiamen (China); Lin, Feng; Yang, Bilan; Lin, Shilin [San' an Optoelectronics Co., Ltd, Xiamen (China); Shen, Wenzhong [Shanghai Jiao Tong University, Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education), Department of Physics, Shanghai (China); Zhang, Tong-Yi [Shanghai University, Shanghai University Materials Genome Institute and Shanghai Materials Genome Institute, Shanghai (China)

    2016-02-15

    Interface modification of high indium content InGaN/GaN quantum wells was carried out by Mg pretreatment of the GaN barrier surface. The indium in the Mg-pretreated InGaN layer was homogeneously distributed, making the interfaces abrupt. The improved interface quality greatly enhanced light emission capacity. The cathodoluminescence intensity of the Mg-pretreated InGaN/GaN quantum wells was correspondingly much stronger than those of the InGaN/GaN quantum wells without Mg pretreatment. (orig.)

  11. Generation of coherent terahertz radiation by polarized electron-hole pairs in GaAs/AlGaAs quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Andrianov, A. V., E-mail: alex.andrianov@mail.ioffe.ru; Alekseev, P. S.; Klimko, G. V.; Ivanov, S. V.; Shcheglov, V. L.; Sedova, M. A.; Zakhar' in, A. O. [Russian Academy of Sciences, Ioffe Physical-Technical Institute (Russian Federation)

    2013-11-15

    The generation of coherent terahertz radiation upon the band-to-band femtosecond laser photoexcitation of GaAs/AlGaAs multiple-quantum-well structures in a transverse electric field at room temperature is investigated. The properties of the observed terahertz radiation suggest that it is generated on account of the excitation of a time-dependent dipole moment as a result of the polarization of nonequilibrium electron-hole pairs in quantum wells by the electric field. The proposed theoretical model taking into account the dynamic screening of the electric field in the quantum wells by nonequilibrium charge carriers describes the properties of the observed terahertz signal.

  12. Exciton and donor binding energies in quantum-well wires and quantum dots a fractional-dimensional space approach

    Institute of Scientific and Technical Information of China (English)

    Li Hong; Kong Xiao-Jun

    2004-01-01

    A simple method for calculating the free-exciton binding energies in the fractional-dimensional-space model for single-quantum-well structure has been extended to quantum-well wires and quantum dots, in which the real anisotropic system is modelled through an effective isotropic environment with a fractional dimension. In this scheme, the fractionaldimensional parameter is chosen via an analytical procedure and involves no ansatz. We calculated the ground-state binding energies of excitons and donors in quantum-well wires with rectangular cross sections. Our results are found to be in good agreement with previous variational calculations and available experimental measurements. We also discussed the ground-state exciton binding energy changing with different shapes of quantum-well wires.

  13. Optical properties of InGaAsBi/GaAs strained quantum wells studied by temperature-dependent photoluminescence

    Institute of Scientific and Technical Information of China (English)

    GU Yi; Zhang Yong-Gang; Song Yu-Xin; Ye Hong; Cao Yuan-Ying; Li Ai-Zhen; Wang Shu-Min

    2013-01-01

    The effect of bismuth on the optical properties of InGaAsBi/GaAs quantum well structures is investigated using the temperature-dependent photoluminescence from 12 K to 450 K.The incorporation of bismuth in the InGaAsBi quantum well is confirmed and found to result in a red shift of photoluminescence wavelength of 27.3 meV at 300 K.The photoluminescence intensity is significantly enhanced by about 50 times at 12 K with respect to that of the InGaAs quantum well due to the surfactant effect of bismuth.The temperature-dependent integrated photoluminescence intensities of the two samples reveal different behaviors related to various non-radiative recombination processes.The incorporation of bismuth also induces alloy non-uniformity in the quantum well,leading to an increased photoluminescence linewidth.

  14. Investigation of reactive-ion-etch-induced damage of InP/InGaAs multiple quantum wells by photoluminescence

    DEFF Research Database (Denmark)

    Steffensen, O. M.; Birkedal, Dan; Hanberg, J.

    1995-01-01

    The effects of CH4/H2 reactive ion etching (RIE) on the optical properties of an InP/InGaAs multiple-quantum-well structure have been investigated by low-temperature photoluminescence (PL). The structure consisted of eight InGaAs quantum wells, lattice matched to InP, with nominal thicknesses of 0.......5, 1, 2, 3, 5, 10, 20, and 70 monolayers, respectively, on top of a 200-nm-thick layer of InGaAs for calibration. The design of this structure allowed etch-induced damage depth to be obtained from the PL spectra due to the different confinement energies of the quantum wells. The samples showed...... no significant decrease of luminescence intensity after RIE. However, the observed shift and broadening of the PL peaks from the quantum wells indicate that intermixing of well and barrier material increased with etch time. ©1995 American Institute of Physics....

  15. High Spatial Resolution of an Optical Addressing Spatial Light Modulator Made by Photorefractive Semi-Insulting Multiple Quantum Wells

    Institute of Scientific and Technical Information of China (English)

    陈兢; 李春勇; 韩英军; 郭丽伟; 黄绮; 张治国; 汤俊雄; 段明浩

    2002-01-01

    We use nondegenerate four-wave mixing to study the spatial resolution of photorefractive semi-insulating multiple quantum wells grown by molecular beam epitaxy. By optimizing the experimental conditions, we have demonstrated that our sample has spatial resolution up to 2.5μm, which approaches the theoretical limit. We also analyse the factors that affect the spatial resolution of multiple quantum wells.

  16. Electron-phonon interaction in the quantum well state of the 1 ML Na/Cu(111) system

    Science.gov (United States)

    Eremeev, S. V.; Rusina, G. G.; Borisova, S. D.; Chulkov, E. V.

    2008-02-01

    The electron-phonon interaction in the quantum well state formed by a Na monolayer coating on Cu(111) is investigated theoretically. The calculations show that the electron-phonon coupling constant γ in this state decreases insignificantly (≈1%) compared to the value of γ for a clean copper surface. The corresponding electron-phonon contribution to the lifetime τ of the quantum well state increases by a factor of 1.5 compared to τ for the clean Cu(111) surface.

  17. Photoelectric behaviour of lattice-matched GaAs/Alx Ga1-xAs quantum well electrodes

    Institute of Scientific and Technical Information of China (English)

    刘尧; 肖绪瑞; 曾一平; 闫春辉; 郑海群; 孙殿照

    1997-01-01

    The photoelectric properties of the lattice-matched GaAs/AlxGa1-xAs quantum well electrodes and the influence of the electrode structure such as well width, the thickness of outer barrier and the number of period were studied in a nonaqueous electrolyte. A new kind of structure of multiple quantum well electrode with varied well width, possessing the quantum yield three times that of GaAs bulk materials, was designed and fabricated.

  18. Electric field dependence of hybridized gap in InAs/GaSb quantum well system

    Science.gov (United States)

    Ruan, Jiufu; Wei, Xiangfei; Wang, Weiyang

    2017-02-01

    We demonstrate theoretically that exchange interaction induced by electron-hole scattering via Coulomb interaction can cause a hybridized gap in InAs/GaSb based type II and broken-gap quantum wells. The hybridized energy spectra are obtained analytically at the low temperature and long wave limits. An electric field depended hybridized gap about 4 meV opens at the anti-crossing points of the hybridized energy spectra, in accordance with experimental measurements. The hybridized gap varies linearly with the gate electric voltage due to the fact that the electric field can change the exchange self-energy by tuning the overlap of the wavefunctions and the Fermi energy. Our theoretical results can give a deep insight of the origin of the hybridized gap and provide a simple way to determine the value and the position of the hybridized gap in the presence of the gate electric voltage.

  19. Transparent waveguides for WDM transmitter arrays using quantum well shape modification

    Science.gov (United States)

    Poole, Philip J.; Buchanan, Margaret; Aers, Geof C.; Wasilewski, Zbigniew R.; Dion, Michael M.; Fallahi, Mahmoud; He, Jian Jun; Charbonneau, N. Sylvain; Koteles, Emil S.; Mitchell, Ian V.; Goldberg, Richard D.

    1995-03-01

    A technique for fabricating transparent waveguides on the same wafer as a quantum well (QW) DBR laser array has been developed. High [MeV] energy ion implantation is used to create a large number of vacancies and interstitials throughout the active region of the device. Upon annealing, these entities enhance the intermixing of the QW and barrier materials resulting in a blue shift of the QW bandgap. Energy shifts (measured using low temperature photoluminescence spectroscopy) of greater than 60 meV can be achieved. Room temperature waveguide absorption measurements verify the shift in the bandgap energy and confirm that the waveguide is now effectively transparent in the wavelength range of the QW lasers. This technique is being used in an eight wavelength WDM transmitter array in which the waveguiding region is selectively implanted and blue shifted.

  20. Epitaxial aluminum on hybridized InAs/GaSb quantum wells

    Science.gov (United States)

    Tong, Bing-Bing; Li, Ting-Xin; Mu, Xiao-Yang; Zhang, Chi; Du, Rui-Rui

    Hybridized InAs/GaSb quantum wells (QW) are approved the existence of helical edge channels. According to the theoretical prediction, the combination with superconductor will lead to superconducting topological phase and realization of Majorana bound state (MBS). Besides, InAs/GaSb material shows a low Schottky barrier to superconductor, and high quality of superconductor-topological insulator interface will result in hard induced gap. In recent report, under low temperature of substrate, there is a good lattice match between InAs naowire and Al in the same direction. In our lab, we perform aluminum epitaxy on the in-situ cleaved InAs/GaSb QW with similar methods in our ultra-high vacuum STM system. After metal epitaxy, the Al layer can be selectively etched for fabricating the superconductor-topological insulator junction devices.

  1. Quantum evolution in the regime of quantum wells in a semiclassical island with artificial interface conditions

    Energy Technology Data Exchange (ETDEWEB)

    Mantile, Andrea, E-mail: andrea.mantile@univ-reims.fr [Laboratoire de Mathématiques de Reims, EA-4535 and FR ARC CNRS-3399, Université de Reims Champagne-Ardenne, Moulin de la Housse, BP 1039, 51687 Reims Cedex 2 (France)

    2014-09-15

    We introduce a modified Schrödinger operator where the semiclassical Laplacian is perturbed by artificial interface conditions occurring at the boundaries of the potential's support. The corresponding dynamics is analyzed in the regime of quantum wells in a semiclassical island. Under a suitable energy constraint for the initial states, we show that the time propagator is stable with respect to the non-self-adjont perturbation, provided that this is parametrized through infinitesimal functions of the semiclassical parameter “h.” It has been recently shown that h-dependent artificial interface conditions allow a new approach to the adiabatic evolution problem for the shape resonances in models of resonant heterostructures. Our aim is to provide with a rigorous justification of this method.

  2. Microscopic theory of the optical properties of Ga(AsBi) quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Imhof, Sebastian; Thraenhardt, Angela [Fakultaet fuer Naturwissenschaften, Technische Universitaet Chemnitz (Germany); Bueckers, Christina; Koch, Stephan W. [Fachbereich Physik und Wissenschaftliches Zentrum fuer Materialwissenschaften, Philipps Universitaet Marburg (Germany); Hader, Joerg; Moloney, Jerome V. [Optical Sciences Center, University of Arizona, Tucson, Arizona (United States)

    2009-07-01

    Ga(AsBi) is a serious candidate for infrared diode lasers because the bandgap of GaAs is reduced by as much as 60-80 meV per percent Bi that is incorporated. Thus, a wide wavelength range in the infrared region can be reached. Although the growth of heterostructures is still not feasible in this material system, we have access to the optical properties, e.g. material gain and photoluminescence as well as radiative and non-radiative laser loss processes of Ga(AsBi)/(AlGa)As quantum wells, by using a consistent microscopic theory. We calculate the bandstructure by using a valence band anticrossing model and investigate the influence of the anticrossing parameters on the optical properties.

  3. Exciton effective mass enhancement in coupled quantum wells in electric and magnetic fields

    Science.gov (United States)

    Wilkes, J.; Muljarov, E. A.

    2016-02-01

    We present a calculation of exciton states in semiconductor coupled quantum wells in the presence of electric and magnetic fields applied perpendicular to the QW plane. The exciton Schrödinger equation is solved in real space in three-dimensions to obtain the Landau levels of both direct and indirect excitons. Calculation of the exciton energy levels and oscillator strengths enables mapping of the electric and magnetic field dependence of the exciton absorption spectrum. For the ground state of the system, we evaluate the Bohr radius, optical lifetime, binding energy and dipole moment. The exciton mass renormalization due to the magnetic field is calculated using a perturbative approach. We predict a non-monotonous dependence of the exciton ground state effective mass on magnetic field. Such a trend is explained in a classical picture, in terms of the ground state tending from an indirect to a direct exciton with increasing magnetic field.

  4. Experimental evidence of hot carriers solar cell operation in multi-quantum wells heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Rodière, Jean; Lombez, Laurent, E-mail: laurent.lombez@chimie-paristech.fr [IRDEP, Institute of R and D on Photovoltaic Energy, UMR 7174, CNRS-EDF-Chimie ParisTech, 6 Quai Watier-BP 49, 78401 Chatou Cedex (France); Le Corre, Alain; Durand, Olivier [INSA, FOTON-OHM, UMR 6082, F-35708 Rennes (France); Guillemoles, Jean-François [IRDEP, Institute of R and D on Photovoltaic Energy, UMR 7174, CNRS-EDF-Chimie ParisTech, 6 Quai Watier-BP 49, 78401 Chatou Cedex (France); NextPV, LIA CNRS-RCAST/U. Tokyo-U. Bordeaux, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8904 (Japan)

    2015-05-04

    We investigated a semiconductor heterostructure based on InGaAsP multi quantum wells (QWs) using optical characterizations and demonstrate its potential to work as a hot carrier cell absorber. By analyzing photoluminescence spectra, the quasi Fermi level splitting Δμ and the carrier temperature are quantitatively measured as a function of the excitation power. Moreover, both thermodynamics values are measured at the QWs and the barrier emission energy. High values of Δμ are found for both transition, and high carrier temperature values in the QWs. Remarkably, the quasi Fermi level splitting measured at the barrier energy exceeds the absorption threshold of the QWs. This indicates a working condition beyond the classical Shockley-Queisser limit.

  5. Fine structures in the electroabsorption spectra of GaAs quantum wells

    Science.gov (United States)

    Wen, Guozhong; Chang, Yia-Chung

    1992-03-01

    We present theoretical calculations of detailed electroabsorption spectra for GaAs quantum wells, using a k-space sampling method. The valence-band mixing, excitonic effect, and Fano resonances due to the interaction of discrete exciton states with continua are all properly taken into account. Our calculation offers a direct comparison between theory and experiment. By including the coupling between states derived from the HH1 and LH1 subbands, we can account for the interesting anticrossing behavior between the 2p excited state of the HH1-CB1 exciton and ground state of the LH1-CB1 exciton, as observed by Vin~a et al. The agreement between experiment and our theory is quite satisfactory.

  6. Exciton binding energies and absorption in intermixed GaAs-AlGaAs quantum wells

    Science.gov (United States)

    Meney, Alistair T.

    1992-12-01

    The optical properties of excitons in layer-intermixed GaAs-AlGaAs quantum wells are studied theoretically. The electronic dispersion is obtained using the 6×6 Luttinger-Kohn Hamiltonian for the valence bands, and an accurate expression for the conduction band dispersion which includes the effects of nonparabolicity and warping to fourth order in k. The HH1-CB1 (1s) and LH1-CB1(1s) exciton binding energies are calculated as a function of diffusion time. The absorption for both TE and TM polarization is obtained at several wavelengths, and is seen to decrease significantly with increased intermixing. The decrease in absorption is larger for narrow wells, where the effects of intermixing are more pronounced for a given diffusion time.

  7. Pressure effect on the electron mobility in AlAs/GaAs quantum wells

    Institute of Scientific and Technical Information of China (English)

    Hao Guo-Dong; Ban Shi-Liang; Jia Xiu-Min

    2007-01-01

    By taking the influence of optical phonon modes into account, this paper adopts the dielectric continuum phonon model and force balance equation to investigate the electronic mobility parallel to the interfaces for AlAs/GaAs semiconductor quantum wells (QWs) under hydrostatic pressure. The scattering from confined phonon modes, interface phonon modes and half-space phonon modes are analysed and the dominant scattering mechanisms in wide and narrow QWs are presented. The temperature dependence of the electronic mobility is also studied in the temperature range of optical phonon scattering being available. It is shown that the electronic mobility reduces obviously as pressure increases from 0 to 4GPa, the confined longitudinal optical (LO) phonon modes play an important role in wide QWs,whereas the interface optical phonon modes are dominant in narrow QWs, the half-space LO phonon modes hardlyinfluence the electronic mobility expect for very narrow QWs.

  8. The second-harmonic generation susceptibility in semiparabolic quantum wells with applied electric field

    Science.gov (United States)

    Yuan, Jian-Hui; Zhang, Yan; Mo, Hua; Chen, Ni; Zhang, Zhihai

    2015-12-01

    The second-harmonic generation susceptibility in semiparabolic quantum wells with applied electric field is investigated theoretically. For the same topic studied by Zhang and Xie [Phys. Rev. B 68 (2003) 235315] [1], some new and reliable results are obtained by us. It is easily observed that the second harmonic generation susceptibility decreases and the blue shift of the resonance is induced with increasing of the frequencies of the confined potential. Moreover, a transition from a two-photon resonance to two single-photon resonances will appear adjusted by the frequencies of the confined potential. Similar results can also be obtained by controlling the applied electric field. Surprisingly, the second harmonic generation susceptibility is weakened in the presence of the electric field, which is in contrast to the conventional case. Finally, the resonant peak and its corresponding resonant energy are also taken into account.

  9. Germanium-tin multiple quantum well on silicon avalanche photodiode for photodetection at two micron wavelength

    Science.gov (United States)

    Dong, Yuan; Wang, Wei; Lee, Shuh Ying; Lei, Dian; Gong, Xiao; Khai Loke, Wan; Yoon, Soon-Fatt; Liang, Gengchiau; Yeo, Yee-Chia

    2016-09-01

    We report the demonstration of a germanium-tin multiple quantum well (Ge0.9Sn0.1 MQW)-on-Si avalanche photodiode (APD) for light detection near the 2 μm wavelength range. The measured spectral response covers wavelengths from 1510 to 2003 nm. An optical responsivity of 0.33 A W-1 is achieved at 2003 nm due to the internal avalanche gain. In addition, a thermal coefficient of breakdown voltage is extracted to be 0.053% K-1 based on the temperature-dependent dark current measurement. As compared to the traditional 2 μm wavelength APDs, the Si-based APD is promising for its small excess noise factor, less stringent demand on temperature stability, and its compatibility with silicon technology.

  10. Magnetoelectronic transport of the two-dimensional electron gas in CdSe single quantum wells

    Indian Academy of Sciences (India)

    P K Ghosh; A Ghosal; D Chattopadhyay

    2009-02-01

    Hall mobility and magnetoresistance coefficient for the two-dimensional (2D) electron transport parallel to the heterojunction interfaces in a single quantum well of CdSe are calculated with a numerical iterative technique in the framework of Fermi–Dirac statistics. Lattice scatterings due to polar-mode longitudinal optic (LO) phonons, and acoustic phonons via deformation potential and piezoelectric couplings, are considered together with background and remote ionized impurity interactions. The parallel mode of piezoelectric scattering is found to contribute more than the perpendicular mode. We observe that the Hall mobility decreases with increasing temperature but increases with increasing channel width. The magnetoresistance coefficient is found to decrease with increasing temperature and increase with increasing magnetic field in the classical region.

  11. Optical studies of charged excitons in II-VI semiconductor quantum wells

    CERN Document Server

    Kossacki, P

    2003-01-01

    A brief review is given of optical studies of doped II-VI quantum wells. The properties of exciton states, neutral as well as positively and negatively charged, are discussed. A wide range of optical measurements is presented: CW as well as picosecond and femtosecond time-resolved absorption, photoluminescence (PL) and PL excitation. The experiments were performed at various carrier concentrations (> 10 sup 1 sup 1 cm sup - sup 2) and temperatures (up to a few tens of kelvins). This review is limited to zero or low magnetic fields, used only to polarize spins of carriers. We discuss the obtained values of various fundamental parameters of the excitonic states: energies, optical transition probabilities and characteristic times of their formation, thermalization and decay. (topical review)

  12. Quantum theory of exciton-photon coupling in photonic crystal slabs with embedded quantum wells

    CERN Document Server

    Gerace, D

    2007-01-01

    A theoretical description of radiation-matter coupling for semiconductor-based photonic crystal slabs is presented, in which quantum wells are embedded within the waveguide core layer. A full quantum theory is developed, by quantizing both the electromagnetic field with a spatial modulation of the refractive index and the exciton center of mass field in a periodic piecewise constant potential. The second-quantized hamiltonian of the interacting system is diagonalized with a generalized Hopfield method, thus yielding the complex dispersion of mixed exciton-photon modes including losses. The occurrence of both weak and strong coupling regimes is studied, and it is concluded that the new eigenstates of the system are described by quasi-particles called photonic crystal polaritons, which can occur in two situations: (i) below the light line, when a resonance between exciton and non-radiative photon levels occurs (guided polaritons), (ii) above the light line, provided the exciton-photon coupling is larger than th...

  13. Coherent nanocavity structures for enhancement in internal quantum efficiency of III-nitride multiple quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Kim, T.; Liu, B.; Smith, R.; Athanasiou, M.; Gong, Y.; Wang, T., E-mail: t.wang@sheffield.ac.uk [Department of Electronic and Electrical Engineering, University of Sheffield, Mappin Street, Sheffield S1 3JD (United Kingdom)

    2014-04-21

    A “coherent” nanocavity structure has been designed on two-dimensional well-ordered InGaN/GaN nanodisk arrays with an emission wavelength in the green spectral region, leading to a massive enhancement in resonance mode in the green spectra region. By means of a cost-effective nanosphere lithography technique, we have fabricated such a structure on an InGaN/GaN multiple quantum well epiwafer and have observed the “coherent” nanocavity effect, which leads to an enhanced spontaneous emission (SE) rate. The enhanced SE rate has been confirmed by time resolved photoluminescence measurements. Due to the coherent nanocavity effect, we have achieved a massive improvement in internal quantum efficiency with a factor of 88, compared with the as-grown sample, which could be significant to bridge the “green gap” in solid-state lighting.

  14. Evaluation of electron mobility in InSb quantum wells by means of percentage-impact

    Energy Technology Data Exchange (ETDEWEB)

    Mishima, T. D.; Edirisooriya, M.; Santos, M. B. [Homer L. Dodge Department of Physics and Astronomy, and Center for Semiconductor Physics in Nanostructure, University of Oklahoma, 440 W. Brooks St., Norman, OK 73019 (United States)

    2014-05-15

    In order to quantitatively analyze the contribution of each scattering factor toward the total carrier mobility, we use a new convenient figure-of-merit, named a percentage impact. The mobility limit due to a scattering factor, which is widely used to summarize a scattering analysis, has its own advantage. However, a mobility limit is not quite appropriate for the above purpose. A comprehensive understanding of the difference in contribution among many scattering factors toward the total carrier mobility can be obtained by evaluating percentage impacts of scattering factors, which can be straightforwardly calculated from their mobility limits and the total mobility. Our percentage impact analysis shows that threading dislocation is one of the dominant scattering factors for the electron transport in InSb quantum wells at room temperature.

  15. Photoluminescence and electroluminescence from Ge/strained GeSn/Ge quantum wells

    Science.gov (United States)

    Lin, Chung-Yi; Huang, Chih-Hsiung; Huang, Shih-Hsien; Chang, Chih-Chiang; Liu, C. W.; Huang, Yi-Chiau; Chung, Hua; Chang, Chorng-Ping

    2016-08-01

    Ge/strained GeSn/Ge quantum wells are grown on a 300 mm Si substrate by chemical vapor deposition. The direct bandgap emission from strained GeSn is observed in the photoluminescence spectra and is enhanced by Al2O3/SiO2 passivation due to the field effect. The electroluminescence of the direct bandgap emission of strained GeSn is also observed from the Ni/Al2O3/GeSn metal-insulator-semiconductor tunneling diodes. Electroluminescence is a good indicator of GeSn material quality, since defects in GeSn layers degrade the electroluminescence intensity significantly. At the accumulation bias, the holes in the Ni gate electrode tunnel to the strained n-type GeSn layer through the ultrathin Al2O3 and recombine radiatively with electrons. The emission wavelength of photoluminescence and electroluminescence can be tuned by the Sn content.

  16. Pseudomorphic GeSn/Ge(001) quantum wells: Examining indirect band gap bowing

    Energy Technology Data Exchange (ETDEWEB)

    Tonkikh, Alexander A. [Max Planck Institute of Microstructure Physics, Weinberg 2 D-06120, Halle (Saale) (Germany); Institute for Physics of Microstructures RAS, GSP-105, Nizhniy Novgorod (Russian Federation); Eisenschmidt, Christian; Schmidt, Georg [Institute of Physics, Martin Luther University Halle-Wittenberg, Von-Danckelmann-Platz 3 D-01620, Halle (Saale) (Germany); Talalaev, Vadim G. [Max Planck Institute of Microstructure Physics, Weinberg 2 D-06120, Halle (Saale) (Germany); ZIK SiLi-Nano, Martin Luther University Halle-Wittenberg, Karl-Freiherr-von-Fritsch-Str. 3 D-06120, Halle (Saale) (Germany); Zakharov, Nikolay D.; Werner, Peter [Max Planck Institute of Microstructure Physics, Weinberg 2 D-06120, Halle (Saale) (Germany); Schilling, Joerg [ZIK SiLi-Nano, Martin Luther University Halle-Wittenberg, Karl-Freiherr-von-Fritsch-Str. 3 D-06120, Halle (Saale) (Germany)

    2013-07-15

    A study of the bandgap character of compressively strained GeSn{sub 0.060-0.091}/Ge(001) quantum wells grown by molecular beam epitaxy is reported. The built-in strain in GeSn wells leads to an increased separation between L and {Gamma} conduction band minima. The prevalent indirect interband transitions in GeSn were probed by photoluminescence spectroscopy. As a result we could simulate the L-valley bowing parameter in GeSn alloys, b{sub L} = 0.80 {+-} 0.06 eV at 10 K. From this we conclude that even compressively strained GeSn/Ge(001) alloys could become direct band gap semiconductors at the Sn-fraction higher than 17.0 at. %.

  17. Nonlinear optics response of semiconductor quantum wells under high magnetic fields

    Energy Technology Data Exchange (ETDEWEB)

    Chemla, D.S.

    1993-07-01

    Recent investigations on the nonlinear optical response of semiconductor quantum wells in a strong perpendicular magnetic field, H, are reviewed. After some introductory material the evolution of the linear optical properties of GaAs QW`s as a function of H is discussed; an examination is made of how the magneto-excitons (MX) extrapolate continuously between quasi-2D QW excitons (X) when H = 0, and pairs of Landau levels (LL) when H {yields} {infinity}. Next, femtosecond time resolved investigations of their nonlinear optical response are presented; the evolution of MX-MX interactions with increasing H is stressed. Finally, how, as the dimensionality is reduced by application of H, the number of scattering channels is limited and relaxation of electron-hole pairs is affected. How nonlinear optical spectroscopy can be exploited to access the relaxation of angular momentum within magneto-excitons is also discussed.

  18. Optical properties of GaInNAs/GaAs quantum well structures

    Energy Technology Data Exchange (ETDEWEB)

    Zhao, Q.X. [Physical Electronics and Photonics, Department of Physics, Goeteborg University, S-412 96 Goeteborg (Sweden)]. E-mail: zhao@fy.chalmers.se; Willander, M. [Physical Electronics and Photonics, Department of Physics, Goeteborg University, S-412 96 Goeteborg (Sweden); Wang, S.M. [Photonics Laboratory, Department of Microtechnology and Nanoscience, Chalmers University of Technology, S-412 96 Goeteborg (Sweden); Wei, Y.Q. [Photonics Laboratory, Department of Microtechnology and Nanoscience, Chalmers University of Technology, S-412 96 Goeteborg (Sweden); Gu, Q.F. [Photonics Laboratory, Department of Microtechnology and Nanoscience, Chalmers University of Technology, S-412 96 Goeteborg (Sweden); Sadeghi, M. [Photonics Laboratory, Department of Microtechnology and Nanoscience, Chalmers University of Technology, S-412 96 Goeteborg (Sweden); Larsson, A. [Photonics Laboratory, Department of Microtechnology and Nanoscience, Chalmers University of Technology, S-412 96 Goeteborg (Sweden)

    2007-03-26

    The radiative recombination in GaInNAs/GaAs quantum well structures was investigated by low temperature optical spectroscopy. In the temperature region, below 100 K, we found that the observed transition energies strongly depend on the excitation intensity and the temperature, which is indicative of carrier localization. The degree of carrier localization depends on the In-concentration but is not significantly influenced by the N-concentration when the N-concentration exceeds 1.6%. Photoluminescence studies indicate that the degree of the carrier localization decreases with increasing In-concentration at a constant N-concentration. In addition, the experimental results show that carrier localization is strongly correlated to deep level emission. Through post-growth thermal treatment at 650 deg. C both carrier localization and deep level emission can be eliminated.

  19. Intersubband energies in strain-compensated InGaN/AlInN quantum well structures

    Energy Technology Data Exchange (ETDEWEB)

    Park, Seoung-Hwan, E-mail: shpark@cu.ac.kr [Department of Electronics Engineering, Catholic University of Daegu, Hayang, Kyeongsan, Kyeongbuk, 712-702 (Korea, Republic of); Ahn, Doyeol [Institute of Quantum Information Processing and Systems, University of Seoul, 90 Jeonnong, Tongdaimoon-Gu, Seoul, Korea 130-743 (Korea, Republic of)

    2016-01-15

    Intersubband transition energies in the conduction band for strain-compensated InGaN/AlInN quantum well (QW) structures were investigated as a function of strain based on an effective mass theory with the nonparabolicity taken into account. In the case of an InGaN/AlInN QW structure lattice-matched to GaN, the wavelength is shown to be longer than 1.55 μm. On the other hand, strain-compensated QW structures show that the wavelength of 1.55 μm can be reached even for the QW structure with a relatively small strain of 0.3 %. Hence, the strain-compensated QW structures can be used for telecommunication applications at 1.55 μm with a small strain, compared to conventional GaN/AlN QW structure.

  20. Voltage tunable multiple quantum well distributed feedback filter with an electron beam written Schottky grating

    Science.gov (United States)

    Zia, O.; Bhattacharya, P. K.; Singh, J.; Brock, T.

    1994-08-01

    A novel optoelectronic filter voltage-tunable characteristics has been developed and implemented in a multiquantum well waveguide device. By virtue of the quantum-confined Stark effect, the refractive index in quantum wells at the periphery of a guiding region can be given a periodicity in the guiding direction by application of a bias on an electron-beam patterned Schottky grating atop the guide. If the period of the Schottky grating and associated index profile satisfies the Bragg condition, as in a resonant distributed feedback structure, band-reject filtering results. Aftering the bias on the Schottky grating changes the refractive index in the wells, thereby providing tunability of the wavelength at which Bragg diffraction occurs.