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
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.
Quantum well nonlinear microcavities
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.
Quantum-Well Thermophotovoltaic Cells
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.
Quantum Wells in Photovoltaic Cells
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).
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.
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.
Excitons in asymmetric quantum wells
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.
Silicon Germanium Quantum Well Solar Cell Project
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...
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
Spin photocurrents in quantum wells
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...
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.
Pyroelectric Quantum Well Energy Harvesters Project
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...
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.
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.
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.
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...
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.
Quantum Well Infrared Photodetectors Physics and Applications
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.
Photonic crystal slab quantum well infrared photodetector
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.
Recombination Dynamics in Quantum Well Semiconductor Structures
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
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...
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.
Strained quantum well photovoltaic energy converter
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.
Entangled States and the Gravitational Quantum Well
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.
Photoemission of switchable mirrors and quantum wells
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 ...
Raman spectroscopy of single quantum well wires
Institute of Scientific and Technical Information of China (English)
无
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.
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.
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
Physics of strained quantum well lasers
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...
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.
The Physics of Quantum Well Infrared Photodetectors
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
Terahertz detection using double quantum well devices
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.
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.
Electronic Quantum Confinement in Cylindrical Potential Well
Baltenkov, A S
2016-01-01
The effects of quantum confinement on the momentum distribution of electrons confined within a cylindrical potential well have been analyzed. The motivation is to understand specific features of the momentum distribution of electrons when the electron behavior is completely controlled by the parameters of a non-isotropic potential cavity. It is shown that studying the solutions of the wave equation for an electron confined in a cylindrical potential well offers the possibility to analyze the confinement behavior of an electron executing one- or two-dimensional motion in the three-dimensional space within the framework of the same mathematical model. Some low-lying electronic states with different symmetries have been considered and the corresponding wave functions have been calculated; the behavior of their nodes and their peak positions with respect to the parameters of the cylindrical well has been analyzed. Additionally, the momentum distributions of electrons in these states have been calculated. The limi...
Quantum wells for high-efficiency photovoltaics
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.
Quantum well intermixing for photonic integrated circuits
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
Bandedge-engineered quantum well laser
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.
The quantum spectra analysis of the circular billiards in wells
Institute of Scientific and Technical Information of China (English)
Zhang Yan-Hui; Zhang Li-Qin; Xu Xue-You; Ge Mei-Hua; Lin Sheng-Lu; Du Meng-Li
2006-01-01
We use a recently defined quantum spectral function and apply the method of closed-orbit theory to the 2D circular billiard system. The quantum spectra contain rich information of all classical orbits connecting two arbitrary points in the well. We study the correspondence between quantum spectra and classical orbits in the circular, 1/2 circular and 1/4 circular wells using the analytic and numerical methods. We find that the peak positions in the Fourier-transformed quantum spectra match accurately with the lengths of the classical orbits. These examples show evidently that semi-classical method provides a bridge between quantum and classical mechanics.
Energy level spectroscopy of InSb quantum wells using quantum-well LED emission
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.
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...
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.
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.
Development of an infrared detector: Quantum well infrared photodetector
Institute of Scientific and Technical Information of China (English)
无
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.
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.
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.
Photoluminescence from narrow InAs-AlSb quantum wells
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.
Multichannel scattering of charge carriers on quantum well heterostructures
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
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.
Fisher information and quantum potential well model for finance
Energy Technology Data Exchange (ETDEWEB)
Nastasiuk, V.A., E-mail: nasa@i.ua
2015-09-25
The probability distribution function (PDF) for prices on financial markets is derived by extremization of Fisher information. It is shown how on that basis the quantum-like description for financial markets arises and different financial market models are mapped by quantum mechanical ones. - Highlights: • The financial Schrödinger equation is derived using the principle of minimum Fisher information. • Statistical models for price variation are mapped by the quantum models of coupled particle. • The model of quantum particle in parabolic potential well corresponds to Efficient market.
Minimal length uncertainty relation and gravitational quantum well
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
Students' Conceptual Difficulties in Quantum Mechanics: Potential Well Problems
Ozcan, Ozgur; Didis, Nilufer; Tasar, Mehmet Fatih
2009-01-01
In this study, students' conceptual difficulties about some basic concepts in quantum mechanics like one-dimensional potential well problems and probability density of tunneling particles were identified. For this aim, a multiple choice instrument named Quantum Mechanics Conceptual Test has been developed by one of the researchers of this study…
Students' Conceptual Difficulties in Quantum Mechanics: Potential Well Problems
Ozcan, Ozgur; Didis, Nilufer; Tasar, Mehmet Fatih
2009-01-01
In this study, students' conceptual difficulties about some basic concepts in quantum mechanics like one-dimensional potential well problems and probability density of tunneling particles were identified. For this aim, a multiple choice instrument named Quantum Mechanics Conceptual Test has been developed by one of the researchers of this study…
Piezo-Phototronic Effect in a Quantum Well Structure.
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.
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.
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.
Performance evaluation of quantum well infrared phototransistor instrumentation through modeling
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.
Dot-in-Well Quantum-Dot Infrared Photodetectors
Gunapala, Sarath; Bandara, Sumith; Ting, David; Hill, cory; Liu, John; Mumolo, Jason; Chang, Yia Chung
2008-01-01
Dot-in-well (DWELL) quantum-dot infrared photodetectors (QDIPs) [DWELL-QDIPs] are subjects of research as potentially superior alternatives to prior QDIPs. Heretofore, there has not existed a reliable method for fabricating quantum dots (QDs) having precise, repeatable dimensions. This lack has constituted an obstacle to the development of uniform, high-performance, wavelength-tailorable QDIPs and of focal-plane arrays (FPAs) of such QDIPs. However, techniques for fabricating quantum-well infrared photodetectors (QWIPs) having multiple-quantum- well (MQW) structures are now well established. In the present research on DWELL-QDIPs, the arts of fabrication of QDs and QWIPs are combined with a view toward overcoming the deficiencies of prior QDIPs. The longer-term goal is to develop focal-plane arrays of radiationhard, highly uniform arrays of QDIPs that would exhibit high performance at wavelengths from 8 to 15 m when operated at temperatures between 150 and 200 K. Increasing quantum efficiency is the key to the development of competitive QDIP-based FPAs. Quantum efficiency can be increased by increasing the density of QDs and by enhancing infrared absorption in QD-containing material. QDIPs demonstrated thus far have consisted, variously, of InAs islands on GaAs or InAs islands in InGaAs/GaAs wells. These QDIPs have exhibited low quantum efficiencies because the numbers of QD layers (and, hence, the areal densities of QDs) have been small typically five layers in each QDIP. The number of QD layers in such a device must be thus limited to prevent the aggregation of strain in the InAs/InGaAs/GaAs non-lattice- matched material system. The approach being followed in the DWELL-QDIP research is to embed In- GaAs QDs in GaAs/AlGaAs multi-quantum- well (MQW) structures (see figure). This material system can accommodate a large number of QD layers without excessive lattice-mismatch strain and the associated degradation of photodetection properties. Hence, this material
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.
Crystal Phase Quantum Well Emission with Digital Control.
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.
Quantum well electronic states in a tilted magnetic field
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.
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.
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...
Microscopic Theory and Simulation of Quantum-Well Intersubband Absorption
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
GaSbBi/GaSb quantum well laser diodes
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.
Detection of electromagnetic radiation using micromechanical multiple quantum wells structures
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.
Superradiant modes in Fibonacci quantum wells under resonant conditions
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.
Neutron quantum well states in Fe/Co/Fe trilayers
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.
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.
Spatial Light Modulators with Arbitrary Quantum Wells Profiles
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
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...
Multiple Quantum Wells for P T -Symmetric Phononic Crystals
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.
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 ...
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...
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...
Design and Analysis of a Quantum Well Light Emitting Triode.
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.
Quantum anomalous Hall effect in magnetically doped InAs/GaSb quantum wells.
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.
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.}
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.
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.
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.
High signal-to-noise ratio quantum well bolometer materials
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).
A real-time spectrum acquisition system design based on quantum dots-quantum well detector
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.
Characteristics of surface plasmon coupled quantum well infrared photodetectors
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.
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.
Development of high power quantum well lasers at RRCAT
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.
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.
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.)
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....
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.
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.
SWKB Quantization Rules for Bound States in Quantum Wells
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.
Hole transport simulations in SiGe cascade quantum wells
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.
Photonic integrated circuits based on quantum well intermixing techniques
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...
Optical Detection Properties of Silicon-Germanium Quantum Well Structures
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
Voltage controlled terahertz transmission through GaN quantum wells
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 ...
Photonic Integrated Circuits Based on Quantum well Intermixing Techniques
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...
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.
Symbolic Solution for Generalized Quantum Cylindrical Wells using Computer Algebra
Villegas, Edward Yesid
2012-01-01
This paper present how to solve the problem of cylindrical quantum wells with potential energy different from zero and with singularity of the energy on the axis of the cylinder. The solution to the problem was obtained using methods of computer algebra. The results depend of Bessel and Kummer functions. This paper present energy levels and wave functions in some of the cases with an exactly form and in other cases with an approximated form, this form depended on the possibility of integrating the special functions and calculating the zeros of these functions. Here we can see the power of the method in the applications concerning complex problems of quantum mechanics, and the possibility of being able to apply this method in order to solve other problems in science and also in engineering.
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....
Multi-Well Potentials in Quantum Mechanics and Stochastic Processes
Directory of Open Access Journals (Sweden)
Victor P. Berezovoj
2010-12-01
Full Text Available Using the formalism of extended N=4 supersymmetric quantum mechanics we consider the procedure of the construction of multi-well potentials. We demonstrate the form-invariance of Hamiltonians entering the supermultiplet, using the presented relation for integrals, which contain fundamental solutions. The possibility of partial N=4 supersymmetry breaking is determined. We also obtain exact forms of multi-well potentials, both symmetric and asymmetric, using the Hamiltonian of harmonic oscillator as initial. The modification of the shape of potentials due to variation of parameters is also discussed, as well as application of the obtained results to the study of tunneling processes. We consider the case of exact, as well as partially broken N=4 supersymmetry. The distinctive feature of obtained probability densities and potentials is a parametric freedom, which allows to substantially modify their shape. We obtain the expressions for probability densities under the generalization of the Ornstein-Uhlenbeck process.
Optical spectroscopy of GaAs/AlGaAs V-groove quantum wires Quantum wells
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 ...
Theoretical Studies of the Optoelectronic Properties of Semiconductor Quantum Wells.
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.
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.
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.
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....
Strong photoluminescence emission from resonant Fibonacci quantum wells.
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.
Relative Intensity Noise in the Single Quantum Well Diode
Institute of Scientific and Technical Information of China (English)
无
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.
Reliability assessment of multiple quantum well avalanche photodiodes
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.
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.
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.
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.
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.
Ground- and excited-state impurity bands in quantum wells
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.
Highly efficient metallic optical incouplers for quantum well infrared photodetectors
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
Highly efficient metallic optical incouplers for quantum well infrared photodetectors
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.
Optimized photonic crystal design for quantum well infrared photodetectors
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.
Bose condensation of interwell excitons in double quantum wells
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...
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.
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.
Polarization converters on double hetero structures containing strained quantum wells
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.
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.
Quantum Algorithms for Some Well-Known NP Problems
Institute of Scientific and Technical Information of China (English)
GUO Hao; LONG Gui-Lu; LI Feng
2002-01-01
It is known that quantum computer is more powerful than classical computer.In this paper we present quantum algorithms for some famous NP problems in graph theory and combination theory,these quantum algorithms are at least quadratically faster than the classical ones.
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.
Multiple quantum wells for passive ultra short laser pulse generation
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.
Indirect excitons in (111) GaAs double quantum wells
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.
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.
Integrated photonic crystals and quantum well infrared photodetector
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.
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.
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.
Probing light emission from quantum wells within a single nanorod
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.
DEFF Research Database (Denmark)
Xu, Zhangcheng; Jia, G.Z.; Sun, L.
2005-01-01
Time-resolved photoluminescence (PL) of sub-monolayer (SML) InGaAs/GaAs quantum-dot-quantum-well heterostructures was measured at 5 K for the first time. The radiative lifetime of SML quantum dots (QDs) increases from 500 ps to 800 ps with the increase of the size of QDs, which is related...
Leon, R.; Swift, G. M.; Magness, B.; Taylor, W. A.; Tang, Y. S.; Wang, K. L.; Dowd, P.; Zhang, Y. H.
2000-01-01
The photoluminescence emission from InGaAs/GaAs quantum-well and quantum-dot (QD) structures are compared after controlled irradiation with 1.5 MeV proton fluxes. Results presented here show a significant enhancement in radiation tolerance with three-dimensional quantum confinement.
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.
Ultrafast dynamics in InAs quantum dot and GaInNAs quantum well semiconductor heterostructures
Malins, David B
2007-01-01
The quantum confined Stark effect (QCSE) and ultrafast absorption dynamics near the bandedge have been investigated in p-i-n waveguides comprising quantum confined heterostructures grown on GaAs substrates, for emission at 1.3um. The materials are; isolated InAs/InGaAs dot-in-a-well (DWELL) quantum dots (QD), bilayer InAs quantum dots and GaInNAs multiple quantum wells (MQW). The focus was to investigate these dynamics in a planar waveguide geometry, for the purpose of large scale integ...
Quantum theory of exciton-photon coupling in photonic crystal slabs with embedded quantum wells
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...
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.
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.
Intermixing effects on emission properties of InGaN/GaN coupled Quantum wells
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.
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
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.
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.
Quantum Confinement Effects in Strained SiGe/Si Multiple Quantum Wells
Institute of Scientific and Technical Information of China (English)
无
2000-01-01
Strained SiGe/Si multiple quantum wells (MQWs) were grown by cold-wall ultrahigh vacuum chemical vapor deposition (UHV/CVD). Photoluminescence measurement was performed to study the exciton energies of strained Si0.84 Ge0.16/Si MQWs with SiGe well widths ranging from 4.2nm to 25.4nm. The confinement energy of 43meV is found in the Si0.84Ge0.16/Si MQWs with well width of 4.2nm. The confinement energy was calculated by solving the problem of a particle confined in a single finite rectangular poteintial well using one band effect mass model. Experimental and theoretical confinement energies are in good agreement
Quantum spin Hall effect in α -Sn /CdTe(001 ) quantum-well structures
Küfner, Sebastian; Matthes, Lars; Bechstedt, Friedhelm
2016-01-01
The electronic and topological properties of heterovalent and heterocrystalline α -Sn/CdTe(001) quantum wells (QWs) are studied in dependence on the thickness of α -Sn by means of ab initio calculations. We calculate the topological Z2 invariants of the respective bulk crystals, which identify α -Sn as strong three-dimensional (3D) topological insulators (TIs), whereas CdTe is a trivial insulator. We predict the existence of two-dimensional (2D) topological interface states between both materials and show that a topological phase transition from a trivial insulating phase into the quantum spin Hall (QSH) phase in the QW structures occurs at much higher thicknesses than in the HgTe case. The QSH effect is characterized by the localization, dispersion, and spin polarization of the topological interface states. We address the distinction of the 3D and 2D TI characters of the studied QW structures, which is inevitable for an understanding of the underlying quantum state of matter. The 3D TI nature is characterized by two-dimensional topological interface states, while the 2D phase exhibits one-dimensional edge states. The two different state characteristics are often intermixed in the discussion of the topology of 2D QW structures, especially, the comparison of ab initio calculations and experimental transport studies.
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.
High Efficiency Quantum Well Waveguide Solar Cells Project
National Aeronautics and Space Administration — The long-term objective of this program is to develop flexible, lightweight, single-junction solar cells using quantum structured designs that can achieve ultra-high...
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....
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.
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.
Wang, Z H; Zheng, Q; Wang, Xiaoguang; Li, Yong
2016-03-02
We study the energy-level crossing behavior in a two-dimensional quantum well with the Rashba and Dresselhaus spin-orbit couplings (SOCs). By mapping the SOC Hamiltonian onto an anisotropic Rabi model, we obtain the approximate ground state and its quantum Fisher information (QFI) via performing a unitary transformation. We find that the energy-level crossing can occur in the quantum well system within the available parameters rather than in cavity and circuit quantum eletrodynamics systems. Furthermore, the influence of two kinds of SOCs on the QFI is investigated and an intuitive explanation from the viewpoint of the stationary perturbation theory is given.
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.
Energy Technology Data Exchange (ETDEWEB)
Prasankumar, Rohit P [Los Alamos National Laboratory; Taylor, Antoinette J [Los Alamos National Laboratory
2009-01-01
Ultrafast density-dependent optical spectroscopic measurements on a quantum dots-in-a-well heterostructure reveal several distinctive phenomena, most notably a strong coupling between the quantum well population and light absorption at the quantum dot excited state.
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).
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...
Transversal confined polar optical phonons in spherical quantum-dot/quantum-well nanostructures
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.
Silicon quantum wires on Ag(1 1 0): Fermi surface and quantum well states
Energy Technology Data Exchange (ETDEWEB)
Valbuena, M.A. [Instituto de Ciencia de Materiales de Madrid, Consejo Superior de Investigaciones Cientificas (CSIC), C/ Sor Juana Ines de la Cruz, 3, 28049 Madrid (Spain); Avila, J. [Synchrotron SOLEIL, Orme des Merisiers, Saint Aubin BP 48, 91192 Gif sur Yvette Cedex (France)], E-mail: jose.avila@synchrotron-soleil.fr; Davila, M.E. [Instituto de Ciencia de Materiales de Madrid, Consejo Superior de Investigaciones Cientificas (CSIC), C/ Sor Juana Ines de la Cruz, 3, 28049 Madrid (Spain); Leandri, C.; Aufray, B.; Le Lay, G. [CRMCN-CNRS, Campus de Luminy, Case 913, 13288 Marseille Cedex 9 (France); Asensio, M.C. [Synchrotron SOLEIL, Orme des Merisiers, Saint Aubin BP 48, 91192 Gif sur Yvette Cedex (France)
2007-10-31
One-dimensional Si quantum wires have been grown on silver single crystals upon deposition of {approx}0.25 monolayer of Si on Ag(1 1 0) surfaces. Scanning tunneling microscopy (STM) clearly shows parallel 1D Si chains along the [-1 1 0] Ag crystallographic direction. Low Energy Electron Diffraction (LEED) confirms the massively parallel assembly of these selforganized Nanowires (NWs). We have characterized these nano-objects by measuring the dispersion of the NWs valence band at room temperature using Angle-Resolved PhotoEmission Spectroscopy (ARPES). Also, the Fermi Surface (FS) of the Ag(1 1 0) substrate has been mapped before and after the silicon deposition, trying to put in evidence the metallic or semiconductor character of the NWs silicon's states close to the Fermi level. Our results show the existence of well-defined quantum states associated to the silicon super-structure. Both LEED and ARUPS results confirm that the NWs have typical 1D features, however their metallic or semiconductor character could not be confirmed.
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.
Electrode-induced In-plane Strain Variation in Si Quantum Well
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.
Higgins, L J; Karanikolas, V D; Marocico, C A; Bell, A P; Sadler, T C; Parbrook, P J; Bradley, A L
2015-01-26
An array of Ag nanoboxes fabricated by helium-ion lithography is used to demonstrate plasmon-enhanced nonradiative energy transfer in a hybrid quantum well-quantum dot structure. The nonradiative energy transfer, from an InGaN/GaN quantum well to CdSe/ZnS nanocrystal quantum dots embedded in an ~80 nm layer of PMMA, is investigated over a range of carrier densities within the quantum well. The plasmon-enhanced energy transfer efficiency is found to be independent of the carrier density, with an efficiency of 25% reported. The dependence on carrier density is observed to be the same as for conventional nonradiative energy transfer. The plasmon-coupled energy transfer enhances the QD emission by 58%. However, due to photoluminescence quenching effects an overall increase in the QD emission of 16% is observed.
Internal quantum efficiency enhancement of GaInN/GaN quantum-well structures using Ag nanoparticles
Energy Technology Data Exchange (ETDEWEB)
Iida, Daisuke [Department of Applied Physics, Tokyo University of Science, Katsushika, 125-8585 Tokyo (Japan); Department of Photonics Engineering, Technical University of Denmark, 2800 Lyngby (Denmark); Faculty of Science and Technology, Meijo University, 1-501 Shiogamaguchi Tempaku, 468-8502 Nagoya (Japan); Fadil, Ahmed, E-mail: afad@fotonik.dtu.dk; Ou, Yiyu; Kopylov, Oleksii; Ou, Haiyan [Department of Photonics Engineering, Technical University of Denmark, 2800 Lyngby (Denmark); Chen, Yuntian, E-mail: yuntian@hust.edu.cn [Department of Photonics Engineering, Technical University of Denmark, 2800 Lyngby (Denmark); School of Optical and Electronic Information, Huazhong University of Science and Technology, 430074 Wuhan (China); Iwaya, Motoaki; Takeuchi, Tetsuya; Kamiyama, Satoshi [Faculty of Science and Technology, Meijo University, 1-501 Shiogamaguchi Tempaku, 468-8502 Nagoya (Japan); Akasaki, Isamu [Faculty of Science and Technology, Meijo University, 1-501 Shiogamaguchi Tempaku, 468-8502 Nagoya (Japan); Akasaki Research Center, Nagoya University, Furo-cho Chikusa, 464-8603 Nagoya (Japan)
2015-09-15
We report internal quantum efficiency enhancement of thin p-GaN green quantum-well structure using self-assembled Ag nanoparticles. Temperature dependent photoluminescence measurements are conducted to determine the internal quantum efficiency. The impact of excitation power density on the enhancement factor is investigated. We obtain an internal quantum efficiency enhancement by a factor of 2.3 at 756 W/cm{sup 2}, and a factor of 8.1 at 1 W/cm{sup 2}. A Purcell enhancement up to a factor of 26 is estimated by fitting the experimental results to a theoretical model for the efficiency enhancement factor.
Internal quantum efficiency enhancement of GaInN/GaN quantum-well structures using Ag nanoparticles
Directory of Open Access Journals (Sweden)
Daisuke Iida
2015-09-01
Full Text Available We report internal quantum efficiency enhancement of thin p-GaN green quantum-well structure using self-assembled Ag nanoparticles. Temperature dependent photoluminescence measurements are conducted to determine the internal quantum efficiency. The impact of excitation power density on the enhancement factor is investigated. We obtain an internal quantum efficiency enhancement by a factor of 2.3 at 756 W/cm2, and a factor of 8.1 at 1 W/cm2. A Purcell enhancement up to a factor of 26 is estimated by fitting the experimental results to a theoretical model for the efficiency enhancement factor.
Bandgap Engineering of 1300 nm Quantum Dots/Quantum Well Nanostructures Based Devices
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
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.
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.
Optical Absorption, Emission, and Modulation in Iii-V Semiconductor Quantum Well Structures
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
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...
The Double-Well Potential in Quantum Mechanics: A Simple, Numerically Exact Formulation
Jelic, V.; Marsiglio, F.
2012-01-01
The double-well potential is arguably one of the most important potentials in quantum mechanics, because the solution contains the notion of a state as a linear superposition of "classical" states, a concept which has become very important in quantum information theory. It is therefore desirable to have solutions to simple double-well potentials…
The Double-Well Potential in Quantum Mechanics: A Simple, Numerically Exact Formulation
Jelic, V.; Marsiglio, F.
2012-01-01
The double-well potential is arguably one of the most important potentials in quantum mechanics, because the solution contains the notion of a state as a linear superposition of "classical" states, a concept which has become very important in quantum information theory. It is therefore desirable to have solutions to simple double-well potentials…
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...
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.
Role of spatial dispersion of electromagnetic wave at its transmission through quantum well
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
Observation of a fractional quantum Hall state at v=1/4 in a wide GaAs quantum well.
Energy Technology Data Exchange (ETDEWEB)
Pan, Wei; Tsui, Daniel Chee (Princeton University, Princeton, NJ); Baldwin, K. W. (Bell Labs, Lucent Technologies, Murray Hill, NJ); West, Ken W. (Bell Labs, Lucent Technologies, Murray Hill, NJ); Pfeiffer, Loren N.; Luhman, D. R. (Princeton University, Princeton, NJ)
2008-10-01
We report the observation of an even-denominator fractional quantum Hall state at {nu}=1/4 in a high quality, wide GaAs quantum well. The sample has a quantum well width of 50 nm and an electron density of n{sub e}=2.55 x 10{sup 11} cm{sup -2}. We have performed transport measurements at T{approx}35 mK in magnetic fields up to 45 T. When the sample is perpendicular to the applied magnetic field, the diagonal resistance displays a kink at {nu}=1/4. Upon tilting the sample to an angle of {theta}=20.3{sup o} a clear fractional quantum Hall state emerges at {nu}=1/4 with a plateau in the Hall resistance and a strong minimum in the diagonal resistance.
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%.
Microwave spectroscopic observation of distinct electron solid phases in wide quantum wells.
Hatke, A T; Liu, Yang; Magill, B A; Moon, B H; Engel, L W; Shayegan, M; Pfeiffer, L N; West, K W; Baldwin, K W
2014-06-20
In high magnetic fields, two-dimensional electron systems can form a number of phases in which interelectron repulsion plays the central role, since the kinetic energy is frozen out by Landau quantization. These phases include the well-known liquids of the fractional quantum Hall effect, as well as solid phases with broken spatial symmetry and crystalline order. Solids can occur at the low Landau-filling termination of the fractional quantum Hall effect series but also within integer quantum Hall effects. Here we present microwave spectroscopy studies of wide quantum wells that clearly reveal two distinct solid phases, hidden within what in d.c. transport would be the zero diagonal conductivity of an integer quantum-Hall-effect state. Explanation of these solids is not possible with the simple picture of a Wigner solid of ordinary (quasi) electrons or holes.
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.
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.
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...
Murphy, Graham P; Higgins, Luke J; Karanikolas, Vasilios D; Wilson, Keith M; Coindreau, Jorge A Garcia; Zubialevich, Vitaly Z; Parbrook, Peter J; Bradley, A Louise
2016-01-01
Ag nanoparticles in the form of colloids and ordered arrays are used to demonstrate plasmon-mediated non-radiative energy transfer from quantum dots to quantum wells with varying top barrier thicknesses. Plasmon-mediated energy transfer efficiencies of up to ~25% are observed with the Ag colloids. The distance dependence of the plasmon-mediated energy transfer is found to follow the same d^{-4} dependence as the direct quantum dot to quantum well energy transfer. There is also evidence for an increase in the characteristic distance of the interaction, thus indicating that it follows a F\\"orster-like model with the Ag nanoparticle-quantum dot acting as an enhanced donor dipole. Ordered Ag nanoparticle arrays display plasmon-mediated energy transfer efficiencies up to ~21%. To explore the tunability of the array system, two arrays with different geometries are presented. It is demonstrated that changing the geometry of the array allows a transition from overall quenching of the acceptor quantum well emission to...
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.
Nonadiabatic quantum state control of many bosons in few wells
DEFF Research Database (Denmark)
Tichy, Malte C.; Kock Pedersen, Mads; Mølmer, Klaus;
2013-01-01
We present a fast scheme for arbitrary unitary control of interacting bosonic atoms in a double well. Assuming fixed interwell tunneling rate and intrawell interaction strength, we control the many-atom state by a discrete sequence of shifts of the single-well energies. For strong interactions...
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.
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.
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.
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.
A new switching characteristics of highly doped multi-quantum well
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.
Teitelboim, Ayelet; Oron, Dan
2016-09-01
Upconversion (UC) is a nonlinear process in which two, or more, long wavelength photons are converted to a shorter wavelength photon. This process is based on sequential absorption of two or more photons, involving metastable, long lived intermediate energy states, thus is not restricted to upconversion of coherent laser radiation as a non-coherent process. Hence, requirements for UC processes are long lived excited states, a ladder like arrangement of energy levels and a mechanism inhibiting cooling of the hot charge carrier. UC holds great promise for bioimaging, enabling spatially resolved imaging in a scattering specimen and for photovoltaic devices as a mean to surpass the Shockley-Queisser efficiency limit. Here, we present a novel luminescence upconversion nano-system based on colloidal semiconductor double quantum dots, consisting of a NIR-emitting component and a visible emitting component separated by a tunneling barrier in a spherical onion-like geometry. These dual near-infrared and visible emitting core/shell/shell PbSe/CdSe/CdS nanocrystals are shown to upconvert a broad range of NIR wavelengths to visible emission at room temperature, covering a spectral range where there are practically no alternative upconversion systems. The synthesis is a three-step process, which enables versatility and tunability of both the visible emission color and the NIR absorption edge. Using this method one can achieve a range of desired upconverted emission peak positions with a suitable NIR band gap. The physical mechanism for upconversion in this structure, as well as possible extensions and improvements will be discussed. 1 (1) Teitelboim, A.; Oron, D. ACS Nano 2015, acsnano.5b05329.
Simulation of a broadband nano-biosensor based on an onion-like quantum dot-quantum well structure
Energy Technology Data Exchange (ETDEWEB)
Absalan, H; SalmanOgli, A; Rostami, R
2013-07-31
The fluorescence resonance energy transfer is studied between modified quantum-dots and quantum-wells used as a donor and an acceptor. Because of the unique properties of quantum dots, including diverse surface modification flexibility, bio-compatibility, high quantum yields and wide absorption, their use as nano-biosensors and bio-markers used in diagnosis of cancer is suggested. The fluorescence resonance energy transfer is simulated in a quantum dot-quantum well system, where the energy can flow from donor to acceptor. If the energy transfer can be either turned on or off by a specific interaction, such as interaction with any dyes, a molecular binding event or a cleavage reaction, a sensor can be designed (under assumption that the healthy cells have a known effect or unyielding effect on output parameters while cancerous cells, due to their pandemic optical properties, can impact the fluorescence resonance energy transfer parameters). The developed nano-biosensor can operate in a wide range of wavelengths (310 - 760 nm). (laser applications in biology and medicine)
Stretchable Persistent Spin Helices in GaAs Quantum Wells
Dettwiler, Florian; Fu, Jiyong; Mack, Shawn; Weigele, Pirmin J.; Egues, J. Carlos; Awschalom, David D.; Zumbühl, Dominik M.
2017-07-01
the extracted spin-diffusion lengths and decay times show a significant enhancement near α =β . Since within the continuous-locking regime quantum transport is diffusive (2D) for charge while ballistic (1D) for spin and thus amenable to coherent spin control, stretchable PSHs could provide the platform for the much heralded long-distance communication ˜8 - 25 μ m between solid-state spin qubits, where the spin diffusion length for α ≠β is an order of magnitude smaller.
Stretchable Persistent Spin Helices in GaAs Quantum Wells
Directory of Open Access Journals (Sweden)
Florian Dettwiler
2017-07-01
sufficiently weak so that the extracted spin-diffusion lengths and decay times show a significant enhancement near α=β. Since within the continuous-locking regime quantum transport is diffusive (2D for charge while ballistic (1D for spin and thus amenable to coherent spin control, stretchable PSHs could provide the platform for the much heralded long-distance communication ∼8–25 μm between solid-state spin qubits, where the spin diffusion length for α≠β is an order of magnitude smaller.
High Speed Quantum-Well Optoelectronic Devices by MBE
1989-05-01
26 Aline width. Broad area contacts were deposited, and laser fabrication and testing as well as photoconductivity measurements were carried out. Our...alignment to obtain lateral current confinement. In order to simplify the laser fabrication , a possible approach is to design a structure which can employ the
Electromagnetically induced transparency due to intervalence band coherence in a GaAs quantum well.
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.
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...
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...
Experimental signatures of the inverted phase in InAs/GaSb coupled quantum wells
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.
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...
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.
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...
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...
International Workshop on "Intersubband Transitions in Quantum Wells : Physics and Applications"
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...
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.
Spontaneous Coherence Effects in Quantum Dots and Quantum Wells Placed in Microcavities
Directory of Open Access Journals (Sweden)
Kaputkina N.E.
2016-01-01
Full Text Available The Bose-Einstein condensation temperature Tc for a system of coupled quantum dots in a microcavity was estimated in function of the confining potential steepness, the external magnetic field strength, and the barrier layer width for indirect excitons. The effect of the magnetic field on Tc was found to be nonmonotonic over a certain range of the control parameters. The reason is the presence of two competing mechanisms accompanying the increase of the magnetic field: (a increase of the magnetoexciton effective mass and (b increase of the effective confining potential steepness for quantum dots.
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....
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....
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.; GONZLEZ-HERNNDEZ
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 Schrdinger 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.
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.
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.
Modeling of carrier dynamics in quantum-well electroabsorption modulators
DEFF Research Database (Denmark)
Højfeldt, Sune; Mørk, Jesper
2002-01-01
We present a comprehensive drift-diffusion-type electroabsorption modulator (EAM) model. The model allows us to investigate both steady-state properties and to follow the sweep-out of carriers after pulsed optical excitation. Furthermore, it allows for the investigation of the influence that vari......We present a comprehensive drift-diffusion-type electroabsorption modulator (EAM) model. The model allows us to investigate both steady-state properties and to follow the sweep-out of carriers after pulsed optical excitation. Furthermore, it allows for the investigation of the influence...... that various design parameters have on the device properties, in particular how they affect the carrier dynamics and the corresponding field dynamics. A number of different types of results are presented. We calculate absorption spectra and steady-state field screening due to carrier pile-up at the separate......-confinement heterobarriers. We then move on to look at carrier sweep-out upon short-pulse optical excitation. For a structure with one well, we analyze how the well position affects the carrier sweep-out and the absorption recovery. We calculate the field dynamics in a multiquantum-well structure and discuss how the changes...
DEFF Research Database (Denmark)
Lyssenko, V. G.; Østergaard, John Erland; Hvam, Jørn Märcher;
1999-01-01
Summary form only given. We focus on the ability to control the electronic coupling in coupled quantum wells with external E-fields leading to a strong modification of the coherent light emission, in particular at a bias where a superlattice-like miniband is formed. More specifically, we investig...... investigate a MBE-grown GaAs sample with a sequence of 15 single quantum wells having a successive increase of 1 monolayer in width ranging from 62 A to 102 A and with AlGaAs barriers of 17 Å....
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.
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.
Quantum information entropies for a squared tangent potential well
Energy Technology Data Exchange (ETDEWEB)
Dong, Shishan [Information and Engineering College, DaLian University, 116622 (China); Sun, Guo-Hua, E-mail: sunghdb@yahoo.com [Centro Universitario Valle de Chalco, Universidad Autónoma del Estado de México, Valle de Chalco Solidaridad, Estado de México, 56615 (Mexico); Dong, Shi-Hai, E-mail: dongsh2@yahoo.com [Departamento de Física, Escuela Superior de Física y Matemáticas, Instituto Politécnico Nacional, Unidad Profesional Adolfo López Mateos, Edificio 9, México D.F. 07738 (Mexico); Department of Physics and Astronomy, Louisiana State University, Baton Rouge, LA 70803-4001 (United States); Draayer, J.P., E-mail: draayer@sura.org [Department of Physics and Astronomy, Louisiana State University, Baton Rouge, LA 70803-4001 (United States)
2014-01-10
The particle in a symmetrical squared tangent potential well is studied by examining its Shannon information entropy and standard deviations. The position and momentum information entropy densities ρ{sub s}(x), ρ{sub s}(p) and probability densities ρ(x), ρ(p) are illustrated with different potential range L and potential depth U. We present analytical position information entropies S{sub x} for the lowest two states. We observe that the sum of position and momentum entropies S{sub x} and S{sub p} expressed by Bialynicki-Birula–Mycielski (BBM) inequality is satisfied. Some eigenstates exhibit entropy squeezing in the position. The entropy squeezing in position will be compensated by an increase in momentum entropy. We also note that the S{sub x} increases with the potential range L, while decreases with the potential depth U. The variation of S{sub p} is contrary to that of S{sub x}.
Efficient method for calculating electronic bound states in arbitrary one-dimensional quantum wells
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.
Miyoshi, Makoto; Tsutsumi, Tatsuya; Kabata, Tomoki; Mori, Takuma; Egawa, Takashi
2017-03-01
We investigated the effect of well layer thicknesses on the external quantum efficiency (EQE) and energy conversion efficiency (ECE) for InGaN/GaN multiple quantum well (MQW) solar cells grown on sapphire substrates by metalorganic chemical vapor deposition. The results indicated that EQE and ECE have maximum values at a specific well thickness. When the well thickness is sufficiently thin, EQE and ECE increase with an increase in the well thickness owing to an increase in light absorption. Then, once the well thickness surpasses a critical thickness, EQE and ECE begin to decrease owing to the influence of nonradiative recombination processes, which was indicated by the static and dynamic photoluminescence analyses. The critical well thickness probably depends not only on the MQW design but also on growth conditions. Further, we confirmed that the increased total thickness of the stacked well layers leads to increased light absorption and thereby contributes to the improvement of solar cell performance. A high short circuit current density of 1.34 mA/cm2 and a high ECE of 1.31% were achieved for a InGaN/GaN MQW solar cell with a 3.2-nm-thick InGaN well with total well thickness of 115 nm.
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...
Breakdown of the quantum Hall effect in InAs/AlSb quantum wells due to counterflowing edge channels
Wees, B.J. van; Meijer, G.I.; Kuipers, J.J.; Klapwijk, T.M.; Graaf, W. van de; Borghs, G.
1995-01-01
We investigated magnetotransport in the two-dimensional electron gas (2DEG) present in InAs/AlSb quantum wells. The filling factor Ng underneath a gate electrode was reduced relative to the bulk filling factor Nb. For Ng
Wavelength sensitive detector based on ICD in two coupled quantum wells
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.
Magneto-Gyrotropic Photogalvanic Effects in Semiconductor Quantum Wells
Ganichev, S. D.
gas a charge current, the anomalous Hall effect, can be observed. As both magnetic fields and gyrotropic mechanisms were used authors introduced the notation "magneto-gyrotropic photogalvanic effects" for this class of phenomena. The effect is observed in GaAs and InAs low dimensional structures at free-carrier absorption of terahertz radiation in a wide range of temperatures from liquid helium temperature up to room temperature. The results are well described by the phenomenological description based on the symmetry. Experimental and theoretical analysis evidences unumbiguously that the observed photocurrents are spin-dependent. Microscopic theory of this effect based on asymmetry of photoexcitation and relaxation processes are developed being in a good agreement with experimental data. Note from Publisher: This article contains the abstract only.
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.
Efficiency dip observed with InGaN-based multiple quantum well solar cells
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.
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.
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.
Institute of Scientific and Technical Information of China (English)
卞松保; 唐艳; 李桂荣; 李月霞; 杨富华; 郑厚植; 曾一平
2003-01-01
We report a new type of photonic memory cell based on a semiconductor quantum dot (QD)-quantum well (QW)hybrid structure, in which photo-generated excitons can be decomposed into separated electrons and holes, and stored in QW and QDs respectively. Storage and retrieval of photonic signals are verified by time-resolved photoluminescence experiments. A storage time in excess of 100ms has been obtained at a temperature of 10K while the switching speed reaches the order of ten megahertz.
Institute of Scientific and Technical Information of China (English)
无
2002-01-01
A complete quantum mechanical model for GaAs/AlGaAs quantum well infrared photodetectors(QWIPs) was presented. The photocurrent was investigated by the optical transition(absorption coefficient)between the ground state and the excited states due to the nonzero component of the radiation field along the sample growth direction. By studying the inter-diffusion of the Al atoms across the GaAs/AlGaAs heterointer faces, the mobility of the drift-diffusion carriers in the excited states was calculated. As a result, the measurement results of the dark current and the photocurrent spectra are explained theoretically.
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.
Yang, Di; Wang, Lai; Lv, Wen-Bin; Hao, Zhi-Biao; Luo, Yi
2015-06-01
Phosphor-free white light-emitting diodes consisting of 4 layers of InGaN/GaN quantum dots and 4 layers of quantum wells have been grown by metal organic chemical vapor deposition. A white emission was demonstrated under electrical injection by mixing the green-yellow light from quantum dots and the blue light from quantum wells. At the injection current of 5 mA, the electroluminescence peak wavelengths of quantum dots and quantum wells were 548 nm and 450 nm, respectively, resulting in the color-rendering index Ra of 62. As the injection current increased, a faster emission enhancement of quantum well and an emission blue shift of the quantum dots were observed, which led to the decrease of Ra.
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.
Multi-quantum-well nanowire heterostructures for wavelength-controlled lasers
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.
Modeling of dilute nitride cascaded quantum well solar cells for high efficiency photovoltaics
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.
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.
Morrison, C.; Casteleiro, C.; Leadley, D. R.; Myronov, M.
2016-09-01
The complex quantum transport of a strained Ge quantum well (QW) modulation doped heterostructure with two types of mobile carriers has been observed. The two dimensional hole gas (2DHG) in the Ge QW exhibits an exceptionally high mobility of 780 000 cm2/Vs at temperatures below 10 K. Through analysis of Shubnikov de-Haas oscillations in the magnetoresistance of this 2DHG below 2 K, the hole effective mass is found to be 0.065 m0. Anomalous conductance peaks are observed at higher fields which deviate from standard Shubnikov de-Haas and quantum Hall effect behaviour due to conduction via multiple carrier types. Despite this complex behaviour, analysis using a transport model with two conductive channels explains this behaviour and allows key physical parameters such as the carrier effective mass, transport, and quantum lifetimes and conductivity of the electrically active layers to be extracted. This finding is important for electronic device applications, since inclusion of highly doped interlayers which are electrically active, for enhancement of, for example, room temperature carrier mobility, does not prevent analysis of quantum transport in a QW.
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.
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.
Temperature-driven single-valley Dirac fermions in HgTe quantum wells
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.
Asymmetric double quantum well structure as a tunable detector in the far-infrared range
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.
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.
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.
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.
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…
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.
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)
InGaAs Quantum Well Grown on High-Index Surfaces for Superluminescent Diode Applications.
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.
Controlling the Spontaneous Emission Rate of Quantum Wells in Rolled-Up Hyperbolic Metamaterials.
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.
The effects of strain on indirect absorption in Ge/SiGe quantum wells
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.
Controlling the Spontaneous Emission Rate of Quantum Wells in Rolled-Up Hyperbolic Metamaterials
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.
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.
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.
Generation of acoustic terahertz waves in hybrid InGaN/GaN quantum wells
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.
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.
Impurity-free quantum well intermixing for large optical cavity high-power laser diode structures
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.
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....
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....
Nonlinear photonic diode behavior in energy-graded core-shell quantum well semiconductor rod.
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.
Pseudo-square AlGaN/GaN quantum wells for terahertz absorption
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.
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.
Formulation of a self-consistent model for quantum well pin solar cells
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.
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.
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.
The robustness of the quantum spin Hall effect to the thickness fluctuation in HgTe quantum wells
Institute of Scientific and Technical Information of China (English)
Guo Huai-Ming; Zhang Xiang-Lin; Feng Shi-Ping
2012-01-01
The quantum spin Hall effect (QSHE) was first realized in HgTe quantum wells (QWs),which remain the only known two-dimensional topological insulator so far.In this paper,we have systematically studied the effect of the thickness fluctuation of HgTe QWs on the QSHE.We start with the case of constant mass with random distributions,and reveal that the disordered system can be well described by a virtual uniform QW with an effective mass when the number of components is small.When the number is infinite and corresponds to the real fluctuation,we find that the QSHE is not only robust,but also can be generated by relatively strong fluctuation.Our results imply that the thickness fluctuation does not cause backscattering,and the QSHE is robust to it.
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.
Institute of Scientific and Technical Information of China (English)
WANG Zhi-Cheng; XU Bo; CHEN Yong-Hai; SHI Li-Wei; LIANG Zhi-Mei; WANG Zhan-Guo
2008-01-01
Theoretical calculation of electronic energy levels of an asymmetric InAs/ InGaAs/ GaAs quantum-dots-in-a-well (DWELL) structure for infrared photodetectors is performed in the framework of effective-mass envelope-function theory. Our calculated results show that the electronic energy levels in quantum dots (QDs) increase when the asymmetry increases and the ground state energy increases faster than the excited state energies. Furthermore, the results also show that the electronic energy levels in QDs decrease as the size of QDs and the width of quantum well (QW) in the asymmetric DWELL structure increase. Additionally, the effects of asymmetry, the size of QDs and the width of QW on the response peak of asymmetry DWELL photodetectors are also discussed.
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.)
Institute of Scientific and Technical Information of China (English)
LIANG Zhi-Mei; JIN Can; JIN Peng; WU Ju; WANG Zhan-Guo
2009-01-01
Both the peak position and linewidth in the photoluminescence spectrum of the InAs/GaAs quantum dots usually vary in an anomalous way with increasing temperature. Such anomalous optical behaviour is eliminated by inserting an In0.2Ga0.8As quantum well below the quantum dot layer in molecular beam epitaxy. The insensitivity of the photoluminescence spectra to temperature is explained in terms of the effective carrier redistribution between quantum dots through the ln0.2Ga0.8As quantum well.
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.
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.
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.
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...
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...
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.
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...
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...
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.
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...
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.
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.
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...
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...
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...
Closed form solution for a double quantum well using Gr\\"obner basis
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.
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.
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.
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....
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...
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...
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.
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.
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....
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...
High-resolution x-ray diffraction investigations of highly mismatched II-VI quantum wells
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.
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...
Monte Carlo modeling of the dual-mode regime in quantum-well and quantum-dot semiconductor lasers.
Chusseau, Laurent; Philippe, Fabrice; Disanto, Filippo
2014-03-10
Monte Carlo markovian models of a dual-mode semiconductor laser with quantum well (QW) or quantum dot (QD) active regions are proposed. Accounting for carriers and photons as particles that may exchange energy in the course of time allows an ab initio description of laser dynamics such as the mode competition and intrinsic laser noise. We used these models to evaluate the stability of the dual-mode regime when laser characteristics are varied: mode gains and losses, non-radiative recombination rates, intraband relaxation time, capture time in QD, transfer of excitation between QD via the wetting layer... As a major result, a possible steady-state dual-mode regime is predicted for specially designed QD semiconductor lasers thereby acting as a CW microwave or terahertz-beating source whereas it does not occur for QW lasers.
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.
Long-wavelength quantum well infrared photodetector (QWIP) research at Jet Propulsion Laboratory
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.
Low-temperature illumination and annealing of ultrahigh quality quantum wells
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.
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.
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.
Temperature-dependent exciton recombination in asymmetrical ZnCdSe/ZnSe double quantum wells
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)
Energy Technology Data Exchange (ETDEWEB)
Curilef, S [Departamento de Fisica, Universidad Catolica del Norte, Antofagasta (Chile); Zander, C [Physics Department, University of Pretoria, Pretoria 0002 (South Africa); Plastino, A R [Physics Department, University of Pretoria, Pretoria 0002 (South Africa)
2006-09-01
The connection between entanglement and the speed of quantum evolution (as measured by the time needed to reach an orthogonal state) is discussed in the case of two quantum particles moving in a one-dimensional double well. The aforementioned connection offers an interesting opportunity of discussing the basic features of quantum entanglement within an elementary context, using concepts and methods usually included in university courses of quantum mechanics.
Control of the probe absorption in coupled quantum wells in two dimensions
Kang, Chengxian; Ma, Yangcheng; Wang, Zhiping; Yu, Benli
2016-06-01
We investigate the probe absorption of a weak probe field in two dimensions (the so-called two-dimensional probe absorption) in an asymmetric two coupled quantum wells. It is found that, due to the joint quantum interference induced by the standing-wave and coherent coupling fields, the probe absorption can be easily controlled via adjusting the system parameters in two dimensions. Most importantly, the pattern of probe absorption can be localized at a particular position and the maximal probability of finding the pattern in one period of the standing-wave fields reaches unity by properly adjusting the system parameters. Thus, our scheme may provide some technological applications in solid-state optoelectronics and quantum information science.
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)
Plasmonic photocatalytic reactions enhanced by hot electrons in a one-dimensional quantum well
Directory of Open Access Journals (Sweden)
H. J. Huang
2015-11-01
Full Text Available The plasmonic endothermic oxidation of ammonium ions in a spinning disk reactor resulted in light energy transformation through quantum hot charge carriers (QHC, or quantum hot electrons, during a chemical reaction. It is demonstrated with a simple model that light of various intensities enhance the chemical oxidization of ammonium ions in water. It was further observed that light illumination, which induces the formation of plasmons on a platinum (Pt thin film, provided higher processing efficiency compared with the reaction on a bare glass disk. These induced plasmons generate quantum hot electrons with increasing momentum and energy in the one-dimensional quantum well of a Pt thin film. The energy carried by the quantum hot electrons provided the energy needed to catalyze the chemical reaction. The results indicate that one-dimensional confinement in spherical coordinates (i.e., nanoparticles is not necessary to provide an extra excited state for QHC generation; an 8 nm Pt thin film for one-dimensional confinement in Cartesian coordinates can also provide the extra excited state for the generation of QHC.
Plasmonic photocatalytic reactions enhanced by hot electrons in a one-dimensional quantum well
Energy Technology Data Exchange (ETDEWEB)
Huang, H. J., E-mail: hjhuang@narlabs.org.tw, E-mail: hhjhuangkimo@gmail.com; Liu, B. H.; Lin, C. T. [Instrument Technology Research Center, National Applied Research Laboratories, Hsinchu, 300, Taiwan (China); Su, W. S. [National Center for High-performance Computing, Hsinchu 300, Taiwan and Department of Physics, National Chung Hsing University, Taichung 402, Taiwan (China)
2015-11-15
The plasmonic endothermic oxidation of ammonium ions in a spinning disk reactor resulted in light energy transformation through quantum hot charge carriers (QHC), or quantum hot electrons, during a chemical reaction. It is demonstrated with a simple model that light of various intensities enhance the chemical oxidization of ammonium ions in water. It was further observed that light illumination, which induces the formation of plasmons on a platinum (Pt) thin film, provided higher processing efficiency compared with the reaction on a bare glass disk. These induced plasmons generate quantum hot electrons with increasing momentum and energy in the one-dimensional quantum well of a Pt thin film. The energy carried by the quantum hot electrons provided the energy needed to catalyze the chemical reaction. The results indicate that one-dimensional confinement in spherical coordinates (i.e., nanoparticles) is not necessary to provide an extra excited state for QHC generation; an 8 nm Pt thin film for one-dimensional confinement in Cartesian coordinates can also provide the extra excited state for the generation of QHC.
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.
Raman gain in a Boron based Group-III nitride quantum well
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.
Han, Yu; Li, Qiang; Lau, Kei May
2016-12-01
We report the characteristics of indium gallium arsenide stacked quantum structures inside planar indium phosphide nanowires grown on exact (001) silicon substrates. The morphological evolution of the indium phosphide ridge buffers inside sub-micron trenches has been studied, and the role of inter-facet diffusion in this process is discussed. Inside a single indium phosphide nanowire, we are able to stack quantum structures including indium gallium arsenide flat quantum wells, quasi-quantum wires, quantum wires, and ridge quantum wells. Room temperature photoluminescence measurements reveal a broadband emission spectrum centered at 1550 nm. Power dependent photoluminescence analysis indicates the presence of quasi-continuum states. This work thus provides insights into the design and growth process control of multiple quantum wells in wire structures for high performance nanowire lasers on a silicon substrate with 1550 nm band emission.
Quantum-Carnot engine for particle confined to 2D symmetric potential well
Belfaqih, Idrus Husin; Sutantyo, Trengginas Eka Putra; Prayitno, T. B.; Sulaksono, Anto
2015-09-01
Carnot model of heat engine is the most efficient cycle consisting of isothermal and adiabatic processes which are reversible. Although ideal gas usually used as a working fluid in the Carnot engine, Bender used quantum particle confined in 1D potential well as a working fluid. In this paper, by following Bender we generalize the situation to 2D symmetric potential well. The efficiency is express as the ratio of the initial length of the system to the final length of the compressed system. The result then is shown that for the same ratio, 2D potential well is more efficient than 1D potential well.
Quantum-Carnot engine for particle confined to 2D symmetric potential well
Energy Technology Data Exchange (ETDEWEB)
Belfaqih, Idrus Husin, E-mail: idrushusin21@gmail.com; Sutantyo, Trengginas Eka Putra, E-mail: trengginas.eka@gmail.com; Prayitno, T. B., E-mail: teguh-budi@unj.ac.id [Department of Physics, Universitas Negeri Jakarta, Jl. Pemuda Rawamangun, Jakarta Timur, 13220 (Indonesia); Sulaksono, Anto, E-mail: anto.sulaksono@sci.ui.ac.id [Department of Physics, Universitas Indonesia, Depok, Jawa Barat, 164242 (Indonesia)
2015-09-30
Carnot model of heat engine is the most efficient cycle consisting of isothermal and adiabatic processes which are reversible. Although ideal gas usually used as a working fluid in the Carnot engine, Bender used quantum particle confined in 1D potential well as a working fluid. In this paper, by following Bender we generalize the situation to 2D symmetric potential well. The efficiency is express as the ratio of the initial length of the system to the final length of the compressed system. The result then is shown that for the same ratio, 2D potential well is more efficient than 1D potential well.
Limits to mobility in InAs quantum wells with nearly lattice-matched barriers
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.
Investigation of temperature-dependent photoluminescence in multi-quantum wells.
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.
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.
Modeling of novel lateral AlGaAs/GaAs quantum well solar cell
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...
Coherent Interband and Intersubband Dynamics in Terahertz-Driven GaAs Quantum Wells
Institute of Scientific and Technical Information of China (English)
无
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.
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.
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.
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.
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.
(110) oriented GaAs/Al0.3Ga0.7As quantum wells for optimized T-shaped quantum wires
DEFF Research Database (Denmark)
Gislason, Hannes; Sørensen, Claus Birger; Hvam, Jørn Märcher
1996-01-01
High control of (110) oriented GaAs/Al0.3Ga0.7As quantum wells is very important for the growth of optimized T-shaped GaAs/AlGaAs quantum wires, We investigate theoretically and experimentally 20-200 Angstrom wide (110) oriented GaAs quantum wells grown on (110) oriented substrates and cleaved...... edges. Photoluminescence transition energies are found to be in good agreement with theory for all well widths. The mean well width is controllable to 1 monolayer accuracy and an effective well width fluctuation of 3.7 Angstrom is derived from the photoluminescence linewidths. The growth rate...
Energy Technology Data Exchange (ETDEWEB)
Odendaal, R Q [Physics Department, University of Pretoria, Pretoria 0002 (South Africa); Plastino, A R [National University La Plata, UNLP-CREG-Conicet, CC 727, La Plata 1900 (Argentina)], E-mail: arplastino@maple.up.ac.za
2010-01-15
Entangled states of composite quantum systems exhibit one of the most distinct and non-classical features of the quantum mechanical description of Nature, first pointed out by Schroedinger: 'Maximal knowledge of a total system does not necessarily imply maximal knowledge of all its parts'. We provide an elementary illustration of this fundamental aspect of quantum physics by considering a system of two particles in an infinite, one-dimensional square potential well. In contrast to standard introductory presentations of quantum entanglement, our present considerations do not require density matrix formalism, nor explicit use of the tensor product structure for the description of composite quantum systems.
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.
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.
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.
Photoluminescence study of InGaN/GaN double quantum wells with varying barrier widths
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.
Strain Compensation in Single ZnSe/CdSe Quantum Wells: Analytical Model and Experimental Evidence.
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.
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.
Mid/far-infrared photo-detectors based on graphene asymmetric quantum wells
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.
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)
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.
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.
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.
Pressure- and temperature-driven phase transitions in HgTe quantum wells
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.
Quantum wells, wires and dots theoretical and computational physics of semiconductor nanostructures
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...
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.
Murphy, Graham P.; Gough, John J.; Higgins, Luke J.; Karanikolas, Vasilios D.; Wilson, Keith M.; Garcia Coindreau, Jorge A.; Zubialevich, Vitaly Z.; Parbrook, Peter J.; Bradley, A. Louise
2017-03-01
Non-radiative energy transfer (NRET) can be an efficient process of benefit to many applications including photovoltaics, sensors, light emitting diodes and photodetectors. Combining the remarkable optical properties of quantum dots (QDs) with the electrical properties of quantum wells (QWs) allows for the formation of hybrid devices which can utilize NRET as a means of transferring absorbed optical energy from the QDs to the QW. Here we report on plasmon-enhanced NRET from semiconductor nanocrystal QDs to a QW. Ag nanoparticles in the form of colloids and ordered arrays are used to demonstrate plasmon-mediated NRET from QDs to QWs with varying top barrier thicknesses. Plasmon-mediated energy transfer (ET) efficiencies of up to ∼25% are observed with the Ag colloids. The distance dependence of the plasmon-mediated ET is found to follow the same d ‑4 dependence as the direct QD to QW ET. There is also evidence for an increase in the characteristic distance of the interaction, thus indicating that it follows a Förster-like model with the Ag nanoparticle-QD acting as an enhanced donor dipole. Ordered Ag nanoparticle arrays display plasmon-mediated ET efficiencies up to ∼21%. To explore the tunability of the array system, two arrays with different geometries are presented. It is demonstrated that changing the geometry of the array allows a transition from overall quenching of the acceptor QW emission to enhancement, as well as control of the competition between the QD donor quenching and ET rates.
Sharma, Manoj; Gungor, Kivanc; Yeltik, Aydan; Olutas, Murat; Guzelturk, Burak; Kelestemur, Yusuf; Erdem, Talha; Delikanli, Savas; McBride, James R; Demir, Hilmi Volkan
2017-08-01
Doping of bulk semiconductors has revealed widespread success in optoelectronic applications. In the past few decades, substantial effort has been engaged for doping at the nanoscale. Recently, doped colloidal quantum dots (CQDs) have been demonstrated to be promising materials for luminescent solar concentrators (LSCs) as they can be engineered for providing highly tunable and Stokes-shifted emission in the solar spectrum. However, existing doped CQDs that are aimed for full solar spectrum LSCs suffer from moderately low quantum efficiency, intrinsically small absorption cross-section, and gradually increasing absorption profiles coinciding with the emission spectrum, which together fundamentally limit their effective usage. Here, the authors show the first account of copper doping into atomically flat colloidal quantum wells (CQWs). In addition to Stokes-shifted and tunable dopant-induced photoluminescence emission, the copper doping into CQWs enables near-unity quantum efficiencies (up to ≈97%), accompanied by substantially high absorption cross-section and inherently step-like absorption profile, compared to those of the doped CQDs. Based on these exceptional properties, the authors have demonstrated by both experimental analysis and numerical modeling that these newly synthesized doped CQWs are excellent candidates for LSCs. These findings may open new directions for deployment of doped CQWs in LSCs for advanced solar light harvesting technologies. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
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.
Quantum Well Infrared Photodetectors:the Basic Design and New Research Directions
Institute of Scientific and Technical Information of China (English)
无
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.
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.
Carrier localization mechanisms in InGaN/GaN quantum wells
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...
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.
On the Matsubara-Toyozawa Formalism to Treat Impurity Bands in δ-DOPED Quantum Wells
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.
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.
Simulation of the dark current of quantum-well infrared photodetectors
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.
Long Wavelength 256 X 256 Quantum Well Infrared Photodetector Portable Camera
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.
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.
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.
Numerical analysis of AlGaAs/GaAs multi-quantum well superluminescent diodes
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.
Selection of the lasing frequency and heating the quantum-well heterostructure laser diodes
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...
A 980 nm pseudomorphic single quantum well laser for pumping erbium-doped optical fiber amplifiers
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.
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....
Thermoelectric properties of Mg2X (X = Si, Ge) based bulk and quantum well systems
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.
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.
Variational Method for the Three-Dimensional Many-Electron Dynamics of Semiconductor Quantum Wells
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.
Effects of impurity location on the impurity bands and their spectral densities in quantum wells
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.
A chart for the energy levels of the square quantum well
Chiani, M
2016-01-01
A chart for the quantum mechanics of a particle of mass $m$ in a one-dimensional potential well of width $w$ and depth $V_0$ is derived. The chart is obtained by normalizing energy and potential through multiplication by ${8 m}{h^2} / w^2$, and gives directly the allowed couples (potential, energy), providing insights on the relation between the parameters and the number of allowed energy levels.
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.
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.
Influence of metalorganic precursors flow interruption timing on green InGaN multiple quantum wells
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.
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.
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.
Study of intersubband transitions in GaN-ZnGeN2 coupled quantum wells
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.
Magnetoconductance in InN/GaN quantum wells in topological insulator phase
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.
Terahertz intersubband transition in GaN/AlGaN step quantum well
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.
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...
InAsP-based quantum wells as infrared pressure gauges for use in a diamond anvil cell
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.
Influence of Plasmonic Array Geometry on Energy Transfer from a Quantum Well to a Quantum Dot Layer
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...
Datta, Kanak; Khosru, Quazi D. M.
2016-04-01
In this work, quantum ballistic simulation study of a III-V tri-gate MOSFET has been presented. At the same time, effects of device parameter variation on ballistic, subthreshold and short channel performance is observed and presented. The ballistic simulation result has also been used to observe the electrostatic performance and Capacitance-Voltage characteristics of the device. With constant urge to keep in pace with Moore's law as well as aggressive scaling and device operation reaching near ballistic limit, a full quantum transport study at 10 nm gate length is necessary. Our simulation reveals an increase in device drain current with increasing channel cross-section. However short channel performance and subthreshold performance get degraded with channel cross-section increment. Increasing device cross-section lowers threshold voltage of the device. The effect of gate oxide thickness on ballistic device performance is also observed. Increase in top gate oxide thickness affects device performance only upto a certain value. The thickness of the top gate oxide however shows no apparent effect on device threshold voltage. The ballistic simulation study has been further used to extract ballistic injection velocity of the carrier and ballistic carrier mobility in the channel. The effect of device dimension and gate oxide thickness on ballistic velocity and effective carrier mobility is also presented.
Gate-Defined Wires in HgTe Quantum Wells: From Majorana Fermions to Spintronics
Directory of Open Access Journals (Sweden)
Johannes Reuther
2013-08-01
Full Text Available We introduce a promising new platform for Majorana zero modes and various spintronics applications based on gate-defined wires in HgTe quantum wells. Because of the Dirac-like band structure for HgTe, the physics of such systems differs markedly from that of conventional quantum wires. Most strikingly, we show that the subband parameters for gate-defined HgTe wires exhibit exquisite tunability: Modest gate voltage variation allows one to modulate the Rashba spin-orbit energies from zero up to about 30 K, and the effective g factors from zero up to giant values exceeding 600. The large achievable spin-orbit coupling and g factors together allow one to access Majorana modes in this setting at exceptionally low magnetic fields while maintaining robustness against disorder. As an additional benefit, gate-defined wires (in HgTe or other settings should greatly facilitate the fabrication of networks for refined transport experiments used to detect Majoranas, as well as the realization of non-Abelian statistics and quantum information devices.
Temperature dependence of the lowest excitonic transition for an InAs ultrathin quantum well
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.
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.
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.
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...
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.
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.
Electron-electron correlations in square-well quantum dots: direct energy minimization approach.
Goto, Hidekazu; Hirose, Kikuji
2011-04-01
Electron-electron correlations in two-dimensional square-well quantum dots are investigated using the direct energy minimization scheme. Searches for groundstate charges and spin configurations are performed with varying the sizes of dots and the number of electrons. For a two-electron system, a standout difference between the configurations with and without counting correlation energy is demonstrated. The emergence and melting of Wigner-molecule-like structures arising from the interplay between the kinetic energy and Coulombic interaction energy are described. Electron-electron correlation energies and addition energy spectra are calculated, and special electron numbers related to peculiar effects of the square well are extracted.
Terahertz study of ultrafast carrier dynamics in InGaN/GaN multiple quantum wells
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.
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.
One-dimensional multiple-well oscillators: A time-dependent quantum mechanical approach
Indian Academy of Sciences (India)
Neetu Gupta; Amlan K Roy; B M Deb
2002-10-01
Time-dependent Schrödinger equation (TDSE) is solved numerically to calculate the ground- and ﬁrst three excited-state energies, expectation values $\\langle x^{2j}\\rangle$, $j=1,2,\\ldots,6$ and probability densities of quantum mechanical multiple-well oscillators. An imaginary-time evolution technique, coupled with the minimization of energy expectation value to reach a global minimum, subject to orthogonality constraint (for excited states) has been employed. Pseudodegeneracy in symmetric, deep multiple-well potentials, probability densities and the effect of an asymmetry parameter on pseudodegeneracy are discussed.
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.
Quantum Creation of Closed Universe with Both Effects of Tunnelling and Well
Institute of Scientific and Technical Information of China (English)
ZHANG De-Hai
2001-01-01
A new "twice loose shoe" method in the Wheeler-DeWitt equation of the universe wavefunction on the cosmic scale factor a and a scalar field φ is suggested.We analyze both the affections coming from the tunnelling effect of a and the potential well effect ofφ,and obtain the initial values a0 and φ0 about a primary closed universe which is born with the largest probability in the quantum manner.Our result is able to overcome the "large field difficulty" of the universe quantum creation probability with only tunnelling effect.This new born universe has to suffer a startup of inflation,and then comes into the usual slow rolling inflation.The universe with the largest probability maybe has a "gentle" inflation or an eternal chaotic inflation,this depends on a new parameter q which describes the tunnelling character.
Giant Spin-Orbit Splitting in Inverted InAs /GaSb Double Quantum Wells
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.
Investigation of the confinement potential within GaNAs/GaAs multiple quantum wells
Energy Technology Data Exchange (ETDEWEB)
Goshima, Keishiro; Kittaka, Akinobu; Fujii, Kensuke; Shiraga, Masahiro; Tsurumachi, Noriaki; Nakanishi, Shunsuke; Koshiba, Shyun; Itoh, Hiroshi [Engineering, Kagawa University, 2217-20, Takamatsu, Kagawa 761-0396 (Japan); Akiyama, Hidefumi [Institute of Solid State Physics, University of Tokyo, Chiba 277-8581 (Japan)
2011-02-15
We conducted a detailed investigation of the potential structure within GaNAs/GaAs multiple quantum wells (MQWs) using three independent experimental techniques: the temperature dependence of Photo-luminescence (PL) spectroscopy, time-resolved PL spectroscopy, and degenerate four-wave mixing (DFWM) measurements. We observed a very long lifetime (T{sub 1} = 12 ns) and dephasing time (T{sub 2} = 130 ps) of excitons in the GaNAs/GaAs MQWs. We suggested that the GaNAs/GaAs MQWs have a strong and deep confinement structure that is comparable to that of quantum dots (copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)
Spin-polarized spin-orbit-split quantum-well states in a metal film
Energy Technology Data Exchange (ETDEWEB)
Varykhalov, Andrei; Sanchez-Barriga, Jaime; Gudat, Wolfgang; Eberhardt, Wolfgang; Rader, Oliver [BESSY Berlin (Germany); Shikin, Alexander M. [St. Petersburg State University (Russian Federation)
2008-07-01
Elements with high atomic number Z lead to a large spin-orbit coupling. Such materials can be used to create spin-polarized electronic states without the presence of a ferromagnet or an external magnetic field if the solid exhibits an inversion asymmetry. We create large spin-orbit splittings using a tungsten crystal as substrate and break the structural inversion symmetry through deposition of a gold quantum film. Using spin- and angle-resolved photoelectron spectroscopy, it is demonstrated that quantum-well states forming in the gold film are spin-orbit split and spin polarized up to a thickness of at least 10 atomic layers. This is a considerable progress as compared to the current literature which reports spin-orbit split states at metal surfaces which are either pure or covered by at most a monoatomic layer of adsorbates.
Energy Technology Data Exchange (ETDEWEB)
Tzimis, A.; Savvidis, P. G. [Department of Materials Science and Technology, University of Crete, 71003 Heraklion, Crete (Greece); Institute of Electronic Structure and Laser, Foundation for Research and Technology - Hellas, 71110 Heraklion, Crete (Greece); Trifonov, A. V.; Ignatiev, I. V. [Spin Optics Laboratory, State University of Saint-Petersburg, 1 Ulianovskaya, 198504 St. Petersburg (Russian Federation); Christmann, G.; Tsintzos, S. I. [Institute of Electronic Structure and Laser, Foundation for Research and Technology - Hellas, 71110 Heraklion, Crete (Greece); Hatzopoulos, Z. [Institute of Electronic Structure and Laser, Foundation for Research and Technology - Hellas, 71110 Heraklion, Crete (Greece); Department of Physics, University of Crete, 71003 Heraklion, Crete (Greece); Kavokin, A. V. [Spin Optics Laboratory, State University of Saint-Petersburg, 1 Ulianovskaya, 198504 St. Petersburg (Russian Federation); School of Physics and Astronomy, University of Southampton, Southampton SO17 1BJ (United Kingdom)
2015-09-07
We report observation of strong light-matter coupling in an AlGaAs microcavity (MC) with an embedded single parabolic quantum well. The parabolic potential is achieved by varying aluminum concentration along the growth direction providing equally spaced energy levels, as confirmed by Brewster angle reflectivity from a reference sample without MC. It acts as an active region of the structure which potentially allows cascaded emission of terahertz (THz) light. Spectrally and time resolved pump-probe spectroscopy reveals characteristic quantum beats whose frequencies range from 0.9 to 4.5 THz, corresponding to energy separation between relevant excitonic levels. The structure exhibits strong stimulated nonlinear emission with simultaneous transition to weak coupling regime. The present study highlights the potential of such devices for creating cascaded relaxation of bosons, which could be utilized for THz emission.
Energy Technology Data Exchange (ETDEWEB)
Arapov, Yu. G.; Gudina, S. V.; Neverov, V. N.; Podgornykh, S. M.; Popov, M. R., E-mail: rafaelp@yandex.ru; Harus, G. I.; Shelushinina, N. G.; Yakunin, M. V. [Russian Academy of Sciences, Mikheev Institute of Metal Physics, Ural Branch (Russian Federation); Mikhailov, N. N.; Dvoretsky, S. A. [Russian Academy of Sciences, Rzhanov Institute of Semiconductor Physics, Siberian Branch (Russian Federation)
2015-12-15
The longitudinal and Hall magnetoresistances of HgTe/HgCdTe heterostructures with an inverted energy spectrum (the HgTe quantum well width is d = 20.3 nm) are measured in the quantum-Hall-effect regime at T = 2–50 K in magnetic fields up to B = 9 T. Analysis of the temperature dependences of conductivity in the transition region between the first and second plateaus of the quantum Hall effect shows the feasibility of the scaling regime for a plateau–plateau quantum phase transition in 2D-structures on the basis of mercury telluride.
Aleshkin, VY; Zvonkov, BN; Malkina, IG; Chernov, AL; Romanov, YA
1999-01-01
The mechanisms for linear polarization loss of photoluminescence from quantum wells and quantum dots in InGaAs/GaAs structures observed from cleavages have been investigated. It is found that the mechanisms for polarization loss of in-plane photoluminescence are different for OD and 2D hole states.
Excitonic field screening and bleaching in InGaN/GaN multiple quantum wells
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.
Toward 17µm pitch heterogeneously integrated Si/SiGe quantum well bolometer focal plane arrays
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.
Time-Resolved Photoluminescence Studies of InGaN/AlGaN Multiple Quantum Wells
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.
Modeling the band gap of CdS quantum well structures
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.
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.
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
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.
Two Interacting Electrons in a Spherical Gaussian Confining Potential Quantum Well
Institute of Scientific and Technical Information of China (English)
XIE Wen-Fang
2004-01-01
Two-electron states of a three-dimensional spherical GaAs quantum dot (QD) with a Gaussian confining potential confinement are studied. Calculations are made by using the method of few-body physics within the effectivemass approximation. We have calculated the energy levels of single and triplet states as functions of the range and depth of the confining potential well in the spherical QDs. The same calculations performed with the parabolic approximation of the Gaussian potential lead to the results, which are qualitatively and quantitatively different.
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....
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.
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...
Magneto optical rotation in a GaAs Quantum Well Waveguide
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.
Confinement effect in a quantum well dot induced by an InP stressor
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.
Magnetization dynamics down to a zero field in dilute (Cd,Mn)Te quantum wells.
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.
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.)
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.)
RT CW operation of InGaN multi-quantum-well structure laser diodes
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...
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.
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.)
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.
Intersubband carrier scattering in n - and p-Si/SiGe quantum wells with diffuse interfaces
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.
Circularly polarized lasing in chiral modulated semiconductor microcavity with GaAs quantum wells
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.
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.
Phosphor-free white light-emitting diode with laterally distributed multiple quantum wells
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.
Room temperature ballistic transport in InSb quantum well nanodevices.
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.
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.
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.
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.
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...
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)
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.
Voltage-controlled sub-terahertz radiation transmission through GaN quantum well structure
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.
Quantum Wells, Wires and Dots Theoretical and Computational Physics of Semiconductor Nanostructures
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
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.
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.
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.
Reduced threshold all-optical bistability in etched quantum well microresonators
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.
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)
Optical spectroscopy of single beryllium acceptors in GaAs/AlGaAs quantum well
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.
SEMICONDUCTOR PHYSICS: Phonon-induced magnetoresistance oscillations in a high-mobility quantum well
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.
Strained InGaAs/InAlAs Quantum Wells for Complementary III-V Transistors
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
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...
Chen, Y.; Maharjan, N.; Liu, Z.; Nakarmi, M. L.; Chaldyshev, V. V.; Kundelev, E. V.; Poddubny, A. N.; Vasil'ev, A. P.; Yagovkina, M. A.; Shakya, N. M.
2017-03-01
An AlGaAs/GaAs multiple-quantum-well based resonant Bragg structure was designed to match the optical Bragg resonance with the exciton-polariton resonance at the second quantum state in the GaAs quantum wells. The sample structure with 60 periods of AlGaAs/GaAs quantum wells was grown on a semi-insulating GaAs substrate by molecular beam epitaxy. Angle- and temperature-dependent photoluminescence, optical reflectance, and electro-reflectance spectroscopies were employed to study the resonant optical properties of the Bragg structure. Broad and enhanced optical and electro-reflectance features were observed when the Bragg resonance was tuned to the second quantum state of the GaAs quantum well excitons, manifesting a strong light-matter interaction. From the electro-optical experiments, we found the electro-reflectance features related to the transitions of x(e2-hh2) and x(e2-hh1) excitons. The excitonic transition x(e2-hh1), which is prohibited at zero electric field, was allowed by a DC bias due to the brake of symmetry and increased overlap of the electron and hole wave functions caused by the electric field. By tuning the Bragg resonance frequency, we have observed the electro-reflectance feature related to the second quantum state up to room temperature, which evidences a robust light-matter interaction in the resonant Bragg structure.
Influence of plasmonic array geometry on energy transfer from a quantum well to a quantum dot layer.
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.
Mobility modulation in inverted delta doped coupled double quantum well structure
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.
Some reasons of emission variation in InAs quantum dot-in-a-well structures
Torchynska, T. V.; Palacios Gomez, J.; Gómez Gasga, G.; Vivas Hernandez, A.; Velazquez Lozada, E.; Polupan, G.; Shcherbyna, Ye S.
2010-09-01
Photoluminescence (PL) and X ray diffraction have been studied in InAs quantum dots (QDs) embedded in symmetric In0.15Ga1-0.15As/GaAs quantum wells (dot-in-a-well, DWELL) with QDs grown at different temperatures. The density of QDs decreases from 1.1×1011 down to 1.3×1010 cm-2 with increasing the QD growth temperatures from 470 to 535°C. The QD density decreasing in DWELLs is accompanied by the non monotonous variation of QD parameters. The PL intensity increases and the PL peak shifts to low energy in structures with QDs grown at 490 and 510°C. On the contrary the structures with QDs grown at 525 and 535°C are characterized by lower PL intensities and PL peak positions shifted to higher energy. The method of X-ray diffraction has been applied with the aim to study the variation of elastic strain in DWELL structures with QDs grown at different temperatures. It was shown that the minimum of elastic strain corresponds to DWELL with QDs grown at 490-525 °C. For lower (470 °C) and higher (535 °C) QD growth temperatures the level of compressive strain increased in DWELLs. The reasons of strain variation are discussed as well.
Nonlinear optical rectification in laterally-coupled quantum well wires with applied electric field
Liu, Guanghui; Guo, Kangxian; Zhang, Zhongmin; Hassanbadi, Hassan; Lu, Liangliang
2017-03-01
Nonlinear optical rectification coefficient χ0(2) in laterally-coupled AlxGa1-xAs/GaAs quantum well wires with an applied electric field is theoretically investigated using the effective mass approximation as well as the numerical energy levels and wavefunctions of electrons. We find that χ0(2) is greatly influenced by the electric field as well as both the distance and the radius of the coupled system. A blue shift of χ0(2) with increasing electric field is exhibited while a red shift followed by a blue shift with increasing distance or radius is exhibited. A nonmonotonic behavior can be found in the resonant peak values of χ0(2) along with the increase of the electric field, the distance or the radius. One or two of the following physical mechanisms: the increased localization of the ground and first-excited states, the reduced coupling and the reduced quantum confinement effect are applied to elucidate the results above. Our results play a potential role in infrared photodetectors based on the coupled system.
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.
High Efficiency Quantum Well Waveguide Solar Cells and Methods for Constructing the Same
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.
Institute of Scientific and Technical Information of China (English)
ZHANG Yejin; CHEN Weiyou; LIU Caixia; LIU Shiyong
2001-01-01
We have used Harrison′s model and anisotropic parabolic approximation to calculate band structure of In1-x-yGayAlxAs compressively strained quantum well. For design of 1.55 μm wavelength lasers, well widths for the possible compositions are presented. A useful empirical formula is given.
Optical studies of charged excitons in II-VI semiconductor quantum wells
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)
Tunability of InGaN/GaN quantum well light emitting diodes through current
Biswas, Dipankar; Panda, Siddhartha
2013-07-01
In the recent years, InGaN/GaN quantum well (QW) light emitting diodes (LEDs) have gathered much importance through the introduction of white LEDs and dual wavelength LEDs. However, the continuous tunability of InGaN/GaN QW LEDs has not been well addressed or discussed. In this paper, we introduce the tunability of an InGaN/GaN QW LED having a well width of 4 nm and In mole fraction of 0.3. The results, obtained from self-consistent solutions of the Schrödinger and Poisson equations, show that the transition energy of the LED may be continuously tuned by the device current. A prominent nonlinearity of the transition energy with the device current is generated, which should be of interest to the research workers in the field of optoelectronics.
Terahertz intersubband absorption in GaN/AlGaN step quantum wells
Machhadani, H.; Kotsar, Y.; Sakr, S.; Tchernycheva, M.; Colombelli, R.; Mangeney, J.; Bellet-Amalric, E.; Sarigiannidou, E.; Monroy, E.; Julien, F. H.
2010-11-01
We demonstrate terahertz intersubband absorptions at frequencies of 2.1 THz (λ ≈143 μm) and 4.2 THz (λ ≈70 μm) in nitride-based semiconductor quantum wells. The structures consist of a 3 nm thick GaN well, an Al0.05Ga0.95N step barrier, and a 3 nm thick Al0.1Ga0.9N barrier. The absorption is detected at 4.7 K. The structure design has been optimized to approach a flat-band potential in the wells to allow for an intersubband absorption in the terahertz frequency range and to maximize the optical dipole moments.
Excitons Bound to Shallow Donors in Thin GaAs/AlAs Quantum Wells
da Cunha Lima, I. C.; Ghazali, A.; Emmel, P. D.
1996-03-01
The binding energy of excitons to ionized shallow donors in GaAs/AlAs quantum well in the vicinity of the type-I to type-II transition was obtained for impurities lying anywhere in the structure. We included the Γ -X hybridization in the Brillouin zone, which comes into play when the energies of the conduction subband minima in the two materials become close. The calculation is performed variationally using a three parameters trial function similar to the one describing a singly ionized molecule. We obtain a ratio between the binding energy of the bound exciton and that of the neutral donor equals to 0.95± 0.005, for all values of well widths explored, and independent on the impurity position inside the well. The joint density of states for the transition from free to bound exciton was obtained, and the role played by the doping and the compensation on the exciton dynamics was made clear.
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.)
Anomalous effect of phonon wind on lateral migration of excitons in ultrathin quantum CdTe/ZnTe well
Onishchenko, E E; Zajtsev, V V
2001-01-01
The effect of the acoustic phonons nonequilibrium flux on the photoluminescence of the CdTe/ZnTe thin quantum well, excited quasi-resonantly by the He-Ne-laser is studied. It is established that the phonon flux leads to the change in the form of the quantum well luminescence band even by low generation capacities. It is assumed that the nonequilibrium phonons flux stimulates the excitons migration in the quantum well plane, conditioned by the tunnel transitions between the potential local minima, which are accompanied by the phonons induced emission
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.
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....
The electron-phonon interaction in GaAs/(AlGa)As quantum wells
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...
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.
Enhancement of Two-photon Absorption in Quantum Wells for Extremely Nondegenerate Photon Pairs
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...
Pumping dynamics of nuclear spins in GaAs quantum wells
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...
Optical gain in GaAsBi/GaAs quantum well diode lasers
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.
Hole weak anti-localization in a strained-Ge surface quantum well
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.
Institute of Scientific and Technical Information of China (English)
无
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
Development and application of InAsP/InP quantum well infrared detector
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.
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.
Transport of dipolar excitons in (Al,Ga)N/GaN quantum wells
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.
Effect of III-V on insulator structure on quantum well intermixing
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.
Interband magneto-spectroscopy in InSb square and parabolic quantum wells
Energy Technology Data Exchange (ETDEWEB)
Kasturiarachchi, T.; Edirisooriya, M.; Mishima, T. D.; Doezema, R. E.; Santos, M. B. [Homer L. Dodge Department of Physics and Astronomy and Center for Semiconductor Physics in Nanostructures, University of Oklahoma, Norman, Oklahoma 73019 (United States); Saha, D.; Pan, X.; Sanders, G. D.; Stanton, C. J. [Department of Physics, University of Florida, Gainesville, Florida 32611 (United States)
2015-06-07
We measure the magneto-optical absorption due to intersubband optical transitions between conduction and valence subband Landau levels in InSb square and parabolic quantum wells. InSb has the narrowest band gap (0.24 eV at low temperature) of the III–V semiconductors leading to a small effective mass (0.014 m{sub 0}) and a large g–factor (−51). As a result, the Landau level spacing is large at relatively small magnetic fields (<8 T), and one can observe spin-splitting of the Landau levels. We examine two structures: (i) a multiple-square-well structure and (ii) a structure containing multiple parabolic wells. The energies and intensities of the strongest features are well explained by a modified Pidgeon-Brown model based on an 8-band k•p model that explicitly incorporates pseudomorphic strain. The strain is essential for obtaining agreement between theory and experiment. While modeling the square well is relatively straight-forward, the parabolic well consists of 43 different layers of various thickness to approximate a parabolic potential. Agreement between theory and experiment for the parabolic well validates the applicability of the model to complicated structures, which demonstrates the robustness of our model and confirms its relevance for developing electronic and spintronic devices that seek to exploit the properties of the InSb band structure.
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.
Exciton binding energies and absorption in intermixed GaAs-AlGaAs quantum wells
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.
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. %.
Geometry effect on energy transfer rate in a coupled-quantum-well structure: nonlinear regime
Salavati-fard, T.; Vazifehshenas, T.
2014-12-01
We study theoretically the effect of geometry on the energy transfer rate at nonlinear regime in a coupled-quantum-well system using the balance equation approach. To investigate comparatively the effect of both symmetric and asymmetric geometry, different structures are considered. The random phase approximation dynamic dielectric function is employed to include the contributions from both quasiparticle and plasmon excitations. Also, the short-range exchange interaction is taken into account through the Hubbard approximation. Our numerical results show that the energy transfer rate increases by increasing the well thicknesses in symmetric structures. Furthermore, by increasing spatial asymmetry, the energy transfer rate decreases for the electron temperature range of interest. From numerical calculations, it is obtained that the nonlinear energy transfer rate is proportional to the square of electron drift velocity in all structures and also, found that the influence of Hubbard local field correction on the energy transfer rate gets weaker by increasing the strength of applied electric field.
Enhancement of coherent acoustic phonons in InGaN multiple quantum wells
Hafiz, Shopan D.; Zhang, Fan; Monavarian, Morteza; Avrutin, Vitaliy; Morkoç, Hadis; Özgür, Ümit
2015-03-01
Enhancement of coherent zone folded longitudinal acoustic phonon (ZFLAP) oscillations at terahertz frequencies was demonstrated in InGaN multiple quantum wells (MQWs) by using wavelength degenerate time resolved differential transmission spectroscopy. Screening of the piezoelectric field in InGaN MQWs by photogenerated carriers upon femtosecond pulse excitation gave rise to terahertz ZFLAPs, which were monitored at the Brillouin zone center in the transmission geometry. MQWs composed of 10 pairs InxGa1-xN wells and In0.03Ga0.97N barriers provided coherent phonon frequencies of 0.69-0.80 THz depending on the period of MQWs. Dependences of ZFLAP amplitude on excitation density and wavelength were also investigated. Possibility of achieving phonon cavity, incorporating a MQW placed between two AlN/GaN phonon mirrors designed to exhibit large acoustic gaps at the zone center, was also explored.
Thermal Behaviour for InGaAsP/InP Multi-Quantum-Well Superluminescent Diodes
Institute of Scientific and Technical Information of China (English)
LI Lan; FU Li-Wei; YANG Rui-Xia; LI Guang-Min; TAO Yi; ZHANG Na; ZHANG Xiao-Song
2005-01-01
@@ Using a two-dimensional thermal flow model, we calculate the thermal resistance and the temperature distribution of In GaAsP/InP multi-quantum-well superluminescent diodes. The influence of lateral chip size and composition are evaluated. The results reveal that when the injection power reaches 1 W, temperatures in the active region rises up to almost 50K. The width and length of the chip also have strong influence on the thermal resistance that can reach two orders of magnitude. The thermal resistance will change from 290 K/W to 68 K/W when the chip width increases from 500μm to 2500 μm, and a similar result exists for the length. There is small effect on thermal resistance for active width. In view of the characteristics of output power versus the input current under pulsed and continues currents, the fitted experimental thermal resistance matches well with the measured results.
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.
Ko, T. S.; Lu, T. C.; Wang, T. C.; Chen, J. R.; Gao, R. C.; Lo, M. H.; Kuo, H. C.; Wang, S. C.; Shen, J. L.
2008-11-01
a-plane InGaN/GaN multiple quantum wells of different widths ranging from 3 to 12 nm grown on r-plane sapphire by metal-organic chemical vapor deposition were investigated. The peak emission intensity of the photoluminescence (PL) reveals a decreasing trend as the well width increases from 3 to 12 nm. Low temperature (9 K) time-resolved PL (TRPL) study shows that the sample with 3-nm-thick wells has the best optical property with a fastest exciton decay time of 0.57 ns. The results of cathodoluminescence and micro-PL scanning images for samples of different well widths further verify that the more uniform and stronger luminescence intensity distribution are observed for the samples of thinner quantum wells. In addition, more effective capturing of excitons due to larger localization energy Eloc and shorter radiative lifetime of localized excitons are observed in thinner well width samples in the temperature dependent TRPL.
Exciton spectrum of surface-corrugated quantum wells: the adiabatic self-consistent approach
Energy Technology Data Exchange (ETDEWEB)
Atenco A, N.; Perez R, F. [lnstituto de Fisica, Universidad Autonoma de Puebla, A.P. J-48, 72570 Puebla (Mexico); Makarov, N.M. [lnstituto de Ciencias, Universidad Autonoma de Puebla, Priv. 17 Norte No 3417, Col. San Miguel Hueyotlipan, 72050 Puebla (Mexico)
2005-07-01
A theory for calculating the relaxation frequency {nu} and the shift {delta} {omega} of exciton resonances in quantum wells with finite potential barriers and adiabatic surface disorder is developed. The adiabaticity implies that the correlation length R{sub C} for the well width fluctuations is much larger than the exciton radius a{sub 0} (R{sub C} >> a{sub 0}). Our theory is based on the self-consistent Green's function method, and therefore takes into account the inherent action of the exciton scattering on itself. The self-consistent approach is shown to describe quantitatively the sharp exciton resonance. It also gives the qualitatively correct resonance picture for the transition to the classical limit, as well as within the domain of the classical limit itself. We present and analyze results for h h-exciton in a GaAs quantum well with Al{sub 0.3} Ga{sub 0.7}As barriers. It is established that the self-consistency and finite height of potential barriers significantly influence on the line-shape of exciton resonances, and make the values of {nu} and {delta} {omega} be quite realistic. In particular, the relaxation frequency {nu} for the ground-state resonance has a broad, almost symmetric maximum near the resonance frequency {omega}{sub 0}, while the surface-induced resonance shift {delta} {omega} vanishes near {omega}{sub 0}, and has different signs on the sides of the exciton resonance. (Author) 43 refs., 4 figs.
Energy Technology Data Exchange (ETDEWEB)
Baidus, N. V.; Vikhrova, O. V., E-mail: vikhrova@nifti.unn.ru; Zvonkov, B. N.; Malysheva, E. I. [Lobachevsky State University of Nizhni Novgorod, Physical-Technical Research Institute (Russian Federation); Trufanov, A. N. [Sedakov Research Institute of Measurement Systems, GSP-486 (Russian Federation)
2015-03-15
The effect of neutron radiation on the luminescence of InGaAs/GaAs heterostructures with quantum wells and quantum dots is studied. It is found that neutron radiation results both in the formation of defects and in the radiation-induced annealing of growth-related defects. Quantum dots are more stable to neutron radiation in comparison with quantum wells. It is shown that the layer of InGaAs/GaAs quantum dots located near the surface is less sensitive to irradiation with neutrons compared with a similar layer located in the bulk. In the first case, one can observe an increase in the photoluminescence and electroluminescence intensities after irradiation with neutrons, which is related to the effects of radiation-induced annealing. The pronounced effect of elastic strains in the InGaAs/GaAs quantum wells on the extent of quenching of the photoluminescence intensity upon irradiation with neutrons is revealed. In heterostructures with quantum wells, the effect of radiation-induced annealing manifests itself in a shift of the photoluminescence peak to longer wavelengths as a result of a decrease in elastic strains upon irradiation with neutrons. Doping of the GaAs buffer layer with silicon also reduces the value of this spectral shift.
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.
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.
Electron-phonon interaction in the quantum well state of the 1 ML Na/Cu(111) system
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.
Internal quantum efficiency enhancement of GaInN/GaN quantum-well structures using Ag nanoparticles
DEFF Research Database (Denmark)
Iida, Daisuke; Fadil, Ahmed; Chen, Yuntian
2015-01-01
We report internal quantum efficiency enhancement of thin p-GaN green quantumwell structure using self-assembled Ag nanoparticles. Temperature dependent photoluminescence measurements are conducted to determine the internal quantum efficiency. The impact of excitation power density...... on the enhancement factor is investigated. We obtain an internal quantum efficiency enhancement by a factor of 2.3 at 756 W/cm2 , and a factor of 8.1 at 1 W/cm2 . A Purcell enhancement up to a factor of 26 is estimated by fitting the experimental results to a theoretical model for the efficiency enhancement factor....
Energy Technology Data Exchange (ETDEWEB)
Restrepo, R.L., E-mail: pfrire@eia.edu.co [Department of Physics, Cumhuriyet University, 58140 Sivas (Turkey); Escuela de Ingeniería de Antioquia-EIA, Envigado (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); Ungan, F.; Kasapoglu, E. [Department of Physics, Cumhuriyet University, 58140 Sivas (Turkey); Mora-Ramos, M.E. [Facultad de Ciencias, Universidad Autonóma del Estado de Morelos, Ave. Universidad 1001, CP 62209, Cuernavaca, Morelos (Mexico); Morales, A.L.; Duque, C.A. [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)
2015-01-15
This paper presents the results of the theoretical study of the effects of non-resonant intense laser field and electric and magnetic fields on the optical properties (the linear and third-order nonlinear refractive index and absorption coefficients) in an asymmetric quantum well. The electric field and intense laser field are applied along the growth direction of the asymmetric quantum well and the magnetic field is oriented perpendicularly. To calculate the energy and the wave functions of the electron in the asymmetric quantum well, the effective mass approximation and the method of envelope wave function are used. The asymmetric quantum well is constructed by using different aluminium concentrations in both right and left barriers. The confinement in the quantum well is changed drastically by either the effect of electric and magnetic fields or by the application of intense laser field. The optical properties are calculated using the compact density matrix approach. The results show that the effect of the intense laser field competes with the effects of the electric and magnetic fields. Consequently, peak position shifts to lower photon energies due to the effect of the intense laser field and it shifts to higher photon energies by the effects of electric and magnetic fields. In general, it is found that the concentration of aluminum, electric and magnetic fields and intense laser field are external agents that modify the optical responses in the asymmetric quantum well.
Perovskite light-emitting diodes based on solution-processed self-organized multiple quantum wells
Wang, Nana; Cheng, Lu; Ge, Rui; Zhang, Shuting; Miao, Yanfeng; Zou, Wei; Yi, Chang; Sun, Yan; Cao, Yu; Yang, Rong; Wei, Yingqiang; Guo, Qiang; Ke, You; Yu, Maotao; Jin, Yizheng; Liu, Yang; Ding, Qingqing; di, Dawei; Yang, Le; Xing, Guichuan; Tian, He; Jin, Chuanhong; Gao, Feng; Friend, Richard H.; Wang, Jianpu; Huang, Wei
2016-11-01
Organometal halide perovskites can be processed from solutions at low temperatures to form crystalline direct-bandgap semiconductors with promising optoelectronic properties. However, the efficiency of their electroluminescence is limited by non-radiative recombination, which is associated with defects and leakage current due to incomplete surface coverage. Here we demonstrate a solution-processed perovskite light-emitting diode (LED) based on self-organized multiple quantum wells (MQWs) with excellent film morphologies. The MQW-based LED exhibits a very high external quantum efficiency of up to 11.7%, good stability and exceptional high-power performance with an energy conversion efficiency of 5.5% at a current density of 100 mA cm-2. This outstanding performance arises because the lower bandgap regions that generate electroluminescence are effectively confined by perovskite MQWs with higher energy gaps, resulting in very efficient radiative decay. Surprisingly, there is no evidence that the large interfacial areas between different bandgap regions cause luminescence quenching.
Two-dimensional hole systems in indium-based quantum well heterostructures
Energy Technology Data Exchange (ETDEWEB)
Loher, Josef
2016-08-01
The complex spin-orbit interaction (SOI) of two-dimensional hole gas (2DHG) systems - the relativistic coupling of the hole spin degree of freedom to their movement in an electric field - is of fundamental interest in spin physics due to its key role for spin manipulation in spintronic devices. In this work, we were able to evaluate the tunability of Rashba-SOI-related parameters in the 2DHG system of InAlAs/InGaAs/InAs:Mn quantum well heterostructures experimentally by analyzing the hole density evolution of quantum interference effects at low magnetic fields. We achieved to cover a significant range of hole densities by the joint action of the variation of the manganese modulation doping concentration during molecular beam epitaxy and external field-effect-mediated manipulation of the 2D carrier density in Hall bar devices by a metallic topgate. Within these magnetotransport experiments, a reproducible phenomenon of remarkable robustness emerged in the transverse Hall magnetoresistivity of the indium 2DHG systems which are grown on a special InAlAs step-graded metamorphic buffer layer structure to compensate crystal lattice mismatch. As a consequence of the strain relaxation process, these material systems are characterized by anisotropic properties along different crystallographic directions. We identify a puzzling offset phenomenon in the zero-field Hall magnetoresistance and demonstrate it to be a universal effect in systems with spatially anisotropic transport properties.
Properties of a charge in the nanoheterosystems with quantum wells and barriers
Directory of Open Access Journals (Sweden)
V.I. Boichuk
2010-01-01
Full Text Available In the paper a quasi-one-dimensional three-layer nanowire (NW with an intermediate layer at the separation boundaries is described by the Kronig-Penney model with δ-function potentials. The distance between the last or supreme atoms of the intermediate layer is a parameter of the problem and ranges from zero to two lattice parameters of crystals. A precise solution is obtained for the quantum-mechanical reflection coefficient R which makes it possible to determine the dependence of the factor on a wave vector, widths of an intermediate layer and a monolayer of the nanoheterostructure. The specific calculations are performed for the GaAs/AlAs/GaAs and AlAs/GaAs/AlAS nanowires. The comparison of the reflection coefficients in the envelope-function approximation and in the effective mass method is performed at small values of a wave vector. It is shown that similar results can be received using the refined procedure, originally proposed by Harrison, with appropriately taken parameters. For the cosinusoidal dependence of the energy on a wave vector which arises in the Kronig-Penney model within the framework of the S-matrix scattering method, we determined the binding states energy for a AlAs/GaAs/AlAs quantum well wire.
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.
RT CW operation of InGaN multi-quantum-well structure laser diodes
Directory of Open Access Journals (Sweden)
Shuji Nakamura
1998-01-01
Full Text Available 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 external quantum efficiencies of 7.5% at 371 nm (UV, 11.2% at 468 nm (blue and 11.6% at 520 nm (green, respectively, which were the highest values ever reported for the LEDs with those shorter emission wavelengths. The luminous efficiencies of blue and green LEDs were 5 lm/W and 30 lm/W, respectively, which values are almost identical to that of the white conventional incandescent bulb lamp (20 lm/W. By combining the blue, green and red LEDs, we could fabricate white LEDs with a luminous efficiency of 20–30 im/W which is almost comparable to that of the incandescent bulb lamp. Thus, we can replace the conventional incandescent bulb lamps with these LEDs in order to save an energy consumption and natural resources now.
Directory of Open Access Journals (Sweden)
Manvir S. Kushwaha
2012-09-01
Full Text Available The most fundamental approach to an understanding of electronic, optical, and transport phenomena which the condensed matter physics (of conventional as well as nonconventional systems offers is generally founded on two experiments: the inelastic electron scattering and the inelastic light scattering. This work embarks on providing a systematic framework for the theory of inelastic electron scattering and of inelastic light scattering from the electronic excitations in GaAs/Ga1−xAlxAs quantum wells. To this end, we start with the Kubo's correlation function to derive the generalized nonlocal, dynamic dielectric function, and the inverse dielectric function within the framework of Bohm-Pines’ random-phase approximation. This is followed by a thorough development of the theory of inelastic electron scattering and of inelastic light scattering. The methodological part is then subjected to the analytical diagnoses which allow us to sense the subtlety of the analytical results and the importance of their applications. The general analytical results, which know no bounds regarding, e.g., the subband occupancy, are then specified so as to make them applicable to practicality. After trying and testing the eigenfunctions, we compute the density of states, the Fermi energy, the full excitation spectrum made up of intrasubband and intersubband – single-particle and collective (plasmon – excitations, the loss functions for all the principal geometries envisioned for the inelastic electron scattering, and the Raman intensity, which provides a measure of the real transitions induced by the (laser probe, for the inelastic light scattering. It is found that the dominant contribution to both the loss peaks and the Raman peaks comes from the collective (plasmon excitations. As to the single-particle peaks, the analysis indicates a long-lasting lack of quantitative comparison between theory and experiments. It is inferred that the inelastic electron
Wang, Qin; Savage, Susan; Persson, Sirpa; Noharet, Bertrand; Junique, Stéphane; Andersson, Jan Y.; Liuolia, Vytautas; Marcinkevicius, Saulius
2009-02-01
We have demonstrated surface normal detecting/filtering/emitting multiple functional ultraviolet (UV) optoelectronic devices based on InGaN/GaN, InGaN/AlGaN and AlxGa1-xN/AlyGa1-yN multiple quantum well (MQW) structures with operation wavelengths ranging from 270 nm to 450 nm. Utilizing MQW structure as device active layer offers a flexibility to tune its long cut-off wavelength in a wide UV range from solar-blind to visible by adjusting the well width, well composition and barrier height. Similarly, its short cut-off wavelength can be adjusted by using a GaN or AlGaN block layer on a sapphire substrate when the device is illuminated from its backside, which further provides an optical filtering effect. When a current injects into the device under forward bias the device acts as an UV light emitter, whereas the device performs as a typical photodetector under reverse biases. With applying an alternating external bias the device might be used as electroabsorption modulator due to quantum confined Stark effect. In present work fabricated devices have been characterized by transmission/absorption spectra, photoresponsivity, electroluminescence, and photoluminescence measurements under various forward and reverse biases. The piezoelectric effect, alloy broadening and Stokes shift between the emission and absorption spectra in different InGaN- and AlGaN-based QW structures have been investigated and compared. Possibilities of monolithic or hybrid integration using such multiple functional devices for biological warfare agents sensing application have also be discussed.
Energy Technology Data Exchange (ETDEWEB)
Naquin, Clint; Lee, Mark [Department of Physics, University of Texas at Dallas, Richardson, Texas 75080 (United States); Edwards, Hal; Mathur, Guru; Chatterjee, Tathagata; Maggio, Ken [Texas Instruments, Inc., Richardson, Texas 75243 (United States)
2014-11-24
Introducing explicit quantum transport into Si transistors in a manner amenable to industrial fabrication has proven challenging. Hybrid field-effect/bipolar Si transistors fabricated on an industrial 45 nm process line are shown to demonstrate explicit quantum transport signatures. These transistors incorporate a lateral ion implantation-defined quantum well (QW) whose potential depth is controlled by a gate voltage (V{sub G}). Quantum transport in the form of negative differential transconductance (NDTC) is observed to temperatures >200 K. The NDTC is tied to a non-monotonic dependence of bipolar current gain on V{sub G} that reduces drain-source current through the QW. These devices establish the feasibility of exploiting quantum transport to transform the performance horizons of Si devices fabricated in an industrially scalable manner.
Dzyadukh, S.; Nesmelov, S.; Voitsekhovskii, A.; Gorn, D.
2016-08-01
The paper presents brief research results of the admittance of metal-insulator- semiconductor (MIS) structures based on Hg1-xCdxTe grown by molecular-beam epitaxy (MBE) method including single HgCdTe/HgTe/HgCdTe quantum wells (QW) in the surface layer. The thickness of a quantum well was 5.6 nm, and the composition of barrier layers with the thickness of 35 nm was close to 0.65. Measurements were conducted in the range of temperatures from 8 to 200 K. It is shown that for structure with quantum well based on HgTe capacitance and conductance oscillations in the strong inversion are observed. Also it is assumed these oscillations are related with the recharging of quantum levels in HgTe.
Well-width dependence of exciton-phonon scattering in InxGa1 - xAs/GaAs single quantum wells
DEFF Research Database (Denmark)
Borri, Paola; Langbein, Wolfgang Werner; Hvam, Jørn Märcher
1999-01-01
The temperature and density dependencies of the exciton dephasing time in In0.18Ga0.82As/GaAs single quantum wells with different thicknesses have been measured by degenerate four-wave mixing; The exciton-phonon scattering contribution to the dephasing is isolated by extrapolating the dephasing r...
Electric field dependence of hybridized gap in InAs/GaSb quantum well system
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.
Transparent waveguides for WDM transmitter arrays using quantum well shape modification
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.
Epitaxial aluminum on hybridized InAs/GaSb quantum wells
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.
Harsh photovoltaics using InGaN/GaN multiple quantum well schemes
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.
THz Acoustic Spectroscopy by using Double Quantum Wells and Ultrafast Optical Spectroscopy
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.
Exciton effective mass enhancement in coupled quantum wells in electric and magnetic fields
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.
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.
Fine structures in the electroabsorption spectra of GaAs quantum wells
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.
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.
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.
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.
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.
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.
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.
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.
Photoluminescence and electroluminescence from Ge/strained GeSn/Ge quantum wells
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.
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.
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.
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.
Room-temperature mid-infrared quantum well lasers on multi-functional metamorphic buffers
Jung, Daehwan; Yu, Lan; Dev, Sukrith; Wasserman, Daniel; Lee, Minjoo Larry
2016-11-01
The modern commercial optoelectronic infrastructure rests on a foundation of only a few, select semiconductor materials, capable of serving as viable substrates for devices. Any new active device, to have any hope of moving past the laboratory setting, must demonstrate compatibility with these substrate materials. Across much of the electromagnetic spectrum, this simple fact has guided the development of lasers, photodetectors, and other optoelectronic devices. In this work, we propose and demonstrate the concept of a multi-functional metamorphic buffer (MFMB) layer that not only allows for growth of highly lattice-mismatched active regions on InP substrates but also serves as a bottom cladding layer for optical confinement in a laser waveguide. Using the MFMB concept in conjunction with a strain-balanced multiple quantum well active region, we demonstrate laser diodes operating at room temperature in the technologically vital, and currently underserved, 2.5-3.0 μm wavelength range.
Gain properties of doped GaAs/AlGaAs multiple quantum well avalanche photodiode structures
Menkara, H. M.; Wagner, B. K.; Summers, C. J.
1995-01-01
A comprehensive characterization has been made of the static and dynamical response of conventional and multiple quantum well (MQW) avalanche photodiodes (APDs). Comparison of the gain characteristics at low voltages between the MQW and conventional APDs show a direct experimental confirmation of a structure-induced carrier multiplication due to interband impact ionization. Similar studies of the bias dependence of the excess noise characteristics show that the low-voltage gain is primarily due to electron ionization in the MQW-APDS, and to both electron and hole ionization in the conventional APDS. For the doped MQW APDS, the average gain per stage was calculated by comparing gain data with carrier profile measurements, and was found to vary from 1.03 at low bias to 1.09 near avalanche breakdown.