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1
Dynes, James Francis. "Quantum optics in intersubband transitions in semiconductor quantum wells." Thesis, Imperial College London, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.413944.
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2
Serapiglia, Gerard Brendan. "High intensity mid infra-red spectroscopy of intersubband transitions in semiconductor quantum wells." Thesis, Imperial College London, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.313400.
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Chaminda, Thirimadura De Zoysa Menaka. "Thermal Emission Control by Intersubband Transitions in Quantum Wells and Two-Dimensional Photonic Crystals." 京都大学 (Kyoto University), 2012. http://hdl.handle.net/2433/157590.
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4
Alves, Fábio Durante Pereira. "Three-band quantum well infrared photodetector using interband and intersubband transitions." Instituto Tecnológico de Aeronáutica, 2008. http://www.bd.bibl.ita.br/tde_busca/arquivo.php?codArquivo=523.
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This thesis presents the modeling, design, fabrication and characterization of a quantum well infrared photodetector (QWIP) capable of detecting near infrared (NIR), mid wavelength infrared (MWIR) and long wavelength infrared (LWIR), simultaneously. The NIR detection was achieved using interband transition while MWIR and LWIR were based on intersubband transition in the conduction band. The quantum-well structure was modeled by solving self-consistently the Schrödinger and Poisson equations with the help of the shooting method. A sample with three different stacks of quantum wells formed by different configurations of GaAs, AlGaAs and InGaAs, separated by n-doped GaAs contact layers was grown on a semi-insulated GaAs substrate using MBE (Molecular Beam Epitaxy). Intersubband absorption in the sample was measured for the MWIR and LWIR using Fourier transform spectroscopy (FTIR) and the measured peak positions were found at 5.3 and 8.7 ?m, respectively which are within 5% of the theoretical values, indicating the good accuracy of the self-consistent model. The test photodetectors were fabricated using a standard photolithography process with exposed middle contacts to allow separate bias and readout of signals from the three wavelength bands. A 45 degree facet was polished to allow light coupling. Performance analyses were conducted in order to obtain the I-V characteristics, responsivity and detectivity of each detection band. The background-limited infrared performance (BLIP) for the LWIR quantum wells shows an upper operating temperature of about 70 K, limiting the overall device. Photocurrent spectroscopy was performed and gave three peaks at 0.84, 5.0 and 8.5 m wavelengths with approximately 0.5, 0.03 and 0.13 A/W peak responsivities for NIR, MWIR and LWIR bands, respectively. Estimated peak detectivities, limited by the number of quantum well repetitions, are 140, 1.6 and 1.2x109 cm.Hz1/2/W for NIR, MWIR and LWIR, respectively. The overall results demonstrate the possibility of detection of widely separated wavelength bands, in a single pixel device, using interband and intersubband transitions in quantum wells.
5
Zybell, Sabine. "Relaxation dynamics in photoexcited semiconductor quantum wells studied by time-resolved photoluminescence." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-187690.
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Gegenstand der vorliegenden Arbeit ist die Untersuchung der Photoluminenzenzdynamik von Halbleiter-Quantentöpfen (Quantum Wells), die durch Anregung von Intraband-Übergängen mittels resonanter Laserpulse im mittleren Infrarot- und Terahertz-Spektralbereich verändert wird. Diese Zweifarbenexperimente wurden mit Hilfe eines optischen Aufbaus für zeitaufgelöste Photolumineszenzspektroskopie am Großgerät Freie-Elektronen Laser FELBE am Helmholtz-Zentrum Dresden-Rossendorf realisiert. Zeitlich verzögert zur gepulsten optischen Anregung über die Bandlücke wurden Intersubband- oder Intraexziton-Übergänge in den Quantum Wells resonant angeregt.
Die dadurch erreichte Ladungsträgerumverteilung zeigt sich in einer deutlichen Verringerung der Photolumineszenzintensität zum Zeitpunkt des zweiten Anregepulses, die im Folgenden als Photolumineszenz-Quenching bezeichnet wird. Zunächst wird die Stärke des Photolumineszenz-Quenchings in Abhängigkeit der Polarisationsrichtung des midinfraroten Laserstrahls ausgewertet. Während die Absorption durch freie Ladungsträger für beide Polarisationsrichtungen nachweisbar ist, wird experimentell gezeigt, dass Intersubbandabsorption nur möglich ist, wenn ein Anteil der anregenden Strahlung senkrecht zur Quantum-Well-Ebene polarisiert ist.
Das Photolumineszenzsignal ist überwiegend an der energetischen Position der 1s-Exzitonresonanz unterhalb der Bandkante messbar. Die intraexzitonischen Übergangsenergien in Quantum Wells liegen typischerweise im Terahertzbereich. Unter intraexzitonischer 1s-2p Anregung erscheint auch auf dieser Energieskala ein abrupter Intensitätsverlust in der langsam abklingenden Photolumineszenztransiente. Erstmalig wurde im Photolumineszenzspektrum bei höheren Energien im Abstand der Terahertz-Photonenenergie ein zusätzliches 2s-Photolumineszenzsignal detektiert.
Eine detaillierte theoretische Beschreibung dieses Problems durch unsere Kooperationspartner Koch et al. von der Phillips-Universität Marburg zeigt, dass unter intraexzitonischer 1s-2p Anregung eine effziente Coulombstreuung zwischen den nahezu entarteten exzitonischen 2p- und 2s-Zuständen stattfindet. Während der 2p-Zustand optisch dunkel ist, kann die 2s-Population strahlend rekombinieren, was zu dem besagten 2s-Photolumineszenzsignal führt. Die Zeitkonstanten der untersuchten Ladungsträgerdynamik werden durch ein phänomenologisches Modell bestimmt, das die experimentellen Kurven sehr gut abbildet.
Es wird ein Ratengleichungsmodell eingeführt, bei dem die involvierten Zustände auf optisch helle und optisch dunkle Besetzungsdichten reduziert werden. Darüber hinaus werden mit einem modifizierten Versuchsaufbau die Terahertz-induzierten Photolumineszenzsignaturen von Magnetoexzitonen untersucht. Die Stärke des 1s-Photolumineszenz-Quenchings ändert sich dabei entsprechend der magnetoexzitonischen Übergänge, die im betrachteten Feldstärkebereich zwischen 0T und 7T liegen. Für Magnetfelder größer als 3T sind keine 2s-Photolumineszenzsignale mehr messbar, da durch das externe magnetische Feld die Entartung der 2p- und 2s-Zustände aufgehoben wird.
6
Chazapish, Vassilis. "Mid-infrared saturation spectroscopy of III-V multi-quantum well intersubband transitions." Thesis, Imperial College London, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.265245.
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7
Smet, Jurgen Hubert. "Intrawell and interwell intersubband transitions in single and multiple quantum well heterostructures." Thesis, Massachusetts Institute of Technology, 1995. http://hdl.handle.net/1721.1/11853.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1995.<br>Includes bibliographical references (p. 228-251).<br>by Jurgen Hubert Smet.<br>Ph.D.
8
Dang, Thi Uyen-Khanh [Verfasser], and Andreas [Akademischer Betreuer] Knorr. "Intersubband transitions in low-dimensional nanostructures Many-body effects in quantum wells and quantum dots / Thi Uyen-Khanh Dang. Betreuer: Andreas Knorr." Berlin : Universitätsbibliothek der Technischen Universität Berlin, 2012. http://d-nb.info/1028912927/34.
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9
Dongyeon, Kang. "Mid-Wavelength Infrared Thermal Emitters using GaN/AIGaN Quantum Wells and Photonic Crystals." Kyoto University, 2018. http://hdl.handle.net/2433/232483.
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10
Machhadani, Houssaine. "Transitions intersousbandes dans les puits quantiques GaN/AlN du proche infrarouge au THz." Phd thesis, Université Paris Sud - Paris XI, 2011. http://tel.archives-ouvertes.fr/tel-00591962.
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Les transitions intersousbandes dans les hétérostructures de nitrure d'éléments III ont été intensément étudiées dans le proche infrarouge pour des applications télécoms. L'accordabilité dans le proche infrarouge est rendu possible grâce à la discontinuité de potentiel en bande de conduction qui peut atteindre 1.75 eV pour le système GaN/AlN. Les matériaux nitrures suscitent actuellement un grand intérêt à plus grande longueur d'onde infrarouge. C'est par exemple le développement de détecteurs et d'imageurs rapides à cascade quantique dans la gamme 2-5 µm. C'est aussi l'extension des dispositifs intersousbandes dans le domaine de fréquences THz. Ce travail de thèse porte sur l'étude des transitions intersousbandes dans les puits quantiques GaN/Al(Ga)N épitaxiés par jets moléculaires. Le but est d'accorder ces transitions dans une gamme spectrale très large allant du proche au lointain infrarouge. Je montre que les transitions ISB peuvent être accordées dans la gamme 1-12 µm dans les puits quantiques GaN/AlGaN en phase hexagonale synthétisés selon l'axe polaire c [0001]. Ceci impose l'ingénierie du champ électrique interne, dont la valeur peut atteindre dans le GaN 10 MV/cm. Une solution alternative consiste à utiliser une orientation particulière, dite semipolaire, qui conduit à une réduction du champ électrique interne le long de l'axe de croissance [11-22]. J'ai montré que cette réduction du champ interne permet d'accorder les résonances intersousbandes des puits quantiques GaN/AlN dans le proche infrarouge et j'ai pu estimer le champ en comparant les résultats de spectroscopie et simulations. J'ai d'autre part étudié les propriétés interbandes et intersousbandes des puits quantiques de symétrie cubique, qui par raison de symétrie, ne présentent pas de champ électrique interne. Finalement j'ai mis en évidence les premières transitions intersousbandes aux fréquences THz dans les puits quantiques GaN/AlGaN polaires mais aussi cubiques.
11
Yildirim, Hasan. "Nonlinear Optical Properties Of Semiconductor Heterostructures." Phd thesis, METU, 2006. http://etd.lib.metu.edu.tr/upload/12607438/index.pdf.
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The nonlinear optical properties of semiconductor heterostructures, such as GaAsAl/GaAs alloys, are studied with analytic and numerical methods on the basis of quantum mechanics. Particularly, second and third-order nonlinear optical properties of quantum wells described by the various types of confining potentials are considered within the density matrix formalism. We consider a Pö<br>schl-Teller type potential which has been rarely considered in this area. It has a tunable asymmetry parameter, making it a good candidate to investigate the effect of the asymmetry on the nonlinear optical properties. The calculated nonlinear quantities include nonlinear absorption coefficient, second-harmonic generation, optical rectification, third-harmonic generation and the intensity-dependent refractive index. The effects of the DC electric field on the corresponding nonlinearities are also studied. The results are in good agreement with the results obtained in other types of quantum wells, such as square and parabolic quantum wells. The effects of the Coulomb interaction among the electrons on the nonlinear intersubband absorption are considered within the rotating wave approximation. The result is applied to a Si-delta-doped, square quantum well in which the Coulomb interaction among the electrons are relatively important, since there has been no work on the nonlinear absorption spectrum of the Si-delta-doped quantum well. The results are found to be new and interesting, especially when a DC electric field is included in the calculations.
12
Xu, Yuanjian Yariv Amnon. "Quantum well intersubband transition detection and modulation /." Diss., Pasadena, Calif. : California Institute of Technology, 1997. http://resolver.caltech.edu/CaltechETD:etd-05112005-153655.
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13
Cheung, Colleen Yue Ling. "Intersubband optical processes in semiconductor quantum wells." Thesis, Bangor University, 1998. https://research.bangor.ac.uk/portal/en/theses/intersubband-optical-processes-in-semiconductor-quantum-wells(d2bab1ac-50a1-4390-a2f1-7a100e2776ad).html.
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In this thesis, several aspects of the optical properties of intersubband semiconductor lasers are studied theoretically, including the waveguiding properties of quantum cascade lasers (QCLs), the anticipated modulation bandwidth, gain and threshold current of intersubband lasers, and the engineering of nonlinear susceptibilities in intersubband quantum well structures. Using two computational solvers, for the Helmholtz and Schrödinger Equations respectively, optical waveguide structures and multi quantum well (MQW) structures are designed for subsequent research. The waveguide design of a QCL reported by the Bell Labs reseachers is analysed and improved upon. A four level rate equation model was used to obtain the population inversion condition and modulation response for a triple quantum well structure (TQW) designed for intersubband lasing. An analytical expression for the modulation response is first obtained, followed by a numerical computation to verify the results. It is demonstrated that there is a unique dependence of the modulation bandwidth upon the output power of the laser, and that the maximum modulation frequency does not increase monotonically with optical output power as is the case with conventional semiconductor lasers. An expression describing the optical gain of intersubband lasers is also derived. Using this, investigations into the predicted achievable gain in mid-infrared (MIR) and near-infrared (NIR) intersubband lasers are conducted. It is found that the NIR gain is at least an order of magnitude higher than that of the MIR case. Self-consistent calculations of the optical gain are also undertaken, where the rate equations and the optical gain equations are solved alternately. An intersubband structure is designed for both triple harmonic generation (THG) and four-wave mixing (FWM). The third order nonlinear susceptibilities of these respective processes in the structure were calculated and found to be comparable to those of structures designed for just one process.
14
Khan-ngern, Somporn. "Theroretical investigations of intersubband relaxation in quantum wells." Thesis, University of Sheffield, 2002. http://etheses.whiterose.ac.uk/5985/.
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In this thesis intersubband relaxation of electrons in quantum wells is theoretically investigated. Firstly, the in-plane kinetic energy, and also well width dependences of electron intra- or intersubband scattering rates (or times), associated by longitudinal optical (LO) phonon emission in a semiconductor single quantum well (SQW) structure are presented. Semi-analytic calculations are carried out for a GaAs/AlO. 3GaO. 7As SQW structure. The results show that the scattering rates (both for intra- and intersubband scattering) weakly depend on in-plane kinetic energy of the electron. Further- more, the resulting calculations of well width dependence show that intrasubband scattering times gradually increase with well width contrasting with the intersubband scattering times which display a monotonic decrease. A theoretical study of the condition to achieve inverted population in a semiconductor double quantum well (DQW) structure is also presented. The LO-phonon assisted tunneling rates, based on the Fr6hlich interaction and Fermi's golden rule, has been performed for a GaAs/Alo. 3Gao. 7As DQW structure. The calculated results show that the tunneling rates monotonically decrease with the energy difference El- El and strongly depend on the magnitude of the transfer integral M. This work has been extended to calculate the electron transport and its kinetics, due to various types of scattering and tunneling mechanisms in a triple barrier resonant tunneling structure (TBRTS). A system of coupled kinetic equations that describe the nonequilibrium electrons in the structure has been solved analytically to obtain sub- band distribution functions and gain spectra. Finally, the concept of sequential tunneling has been introduced to explain an in- plane magnetic field dependence of resonant tunneling in a TBRTS. Typical current- voltage characteristics and derivatives for the TBRTS with particular design parameters have been calculated. It is found in the second derivative of the current that the resonance between El and Ej is manifested as a visible feature in the background of a wide E2 resonance. This feature has a sharp local maximum in the absence of applied magnetic field, and becomes flattened with increasing magnetic field in agreement with experiments.
15
Wong, KuanMeng. "Modelling of intersubband absorption in modulation doped deep quantum wells." Thesis, University of Bath, 2007. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.438621.
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Schumacher, Kimberly Lydia. "Femtosecond time-resolved intersubband relaxation measurements in GaAs/AlGaAs quantum wells." Thesis, University of Cambridge, 1995. https://www.repository.cam.ac.uk/handle/1810/270439.
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Waldmüller, Inès. "Intersubband dynamics in semiconductor quantum wells linear and nonlinear response of quantum confined electrons /." [S.l.] : [s.n.], 2005. http://deposit.ddb.de/cgi-bin/dokserv?idn=973598247.
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18
Eickemeyer, Felix. "Ultrafast dynamics of coherent intersubband polarizations in quantum wells and quantum cascade laser structures." Doctoral thesis, [S.l.] : [s.n.], 2002. http://dochost.rz.hu-berlin.de/dissertationen/eickemeyer-felix-2002-07-03.
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Archambault, Alexandre. "Optique des ondes de surface : super-résolution et interaction matière-rayonnement." Phd thesis, Université Paris Sud - Paris XI, 2011. http://tel.archives-ouvertes.fr/tel-00678073.
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Il existe au niveau d'interfaces séparant des milieux de constantes diélectriques de signes opposés des ondes électromagnétiques confinées à proximité de ces interfaces. On parle d'ondes de surface. C'est notamment le cas des métaux et des cristaux polaires : on parle alors de plasmons-polaritons de surface et de phonons-polaritons de surface respectivement. L'objectif de cette thèse est de revisiter certains aspects théoriques associés à ces ondes de surface.Dans un premier temps, en nous basant sur le formalisme de Green, nous donnons un moyen d'obtenir une expression du champ des ondes de surface sous forme de somme de modes. En présence de pertes, ces ondes ont nécessairement un vecteur d'onde ou une pulsation complexe. Nous donnons ainsi deux expressions de leur champ, correspondant à chacun de ces deux cas, et discutons de l'opportunité d'utiliser l'une ou l'autre de ces expressions.Nous posons par la suite les bases d'une optique de Fourier et d'une optique géométrique des ondes de surface. Nous montrons comment obtenir une équation de Helmholtz à deux dimensions pour les ondes de surface, un principe d'Huygens-Fresnel pour les ondes de surface, ainsi qu'une équation eikonale pour les ondes de surface, qui s'applique sous certaines hypothèses. Nous nous intéressons également à la superlentille proposée par Pendry, qui s'appuie sur les ondes de surface. Nous étudions notamment le fonctionnement de cette superlentille en régime impulsionnel, et montrons qu'en présence de pertes, il est possible d'obtenir une meilleure résolution avec certaines formes d'impulsion par rapport au régime harmonique, au prix d'une importante baisse de signal toutefois.Nous développons ensuite un traitement quantique des ondes de surface. Nous calculons au préalable une expression de leur énergie, et nous donnons une expression de leur hamiltonien et de leurs opérateurs champ. Sans pertes, nous montrons que le facteur de Purcell prédit par notre théorie quantique est rigoureusement égal au facteur de Purcell calculé avec des outils classiques. Nous comparons ensuite ce facteur de Purcell à celui calculé classiquement avec pertes, et montrons sur un exemple que les pertes peuvent être négligées dans de nombreux cas. Nous donnons enfin une expression des coefficients d'Einstein associés aux ondes de surface permettant d'étudier la dynamique de l'inversion de population d'un milieu fournissant un gain aux ondes de surface. Nous appliquons par la suite ce formalisme quantique à l'interaction électrons-phonons-polaritons de surface dans les puits quantiques, notamment leur interaction avec un mode de phonon du puits particulièrement confiné grâce à un effet de constante diélectrique proche de zéro (epsilon near zero, ENZ).
20
Steed, Robert John. "Saturation of Intersubband Transitions in p-type and N-type III-V Qua'ntum Wells." Thesis, Imperial College London, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.487524.
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Intersubband transitions (ISBTs) in quantum wells have had extensive prior research but remain interesting. This thesis continues the use of saturation experiments for the characterisation of ISBT relaxation times ie. the time taken for carriers to scatter between a quantum well's subbands. Saturation experiments were carried out using an optical parametric generator as a tunable source of mid-infrared laser light (6.4 --t 8.6 pm) and intensities of -200MWcm-2 were reached. For this thesis, two p-doped samples were saturated, each sample containing multiple GaAs/AIGaAs quantum wells. Both sample's quantum wells had two confined heavy hole levels and the ISBTs between them, had energies of 160meV and 183meV (respectively). The hhl-hh2 ISBTs were saturated for each sample, the measured carrier relaxation times were 0.3 ± 0.1 ps and 2 ± 1.4 ps respectively, indicating that relaxation occurred via LO phonon emission (for comparison, an n-type quantum well with an ISBT of similar energy would have a relaxation time between 0.3 --t 0.6 ps). The effect of circularly polarised light on the carrier dynamics ofn-doped GaAs/AIGaAs quantum wells was also investigated. Circularly polarised light can lead to spin-sensitive ISBTs; this has been shown to lead to a change in the ISBT's saturation intensity for circularly polarised light due to the addition of the spin-relaxation time to the carrier dynamics. For this thesis, saturation experiments were performed using light incident at an oblique incidence to the QWs (via a novel sample geometry) but no significant differences in saturation intensity were {ound between using circularly and linearly polarised light.
21
SOUZA, MARCIO SCARPIM DE. "DEVELOPMENT OF FAR-INFRARED PHOTODETECTORS BASED ON INTRABAND TRANSITIONS IN GAAS/ALGAAS MULTI-QUANTUM WELLS." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2006. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=8714@1.
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FINANCIADORA DE ESTUDOS E PROJETOS<br>Nas Forças Armadas do Brasil existe uma forte demanda pelo
desenvolvimento de detectores de infravermelho nacionais
para uso em diversas
aplicações sujeitas a rígidas restrições de importação,
como sistemas de
imageamento infravermelho para visão noturna, guiamento de
mísseis, sistemas de
mira, etc. O objetivo deste trabalho foi desenvolver
fotodetectores para o
infravermelho distante em 10µm, baseados em estruturas
semicondutoras de poços
quânticos múltiplos de GaAs/AlGaAs utilizando transições
intrabanda. Os
materiais foram crescidos pela técnica de epitaxia de fase
vapor de metalorgânicos
(MOVPE). A calibração dos parâmetros de crescimento foi
realizada por meio de
medidas de difração de raios x, efeito Hall, e
fotoluminescência. Devido à regra de
seleção de que não é possível haver absorção intrabanda da
luz sob incidência
normal, foram aplicadas duas técnicas de acoplamento:
geometria de guia de onda
com incidência a 45º pela borda, e utilização de grades de
difração metalizadas.
Os detectores produzidos foram caracterizados quanto à
corrente de escuro e
quanto aos espectros de absorção óptica e de fotocorrente,
ambos obtidos por
espectroscopia FTIR. Ao final dos trabalhos, foi obtido um
fotodetector de
GaAs/AlGaAs do qual foi possível medir a fotocorrente
através dos contatos
elétricos do dispositivo, com pico em 9µm. Os resultados
obtidos são promissores
no sentido de que apontam para a possibilidade de se
produzir detectores de
infravermelho nacionais para diversas aplicações (defesa,
medicina, astronomia,
telecomunicações, etc).<br>In the Brazilian Army there is a strong demand for the
development of
national infrared detectors for use in many applications
subjected to severe trade
restrictions, like infrared imaging systems for night
vision, missile guidance, sight
systems, etc. The aim of this work was to develop far-
infrared photodetectors for
10µm, based on semiconductor structures of GaAs/AlGaAs
multi-quantum wells
using intraband transitions. The materials were grown by
metalorganic vapor
phase epitaxy (MOVPE). The calibration of the growing
parameters was done by
x ray diffraction, Hall effect, and photoluminescence
measurements. Since
intraband transition of light is not possible to normal
incidence, due to selection
rules, two coupling techniques were applied: waveguide
geometry with 45o
incidence on the edge, and metalized diffraction gratings.
The produced detectors
were characterized in terms of dark current, optical
absorption and spectral
response. Infrared measurements were made using FTIR
spectroscopy. A
GaAs/AlGaAs photodetector was obtained. The photocurrent
through the
electrical contacts of the device showed a peak at 9µm.
The results are promising
in the sense of revealing the possibility of producing
national infrared
photodetectors for many applications (defense, medicine,
astronomy,
telecommunications, etc).
22
Semtsiv, Mykhaylo. "InGaAs-AlAs and InGaAs-InGaP strain-compensated heterostructures for short wavelength intersubband transitions and lasers." Doctoral thesis, [S.l. : s.n.], 2004. http://deposit.ddb.de/cgi-bin/dokserv?idn=972710450.
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Bai, Jing. "Optimization of Optical Nonlinearities in Quantum Cascade Lasers." Diss., Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/19797.
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Nonlinearities in quantum cascade lasers (QCL¡¯s) have wide applications in wavelength tunability and ultra-short pulse generation. In this thesis, optical nonlinearities in InGaAs/AlInAs-based mid-infrared (MIR) QCL¡¯s with quadruple resonant levels are investigated. Design optimization for the second-harmonic generation (SHG) of the device is presented. Performance characteristics associated with the third-order nonlinearities are also analyzed.
The design optimization for SHG efficiency is obtained utilizing techniques from supersymmetric quantum mechanics (SUSYQM) with both material-dependent effective mass and band nonparabolicity. Current flow and power output of the structure are analyzed by self-consistently solving rate equations for the carriers and photons. Nonunity pumping efficiency from one period of the QCL to the next is taken into account by including all relevant electron-electron (e-e) and longitudinal (LO) phonon scattering mechanisms between the injector/collector and active regions. Two-photon absorption processes are analyzed for the resonant cascading triple levels designed for enhancing SHG. Both sequential and simultaneous two-photon absorption processes are included in the rate-equation model. The current output characteristics for both the original and optimized structures are analyzed and compared. Stronger resonant tunneling in the optimized structure is manifested by enhanced negative differential resistance. Current-dependent linear optical output power is derived based on the steady-state photon populations in the active region. The second-harmonic (SH) power is derived from the Maxwell equations with the phase mismatch included. Due to stronger coupling between lasing levels, the optimized structure has both higher linear and nonlinear output powers. Phase mismatch effects are significant for both structures leading to a substantial reduction of the linear-to-nonlinear conversion efficiency. The optimized structure can be fabricated through digitally grading the submonolayer alloys by molecular beam epitaxy (MBE).
In addition to the second-order nonlinearity, performance characteristics brought by the third-order nonlinearities are also discussed, which include third-harmonic generation (THG) and intensity dependent (Kerr) refractive index. Linear to third-harmonic (TH) conversion efficiency is evaluated based on the phase-mismatched condition. The enhanced self-mode-locking (SML) effect over a typical three-level laser is predicted, which will stimulate further investigations of pulse duration shortening by structures with multiple harmonic levels.
24
Chastanet, Daniel. "Nouvelles sources compactes dans le moyen-infrarouge : Lasers à cascade quantique au-delà de 16 microns et LED électroluminescentes en régime de couplage fort." Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLS143/document.
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Le lointain infrarouge (16 µm < λ < 30 µm) est un domaine important pour des applications telles que la détection de large molécules organiques (dont les empreintes d'absorption tombe dans cette gamme de longueur d'onde) et pour la radio-astronomie (oscillateurs locaux pour la détection hétérodyne). Malheureusement, cette fenêtre de transparence atmosphérique, communément appelé la 4eme fenêtre de transparence, est un domaine quasi inexploré.Les LCQ sont des sources de lumière cohérentes, couvrant une gamme allant du moyen infrarouge jusqu'au THz, basées sur l'ingénierie de structures de bandes de matériaux semi-conducteurs. Ils démontrent d'excellentes performances dans le domaine du proche infrarouge mais leur efficacité diminue dans la 4ème fenêtre et au-delà.L'un des buts de cette thèse est le développement d'une nouvelle génération de LCQ capable de couvrir cette zone spectral avec de bonnes performances, en terme de puissance de sortie du dispositif et de température maximale d'opération. Un point clé dans cette optique est l'utilisation d'un nouveau système de matériaux pour ces longueurs d'onde : l'InAs/AlSb. L'avantage de cette solution réside dans sa très faible masse effective : 0,023 m0 (comparée à 0,043 m0 dans les puits d'InGaAs), qui permet d’obtenir un gain plus élevé, résultant dans l'amélioration significative des performances.Une autre approche fondamentalement différente réside dans le régime de couplage fort. L'utilisation d'un temps caractéristique ultra-rapide, associé aux oscillations de Rabi, peut permettre dans un premier temps de réaliser des sources électroluminescentes avec un meilleur rendement quantique (comparé à une transition inter-sous-bandes nue). Les pseudos particules qui découlent du régime de couplage fort dans les transitions inter-sous-bandes (appelés polaritons inter-sous-bandes) peuvent sous certaines limites se comporter comme des bosons. On entrevoit alors la possibilité de réaliser des sources cohérentes basées sur la relaxation d'un condensat polaritonique<br>The far infrared (16 µm < λ < 30 µm) is an important area for applications such as detecting wide organic molecules (whose absorption fingerprints falls in this wavelength range) and for radio-astronomy (local oscillator for the heterodyne detection). Unfortunately, the atmospheric transparency window, commonly called the 4th transparency window is almost unexplored.QCL are coherent light sources, covering a range from infrared to THz, based on the engineering of band structures of semiconductors. They have excellent performances in the mid infrared but their effectiveness diminishes in the 4th window and beyond.One aim of this thesis is the development of a new generation of QCL able to cover this spectral region with good performance in terms of output power and maximum operating temperature. A key point in this context is the use of a new material system for these wavelengths: InAs / AlSb. The advantage of this solution is its very small effective mass : 0.023 m0 (compared to 0.043 m0 in the InGaAs wells), which provides a higher gain, resulting in significant performances improvement.Another fundamentally different approach lies in the strong coupling regime. Using an ultra-fast characteristic time associated with Rabi oscillations, can allow the realization of emitting sources with improved quantum efficiency (compared to an bare inter-subband transition). pseudo particles arising from the strong coupling regime in the inter-subband transitions (called polaritons inter-sub-bands) may under certain limits behave as bosons. One then sees the possibility of coherent sources based on the relaxation of a polariton condensate
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Cho, Eun Chel Electrical Engineering UNSW. "Optical transitions in SiO2/crystalline Si/SiO2 quantum wells and nanocrystalline silicon (nc-Si)/SiO2 superlattice fabrication (Restricted for 24 months until Feb. 2006)." Awarded by:University of New South Wales. Electrical Engineering, 2003. http://handle.unsw.edu.au/1959.4/22492.
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Innovation in photovoltaic technology may offer cost competitive options to other energy sources and become a viable solution for the energy and environmental challenges of the 21st century. One proposed innovative technology is based on all-silicon tandem cells, which are constructed using superlattices consisting of environmental friendly Si and its compounds. The well and barrier materials in superlattices are restricted to silicon and silicon oxide during the present study. Single crystalline Si/SiO2 quantum wells (QWs) have been fabricated by thermal oxidation of silicon-on-insulator (SOI) wafers. It is found that oxide properties in QWs are important for SOI wafers prepared by the SIMOX (Separation by Implantation of Oxygen) technique. However, QWs fabricated from SOI wafers prepared by the ELTRAN (Epitaxial Layer TRANsfer) approach show the effect of quantum confinement without evidence of strong oxide interfacial transitions. In these wafers, evidence for an apparently ordered silicon oxide was found with 1.92?atomic fringe spacing along the (110) direction of the Si structure and with the thickness about 17?along the (100) direction of the Si structure. Luminescence wavelength ranges are from 700nm to 918nm depending on the Si thickness. The luminescence measurements on other positions of the sample show peak and shoulder spectra, which are explained by monolayer fluctuations in QW thicknesses, previously observed in III-V QWs and II-VI QWs. Si/SiO2 superlattices are fabricated by RF magnetron sputtering. Si density is the key issue in crystallizing the superlattice. High-density Si layers crystallize either under high temperature furnace annealing or rapid thermal process annealing. However, low density Si would not crystallize even at high temperature. Crystallized nanocrystals in the Si layers are observed by high resolution transmission electron microscopy (HRTEM) when the Si layer is thicker than 3nm. When Si layers are thinner than 3nm, the Si layers are discontinuous and finally deteriorate into small nanocrystals. The suitability of such superlattices for surface passivation and antireflection coatings is reviewed. Initial attempts to fabricate heterojunctions between Si wafers and Si/SiO2 superlattices resulted in open circuit voltage of 252mV. However, it is expected that better results would be obtained if Si/SiO2 superlattices were fully crystallized.
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Lim, Caroline Botum. "Hétérostructures GaN/Al(Ga)N pour l'optoélectronique infrarouge : orientations polaires et non-polaires." Thesis, Université Grenoble Alpes (ComUE), 2017. http://www.theses.fr/2017GREAY030/document.
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Les transitions intersousbandes (ISB) sont des transitions d’énergie entre des états électroniques dans un puits quantique. Les nanostructures GaN/AlGaN sont prometteuses pour le développement de composants optoélectroniques ISB pouvant couvrir la totalité de la gamme infrarouge. Leur large décalage de bande de conduction (~1.8 eV pour les systèmes GaN/AlN) et temps de vie ISB inférieurs au picoseconde les rendent attractifs pour l’optronique ultra-rapide en régime infrarouge courte longueur d’onde (SWIR, 1-3 µm) et moyenne longueur d’onde (MWIR, 3-8 µm). De plus, la grande énergie de phonon longitudinal-optique du GaN (92 meV, 13 µm) offre la possibilité de développer des composants ISB couvrant la bande 5-10 THz, interdite au GaAs, et opérant à température ambiante.Le travail décrit dans ce manuscrit a eu pour objectif d'améliorer les performances des technologies ISB GaN/AlGaN et de contribuer à une meilleure compréhension des problématiques posées par leur extension à la gamme des THz. D’une part, la photodétection ISB nécessite le dopage n des nanostructures. Dans ce travail de thèse, on étudie le Si et le Ge en tant que dopants de type n potentiels pour le GaN. D’autre part, la présence de champs électriques internes dans la direction de confinement des hétérostructures plan c constitue l’un des principaux défis de la technologie GaN ISB. C'est pourquoi on étudie la possibilité d’utiliser des orientations cristalline non-polaires a ou m alternatives pour obtenir des systèmes opérant sans l’influence de ces champs électriques.Concernant l'étude du Ge et du Si comme dopants potentiels, on montre que l’incorporation de Ge dans des couches mince de GaN n’affecte pas leur morphologie, mosaïcité ni photoluminescence. Les propriétés bande-à-bande des nanostructures GaN/AlGaN plan c étudiées sont indifférentes à la nature du dopant, mais les structures à grand désaccord de maille voient leur qualité structurale améliorée par le dopage Ge. Concernant l’alternative non-polaire, on compare des structures à multi-puits quantiques GaN/AlN plan a et plan m. Les meilleurs résultats en termes de performances structurales et optiques (bande-à-bande et ISB) sont obtenues pour les structures plan m. Elles montrent de l’absorption ISB à température ambiante couvrant la fenêtre SWIR, avec des performances comparables aux structures plan c, mais avec une qualité structurale trop faible pour envisager la fabrication de composants. En incorporant du Ga dans les barrières d’AlN, on réduit de désaccord de maille et donc la densité de fissures. Ces structures plan m montrent de l’absorption ISB à température ambiante dans la gamme MWIR 4.0-4.8 µm, mais présentent toujours des défauts de structure. Finalement, on a étendu l’étude à la gamme lointain infrarouge, en utilisant des barrières d’AlGaN avec une composition bien plus basse en Al. Les structures plan m étudiées présentent une excellente qualité cristalline, sans défauts de structures, et présentent de l’absorption intersousbande à basse température entre 6.3 et 37.4 meV (1.5 et 9 THz). Ce résultat constitue une démonstration expérimentale de la faisabilité de composants GaN opérant dans la bande 5-10 THz, interdite aux technologies GaAs<br>Intersubband (ISB) transitions are energy transitions between electronic states in a quantum well. GaN/AlGaN nanostructures have emerged as promising materials for new ISB optoelectronics devices, with the potential to cover the whole infrared spectrum. Their large conduction band offset (~1.8 eV for GaN/AlN) and sub-picosecond ISB recovery times make them appealing for ultrafast photonics devices in the short-wavelength infrared (SWIR, 1-3 µm), and mid-wavelength infrared (MWIR, 3-8 µm) regions. Moreover, the large energy of GaN longitudinal-optical phonon (92 meV, 13 µm) opens prospects for room-temperature ISB devices covering the 5-10 THz band, inaccessible to GaAs.The work described in this thesis has aimed at improving the performance and understanding of the material issues involved in the extension of the GaN/AlGaN ISB technology to the THz range. On the one hand, ISB photodetection requires n-type doping of the active nanostructures. In this work, we explore Si and Ge as potential n-type dopants for GaN. On the other hand, the presence of internal electric fields in the confinement direction of polar c-plane heterostructures constitutes one of the main challenges of the GaN-based ISB technology. In this thesis, we address the use of nonpolar a or m crystallographic orientations as an alternative to operate without the influence of these electric fields.Regarding the use of Si and Ge as n-type dopants for GaN, we show that the use of Ge as a dopant does not affect the morphology, mosaicity and photoluminescence properties of the doped GaN thin films. In the c-plane GaN/AlGaN heterostructures, no effect on the band-to-band properties was observed, but the structures with high lattice mismatch showed better mosaicity when doped with Ge. Regarding the alternative of nonpolar GaN, we compared GaN/AlN multi-quantum wells grown on a and m nonpolar free-standing GaN substrates. The best results in terms of structural and optical (both band-to-band and ISB) performance were obtained for m-plane structures. They showed room-temperature ISB absorption covering the whole SWIR spectrum, with optical performance comparable to polar c-plane structures, in spite of a too low structural quality to consider device processing. By introducing Ga in the AlN barriers, the lattice mismatch of the structure is reduced, leading to lower densities of cracks. Such m-plane structures showed room-temperature ISB absorption tunable in the 4.0-5.8 µm MWIR range, but still with structural defects. Finally, we extended the study to the far-infrared range, using AlGaN barriers with much lower Al content. As a result, the studied m-plane structures displayed an excellent crystalline quality, without extended defects, and showed low-temperature ISB absorption in the 6.3 to 37.4 meV (1.5 to 9 THz) range. This result constitutes an experimental demonstration of the feasibility of GaN devices for the 5-10 THz band, forbidden to GaAs-based technologies
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Wienold, Martin. "Development of terahertz quantum-cascade lasers as sources for heterodyne receivers." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2012. http://dx.doi.org/10.18452/16560.
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Die vorliegende Arbeit beschäftigt sich mit der Entwicklung und Optimierung von Terahertz-Quantenkaskadenlasern (THz-QCLs) für die Anwendung als Lokaloszillator in THz-Heterodyndetektoren, insbesondere für die Detektion der astronomisch wichtigen Sauerstoff (OI) Linie bei 4.75 THz. Hierfür wurden zunächst unterschiedliche QCL-Heterostrukturen untersucht. Basierend auf einer Heterostruktur, welche schnelle Intersubbandübergänge über Streuung an Phononen ausnutzt, konnten QCLs mit hoher Ausgangsleistung und niedriger Betriebsspannung bei 3 THz erzielt werden. Während diese Laser auf dem Materialsystem GaAs/Al_xGa_(1-x)As mit $x=0.15$ basieren, führt die Erhöhung des Al-Anteils auf x=0.25 für ähnliche Strukturen zu sehr niedrigen Schwellstromdichten. Durch schrittweise Optimierungen gelang es, QCLs zu realisieren, die bei 4.75 THz emittieren. Mit Hilfe von lateralen Gittern erster Ordnung für die verteilte Rückkopplung (DFB) konnten Einzelmoden-Dauerstrichbetrieb mit hoher Ausgangsleistung, sowie Einzelmoden-Betrieb innerhalb des spezifizierten Frequenzbereichs bei 4.75 THz erzielt werden. Eine allgemeine Methode zur Bestimmung der DFB-Kopplungskonstanten erlaubt eine gute Beschreibung der Laser innerhalb der etablierten Theorie der gekoppelten Moden für DFB-Laser mit reflektiven Endfacetten. Oft steht das Auftreten negativer differentieller Leitfähigkeit bei höheren Feldstärken und die damit verbundenen Bildung von elektrischer Felddomänen (EFDs) im Konflikt mit einem stabilen Betrieb der THz-QCLs. Es wird gezeigt, dass stationäre EFDs mit Diskontinuitäten in der statischen Licht-Strom-Spannungskennlinie verbunden sind, während Selbstoszillationen, verursacht durch nicht-stationäre EFDs, eine zeitliche Modulation der Ausgangsleistung bewirken. Mit Hilfe einer effektiven Driftgeschwindigkeit für QCLs lassen sich viele der beobachteten Phänomene durch die nichtlinearen Transportgleichungen für schwach gekoppelte Übergitter beschreiben.<br>This thesis presents the development and optimization of terahertz quantum-cascade lasers (THz QCLs) as sources for heterodyne receivers. A particular focus is on single-mode emitters for the heterodyne detection of the important astronomic oxygen (OI) line at 4.75 THz. Various active-region designs are investigated. High-output-power THz QCLs with low operating voltages and emission around 3 THz are obtained for an active region, which involves phonon-assisted intersubband transitions. While these QCLs are based on a GaAs/Al_xGa_(1-x)As heterostructure with x=0.15, similar heterostructures with x=0.25 allowed for very low threshold current densities. By successive modifications of the active-region design, THz QCLs have been optimized toward the desired frequency at 4.75 THz. To obtain single-mode operation, first-order lateral distributed-feedback (DFB) gratings are investigated. It shows that such gratings allow for single-mode operation in combination with high continuous-wave (cw) output powers. A general method is presented to calculate the coupling coefficients of lateral gratings. In conjunction with this method, the lasers are well described by the coupled-mode theory of DFB lasers with two reflective end facets. Single-mode operation within the specified frequency bands at 4.75 THz is demonstrated. Stable operation of THz QCLs is often in conflict with the occurrence of a negative differential resistance (NDR) regime at elevated field strengths and the formation of electric-field domains (EFDs). Stationary EFDs are shown to be related to discontinuities in the cw light-current-voltage characteristics, while non-stationary EFDs are related to current self-oscillations and cause a temporal modulation of the output power. To model such effects, the nonlinear transport equations of weakly coupled superlattices are adopted for QCLs by introducing an effective drift velocity-field relation.
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Biermann, Klaus. "Untersuchungen an auf InP basierenden Halbleitern mit sub-ps Responsezeiten." Doctoral thesis, [S.l.] : [s.n.], 2007. http://deposit.ddb.de/cgi-bin/dokserv?idn=985472715.
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Rakotonanahary, Georges. "Spectroscopie des transitions excitoniques dans des puits quantiques GaN/AlGaN." Phd thesis, Université Blaise Pascal - Clermont-Ferrand II, 2011. http://tel.archives-ouvertes.fr/tel-00662445.
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Ce travail de thèse porte sur l'étude des propriétés optiques et électroniques des puits quantiques de GaN / AlGaN grâce à des techniques classiques de réflectivité résolue en angle et de photoluminescence, ainsi qu'avec la technique de photoluminescence résolue temporellement. Les expériences de photoluminescence en régime continu ont permis d'estimer les énergies des transitions excitoniques qui sont également accessibles en réflectivité. Ces techniques ont ainsi permis de mettre en évidence l'effet Stark dans les puits quantiques GaN / AlGaN. L'effet Stark sur les énergies de transition est cohérent avec la théorie des fonctions enveloppes. Les spectres de réflectivité permettent d'accéder à la force d'oscillateur des excitons grâce à leur modélisation par le formalisme des matrices de transfert, prenant en compte les phénomènes d'élargissement homogène et inhomogènes des transitions optiques. Enfin, les mesures de photoluminescence résolue en temps en fonction de la température, ont également permis d'extraire la force d'oscillateur qui est inversement proportionnelle au temps de recombinaison radiative. Cette étude a également permis de mettre en évidence l'effet Stark responsable de la diminution de la force d'oscillateur en fonction de l'épaisseur du puits quantique mais aussi en fonction de la composition d'aluminium. L'augmentation de l'épaisseur du puits entraîne une diminution du recouvrement des fonctions d'onde, et une augmentation de la composition d'aluminium intensifie le champ électrique et diminue également le recouvrement des fonctions d'onde.
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Kotsar, Yulia. "Puits quantiques GaN/Al(Ga)N pour l'optoélectronique inter-sous-bande dans l'infrarouge proche, moyen et lointain." Phd thesis, Université de Grenoble, 2012. http://tel.archives-ouvertes.fr/tel-00870408.
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Ce mémoire résume des efforts dans la conception électronique, la croissance épitaxiale et la caractérisation des puits quantiques GaN/Al(Ga)N qui constituent la région active des composants inter-sous-bande (ISB) à base de semi-conducteurs nitrures pour l'optoélectronique dans l'infrarouge proche, moyen et lointain. Le dessin des puits quantiques GaN/Al(Ga)N pour ajuster la longueur d'onde d'absorption dans le spectre infrarouge a été réalisé en utilisant la méthode k.p à 8 bandes du logiciel Nextnano3 pour la résolution des équations de Schrödinger-Poisson. Les structures ont été synthétisées par épitaxie par jets moléculaires assistée par plasma (PAMBE). Les problèmes de gestion de la contrainte qui apparaissent liés au désaccord de maille pendant la croissance épitaxiale des hétérostructures GaN/Al(Ga)N ont été investigués par combinaison de techniques in-situ et ex-situ. La couche tampon optimale, la teneur en aluminium et les mécanismes de relaxation pendant la croissance par PAMBE ont été déterminés. Pour obtenir une absorption ISB efficace, on a besoin de niveaux élevés de dopage au silicium dans le puits quantiques, situation dans laquelle les théories à une particule conduisent à des déviations significatives par rapport aux résultats expérimentaux. Donc une étude du dopage au silicium des super-réseaux GaN/Al(Ga)N pour les régions spectrales infrarouges proche et moyen est présentée. Ce travail contient aussi une contribution à la compréhension de la technologie de photodétection à cascade quantique. Des résultats importants tels que l'obtention de photodétecteurs cascade fonctionnant à 1.5 µm et dans la plage spectrale de 3-5 µm sont démontrés. Finalement, on décrit la première observation de l'absorption ISB dans l'infrarouge lointain (4.2 THz) utilisant des nanostructures à base de semi-conducteurs nitrures.
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Abadie, Claire. "Détecteurs et lasers THz à base d'antennes accordables en fréquence." Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLS145/document.
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Les dispositifs optoélectroniques sont importants pour nombreuses applications de la vie de tous les jours : ordinateurs, téléphones, les objets connectés en général. La gamme spectrale du THz (0.1-10 THz) reste cependant un domaine industriellement peu exploité en raison de problèmes intrinsèques à la génération et détection des photons THz.De nombreuses applications relèvent pourtant du THz, dans les domaines médicaux par exemple, pour la détection des gaz à l’état de trace, ou bien pour l’imagerie d’objets opaques dans le visible.Cette thèse se focalise sur les photodétecteurs à puits quantiques (QWIPs) et les lasers à cascade quantique (QCLs) fonctionnant dans la gamme du THz dans le but de développer des dispositifs compacts, rapides et sensibles (mais fonctionnant à températures cryogéniques). Nous avons utilisé des résonateurs à anneau fendu, inspirés des travaux sur les métamatériaux, pour concevoir et développer des détecteurs sub-longueur d’onde accordables en fréquence dans la gamme spectrale du térahertz grâce à une inductance externe. En ce qui concerne les émetteurs, cette thèse étudie les micro-lasers THz qui utilisent des résonateurs de type microdisques, avec pour but de concevoir et fabriquer des lasers fonctionnant sur le mode électromagnétique fondamental. Les futures perspectives de ce travail concernent la réalisation d’un laser entièrement sub-longueur d’onde et rapide dans la gamme spectrale du THz<br>Optoelectronic devices are crucial for many applications in everyday life: computers, smartphones, connected objects in general.The THz range (0.1-10 THz) still remains industrially unexploited because of the intrinsic difficulties to produce or generate THz photons. However, many applications exist for THz radiation : in the medical field for example, for the sensitive detection of gases, or for the imaging of concealed objects in the visible range.This thesis focuses on quantum well photodetectors (QWIPs) and quantum cascade lasers (QCLs) operating in the THz range in order to develop compact, fast and sensitive devices (but operating at cryogenic temperatures).We used Split Ring Resonators (SRR), inspired by metamaterial research, in order to design and develop subwavelength tunable THz detectors with an external inductance.Concerning lasers, this thesis studies THz micro-lasers using microdisk resonators with the aim of designing and manufacturing lasers operating on the fundamental electromagnetic mode (dipolar mode). The future perspective of this work is to build an entirely sub-wavelength and fast laser in the THz spectral range
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Candido, Denis Ricardo. "Relaxação de spin via D\'yakonov-Perel\' em poços quânticos com acoplamento spin-órbita intersub-banda." Universidade de São Paulo, 2013. http://www.teses.usp.br/teses/disponiveis/76/76131/tde-25092013-161711/.
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Em sistemas com acoplamento spin-órbita (SO) é possível manipular eletricamente o spin do elétron via a aplicação de um campo elétrico.1 Isso permite a potencial aplicação do grau de liberdade de spin (Spintronica) no desenvolvimento de novos dispositivos e tecnologias, como por exemplo na tecnologia da informação (computação quântica).2,3 No entanto, sabe-se que a interação SO causa efeitos indesejáveis, como por exemplo a relaxação e o defasamento de spin.4 Dessa maneira, do ponto de vista de aplicações, torna-se desejável maximizar o tempo de vida do spin. Neste trabalho, investigamos a relaxação de spin dos elétrons de condução em poços quânticos com duas sub-bandas5 crescidos ao longo das direções [001] e [110] via o mecanismo de D\'yakonov-Perel\'.6 Combinando teoria de grupos, o método k.p, a aproximação da função envelope e teoria de perturbação de Löwdin obtemos um Hamiltoniano efetivo para os elétrons da banda de condução na presença das interações SO de Rashba e Dresselhaus. Aqui, diferentemente de alguns trabalhos anteriores,7,8 além de incluir o termo cúbico de Dresselhaus, também levamos em conta as contribuições devido à influência da segunda sub-banda de mais baixa energia do poço. A partir deste Hamiltoniano derivamos expressões para os tempos de relaxação do spin e analisamos como estas novas contribuições (termos do acoplamento com a segunda sub-banda) afetam os tempos de vida dos spins. Comparamos os tempos de relaxação para as direções [001] com os calculados para a direção [110]. Nossos resultados mostram que as contribuições devido à segunda sub-banda são desprezíveis para ambas as direções. Mostramos também que o tempo de relaxação para a direção [110] é mais longo que o da [001], resultado consistente com experimentos9,10 e outros trabalhos teóricos anteriores.7<br>In systems with spin-orbit (SO) coupling, it is possible to electrically manipulate the electron spin via applied gate voltages.1 This allows for the potential use of the spin degree of freedom (Spintronics) in the development of new devices and technologies, for instance information technology (quantum computing).2,3 It is known however, that the SO interaction leads to the undesired effect of causing spin relaxation and spin dephasing.4 Thus from the point of view of applications, it is desirable to maximize the spin lifetimes. Here, we investigate the spin relaxation of the conduction electrons in quantum wells with two sub-bands5 grown along the [001] and [110] directions via the D\'yakonov-Perel\' mechanism.6 By combining group theory, the k.p method, the envelope function approach and the Löwdin perturbation theory, we obtain an effective Hamiltonian for the conduction electrons in the presence of the Rashba and Dresselhaus SO interactions. Differently from some early works,7,8 in addition to the cubic Dresselhaus term, we also account for the contributions arising from the second lowest sub-band of the well. We derive expressions for the spin relaxation times and analyze how the new contributions (second sub-band terms) affect the spin lifetimes. We compare the relaxation times obtained in the [001] direction with those calculated for the [110] direction. Our results show that the contributions from the second sub-band are negligible for both directions. We also find that the relaxation time in the [110] direction is longer than the one in the [001], a result consistent with experiments9,10 and earlier theoretical works.7
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Vanelle, Eric. "Ecrantage du champ piézo-électrique dans les puits quantiques CdTe/CdZnTe : étude dynamique." Université Joseph Fourier (Grenoble), 1995. http://www.theses.fr/1995GRE10212.
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Les puits quantiques cdte/cdmnte que nous avons etudies ont la particularite d'etre piezo-electriques. Les contraintes exercees par les barrieres sur le puits de cdte provoquent l'apparition d'un champ piezo-electrique de l'ordre de 10#7 v/m dans le puits quantique si l'axe de croissance est polaire pour la structure blende de zinc, ce qui est le cas des structures <111> etudiees. Ce champ a pour effet principal d'incliner les bandes de conduction et de valence, et de decaler vers le rouge l'energie des transitions excitonique et bande a bande, par rapport au puits carre correspondant. Les electrons et les trous photo-crees sont alors separes spatialement et tendent a creer un champ electrique qui s'oppose au champ piezo-electrique permanent. Nous avons etudie en dynamique, tant en photoluminescence qu'en absorption, les mecanismes d'ecrantage de ce champ piezo-electrique et, entre autres, les modulations induites sur les energies de transition, en fonction de la densite de porteurs photo-crees. Des deplacements d'environ 10 mev sont observes, et interpretes theoriquement comme resultant bien d'un ecrantage du champ piezo-electrique. Les experiences resolues en temps montrent de plus le caractere ultra-rapide (<100 fs) de ce phenomene. Nous mettons en evidence le comportement particulier des excitons dans ce type de structures, qui, par bien des aspects, est tres proche de celui des paires libres notamment au niveau de l'efficacite d'ecrantage et des collisions exciton-exciton. Enfin, nous montrons que le champ piezo-electrique permet une tres forte augmentation des effets du couplage aux phonons acoustiques
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Mandray, Ariane. "Etude magnéto-optique de centres D- confinés dans des multi-puits quantiques GaAs/AlGaAs." Université Joseph Fourier (Grenoble), 1994. http://www.theses.fr/1994GRE10075.
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Le centre d#-, ou ion donneur negatif, est l'analogue en physique du solide de l'ion hydrogene negatif h#-. Il s'agit donc d'un systeme correle simple, avec seulement deux electrons. Les transitions magneto-optiques permettant l'etude des donneurs peu profonds (neutres ou charges negativement) dans les multi-puits gaas/algaas se situent dans la gamme de l'infra-rouge lointain. Notre appareillage experimental est essentiellement constitue d'un spectrometre a transformee de fourier, couple a un aimant supraconducteur ou resistif. Nous avons etudie le mecanisme de formation des centres d#- confines dans des multi-puits quantiques. Dans cette configuration, contrairement au materiau massif, les centres d#- sont formes par construction, ce qui permet leur etude a l'equilibre thermodynamique. L'importance de la geometrie de dopage est soulignee, et la possibilite de realiser un dopage d#- de puits quantiques est mise en evidence. Le spectre d'energie des centres d#- confines a ete etudie pour une large gamme de champs magnetiques (jusqu'a 20 t) et pour differentes largeurs de puits. Ces mesures permettent d'observer, outre la non-parabolicite de bande de gaas, les effets de correlation electronique augmentes par la baisse de dimensionalite. L'etude des centres d#- en presence de desordre d'alliage dans des puits de al-gaas met en evidence la possibilite de coexistence, dans ce type de systeme, de centres profonds et de centres peu profonds, tous deux charges negativement
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Kheng, Kuntheak. "L'exciton chargé négativement X- dans les puits quantiques CdTe/CdZnTe." Université Joseph Fourier (Grenoble ; 1971-2015), 1995. http://www.theses.fr/1995GRE10006.
Full textAbstract:
Nous presentons la premiere identification de l'exciton charge negativement x#- dans une heterostructure semi-conductrice, a savoir dans des puits quantiques cdte/cdznte. Nous avons etudie les caracteristiques de la transition optique x#- dans ces puits, notamment en presence d'un champ magnetique. La transition x#- est identifiee dans les spectres d'absorption de puits dopes par modulation avec des donneurs indium. Cette identification est basee sur l'augmentation de l'intensite de la raie x#- avec la concentration d'electrons dans le puits et sur les proprietes de polarisation circulaire de cette raie. Nous avons notamment verifie, par une analyse du taux de polarisation en fonction de la temperature, que le facteur g de l'etat initial de l'absorption x#- est bien celui de l'electron. En placant les plans d'indium dans differentes positions, dans les barrieres et dans les puits, nous avons etudie l'evolution de la raie x#- vers celle de l'exciton piege sur un donneur, d#ox. La force d'oscillateur de x#- est d'environ 10 fois superieure a celle de d#ox. La raie d'absorption x#- est observee pour toute valeur du champ magnetique dans les spectres des echantillons faiblement dopes et l'evolution de sa position en fonction du champ montre que l'espece x#- est probablement localisee par des fluctuations de potentiel dans le plan du puits. En revanche, les spectres de puits contenant un gaz d'electrons concentre (10#1#1cm#-#2) presentent a champ nul un pic associe a l'exciton de mahan et a champ faible des transitions entre niveaux de landau. A champ magnetique suffisamment intense les raies excitoniques x et x#- reapparaissent. Nous attribuons ce phenomene a une reduction des effets d'exclusion et d'ecrantage due au gel des electrons dans les fluctuations de potentiel. Le champ critique de reapparition des raies excitoniques peut servir a definir le seuil du changement de phase metal-isolant detecte optiquement
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Larrabee, Diane. "Intersubband transitions in narrow indium arsenide/aluminum antimide quantum wells." Thesis, 2004. http://hdl.handle.net/1911/17698.
Full textAbstract:
Intersubband resonances in InAs/AlSb are an ideal tool for optically pumped terahertz (THz) generation because of their enormous tunability and their strength at room temperature. We have carried out a systematic temperature-dependent study of intersubband absorption in InAs/AlSb quantum wells from S to 10 nm well width. The resonance energy redshifts with increasing temperature from 10 to 300 K, and the amount of redshift increases with decreasing well width. We have also observed intersubband absorption in wells as narrow as 3 nm, investigated the carrier distribution in the wells and its influence on intersubband absorption, and performed temperature-dependent cyclotron resonance using a THz quantum cascade laser. We have observed multiple intersubband resonances in coupled quantum well structures designed for THz difference frequency generation. We have modeled the resonances using eight-band k·p theory combined with semiconductor Bloch equations, including the main many-body effects. Temperature is incorporated via band filling and nonparabolicity.
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Almogy, Gilad. "Quantum Well Intersubband Transitions: Nonlinear Optics, Refractive Index and Infrared Modulation." Thesis, 1995. https://thesis.library.caltech.edu/3642/1/Almogy_g_1995.pdf.
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<p>The nonperturbative theory for the nonlinear optical interaction of quantum well intersubband transitions is developed. The nonlinear optical response of intersubband transitions in quantum wells is rigorously derived and the implications of their resonantly-enhanced nature are examined. Limitations on the use of the standard expansion of the induced polarization in terms of perturbative nonlinear coefficients are presented and it is shown that an alternative nonperturbative formalism is necessary for analyzing intersubband device applications. Upper limits are derived on the magnitudes of several key intersubband transition-induced nonlinear processes. It is shown that for both electrooptic and all-optic modulation, resonantly-enhanced absorption modulation is inherently preferable to phase modulation. A limit on the second-harmonic intensity that may be generated in a given propagation length and modified design criteria for optimizing second-harmonic generation in quantum wells are also obtained from the nonperturbative formalism.</p>
<p>The large and highly dispersive refractive index contribution of intersubband transitions was observed for the first time through the birefringence induced in a GaAs/AlGaAs multi-quantum well stack. It is shown that this index, rather than the absorption induced by intersubband transitions, may become the dominant limitation on frequency conversion efficiencies. Potential applications of this controllable refractive index for a novel phase-matching technique of second-harmonic generation and for improved waveguiding in semiconductors is suggested and analyzed.</p>
<p>Removal of charge integration limitations upon the performance of thermal imagers through the 'ac'-coupling of infrared focal-plane arrays is suggested. This is achieved by the monolithic integration of an intersubband infrared absorption modulator and detector leading to a modulation depth of 45% at a wavelength of 10.6µm. The uniquely accurate design of the coupled quantum well infrared modulator was based on a self-consistent computer model of the Schrodinger and Poisson equations in quantum wells, taking into account many body effects, band nonparabolicity and flat band boundary conditions. Monolithic integration of the modulator and detector also turns out to be a simple and accurate method of studying the optical properties of quantum wells under bias. This technique led to the first observation of the exchange-interaction's contribution to the charge transfer between coupled quantum wells.</p>
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Chen, Huei-haurng, and 陳輝煌. "Investigation of Intersubband-Optical Transitions and Resonant Interband Tunneling Mechanisms in Supperlattice/Multiple- Quantum-Well Structures and Their Applications to Semi- conductor Devices." Thesis, 1995. http://ndltd.ncl.edu.tw/handle/01066310994105078437.
Full textAbstract:
博士<br>國立成功大學<br>電機工程研究所<br>83<br>In this thesis, both intersubband optical transitions and
resonant interband tunneling mechanisms in superlattice/
multiple-quantum-well structures are systematically
investigated, based on the developed theoretical methods and
numerical techniques. In addition, Their applications to
semiconductor devices are also extensively discussed. First, a
complete description of the theoretical framework within this
thesis is referred to the base of following discussion. The
contents include the k.p perturbation theory, envelope function
approximation, reduced Hamiltonian techno- logy, an energy- and
spatial-dependence effective mass model and the momentum
matrix elements of intersubband optical transitions. A
theoretical study of resonant interband tunneling in polytype
GaSb/AlSb/InAs heterostructure is presented. The resonant
interband tunneling in such homo- and hetero-struc- ture is
modeled by an energy- and spatial-dependence effective mass
equation incorporating general transfer matrix method. The
transmission coefficients of the unipolar and bipolar resonant
interband tunneling structures are calculated and the symmetric
and asymmetric multiple quantum wells resonant inter -band
tunneling structures are also discussed. In this study, A GaAs
delta-doped inducing homostructure tunneling diode have a delta
n+-i-delta p+-i-delta n+ structure is also inves- tigated.
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Xu, Yuanjian. "Quantum well intersubband transition detection and modulation." Thesis, 1997. https://thesis.library.caltech.edu/1723/2/Xu_y_1997.pdf.
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This thesis is a theoretical and experimental investigation of the intersubband transitions in quantum well structures. The I-V characteristics, infrared absorption spectra, and photoresponse spectra of superlattices are used to characterize multiple quantum well structure properties in unipolar devices.
An important numerical method for solving the problem of bound-to-continuum transitions, the transfer matrix method, is presented for the self-consistent calculations. Although the boundary conditions are relaxed due to the calculation self-consistentcy, inappropriate boundary conditions were previously included in the literature.
The first observation of the quantum interference effect in the photocurrent spectra is described using a weakly coupled bound-to-continuum transition quantum well structure and electric field domain formation in the device. This effect persists even at high biases where Kronig-Penny minibands of periodic superlattice potential in the continuum are destroyed. Using this observation, the electric field domain formation and the electron coherence length in superlattices were analyzed. A large off-resonant energy level alignment between two neighboring wells in the high field domain was observed. The effect of temperature on the transport properties was also discussed. As a further study of electric field domain formation in superlattices, an optical experiment using Stark effect is suggested.
The dependence of the absorption spectral linewidth of quantum well intersubband transitions on the electron population in the well is experimentally demonstrated using field-induced charge transfer and thermal-induced charge transfer in an asymmetric coupled quantum well structure. We show that this population-induced broadening is very important in the broadening of intersubband transitions in quantum well structures and that previously reported linewidth values for the contribution from donor scattering were overestimated. Many body effects and single-particle band non-parabolicity are the likely causes. An electronic light chopper based on population modulation was fabricated using the asymmetric coupled quantum well structure. A modulation depth of 45% has been demonstrated using 50 periods of the coupled well structure.
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Juang, Feng-Rurng, and 莊豐榮. "Theoretical Investigation of Infrared Intersubband Absorption Spectra in Semiconductor Quantum Wells and Superlattices." Thesis, 1997. http://ndltd.ncl.edu.tw/handle/28984400982468940446.
Full textAbstract:
碩士<br>國立交通大學<br>電子工程學系<br>85<br>In this thesis, three main topics related to
intersubband absorptionspectra in semiconductor quantum wells
and superlattices are studied: (1) Comparison of TE amd TM
absorption spectra in N-type superlattices.We have calculated
explicitly the TE and TM intersubband absorption in N-typeGaAs/
Al0.3Ga0.7As and In0.4Ga0.6As/GaAs superlattices by using 8x8
super-lattices K-center-dot-p theory. The origin of TE
absorption at K=0 resultsfrom the mixing of s and p states in
the conduction subbands. Due to the cancellation resulting from
opposite signs of some bulk momentum matrix elements, the zone-
center TE momentum matrix elements are small quantities.Away
from the zone center, the enhancement of TE momentum matrix
elementsindicates that the higher doping concentration produces
the larger TEabsorption. Nevertheless, TE absorption is
negligible compared to TM absorption. (2) Strain effects
on TE absorption of P-type superlattices. We usethe 8x8
superlattice K-center-dot-p theory for P-type non-strained GaAs/
Al0.3Ga0.7As and strained In0.4Ga0.6As/GaAs superlattices to
calculate thevalence subband structures, envelope wave
functions, momentum matrix elements, and absorption spectra. The
biaxial compressive strain in the welllayer of In0.4Ga0.6As/GaAs
superlattice enlarges the energy-level separationbetween HH1 and
LH1 subbands. We find that the peak of bound-to-
continuumabsorption coefficient is enhanced in strained
superlattice. Therefore, thestrain effects are useful for the
device application of quantum well infraredphotodetectors.
(3) Analysis of the orientational effects on TE absorption
spectra inP-type quantum wells. We calculated the valence
subband structures in (100),(111), and (112) oriented GaAs/Al0.3
Ga0.7As quantum wells, by solving the 4x4Luttinger-Kohn
Hamiltonian with axial approximation. It is found that
theorientational effects significantly influence the heavy-hole
effective mass.Therefore, energy-level position and subband
dispersion of heavy- and light-hole are largely changed with
respect to different orientations. The TE intervalence subband
absorption spectra are calculated and compared, demonstrating
the larger absorption coefficient in (100)-oriented
quantumwells. According to the theoretical analysis of zone-
center momentum matrixelements we design a narrow-well structure
of (112) quantum well to improvethe bound-to-quasi-bound and
bound-to-continuum absorption spectra. However,our calculations
show the general (100) quantum wells still have largerabsorption
coefficient.
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Eickemeyer, Felix [Verfasser]. "Ultrafast dynamics of coherent intersubband polarizations in quantum wells and quantum cascade laser structures / von Felix Eickemeyer." 2002. http://d-nb.info/965430227/34.
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Waldmüller, Inès [Verfasser]. "Intersubband dynamics in semiconductor quantum wells : linear and nonlinear response of quantum confined electrons / vorgelegt von Inès Waldmüller." 2005. http://d-nb.info/973598247/34.
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蘇偉盛. "Peculiar Optical Transitions in Type-II ZnTe/CdSe Multiple Quantum Wells." Thesis, 2002. http://ndltd.ncl.edu.tw/handle/17336684602535723596.
Full textAbstract:
碩士<br>國立臺灣大學<br>物理學研究所<br>90<br>Abstract
In this thesis we report the studies of optical and electrical properties on type-II ZnTe/CdSe multiple quantum wells. Quite interesting results have been obtained from our studies which should be very useful for the enhancement of our understanding and application in this material.
1. Optical properties of photoluminescence in type-II ZnTe/CdSe multiple quantum wells.
The optical properties of type-II ZnTe/CdSe multiple quantum wells were investigated by photoluminescence. It was found that the peak position of photoluminescence (PL) spectra shows a blueshift under a moderate optical excitation level. The blueshift can be interpreted in terms of the band bending effect due to the spatially photoexcited carriers in a type-II alignment. The electron quantization energy is thus expected to increase proportionally with the third root of the excitation density. In addition, we have shown that the thermal escape of the electrons and holes from the ground state to the excited state is responsible for the PL quenching near room temperature.
2. Polarized optical properties in type-II ZnTe/CdSe multiple quantum wells induced by interface chemical bonds
Photoluminescence(PL) and photoconductivity(PC) spectra were studied in type-II ZnTe/CdSe multiple quantum wells. It was found that the PL spectra exhibit a strong in-plane polarization with respect to <011> axis with polarization degree up to 30%. The degree of polarization does not depend on the excitation intensity and temperature, which exclude extrinsic mechanisms related to the observed in-plane anisotropy. The underlying mechanism of the observed polarization dependence of the optical properties was attributed to the inherent property of the orientation of chemical bonds in ZnTe/CdSe heterostructure with no common atom. In addition, the PC spectra also display a strong polarization dependence. Unlike the PL spectra, the PC response continuously covers a wide range of wavelengths arising from interface imperfections. We therefore point out that polarized PL and PC spectroscopies provide a unique way to probe the effects of the orientation of interface chemical bonds on semiconductor heterostructures.
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Κοσιώνης, Σπυρίδων. "Θεωρητική μελέτη μη-γραμμικών οπτικών διαδικασιών σε ημιαγώγιμα κβαντικά πηγάδια". Thesis, 2012. http://hdl.handle.net/10889/6187.
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Στην εργασία αυτή, μελετάμε, τόσο με αναλυτικό όσο και με υπολογιστικό τρόπο, γραμμικά και μη γραμμικά οπτικά φαινόμενα σε συστήματα ημιαγώγιμων κβαντικών πηγαδιών GaAs/AlGaAs δύο ενεργειακών υποζωνών, όπου επάγονται διαϋποζωνικές μεταβάσεις, υπό την επίδραση ηλεκτρομαγνητικών πεδίων. Στο πρώτο κεφάλαιο, γίνεται μια θεωρητική περιγραφή των ημιαγώγιμων ετεροεπαφών. Ακολουθούν βασικά στοιχεία της στατιστικής και κβαντικής μηχανικής. Στο δεύτερο κεφάλαιο, εξάγονται οι γενικευμένες εξισώσεις Bloch για τις διαϋποζωνικές μεταβάσεις σε ημιαγώγιμα κβαντικά πηγάδια, στις οποίες ενυπάρχουν όροι που υπεισάγουν τις μη αμελητέες, λόγω εμπλουτισμού, αλληλεπιδράσεις μεταξύ των ηλεκτρονίων. Οι εξισώσεις αυτές αποτελούν τη βάση της μελέτης που ακολουθεί. Στα δύο επόμενα κεφάλαια, μελετούμε την αλληλεπίδραση μιας δομής διπλών συζευγμένων ημιαγώγιμων κβαντικών πηγαδιών με ένα ηλεκτρομαγνητικό πεδίο μεταβλητής γωνιακής συχνότητας, καταλήγουμε σε αναλυτικές εκφράσεις για τη οπτική επιδεκτικότητα πρώτης, τρίτης και πέμπτης τάξεως και αναλύουμε τα φάσματα διαφόρων οπτικών φαινομένων, ως προς τη γωνιακή συχνότητα του εξωτερικού πεδίου, για διάφορες τιμές της επιφανειακής ηλεκτρονιακής πυκνότητας της κβαντικής δομής. Επιπλέον, προσδιορίζουμε τις περιοχές όπου λαμβάνουν τιμή οι διάφορες παράμετροι, ούτος ώστε στο σύστημά μας να αναδυθεί η οπτική διστάθεια. Στα τρία τελευταία κεφάλαια, θεωρούμε ότι η ημιαγώγιμη κβαντική δομή αλληλεπιδρά ταυτόχρονα με ένα ισχυρό ηλεκτρομαγνητικό πεδίο (πεδίο άντλησης) καθορισμένης γωνιακής συχνότητας και ένα ασθενές (πεδίο ανίχνευσης) μεταβλητής συχνότητας και μελετούμε τα φάσματα γραμμικών και μη γραμμικών φαινομένων του πεδίου ανίχνευσης (μίξη τεσσάρων κυμάτων, απορρόφηση, διασπορά, μη γραμμικό οπτικό φαινόμενο Kerr), σε στάσιμη κατάσταση, καθώς και τη χρονική εξέλιξη αυτών. Περιγράφουμε τα φαινόμενα τόσο με αναλυτικές εκφράσεις που εξάγουμε, όσο και με την αριθμητική επίλυση των μη-γραμμικών διαφορικών εξισώσεων του πίνακα πυκνότητας που διέπουν τη δυναμική. Στη μελέτη των φαινομένων αυτών, εξετάζεται η επίδραση της επιφανειακής ηλεκτρονιακής πυκνότητας της κβαντικής δομής στις οπτικές ιδιότητες των κβαντικών πηγαδιών.<br>In this PhD thesis, we study analytically and numerically linear and nonlinear optical phenomena in intersubband transitions of a symmetric GaAs/AlGaAs double quantum well structure, with two energy subbands. In the first chapter, a theoretical description of the semiconductor heterostructures is presented. This is accompanied with a brief analysis of the basic elements of statistical and quantum mechanics follows, as far as this kind of structures is concerned. In the second chapter, we derive the generalised optical Bloch equations in intersubband transitions of semiconductor quantum well structures, which constitute the basis of the analysis that follows. These equations contain terms which owe their presence to the electron-electron interactions, because the quantum structure is doped with electron carriers. In the two following chapters, we consider the interaction of intersubband transitions of a double quantum well structure with an electromagnetic field of varying frequency, we derive analytical expressions for the first, third and fifth order optical susceptibility and, at last, we analyze the corresponding spectra, with respect to the frequency of the external field, for different values of electron sheet density of the structure. Furthermore, we identify the areas of values of the parameters used, in which the phenomenon of optical bistability arises. In the last three chapters, we consider the two quantum well subbands to be coupled to a strong pump electromagnetic field with fixed frequency and a weak probe electromagnetic field of varying frequency and study the spectra of various linear and nonlinear optical phenomena, which are due to the existence of the probe field. More specifically, we examine the spectra of four-wave mixing, absorption, dispersion and the nonlinear optical Kerr effect of the probe field as they evolve in time and in the steady state. Both analytical expressions are derived and numerical results are presented by solving the nonlinear differential density matrix equations that govern the dynamics of the system. In the study of the different kinds of optical phenomena, the influence of the electron sheet density on the spectral shapes is carefully examined.
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Cho, Eun Chel. "Optical transitions in SiO2/crystalline Si/SiO2 quantum wells and nanocrystalline silicon (nc-Si)/SiO2 superlattice fabrication /." 2003. http://www.library.unsw.edu.au/~thesis/adt-NUN/public/adt-NUN20040105.171835/index.html.
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Jhang, Min-Jyun, and 張閔鈞. "Theoretical Studies of Topological Phase Transitions inSemiconductor Quantum Wells Driven by Magnetic Fields." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/89uznz.
Full textAbstract:
碩士<br>國立臺灣大學<br>物理學研究所<br>105<br>Quantum spin Hall effect is an effect which has two counter conduction currents and spin order chiral edge states in inverted band materials, in other word, helix edge state. The helical edge states are presumably protected by time reversal symmetry in a quantum spin Hall insulator. However, even in the presence of magnetic field which breaks time-reversal symmetry, the helical edge conduction can still exist, dubbed as pseudo quantum spin Hall effect. The effects of the magnetic fields on the pseudo quantum spin Hall effect and the phase transitions are studied, when out-of-plane magnetic field becomes bigger, it makes quantum spin Hall phase change into normal insulator, or change into quantum Hall phase first and then change into normal insulator. We also illustrate that an in-plane magnetic field drives a pseudo quantum spin Hall state to metallic state at a high field, but never study what happen in tilted magnetic field. In this master thesis, at a fixed in-plane magnetic field, an increasing out-of-plane magnetic field leads to a reentrance of pseudo quantum spin Hall state in an inverted InAs/GaSb quantum well. The origin of the reentrant behavior is attributed to the nonmonotonic bending of Landau levels and the Landau level mixing caused by the orbital effect induced by the in-plane magnetic field. The edge state probability distribution and Chern numbers are calculated to verify that the reentrant states are topologically nontrivial and provide an evidence to the robustness of the reentrant quantum spin Hall effect.