Dissertations / Theses: 'Quantum wells'

1

Snelling, Michael. "Optical orientation in quantum wells." Thesis, University of Southampton, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.305526.

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2

Van, der Laak Nicole Kathleen. "Nano-modified InGaN quantum wells." Thesis, University of Cambridge, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.612841.

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3

Panda, Sudhira. "Quantum confined stark effect and optical properties in quantum wells." Thesis, Hong Kong : University of Hong Kong, 1998. http://sunzi.lib.hku.hk/hkuto/record.jsp?B19324303.

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4

Starvrou, Vasilios N. "Theory of electron-optical phonon interactions in quantum wells and quantum well laser structures." Thesis, University of Essex, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.285854.

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5

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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6

Plaut, Annette Sally. "Laser spectroscopy of semiconductor quantum wells." Thesis, University of Oxford, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.258014.

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7

Wood, A. C. G. "Strain effects in semiconductor quantum wells." Thesis, Durham University, 1990. http://etheses.dur.ac.uk/6263/.

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In this thesis the effect of the strain which is present in a lattice mismatched quantum well (QW) on the properties of the device is investigated. The k.p method is used within the envelope function framework to obtain the bandstructure and the wave functions of bound and unbound states in both lattice matched and strained quantum wells. The model includes spin and interband mixing effects. We show that the mixing of wave function character between adjacent subbands which occurs in a QW can be reduced in a strained structure, and that this can result in the ground state subband having a reduced effective mass. The effect of the reduction in mixing on the optical matrix elements for transitions between the conduction and valence bands is also investigated. A model is developed which enables the calculation of the gain and spontaneous emission spectra and threshold properties of a multiple quantum well (MQW) laser device. The model includes a full description of the non- parabolic subband dispersion and the variation of the optical matrix elements along the subbands, together with an energy dependent lifetime broadening of the spectrum. The model is used to compare the performance of strained and unstrained InGaAs/InP MQW devices operating at 1.3/µm and 1.55µm. The reduced valence band edge effective mass of the strained devices is shown to lead to a reduced threshold current, temperature dependence and linewidth enhancement factor and an enhanced gains lope. The unbound states of the well are used to investigate the bound- unbound intervalence band absorption rate in the above devices. The absorption coefficient for this process is found to be small (<2cm(^1)) in all the cases considered.

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8

Olaizola, S. M. "Ultrafast spectroscopy of InGaN quantum wells." Thesis, University of Sheffield, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.414678.

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9

Grevatt, Treena. "Exciton spin dynamics in quantum wells." Thesis, University of Southampton, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.242274.

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10

Smeeton, Timothy Michael. "The nanostructures of InGaN quantum wells." Thesis, University of Cambridge, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.614901.

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11

Blackwood, Elaine. "Spin polarised dynamics in quantum wells." Thesis, University of Southampton, 1993. https://eprints.soton.ac.uk/206553/.

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The ability to preferentially spin-polarise a photoexcited carrier population in a quantum well by optical pumping methods has enabled us to study the fine structure and some of the parameters governing the spin relaxation dynamics of excitons, heavy-holes and electrons in a number of type I GaAs/AlxGa1-xAs and type I InxGa1-xAs/GaAs single and multiple quantum wells. The electron, hole and excitonic effective Lande g-factors have been measured as a function of quantum well thickness in GaAs/Al0.36Ga0.64As and In0.11Ga0.89As/GaAs. For the GaAs/AlGaAs wells, we observed a change in sign of the exciton g-factor and using k.p perturbation theory to model the form of the electron g-factor, we obtained the hole g-factor as a function of well width. Both the electron and hole g-factors also exhibited a change in sign. In the case of the InGaAs/GaAs wells, the exciton g-factor was small and of positive magnitude for all the wells we studied. Describing the form of the electron g-factor by a strain modified k.p perturbation theory and using the measured exciton g-values, the hole g-factor was calculated to take small, but slightly more positive values than the exciton g-factor. The electron-hole exchange interactions have been measured in GaAs/Al0.36Ga0.64As and GaAs/A1As samples as a function of well width. In both cases the exchange splitting between the optically active and inactive levels was consistent with theory, falling rapidly with decreasing confinement towards the measured value for bulk GaAs. A finite exchange splitting of the optically active levels at zero field demonstrates the symmetry of the quantum well is less than Dja, possibly due to growth induced imperfections. We have measured the spin relaxation times of electrons, holes and excitons in GaAs/Al0.3Ga0.7As quantum wells. We observed a much shorter relaxation time for the excitons, lOOps, compared to the free electron and hole relaxation times which were both of the order of Ins. We have attributed the fast exciton spin relaxation to the strong exchange between the electron and hole forcing the more rapidly relaxing particle to govern the spin relaxation dynamics. Our results suggest that the hole is the more rapidly relaxing particle when confined in an exciton. We have attributed this rapid spin relaxation of the holes to the mixing of the light and heavy-hole bands for wavevectors away from k=0 in a quantum wells. We have also observed a strong temperature dependence of the hole relaxation time which is consistent with a wavevector dependence of the hole relaxation time. Finally we have direct measurements of the wavevector dependence of hole relaxation time and the reduction in this due to the mixing of the valence band states in a quantum well away from k=0.

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12

Siarkos, Anastassios. "Exciton center-of-mass motion in quantum wells and quantum wires." Doctoral thesis, [S.l. : s.n.], 2000. http://deposit.ddb.de/cgi-bin/dokserv?idn=96148098X.

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13

Brown, Iain. "Internal field effects in InGaN quantum wells." Thesis, Cardiff University, 2005. http://orca.cf.ac.uk/55968/.

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InGaN/GaN based quantum well structures are strained and due to the lack of a centre of symmetry large internal fields are present which skew the potential of the quantum wells, this has a large effect on the properties of these structures. InGaN/GaN based quantum well structures are studied using a theoretical method based on the Pade model and comparison made with experimental results. The importance of using a correct description for the depletion widths of p-i-n structures for use in interpreting measurements of the internal field is established in this work. Interpreting the results from reverse bias photocurrent absorption measurements of an In0.1Gao.9N quantum well structure, a value of-1.9 MVcm-1 for the internal field has been determined, which is within 5 % of the field of -1.8 MVcm-1 calculated using piezoelectric constants interpolated from the binaries. Comparison of the results of the Pade model and experiment demonstrate that the experimental absorption magnitude is an unreliable indication of the internal field due to the carrier extraction efficiency at low bias, hence the absorption peak energy should be used. Using a theoretical model governed by pumping and recombination processes time-resolved photoluminescence experiments performed at Sheffield University have been modelled. It was found that the observed shift of the emission peak arises from a delicate balance between the contributions from bandgap renormalisation, screening of the internal field and the Coulomb interaction. Comparisons between the free carrier and Pade models, found that the energy shift and magnitude of the peak intensity are underestimated when using the free carrier model. Although the internal field is strongly screened at high carrier density, the increase in the dipole matrix element is small. It was found that at threshold the screened internal field is still of the order of -1 MVcm-1, hence inclusion of the screened internal field is essential in laser gain-current calculation.

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14

Lee, Shun-Chen. "Electron scattering processes in semiconductor quantum wells." Thesis, Heriot-Watt University, 1997. http://hdl.handle.net/10399/661.

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15

Worsley, Richard Edward. "Time-resolved relaxation processes in quantum wells." Thesis, University of Southampton, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.295867.

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16

Traynor, Nicholas James. "Magneto-optics of excitons in quantum wells." Thesis, University of Southampton, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.242490.

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17

Britton, Robert Stanley. "Spin dynamics of carriers in quantum wells." Thesis, University of Southampton, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.310538.

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18

Gillin, W. P. "Interdiffusion in InGaAs/GaAs strained quantum wells." Thesis, University of Surrey, 1991. http://epubs.surrey.ac.uk/844319/.

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This thesis presents the results of a study of the interdiffusion of InGaAs/GaAs structures. Photoluminescence in conjunction with a model for the interdiffusion has been used to show that the diffusion obeys Fick's law and that there are two distinct diffusion regions. The first is a fast initial diffusion, which is suggested to be caused by the diffusion of point defects in the quantum well, and which is found to occur solely during the first anneal. The second is a steady state diffusion region during which the diffusion coefficient is constant. The steady state diffusion coefficient has been shown to be dependent upon the distance of the quantum well from the surface and upon the incorporation of silicon in the material. The indium concentration of the initial well has been shown to have no effect on the diffusion coefficient as has beryllium doping. An activation energy for the diffusion of 3.0 +/- 0.3 eV has been obtained in all cases.

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19

Zholudev, Maksim. "Terahertz Spectroscopy of HgCdTe / CdHgTe quantum wells." Thesis, Montpellier 2, 2013. http://www.theses.fr/2013MON20218/document.

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Cette thèse est consacrée à l'étude de puits quantiques de HgCdTe / CdHgTe dans le plan [013]. Les données expérimentales sont obtenues par photoconductivité et résonance cyclotron et concordent avec les résultats de simulations numériques. Les calculs sont effectués par approximation des fonctions enveloppe avec un Hamiltonien effectif 8x8. Afin de décrire les hétérostructures dont la croissance est faite sur un plan atomique arbitraire, une approche générale basée sur l'expansion d'invariants et les transformations par rotation, a été développé. La rotation généralisée peut être appliquée à un modèle avec l'ensemble des bandes de façon arbitraire. Le spectre d'énergie du Hamiltonien effectif a été calculé en utilisant l'expansion en onde plane des fonctions enveloppe dans la direction de croissance de l'hétérostructure. Un champ magnétique quantifiant a été pris en compte avec la substitution et l'expansion de Pierls sur les fonctions d'onde des électrons libres en présence du champ magnétique. Les mesures de photoconductivité ont montré une photoréponse correspondant à des transitions interbandes pour des énergies de photons allant jusqu'à 30 meV. Dans l'intervalle de 7 à 30 meV nous avons observé une photoconductivité vraisemblablement due à la photo-ionisation de certains centres de diffusion dans les barrières de CdHgTe. L'analyse théorique de la possibilité d'amplification du rayonnement Terahertz sur les transitions intrabandes dans les puits quantiques HgCdTe / CdHgTe a été effectuée. Des mesures de résonance ont montré la dépendance de la masse cyclotron sur la concentration des porteurs de charges due à la forte non-parabolicité de la bande de conduction. En champs magnétiques quantifiants (jusqu'à 45 T) des résonances interbandes et intrabandes ont été observées. Les mesures de magnétoabsorption ont été également effectuées avec un spectromètre à transformée de Fourier en champs magnétiques quantifiants allant jusqu'à 16 T. Les transitions interbandes et intrabandes ont été étudiés. Dans les puits quantiques de HgTe ayant une structure de bande inversée, une ligne de résonance cyclotron (CR) liée aux trous a été observée. Dans les échantillons ayant des bandes normales, en plus des transitions CR liées aux électrons, une ligne très marquée et probablement liée à des transitions d'impuretés a été découverte. Un anti-croisement des niveaux de Landau d'électrons et de trous dans les échantillons de bandes inversées a été confirmée par l'observation du splitting d'une résonance. Des simulations numériques ont montré que l'anticroisement des niveaux de Landau est causé par l'asymétrie par inversion du cristal massif (Bulk Inversion Asymmetry - BIA) et devrait disparaître pour certaines directions de croissance des hétérostructures. La comparaison des résultats expérimentaux et théoriques a montré de manière générale un bon accord qualitatif, mais un désaccord quantitative systématique allant dans le même sens pour toutes les expériences en champs magnétique. L'accord a été obtenu par l'ajustement de l'offset de la bande de valence du CdTe et du HgTe, et du paramètre de Kane, Ep
The thesis is devoted to study of narrow-gap HgCdTe/CdHgTe quantum wells grown on [013] plane. The experimental data are obtained by means of photoconductivity and cyclotron resonance measurements and fit with results of numerical simulations.The calculations are made within envelope functions approximation with 8x8 effective Hamiltonian. In order to describe heterostructures grown on arbitrary atomic plane a general approach based on expansion over invariants and rotation transformation was developed. The generalized rotation can be applied to a model with arbitrary basis band set.The energy spectrum of the effective Hamiltonian was calculated using plain wave expansion of the envelope functions in heterostructure growth direction. Quantizing magnetic field have been taken into account with Pierls substitution and expansion over wave functions of free electron in magnetic field.Photoconductivity measurements have demonstrated interband photoresponse for photon energies down to 30~meV. In the range from 7 to 30 meV we have observed photoconductivity presumably concerned with photoionization of some centers in CdHgTe barriers. Theoretical analysis of possibility of FIR radiation amplification on intraband transitions in HgCdTe/CdHgTe quantum wells have been performed.Cyclotron resonance measurements in quasiclassical magnetic fields have shown dependence of cyclotron mass on carrier concentration caused by strong non-parabolicity of conduction band. In quantizing magnetic fields (up to 45 T) both interband and intraband magnetoabsorption have been observed.Magnetoabsorption have been also measured with Fourier transform spectrometer in quantizing magnetic fields up to 16 T. Both interband and intraband magnetoabsorption have been studied. In semimetallic HgTe quantum well with inverted band structure, a hole CR line was observed. In normal-band sample in addition to electron CR transitions a strong absorption line presumably related to impurity transitions was discovered.Avoided crossing of electron and hole Landau levels in inverted-band sample was confirmed by splitting of two spectral lines. Numerical simulations showed that Landau level anticrossing is caused by bulk inversion asymmetry and should disappear for some heterostructure growth directions.Comparison of experimental and theoretical results have shown good qualitative agreement with systematic quantitative disagreement in the same direction in all experiments involving magnetic fields. The agreement was achieved by adjustment of valence band offset of CdTe and HgTe, and the Kane parameter Ep

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20

Watson-Parris, Duncan Thomas Stephens. "Carrier localization in InGaN/GaN quantum wells." Thesis, University of Manchester, 2011. https://www.research.manchester.ac.uk/portal/en/theses/carrier-localization-in-ingangan-quantum-wells(d1f06539-6fde-4ec4-beac-31689a571804).html.

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Presented in this thesis are extensive theoretical investigations into the causes and effects of carrier localization in InGaN/GaN quantum wells. The results of the calculations agree well with experimental data, where it is available, and provide additional insights into the mechanisms that lead to some of the experimentally observed effects of localization. Firstly, the wave functions of the electrons and holes in InGaN/GaN quantum wells have been calculated by numerical solution of the effective-mass Schrödinger equation. In our calculations we have assumed a random distribution of indium atoms, as suggested by the results of atom probe tomography: this allows us to find the contributions to the carriers' potential energy that arise from band gap fluctuations, the deformation potential and the spontaneous and piezoelectric fields. We show that the fluctuations in alloy composition can be sufficient to localize the carriers; our results are in good agreement with the results of experiment and more detailed ab-initio calculations, but we also obtain information about the distribution of localized states which those methods cannot yet provide. We find that the holes are localized on a short scale in randomly-occurring regions of high indium content, whereas the electrons are localized on a longer length scale. We consider the effect of well width fluctuations and find that these contribute to electron localization, but not to hole localization. We also simulate the low-temperature photoluminescence spectrum and find good agreement with experiment for the energy, width and shape of the photoluminescence peak. Secondly, we have used first-order time-dependent perturbation theory to study the diffusion of the carriers between their localized states at non-zero temperatures. The rates for scattering via the interaction with acoustic phonons are calculated using the carrier wave functions, and the resulting master equation for the distribution of the carriers is solved by a Monte Carlo method. We find that, even towards room temperature, the carriers are localized to a small number of states, and that their diffusion lengths are proportional to a combination of the density of localized states and the localization length. The experimentally-observed `S-shape' of the photoluminescence peak energy as a function of temperature is reproduced in our results and is explained by the thermal redistribution of holes among the localized states. A reduction of the depth of this S-shape is found as the excitation power is increased, as has been observed experimentally, and which we attribute to the saturation of the localized states.

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21

Chatterjee, Sangam. "Exciton formation dynamics in semiconductor quantum wells." Diss., The University of Arizona, 2003. http://hdl.handle.net/10150/280403.

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Photoluminescence from direct-bandgap semiconductor quantum wells after non-resonant excitation is predominantly observed at energetic position of the 1s exciton resonance. The time evolution of the photoluminescence is generally interpreted as direct monitor of an excitonic population; a rise of the signal is interpreted as a buildup and the decrease as decay of the excitonic population. Recent microscopic calculations, however, have shown that even without an incoherent excitonic population, pure plasma decay yields photoluminescence peaked at the is exciton resonance. Experimental time-resolved photoluminescence spectra are taken across a large region of the parameter space of carrier density and lattice temperature. They are compared to the expected thermal equilibrium spectra, calculated from nonlinear absorption measurements taken under identical conditions. Under none of the experimentally explored parameters is the is emission as bright as expected for thermal equilibrium. To distinguish excitonic and plasma contributions, the deviations from thermal equilibrium at the is exciton resonance are then analyzed using a microscopic calculation. The dipole moment is adjusted to reproduce the excitonic binding energy and oscillator strength of the samples under investigation. The carrier densities and carrier temperatures are determined experimentally; no free fit parameters are necessary. The differences between experimental values and pure plasma calculation are explained with the presence of an incoherent excitonic population. Although at first the emission spectra under all conditions do not vary significantly, a more detailed analysis reveals that the sources of the photoluminescence can be either predominantly excitonic or plasma. For low temperatures and low densities the excitonic emission is extremely sensitive to even minute exciton populations making it possible to extract a phase diagram for incoherent excitonic populations. The maximum contribution of bright excitons is found at intermediate densities and low lattice temperatures; the absolute number of bright excitons is tiny, less than 0.04% of the total carrier density. However, it is not possible to determine the total number of bright and dark exciton by using photoluminescence.

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22

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.

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23

Harris, C. I. "Optical studies of impurities in quantum wells." Thesis, University of Bath, 1991. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.292840.

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24

Johnston, Wesley James. "Nonlinear optics in Bragg-spaced quantum wells." Diss., University of Iowa, 2010. https://ir.uiowa.edu/etd/826.

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Bragg spaced quantum wells represent a unique class of resonant photonic materials, wherein a photonic bandgap is created by the periodic spacing of quantum wells and the associated variation in the complex susceptibility (index and absorption) of the material. Interest in BSQWs has grown in the past decade due to their large ultrafast nonlinearities and the corresponding large ultrafast reflectivity changes and transmissivity. These nonlinearities are of particular interest in areas of communication technology, where ultrafast all-optical logic components have become increasingly in demand. This research will further investigate BSQWs and the for the first time effects of spin-dependent nonlinear excitation on their photonic band structures. It will also investigate how these effects can be used in all-optical polarization switching and tunable optical buffer (slow light) applications.

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25

鄭旭 and Yuk Cheng. "Interdiffused quantum well solar cells." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1996. http://hub.hku.hk/bib/B31213996.

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Cheng, Yuk. "Interdiffused quantum well solar cells /." Hong Kong : University of Hong Kong, 1996. http://sunzi.lib.hku.hk/hkuto/record.jsp?B19740049.

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27

Turner, Keith. "Hot carrier relaxation in GaAs quantum wells and V-groove quantum wires." Thesis, University of Oxford, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.308680.

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Newton, Soraya Reima. "Magneto-optical studies of localised states in quantum wells and quantum wires." Thesis, University of Cambridge, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.615959.

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Huang, Xuren. "Linear, Nonlinear Optical and Transport Properties of Quantum Wells Composed of Short Period Strained InAs/GaAs Superlattices." Thesis, University of North Texas, 1993. https://digital.library.unt.edu/ark:/67531/metadc278855/.

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In this work, ordered all-binary short-period strained InAs/GaAs superlattice quantum wells were studied as an alternative to strained ternary alloy InGaAs/GaAs quantum wells. InGaAs quantum wells QWs have been of great interest in recent years due to the great potential applications of these materials in future generations of electronic and optoelectronic devices. The all binary structures are expected to have all the advantages of their ternary counterparts, plus several additional benefits related to growth, to the elimination of alloy disorder scattering and to the presence of a higher average indium content.

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Barnes, Jennifer M. "An experimental and theoretical study of GaAs/InGaAs quantum well solar cells and carrier escape from quantum wells." Thesis, Imperial College London, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.319305.

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31

Im, Jin Seo. "Spontaneous recombination in group-III nitride quantum wells." [S.l.] : [s.n.], 2001. http://deposit.ddb.de/cgi-bin/dokserv?idn=963180800.

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Rezaee, Amirabbas, and amirabbas rezaee@rmit edu au. "Phase-Periodic Quantum Structures and Perturbed Potential Wells." RMIT University. Electrical and Computer Engineering, 2009. http://adt.lib.rmit.edu.au/adt/public/adt-VIT20091218.160522.

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The restrictions of micro-scale systems are approaching rapidly. In anticipation of this development, nano-scale electronics has become the focus of many researchers and engineers in academia and industry since early 1990s. The basic building blocks of modern integrated circuits have been diodes and transistors with their current-voltage I-V characteristics being of prime significance for the design of complex signal processing and shaping devices and systems. Classical and semi-classical physical principles are no longer powerful enough or even valid to describe the phenomena involved. The application of rich and powerful concepts in quantum theory has become indispensable. These facts have been influential in undertaking this research project. This research is built upon the determination of the Eigenpairs of one and two dimensional positive differential operators with periodic boundary conditions. The Schrödinger equation was solved for positive operators in both one and two dimensions. Fourier series were used to express the derivatives as the summation of Fourier terms. This led to a novel approach for the calculation of the eigenmodels of a perturbed potential well. The perturbation can be done via an electric field applied to the potential well. The research in this thesis includes a thorough understanding of quantum mechanics fundamentals, mastering of different approximation techniques such as the variational technique and results that have been generated and published using the novel techniques.

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Turberfield, A. J. "Hot carrier dynamics in gallium arsenide quantum wells." Thesis, University of Oxford, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.235088.

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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.

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35

Livingstone, Martin. "Band structure and absorption in semiconductor quantum wells." Thesis, Heriot-Watt University, 1996. http://hdl.handle.net/10399/698.

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36

Adams, Stephen J. A. "Optical spectroscopy of InxGa1-xAs/GaAs quantum wells." Thesis, Heriot-Watt University, 1992. http://hdl.handle.net/10399/816.

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37

Neilson, David Thomas. "Optical nonlinearities and switching in InGaAs quantum wells." Thesis, Heriot-Watt University, 1993. http://hdl.handle.net/10399/1515.

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38

Hughes, D. T. "Electronic states in semiconductor superlattices and quantum wells." Thesis, Durham University, 1989. http://etheses.dur.ac.uk/6519/.

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The aim of this thesis is two-fold. Firstly to show how a complex bandstructure matching technique has been developed which allows detailed investigations to be made of various low dimensional structures. Secondly the method will be used to investigate interesting physical properties of quantum wells and superlattices. Consequently the thesis will begin with an exposition of the matching technique, giving an indication of the numerical methods used for computational calculations. Evidence will then be given, in the form of a comparison between the present work and the experimental and theoretical results to be found in the literature, of the efficacy of the method. A detailed description of results of calculations carried out on the valence band of AlAs/GaAs and AlGaAs/GaAs quantum wells will show how energy levels and wavefunctions have been calculated as well as giving an explanation of hybridisation and anti-crossing effects. In order to extend the method to strained systems it will be shown how strain can be incorporated into the model by simple empirical fits of calculated bulk properties to experiment. This method will be used to model two particular Si/Ge structures: a Ge(_0.25)Si(_0.75)/Si/Ge(_0.25)Si(_0.75) quantum well and a (Si)(_4)(Ge)(_4) superlattice. To allow a better comparison with experiment for the superlattice a description is given of a method for calculating optical matrix elements between superlattice states; and the results of such calculations are discussed.

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Harrison, Paul Anthony. "Resonant tunnelling and luminescence in coupled quantum wells." Thesis, University of Nottingham, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.363933.

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Wallace, Chik-Ho Choy. "Modelling and electro-optic quantum-wells modulation devices." Thesis, University of Surrey, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.267967.

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Denton, Graham John. "Coherent optical transient effects in semiconductor quantum wells." Thesis, University of Cambridge, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.320979.

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Wilkes, Joe. "Hydrodynamics of indirect excitons in coupled quantum wells." Thesis, Cardiff University, 2012. http://orca.cf.ac.uk/43296/.

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This thesis comprises a theoretical study of the dynamics of indirect excitons in coupled quantum wells at low lattice temperatures. The results of numerical simulations of the exciton photoluminescence pattern are presented and compared to available experimental data. The in-plane transport of quantum well excitons created by laser excitation is modeled using a non-linear drift-diffusion equation. Combined with a model of exciton relaxation thermodynamics, a complete description of the evolution of the exciton density and temperature is built. The optical decay of indirect excitons is included in the modeling. This is used to make predictions of the spatial photoluminescence patterns which have been observed experimentally. The transport of dipole orientated excitons via externally applied electrostatic potentials is also studied. The drift-diffusion equation is adapted to include the inplane electric field. This is done for some specific forms of the potential landscapes such as a linear potential energy gradient and a propagating lattice. These correspond to some recent experiments for which results are available. The combined theoretical and experimental studies reveal a deeper insight into the transport properties of indirect excitons. Finally, the external ring structure in the indirect exciton emission pattern is studied. Its formation is modeled using a set of coupled transport equations for electrons, holes and indirect excitons. The Coulomb interactions between all three species are incorporated in the model. It is shown that these interactions lead to an instability in the external ring and are responsible for its fragmentation into a periodic array of islands which has been observed experimentally.

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Nixon, Gregor Clark. "Coherent non-linear optical processes in quantum wells." Thesis, University of Cambridge, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.627327.

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Ivanov, V. I., V. K. Dugaev, E. Y. Sherman, and J. Barnas. "Spin current in (110)-oriented GaAs quantum wells." Thesis, Sumy State University, 2011. http://essuir.sumdu.edu.ua/handle/123456789/20556.

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We consider a possibility of generation of the stationary spin current in (110) – oriented GaAs-basedsymmetric quantum well due to the nonlinear response to externalperiodic electric field. The model includes the Dresselhaus spin-orbit interaction and the random Rashbaspin-orbit coupling. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/20556

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Mahat, Meg Bahadur. "Ultrafast Spectroscopy of Hybrid Ingan/gan Quantum Wells." Thesis, University of North Texas, 2012. https://digital.library.unt.edu/ark:/67531/metadc149635/.

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Group III nitrides are efficient light emitters. The modification of internal optoelectronic properties of these materials due to strain, external or internal electric field are an area of interest. Insertion of metal nanoparticles (MNPs) (Ag, Au etc) inside the V-shaped inverted hexagonal pits (IHP) of InGaN/GaN quantum wells (QWs) offers the potential of improving the light emission efficiencies. We have observed redshift and blueshift due to the Au MNPs and Ag MNPs respectively. This shift could be due to the electric field created by the MNPs through electrostatic image charge. We have studied the ultrafast carrier dynamics of carriers in hybrid InGaN/GaN QWs. The change in quantum confinement stark effect due to MNPs plays an important role for slow and fast carrier dynamics. We have also observed the image charge effect on the ultrafast differential transmission measurement due to the MNPs. We have studied the non-linear absorption spectroscopy of these materials. The QWs behave as a discharging of a nanocapacitor for the screening of the piezoelectric field due to the photo-excited carriers. We have separated out screening and excitonic bleaching components from the main differential absorption spectra of InGaN/GaN QWs.

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Baldwin, Thomas. "Trion-based Optical Processes in Semiconductor Quantum Wells." Thesis, University of Oregon, 2016. http://hdl.handle.net/1794/19728.

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In a semiconductor, negative charge is carried by conduction-band electrons and positive charge is carried by valence-band holes. While charge transport properties can be understood by considering the motion of these carriers individually, the optical properties are largely determined by their mutual interaction. The hydrogen-like bound state of an electron with a hole, or exciton, is the fundamental optical excitation in direct-gap materials such as gallium arsenide and cadmium telluride. In this dissertation, we consider charged excitons, or trions. A bound state of an exciton with a resident electron or hole, trions are a relatively pure manifestation of the three-body problem which can be studied experimentally. This is a subject of practical as well as academic interest: Since the trion is the elementary optical excitation of a resident free carrier, the related optical processes can open pathways for manipulating carrier spin and carrier transport. We present three experimental investigations of trion-based optical processes in semiconductor quantum wells. In the first, we demonstrate electromagnetically induced transparency via the electron spin coherence made possible by the trion transition. We explore the practical limits of this technique in high magnetic fields. In the second, we present a direct measurement of trion and exciton oscillator strength at high magnetic fields. These data reveal insights about the structure of the trion's three-body wavefunction relative to that of its next excited state, the triplet trion. In the last, we investigate the mechanism underlying exciton-correlated tunneling, an optically-controllable transport process in mixed-type quantum wells. Extensive experimental studies indicate that it is due to a local, indirect interaction between an exciton and a hole, forming one more example of a trion-mediated optical process. This dissertation includes previously published co-authored material.

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Barnett, Anne. "Quantum well intermixing by ion implantation." View electronic text, 2002. http://eprints.anu.edu.au/documents/disk0/00/00/07/62/index.html.

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Thesis (BSc. (Hons))--Australian National University, 2002.
Available via the Australian National University Library Electronic Pre and Post Print Repository. Title from title screen (viewed Mar. 27, 2003). "A thesis submitted in part fulfillment of the requirements for the degree of Bachelor of Science (Honours), The Australian National University" "November 2002" Includes bibliographical references.

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Little, Reginald Bernard. "The synthesis and characterization of some II-VI semiconductor quantum dots, quantum shells and quantum wells." Diss., Georgia Institute of Technology, 1999. http://hdl.handle.net/1853/30573.

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Sivalertporn, Kanchana. "Strong light-matter coupling in microcavity-embedded semiconductor quantum wells and quantum dots." Thesis, Cardiff University, 2013. http://orca.cf.ac.uk/49358/.

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This thesis presents a theoretical investigation of exciton polaritons in strongly-coupled exciton-photon microcavity systems. Two different systems, a coupled quantum well (CQW) embedded in a planar microcavity and a quantum dot (QD) inside a micropillar cavity, are studied using suitable theoretical models. The exciton-polariton states are calculated and their optical properties are investigated in detail, showing a good agreement with experimental observations. For a CQW structure, the excitonic states in the presence of the electric field applied in the growth direction are calculated by solving the Schrodinger equation in real space. The field dependence of exciton transition energy, binding energy, oscillator strength, lifetime and absorption is studied. The exciton ground state experiences a crossover from direct to indirect state at low electric field. A single state-basis calculation in which only the electron and hole ground states are taken into account is also made and compared with the full accurate calculation model. The polariton effect in a microcavity-embedded CQW is investigated based on the semiclassical theory. The light-matter interaction is treated by solving coupled material and Maxwell's equations. The reflectivity and absorption spectra are calculated for different detunings using the scattering matrix method. When a cavity mode is tuned to an exciton mode (zero detuning), an anticrossing of two polariton modes is observed, showing that the system is in the strong coupling regime. In addition, the fractions of direct exciton, indirect exciton and cavity modes contributed to the polariton states are calculated using the microscopic theory. The resulting polariton state with comparable contributions ofall three components called dipolariton is observed. Finally, the dynamics of the strongly-coupled exciton-cavity system in the QD-micropillar system is studied using the four wave mixing (FWM) theory applied to the Jaynes-Cummings model. Spectrally resolved and time-resolved FWM signals are calculated for different temperatures. Temperature plays the role of the parameter controlling the detuning. The beat periods of the first and second rungs of the JC ladder are also investigated, showing that the second rung has a sqaure- shorter period compared to the beat period of the first rung. To reveal the coherent coupling between two distant QDs, the FWM signals are Fourier-transformed into a two-dimensional frequency domain. It is found that the off-diagonal components in these 2D spectra are nonzero, demonstrating the coherent coupling between isolated QDs. In addition, the phase correction is developed. This procedure is neccessary for a comparison with the experiment which has random phases for different detunings. A quantitative agreement between the prediction and measurement is achieved and demonstrated.

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Kim, Dong Kwon. "Optical properties of asymmetric double quantum wells and optimization for optical modulators." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/22649.

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Thesis (Ph. D.)--Electrical and Computer Engineering, Georgia Institute of Technology, 2008.
Committee Chair: Citrin, David; Committee Member: Dupuis, Russell; Committee Member: Gaylord, Thomas; Committee Member: Rhodes, William; Committee Member: Zhang, Zhuomin.

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Dissertations / Theses on the topic 'Quantum wells'

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