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The OECS11 (International Conference on Optics of Excitons in Confined Systems) was the eleventh of a very successful series of conferences that started in 1987 in Rome (Italy). Afterwards the conference was held at Naxos (Sicily, Italy, 1991), Montpellier (France, 1993), Cortona (Italy, 1995), Göttingen (Germany, 1997), Ascona (Switzerland, 1999), Montpellier (France, 2001), Lecce (Italy, 2003), Southampton (UK, 2005) and Patti (Sicily, Italy, 2007). It is addressed to scientists who lead fundamental and applied research on the optical properties of excitons in novel condensed-matter nanostructures.

The 2009 meeting (7–11 September 2009) has brought together a large representation of the world leading actors in this domain, with the aim of stimulating the exchange of ideas, promoting international collaborations, and coordinating research on the newest exciton-related issues such as quantum information science and exciton quantum-collective phenomena.

The meeting has included invited lectures, contributed oral presentations and posters, covering the following general topics:

• low-dimensional heterostructures: quantum wells, quantum wires and quantum dots

• polaritons

• quantum optics with excitons and polaritons

• many-body effects under coherent and incoherent excitation

• coherent optical spectroscopy

• quantum coherence and quantum-phase manipulation

• Bose-Einstein condensation and other collective phenomena

• excitons in novel materials

The OECS 11 was held at the campus of the Universidad Autónoma de Madrid in Cantoblanco. The scientific program was composed of more than 200 contributions divided into 16 invited talks, 44 oral contributions and 3 poster sessions with a total of 150 presentations. The scientific level of the presentations was guaranteed by a selection process where each contribution was rated by three members of the Program Committee. The Conference has gathered 238 participants from 21 different countries, with the following distribution: Germany (43), France (41), Spain (33), UK (24), Switzerland (21), Italy (14), The Netherlands (12), USA (11), other (23).

The conference was made possible by generous sponsors, whom we thank earnestly: Universidad Autónoma de Madrid, Spanish Ministry of 'Educación y Ciencia', Consejo Superior de Investigaciones Científicas, European Union (ITN- 235114), Europhysics Letters, Semiconductor Science and Technology, Consolider Research Project 'Quantum Optical Information Technology', Lasing S A, Newport, Innova Scientific, Foundation Madrid-2016 and European Physical Society.

We would like to acknowledge the members of the Organizing and Program Committees, who are responsible for the success of the Conference (names are listed below). Finally, the authors are thanked for the quality of their contributions.

Luis Viña Carlos Tejedor José M Calleja EDITORS

Luis Viña-Chair, Universidad Autónoma de Madrid María D Martín-Scientific Secretary, Universidad Autónoma de Madrid José M Calleja, Universidad Autónoma de Madrid Luisa González, Instituto de Microelectrónica de Madrid Herko van der Meulen, Universidad Autónoma de Madrid Enrique Calleja, Instituto de Sistemas Optoelectrónicos y Microtecnología Madrid Daniele Sanvitto, Universidad Autónoma de Madrid

Carlos Tejedor-Chair, Universidad Autónoma de Madrid Israel Bar-Joseph, Weizmann Institute of Science Jeremy J Baumberg, Cambridge University Manfred Bayer, Universität Dortmund Jacqueline Bloch, Laboratoire de Photonique et de Nanostructures - CNRS Wolfgang Langbein, Cardiff University Marek Potemski, Grenoble High Magnetic Field Laboratory Antonio Quattropani, Ecole Polytechnique Fédérale de Lausanne Salvatore Savasta, Università di Messina Vincenzo Savona, Ecole Polytechnique Fédérale de Lausanne David Snoke, University of Pittsburgh Jerome Tignon, Ecole Normale Superieure Paris

All papers published in this volume of Journal of Physics: Conference Series have been peer reviewed through processes administered by the proceedings Editors. Reviews were conducted by expert referees to the professional and scientific standards expected of a proceedings journal published by IOP Publishing.

The PDF contains the complete book of abstracts and the conference program.

We consider the frequency- and angle-dependent reflectivity of hybrid structures containing metallic components and an optically excitable medium such as organic dyes or semiconductor quantum wells. Clear signatures of a coupling between surface plasmon polaritons and excitons in the excitable medium, in particular avoided crossings with hybridization gaps in the range ≈ 10–100 meV, are found both experimentally and theoretically.

We present a new experimental method to obtain the exciton-formation time based on the detection of the zero-magnetic field energy splitting between excitons with spins +1 and −1 created by circularly polarized light. The splitting is proportional to the product of the exciton circular-polarization degree ρ and density n. The dynamics of the exciton density n can be therefore obtained from the values of splitting and ρ. We investigate the exciton formation dynamics in high purity bulk GaAs and Al_0.15Ga_0.85As samples at excitation densities 6×10¹⁴ − 3×10¹⁷ cm⁻³ and obtain the exciton-formation time, which is found to vary from 70 ps to 360 ps.

We present a study of the dephasing of an excitonic qubit trapped within a chain of two semiconductor quantum dots immersed in a bulk material. We consider a specific excitonic wave-function which spreads across the chain. The source of the dephasing is the phonon field of the bulk material interacting with the single exciton within the structure. We show that an excitonic wave function which extends over more than one quantum dot is remarkably more robust against the dephasing. The details of dephasing depends on the distance which separates the two quantum dots. In particular, as this distance increases, the residual coherence increases up to a maximum value. However, the short-time dephasing is shown to be characterised by the appearance of a transient behavior. The actual duration of this transient is determined by the separation between the dots.

The spin dynamics in a single semiconductor quantum dot doped with a single Mn atom are analyzed. We consider a neutral and a negatively charged dot and in both cases we concentrate on the light hole-to-conduction band transition. Both electrons and light holes couple to the Mn spin via the strong exchange interaction. After the excitation by an ultra short laser pulse oscillatory spin dynamics take place, where electron or hole can flip their spin accompanied by a change of the Mn spin. The Mn spin dynamics can be controlled by excitation with additional pulses. Starting from a given initial state we demonstrate that the Mn spin can be flipped all-optically into a steady final state in both neutral or charged quantum dots.

We report on the fabrication and study of (Al,Ga)N microdisks with embedded GaN quantum dots. In order to facilitate the microdisk fabrication, very thin (h < 120 nm) nitride epilayers containing optically efficient GaN quantum dots are grown directly on silicon substrates. The microdisks defined by optical lithography exhibit whispering-gallery modes with a short 1.2 nm mode spacing and quality factors as high as 2000. We show that the quality factor is limited by scattering losses due to the microdisk sidewall roughness. Finally, using e-beam lithography, we obtain microdisks with enhanced features.

A customization of the optical properties of pillar microcavities on the desired applications is essential for their future use as quantum-optical devices. Therefore, all-epitaxial cavities with CdSe quantum dot embedded in pillar structures with different geometries have been realized by focused-ion-beam etching. The quality factors of circularly shaped pillar microcavities have been measured and their dependence on the excitation power is discussed. As a possibility to achieve polarized light emission, asymmetrically shaped microcavities are presented. Examples of an elliptically shaped pillar as well as of photonic molecules are investigated with respect to their photoluminescence characteristics and polarization.

We demonstrate storage of photoexcited electrons in a layer of self assembled CdTe quantum dots embedded in a field-effect structure. We study the storage efficiency with respect to the duration of the photoexcitation pulse. The electrons persist in the quantum dots for as long as 9 milliseconds.

We report on optical investigations of InP quantum dots embedded in a wet-etched GaInP microdisk cavity. The structures exhibit modes with quality factors on the order of 10⁴. A combination of consistent power-dependent measurements of the optical power output, the 2nd-order autocorrelation function g⁽²⁾(τ) and the emission linewidth give proof for high-β lasing. The results correspond very well to those obtained from micropillar cavity lasers.

In this letter, we report on laser light emission in the red spectral range. Self-assembled InP quantum dots being electrically pumped were embedded in a microcavity mesa realized by monolithically grown high-reflectivity AlGaAs distributed Bragg reflectors. Common semiconductor laser processing steps were used to fabricate stand-alone index-guided vertical-cavity surface-emitting lasers with oxide apertures for optical transverse mode confinement and electrical current constriction. Ultra-low threshold current densities of around 10A/cm² and room temperature lasing were achieved.

We have investigated mode spectra and single-photon emission from InP quantum dots in a pillar microcavity. Micropillars are fabricated by milling a planar AlAs/AlGaAs cavity with a focused ion beam, containing self assembled InP quantum dots embedded in AlGaInP barriers as the active medium. We performed micro-photoluminescence measurements to characterize the mode spectra and compared them with a theoretical model revealing excellent agreement. Quality factors up to 3700 were achieved. Furthermore almost background-free single-photon emission was verified by second-order photon auto-correlation measurements under pulsed excitation, yielding g⁽²⁾(0) values of 0.15.

We present non-resonant, polarization-resolved magneto-photoluminescence measurements up to 12 T on single InAs/AlAs quantum dots. We observe typical g-factors between 1 and 2, very low diamagnetic shifts due to strong exciton localization and low-energy sidebands, which are attributed to the piezoelectric exciton-acoustic phonon interaction.

We present an experimental investigation of the magneto optical properties of neutral exciton, neutral biexciton and charged exciton confined in self-assembled GaAs/Al_0.3Ga_0.7As strain free quantum dots grown by droplet epitaxy. We measured the diamagnetic shift γ for several quantum dots spanning an interval of 200 meV of the exciton emission energy. The dependence of γ on quantum dot size and shape is discussed together with a comparison with Stranski Krastanov and fluctuation induced GaAs quantum dots, as well as with quantum well case.

The influence of strain waves traveling across a quantum dot structure on its optical response is studied for two different situations: First, a strain wave is created by the optical excitation of a single quantum dot near a surface which, after reflection at the surface, reenters the dot; second, a phonon wave packet is emitted by the excitation of a nearby second dot and then travels across the quantum dot. Pump-probe type excitations are simulated for quantum dots in the strong confinement limit. We show that the optical signals allow us to monitor crossing strain waves for both structures in the real-time response as well as in the corresponding pump-probe spectra. In the time-derivative of the phase of the polarization a distinct trace reflects the instantaneous shifts of the transition energy during the passage while in the spectra pronounced oscillations reveal the passage of the strain waves.

We have studied the relaxation dynamics of excitons and exciton complexes in a single quantum dot using time-resolved photoluminescence. To avoid any interference of carrier diffusion and trapping we have excited the dot with energies below that of the wetting layer. The times extracted from a quantitative analysis are thus related only to the relaxation of carriers inside the dot. Since the dot is rather large it is possible to observe the recombination of carriers from different atomic shells. We observe a retardation of the carrier relaxation increasing excitation power due to the large number of charges filling the dot.

In this work we develop a detailed experimental study of the exciton recombination dynamics as a function of temperature on QD-ensembles and single QDs in two low density samples having 16.5 and 25 dots/μm². We corroborate at the single QD level the limitation of the exciton recombination time in the smallest QDs of the distribution by thermionic emission (electron emission in transient conditions). A portion of these emitted carriers is retrapped again in other (larger) QDs, but not very distant from those emitting the carriers, because the process is limited by the diffusion length at the considered temperature.

We show how to compute the optical functions (the complex electrosusceptibility tensor, dielectric function, electroreflection spectra and ellipsometric parameters) for semiconductor quantum dots (QD) exposed to a uniform electric field in the growth direction, including the excitonic effects. The method uses the microscopic calculation of the QD excitonic wave functions and energy levels, and the macroscopic real density matrix approach (RDMA) to compute the electromagnetic fields and susceptibilities. The electron-hole screened Coulomb potential is adapted and the valence band structure is taken into account in the cylindrical approximation. In the microscopic calculations we solve the 6-dimensional two-particles Schrödinger equation by transforming it into an infinite set of coupled second order 2-dimensional differential equations with the appropriate boundary conditions. These differential equations are solved numerically giving the eigenfunctions and the energy eigenvalues. Then we used the RDMA and computed the frequency- and electric field strength dependent complex excitonic susceptibility tensor. The above approach enables us to determine the relative oscillator strength connected with excitonic resonances and to find the averaged susceptibilities for light- and heavy-holes excitons. Having the frequency dependent complex susceptibility tensor, we calculate the electrooptical functions for a QD. Numerical calculations have been performed for a InGaAs QD with a constant electric field applied in the growth direction. The optical Stokes parameters and ellipsometric parameters ψ and Δ as functions of the frequency and the angle of incidence are also determined. A good agreement with experiment is obtained.

We examine the resonance fluorescence from localized excitons in GaAs/AlGaAs quantum wells with increasing excitation power and for different temperatures. Extending our experimental setup by a microscope objective with high numerical aperture in the cryostat, the detection of the emission from localized excitons is possible. We find a nonlinear behaviour of the emitted intensity with increasing laser power, which is explained as a transition of the emission from excitonic to electron-hole plasma states due to many-body effects between excited carriers. This is supported by our theoretical description based on the semiconductor Bloch equations.

At the occasion of the OECS conference in Madrid, we give a succinct account of some recent predictions in the spectroscopy of a quantum dot in a microcavity that remain to be observed experimentally, sometimes within the reach of the current state of the art.

A unique nanotemplate deposition technique is utilized in growth of semiconductor quantum dots which enables precise control over the dot dimensions and nucleation site. Here, we demonstrate tuning of the biexciton binding energy in a single, site-selected InAs/InP quantum dot through manipulation of the nanotemplate dimensions and thus, dot size. A monotonic decrease of the biexciton binding energy from the binding to anti-binding regime through zero is observed with increasing dot size. Piezoelectric fields in large quantum dots are suggested as the mechanism to obtain an unbound biexciton state. The tunability of the biexciton binding energy demonstrated here for a deterministically positioned quantum dot is an important step towards a scalable route in the generation of entangled photon pairs that emit around the telecommunications band of 1.55 μm.

We investigate the influence of many-body effects on both the chemical potentials of carriers, and the Mott transition of para-excitons in Cu₂O over a wide range of temperatures and carrier densities, in order to determine the region where an excitonic fraction can exist. In contrast to simplified approximations used in the literature we consider full dynamical screening between carriers and find out that (i) the chemical potentials are much less decreased by the many-body effects, and (ii) for low temperatures the density, where the Mott transition appears, is one order of magnitude higher. This leads to an extension of the region of existence of excitons and, therefore, of a possible BEC, to higher temperatures.

We determine the mean-field ground state of a closed microcavity polariton condensation for various experimentally tunable and material-dependent parameters such as excitation density, detuning and ultraviolet cutoff. The condensate changes its character from excitonic to photonic ones as increasing excitations. This change can be a crossover or a first-order transition depending on these parameters.

Strong coupled organic-inorganic microcavities device has been realized and studied. One of the two cavities contains an organic thin film of tetrakis(4-methoxyphenyl)porphyrin, whereas the other microcavity is a dielectric structure coupled to the organic one by means of a LiF/ZnS Bragg mirror. Reflectivity spectra show the presence of two well defined cavity dips. We observe an energy splitting of the two cavity-modes. Despite only one cavity contains the active layer, the photoluminescence spectra display two peaks at the same energy of the reflectivity dips. These observations indicate the strong coupling of the two cavities. The comparison of the diagonalized effective Hamiltonian with the observed resonances further confirms the strong coupling.

Observation of quantized vortices in non-equilibrium polariton condensates, suggesting parallelisms with conventional superfluids, have been reported either by spontaneous formation and pinning in the presence of disorder [1,2] or by imprinting it onto the signal or idler of an optical parametric oscillator (OPO) [2]. Here we report the first observation of a polariton condensate receiving a quantized angular momentum by means of a short optical pulse and maintaining its rotation for a time much longer than the pulse duration, the polariton and coherence lifetimes. This observation shows a peculiar character of polariton condensates and reveals analogies with supercurrents in superconductors or persistent flow in condensates [3].

The presence of polarization splitting of exciton-polariton branches in planar semiconductor microcavities has a pronounced effect on vortices in polariton condensates. We show that the TE-TM splitting leads to the coupling between the left and right half-vortices (vortices in the right and left circular components of the condensate), that otherwise do not interact. We analyze also the effect of linear polarization pinning resulted from a fixed splitting between two perpendicular linear polarizations. In this case, half-vortices acquire strings (solitons) attached to them. The half-vortices with strings can be detected by observing the interference fringes of light emitted from the cavity in two circular polarizations. The string affects the fringes in both polarizations. Namely, the half-vortex is characterized by an asymmetric fork-like dislocation in one circular polarization; the fringes in the other circular polarization are continuous, but they are shifted by crossing the string.

We study theoretically the photoluminescence of a single quantum dot in a microcavity under incoherent excitation. Analytical results including pure dephasing show that strong coupling and linewidths are largely independent on the pumping intensity (until saturation effects come into play). We show the reliable predicting character in the analysis of some experiments.

We report the observation of the strong coupling regime in a half ZnO cavity. A large Rabi splitting of 130 meV is seen as well as a bottleneck in the exciton-polariton relaxation due to a shorter cavity-photon lifetime. The deposition of the top mirror is expected to yield a Q factor of 620 and the structure would then fulfill the main criteria required for room temperature polariton lasing to occur. This conclusion is supported by simulations based on the solution of Boltzmann equations leading to a polariton density threshold of 10¹⁶ cm⁻³.

Two thin aluminum nitride films have been prepared on sapphire substrates by molecular beam epitaxy technique. Then alkaline and acidic washing were used to remove the back-metal-coating of the sapphire substrate for one of the samples. (It caused also partial film dissolution). The surface polariton (SP) spectra have been measured by attenuated total reflection (ATR) technique. The measured SP dispersion is compared with one calculated using the literature film parameters. Due to the resonance interaction of sapphire substrate SP with the film transverse optical (TO) phonon the splitting of the dispersion curve of sapphire SP was found. The resonance takes place only for the frequency of the film TO phonon polarized along the surface of the anisotropic AlN film (perpendicular to the optical axis). The analysis of ATR and external reflectivity spectra shows the presence of some transition layer between the substrate and the film.

We have studied the lateral coupling between InAs/GaAs quantum dot pairs embedded in a field-effect structure. Quantum dot pairs and molecules have been identified by the correlated evolution of the Coulomb blockade features of each QD in the pair. This behaviour is largely distorted in the presence of resonant coupling states in the QD molecule. Single QD voltage evolution shows a crossover in the lineshape profile, which is associated to Spectral Diffusion processes due to residual charged environment.

The optical characteristics of an indirect type II transition in a series of size and shape-controlled linear CdTe/CdSe/CdTe heterostructure nanorods was studied by steady state and time resolved photoluminescence spectra. The energy and lifetime of the photoluminescence from the charge-separated band structure can be tuned by the band edges of the nanorods. Our results show a size-dependent transition from a type I direct transition (CdSe~600 nm) to an indirect type II transition (CdSe/CdTe). The heterostructure nanorod geometry and dimensions that induce type-II charge separation without type-I recombination were determined. The indirect type II transition at 5 K exhibited a long PL decay time, of more than 1000 nanoseconds, that increased with PL wavelength, which can be rationalized by the changing of wavefunction overlap of electrons and holes induced by the quantum confinement effect in type-II band structure.

We studied the optical Aharonov-Bohm effect for an exciton in a semiconductor quantum ring. A perpendicular electric field applied to a quantum ring with large height, is able to tune the exciton ground state energy such that it exhibits a weak observable Aharonov-Bohm oscillations. This Aharonov-Bohm effect is tunable in strength and period.

We model pump-probe experiments leading to the all-optical initialization of the hole spin of a p-doped InAs/GaAs quantum dots ensemble. We consider selection rules of mixed hole states and include periodic excitation conditions. Hyperfine interaction is taken into account as the common decoherence mechanism for the spins of electrons and holes. We show that the degree of hole spin polarization can be maximized by quenching the action of the hole hyperfine interaction with a small applied magnetic field. However additional hole spin relaxation mechanisms, in the microsecond time range, determine the absolute value of this maximum.

We present a quantum-kinetically exact theoretical framework for the propagation, emission and scattering of light in bounded media in the context of semiconductor optics. The theory is based on the nonequilibrium photon Green's functions. Its advantage is that the spatial inhomogeneity inherent to bounded media and, hence, to many semiconductor optics problems, is fully and exactly considered. The electromagnetic properties of media are treated microscopically rather than in an effective approximation, and media may be arbitrarily dispersive and absorptive. Relations for the propagation of quantized (squeezed) light as well as for the energy transport of incident and emitted light are given and discussed.

We show theoretically that polariton pairs with a high degree of polarization entanglement can be produced through parametric scattering. In our proposed scheme, varying the polarizations of the two pumps, we have a complete control over the symmetries of the produced state (i.e. singlet or triplet output). Our microscopic model shows how a tomographic reconstruction, based on two-time correlation functions, can provide a quantitative assessment of the level of entanglement produced under realistic experimental conditions. Our study provides a suggestive perspective towards hybrid all-optical quantum devices where quantum information can be efficiently generated and controlled within the same structure. This result puts forward the robustness of pair correlations in solid-state devices, even when noise dominates one-body correlations.

We study the strong coupling between photons and bulk excitons in a one-dimensional Bragg grating. The dispersion of the resulting Bragg-polariton states resembles the dispersion of quantum-well microcavity polaritons. We report on a parametric scattering process at two "magic frequencies" occurring due to the strong excitonic nonlinearity.

We report on femtosecond readout of the optical properties of a single CdSe/ZnSe quantum dot. Owing to the uncertainty principle, this timescale represents the ultimate limit for coherent quantum manipulation of such an artificial atom. After resonant excitation of a hot electron-hole pair the absorption of the fundamental exciton resonance is switched off via instantaneous Coulomb renormalization. Subsequently, optical gain builds up after ultrafast intraband relaxation. The speed of thermalization is dominated by the electron spin, since our system is charged permanently with one excess electron. When operating in the nonlinear regime, the number of quanta in a femtosecond light pulse may be changed by exactly ±1. We demonstrate that this deterministic single photon amplifier is characterized by a flat gain spectrum.

We report on polarisation correlation from the cascaded recombination of biexcitons in a quantum dot emitting at a telecommunication wavelength. The fine structure splitting of the exciton state in this InAs/GaAs quantum dot is of the order of 100 μeV and polarisation correlation is expected. Strong polarisation correlation between the biexciton and exciton emission lines is observed under both continuous wave (CW) and pulsed laser excitation so telecom wavelength quantum dots with lower energy splittings could be suitable for entangled photon pair generation. Measurements were performed using nanowire superconducting single photon detectors (SSPDs). SSPDs offer low time-jitter and improve the resolution of features in the correlation spectra, including the asymmetric dip and peak resulting from the cascaded emission with the peak extending more than an order of magnitude above the Poissonian level.

Different InAs/GaAs quantum rings embedded in a photonic crystal microcavity are studied by quantum correlation measurements. Single photon emission, with g⁽²⁾(0) values around 0.3, is demonstrated for a quantum ring not coupled to the microcavity. Characteristic rise-times are found to be longer for excitons than for biexcitons, resulting in the time asymmetry of the exciton-biexciton cross-correlation. No antibunching is observed in another quantum ring weakly coupled to the microcavity.

We demonstrate a high degree of an optical spin preparation of a single Mn atom embedded in a CdTe/ZnTe quantum dot (QD). Due to the strong exchange interaction of the manganese atom with an exciton injected into the QD the spin orientation can be achieved by quasi-resonant or fully-resonant optical creation of the polarized electron-hole pairs. A measured spin memory of the isolated Mn atom, in most of the cases, is in the microsecond range, and depends on the built-in strain in the quantum dot. During the resonant optical pumping process exciton spin-flip can occur without a change of the Mn spin providing a way to directly read the dynamics of the pumped spin state. The manganese spin orientation is achieved in a few tens of ns.

We study the binding energy of excitons in a cylindrical GaAs/Ga_1−xAl_xAs nanowire superlattice, embedded in Ga_1−yAl_yAs matrix, in the presence of magnetic and electric fields applied parallel to the growth direction. We express the exciton trial function as a product of one-particle wave functions of the electron and the hole with variationally determined envelope function, which describes the exciton intrinsic properties and depends only on the electron-hole separation. By using a functional derivative technique, we derive a differential equation for this envelope function, which we solve numerically. By varying the wire radius, interwell barrier width and well sizes we obtain binding energies ranging in character from one for strongly coupled superlattice to that for a system of stack of isolated disks. The behaviour of the binding energies and the charge distributions as functions of the interwell coupling, well sizes, and the external fields is consistently described with our simple formalism.

Binding energies of excitons and excitonic complexes in BeTe/ZnSe type-II core-multishell cylindrical nanowires are calculated by quantum Monte Carlo method. Binding energies are enhanced for negatively charged excitons, and reduced for positively charged excitons and biexcitons. These results are ascribed to excitonic Coulomb potential comes from different spatial distribution of electrons and holes.

The optical properties of InAs/InP multi-layer quantum wire (QWR) structures of various spacer thicknesses have been investigated by means of room temperature surface photovoltage and photoluminescence spectroscopy. Combined with empirical tight binding calculations, the spectra have revealed transitions assigned to QWR families with heights equal to integer number of 5, 6 and 7 monolayers. From the comparison of the experimental and theoretical results the atomic concentration of phosphorus in the wires has been estimated.

We have studied the influence of the polarization angle of linear radiation on the recently measured radiation-induced magnetoresistance oscillations in two-dimensional electron systems. We have applied a previous theoretical framework based in solving the Schrodinger equation of a two-dimensional quantum oscillator subjected to a time-varying force. In agreement with experimental results we have obtained that the magnetoresistance is not affected by the orientation of the electric field of linearly polarized radiation.

The detailed studies of two-dimensional hole gas in an asymmetric 22 nm wide GaAs/Ga_1−xAl_xAs quantum well in polarization-resolved photoluminescence in high magnetic fields (up to B = 20 T) and at low temperatures (down to T = 50 mK) are reported. Additionally to the previously detected in symmetric quantum wells dominant emission channels of various free and acceptor-bound trions, the high-energy hole cyclotron replicas of the bound states are now also observed, corresponding to a the exciton-cyclotron resonance. The identification of transitions in the reach spectra was performed by the analysis of optical selection rules and comparison of the experimental spectra with numerical calculations of the real structure.

Reflectivity and photoluminescence spectra from CdTe/CdMgTe modulation doped quantum well structures were studied. We have found that the value and the sign of the trion reflectivity line's Zeeman splitting depends on the electron concentration in the quantum well, whereas the value and sign of the exciton line splitting are absolutely equal for all studied electron concentrations. In the photoluminescence spectra the sign and value of the exciton and trion Zeeman splittings are found to be equal. Such "renormalization" of the trion g-factor is explained in the model of combined exciton electron processes.

We propose a simple method for calculating the energy spectrum of a magnetoexciton confined in a narrow infinite barrier planar quantum ring with a centreline of an arbitrary shape and a variable width. We show that in the adiabatic approximation the analysis of the low-lying levels of the exciton in such structure can be reduced to study of the angular two-particle motion. We present numerical results for energies of some low-lying levels in circular and elliptical quantum rings with weak variations in their widths as functions of the magnetic field strength. We show that variations in widths produce the quenching of the Aharonov-Bohm oscillations of the energy levels of the magnetoexciton.

We present a model for the incoherent spin dynamics of a Mn atom inside a CdTe quantum dot resonantly pumped by a laser light. The relevant quantum states of the system, 2S + 1 = 6 spin states in the optical ground state and the 24 = (2S + 1) * (2S_e + 1) * (2S_h + 1) are obtained from a effective spin Hamiltonian which describes the basic features of photoluminescence. The model includes the dominant Ising exchange interactions between the spins of the hole, the Mn and the electron but neglects coherent spin-flip terms. The Mn spin dynamics is described with a master equation for the populations of the 30 levels for which dissipative spin-flip processes are permitted. The optical spin pumping observed experimentally is explained if the Mn spin relaxation time in with (T_1X) exciton is much shorter than (T_1G), the Mn spin relaxation time without exciton.

We describe a numerical method to compute exciton wave functions under the influence of an applied electric field. We present results for α-Gallium Nitride fully taking into account the complex 6 × 6 valence-band structure.

Femtosecond pump-probe spectroscopy was performed on ZnO thin film and a double layer structure of ZnO / BaTi0₃ Using a model based on the dielectric function of ZnO obtained by spectral ellipsometry, the observed spectral features were explained. Further, the influence of the BTO layer on the charge carrier dynamics of ZnO was investigated.

Effect of electron-hole (e-h) exchange interaction of exciton in a single-walled carbon nanotube is studied. Large e-h exchange interaction for light field perpendicular to the tube axis drastically changes absorption spectra predicted from a band structure.

A theoretical description of the diffusion, thermalization and photoluminescence of indirect excitons in low temperature (≈ 1K) GaAs/AlGaAs coupled quantum wells is compared with experiments on their photoluminescence dynamics. The results shown in this contribution demonstrate a highly accurate agreement between the two. We concentrate on two key features seen in the photoluminescence pattern: the formation of an inner ring around a tightly focused laser excitation spot and a rapid increase in the intensity from the excitation spot immediately after laser termination – the PL-jump. These striking effects are explained in terms of the diffusion and relaxation thermodynamics of indirect excitons.

We measured photoluminescence (PL) spectra from a 20-nm GaAs/AlGaAs quantum well (QW) grown on an n-type substrate by selectively exciting the GaAs at 2 K. We observed a two-stage change of PL spectra as a function of the total amount of photo-irradiation (p × t) after cooling down. This corresponds to the process of establishing the equilibrium of electrostatic potential between the sample surface and QW and between the QW and n-doped substrate.

In this work the electronic structure of undoped AlGaAs/GaAs wide parabolic quantum wells (PQWs) with different well widths (1000 Å and 3000 Å) were investigated by means of photoluminescence (PL) measurements. Due to the particular potential shape, the sample structure confines photocreated carriers with almost three-dimensional characteristics. Our data show that depending on the well width thickness it is possible to observe very narrow structures in the PL spectra, which were ascribed to emissions associated to the recombination of confined 1s-excitons of the parabolic potential wells. From our measurements, the exciton binding energies (of a few meV) were estimated. Besides the exciton emission, we have also observed PL emissions associated to electrons in the excited subbands of the PQWs.

A theoretical investigation is presented of the properties of heavy- and light-hole excitons in multiple GaAs/Ga_1−xAl_xAs quantum wells in the presence of a magnetic field directed along the growth axis. The low-lying energy levels are calculated as functions of the barrier width, the well size and the magnetic field strength. Effects of interwell coupling on the energies of different exciton levels are consistently included in our calculations. The calculation is realized by means of the diagonalization method.

We present numerical simulations of the generation of coherent LO phonons in an electrically biased quantum well. An ultrashort laser pulse is used to simultaneously excite two exciton levels, which leads to an oscillating dipole moment that couples to the polar lattice and drives the phonons. The generation of coherent phonons becomes resonantly enhanced if the splitting of the two exciton levels is tuned to the LO phonon energy. In this case relaxation by emission of incoherent phonons becomes also possible. Our calculation therefore takes into account incoherent phonons on a quantum kinetic level as well. The intersubband relaxation by excitation of incoherent phonons competes with the generation of coherent phonons and is dominant in terms of the energy transferred.

The theoretical study of the exciton states in the quantum well is performed with regard to the distinctions of the dielectric properties of quantum well and barrier materials. The strong exciton-phonon interaction is shown to be possible in materials with high ionicity. This leads to the essential modification of the exciton states. The relationship between the exciton binding energy, along with oscillator strength and the barrier material dielectric properties is found. This suggests the feasibility of the exciton spectrum parameter control by the choice of the barrier material. It is shown that such exciton spectrum engineering also is possible in the quantum wells based on the materials with low ionicity. The reason is the dielectric confinement effect in the quantum wells.

We compare radiative and nonradiative recombination in polar and nonpolar GaInN/GaN quantum wells and demonstrate that purely radiative recombination can be achieved even at room temperature. The radiative recombination is due to free excitons, which partially dissociate at elevated temperatures. Nonradiative recombination is strongly inhibited in the polar case but not in the nonpolar case.

We measured, for the first time, two photon radiative cascades due to sequential recombination of quantum dot confined electron hole pairs in the presence of an additional spectator charge carrier. We identified direct, all optical cascades involving spin blockaded intermediate states, and indirect cascades, in which non radiative relaxation precedes the second recombination. Our measurements provide also spin dephasing rates of confined carriers.

Non-resonant cavity-quantum dot coupling is an interesting phenomenon with significant consequences for solid state single-photon sources. Here we present studies on the origin of the coupling mechanism by resonant excitation of single quantum dots in micro-pillar cavities. Furthermore, we demonstrate the non-resonant coupling as a powerful tool to 'monitor' the s-shell properties of a quantum dot by observing the behavior of a detuned coupled cavity mode.

We make use of near-field microscopy to image the coupling between two adjacent photonic crystal microcavities A special design of the photonic structures is adopted with selective coupling between different modes having orthogonal spatial extensions Spatial delocalization of coupled-cavity optical modes is found whenever the frequency matching condition is fulfilled On the contrary, in case of large detuning, the modes are localized in each microcavity

Exciton-polaritons, two-dimensional composite bosons arising from the quantum mixture of excitons and photons, can manifest many-body quantum effects at liquid He temperatures (4 K). Interestingly, polaritons are predicted to behave as particular quantum fluids due to their out of equilibrium character, arising from their reduced lifetime (shorter than their thermalization time). Here we report the observation of superfluid motion of polaritons in semiconductor microcavities both under cw and pulsed excitation. Among other signatures, superfluidity is manifested via the absence of scattering of the polariton condensates when encountering a localized defect in their flow path.