Direct observation of new transitions in the absorption spectra of a V-groove quantum wire waveguide

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The present work is devoted to the study of the dynamics of multi-photon processes in semiconductor heterostructures. A time-dependent description is important for understanding in detail the transient response of semiconductors excited by ultrashort optical pulses. In the first part of this thesis, we set up a phenomenological model based on rate equations, in order to investigate the possibility of measuring degenerate two-photon gain in a semiconductor microcavity. The amplification predicted by the mode

We have studied systems of asymmetric coupled GaAs V-groove quantum wires, in which the electrons and holes are injected into different wires. Our experimental results indicate efficient electron and hole tunneling, despite a 7 nm thick AlGaAs tunnel barrier. Temperature dependent electroluminescence exhibit clear effects of tunneling up to room temperature but cannot distinguish electron/hole tunneling from exciton tunneling.

A novel method of controlling light absorption by exciton-polaritons is presented. The coherent light-induced coupling of excitons in multiple quantum well Bragg structures is exploited to sup press dramatically the absorption. Our results show that excitonic light absorption is not an intrinsic property of excitons but rather an extrinsic effect that occurs when the excitons dephase.

The role of Coulomb scattering is studied in the coherent transients of strongly driven exciton resonances in semiconductor quantum wells. Coulomb scattering is treated within the second Born approximation and the light-induced dressing of the electron-hole gas is consistently included. The light dressing is found to decrease the Coulomb collision efficiency and therefore the field-driven dynamics is close to the Hartree-Fock case. Indeed, Coulomb relaxation and dephasing are not strong enough to prevent a

We report on time-resolved and steady-state photoluminescence studies of GaAs/AlGaAs V-groove quantum wire structures. Steady-state photoluminescence experiments are performed in the temperature range from 8 to 200 It. We evaluate the relation between photoluminescence excitation and absorption and determine experimentally the optical density in order to analyze the temperature dependence of the photoluminescence spectra. We find that, at a temperature above 60 K, the photoexcited electron-hole pairs reach

The initial dynamics of resonantly excited secondary emission from quantum wells are dominated by Rayleigh scattering due to excitons localized in the disordered quantum well potential. We show experimentally and theoretically how the temporal shape of the early response is related to details of the two-dimensional disorder potential, and we determine the mean amplitude of the fluctuations and the correlation length. Spectral interferometry performed with a. single speckle allows to investigate the phase of

Picosecond transient reflectometry and dynamic grating techniques have been applied to investigate the perpendicular and parallel transport of optically excited carriers in strained-layer Si0.83Ge0.17/Si superlattices. We present results of the carrier ambipolar diffusivity and effective lifetime measurements in the layered structure and substrate within the 10(17)-10(20) cm(-3) density range. The combined experimental data are discussed in terms of parallel and perpendicular diffusion of carriers, interfac

By using chemical beam epitaxy at growth temperatures as low as 460-480 degrees C, we have overcome strain relaxation problems that prevented so far the successful use of InAsP quantum wells in 1.55 mu m lasers. Five quantum well InAsP/InGaAsP horizontal cavity lasers showed 88% internal efficiency, 1.6 cm(-1) losses per well, and 33 A/cm(2) transparency current density per well, which equal or even surpass the best published characteristics for 1.55 mu m wavelength lasers based on any material system. More

During the past five years, we have developed in our laboratory a new type of solar cell that is based on a photoelectrochemical process. The light absorption is performed by a monolayer of dye (i.e., a Ruthenium complex) that is adsorbed chemically at the surface of a semiconductor (i.e., titanium oxide (TiO2)). When excited by a photon, the dye has the ability to transfer an electron to the semiconductor. The electric field that is inside the material allows extraction of the electron, and the positive ch

The polariton Hamiltonian for a quantum well embedded in a cavity of finite width is derived. The exciton-light interaction is formulated in second quantization and the photon self-interaction term A2 is included. The importance of the A2 term turns out to be relevant in the case of large values of the cavity width. By solving the equation of motion the dispersion relations for upper and lower polaritons are found. A comparison is made with existing measurements of polariton absorption peaks. The limit of i

Detailed investigation of the luminescence features due to the recombination of the exciton-free-carrier process in GaSe is presented. This process shows a well-resolved luminescence line and it is an efficient recombination process in this semiconductor, even at low temperatures. We report accurate photoluminescence spectra measured at 2 K as a function of the excitation intensity, of the excitation energy, and of the lattice temperature from 2 to 200 K. To discriminate between the different kinds of free

We report on a transparent analysis of the luminescence spectra of dense electron-hole plasmas confined in GaAs/(Ga,Al)As quantum wells. We fit the spectra using the fact that the total number of particle states does not depend on collision broadening. Further, the effective dispersion of the valence and conduction subbands and the dependence of the optical matrix elements on wavevector is accounted for. We find (a) that the lowest subbands shift almost rigidly with changing plasma density, and (b) that the

Direct observation of new transitions in the absorption spectra of a V-groove quantum wire waveguide

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Dynamics of multi-photon processes in semiconductor heterostructures

Electrolummescence of asymmetric coupled GaAs/AlGaAs V-groove quantum wires

Is light absorption by excitons in quantum wells an intrinsic process?

Coherence versus Coulomb scattering in resonantly excited quantum wells

Photoluminescence study of V-groove quantum wires: The influence of disorder on the optical spectra and the carrier thermalization

Excitonic dephasing effects studied by time- and phase-resolved secondary emission

Lateral and cross-well transport of highly and moderately excited carriers in Si1-xGex/Si superlattices

Low Threshold 1.55 µm Wavelength InAsP/InGaAsP Strained Multi-Quantum Well Laser Diode Grown by Chemical Beam Epitaxy

Nanocrystalline titanium oxide electrodes for photovoltaic applications

Quantum-Theory Of Quantum-Well Polaritons In Semiconductor Microcavities

Exciton-Carrier Scattering in Gallium Selenide

Spontaneous Emission of Highly Excited Gaas/(Ga,Al)as Quantum-Wells