Mid-Infrared Modulation of Quantum Emitters in Hexagonal Boron Nitride

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The formation mechanisms, structure and optoelectronic properties of Ga(In)As/(Al)GaAs quantum dot (QD) heterostructures grown by organometallic chemical vapor deposition on patterned (111)B GaAs substrates are reviewed. With this approach, it is possible to prepare high-quality semiconductor QDs whose position on a substrate is precisely controlled via a pre-growth photolithography step. The dots are formed at the center of an inverted, tetrahedral pyramid and are surrounded by distinct, low-dimensional ba

We develop a dynamical theory for the optical injection of charge and spin current originating from the interferences between two coherent laser pulses of frequencies omega and 2omega. Multiband Bloch equations which include one- and two-photon interband transitions are derived. They also account for ac Stark shifts and intersubband two-photon transitions. The model is used to describe the case of time-dependent charge and spin current injection in a symmetric GaAs/AlGaAs quantum well. A comparison to the b

Nanostructured materials can be defined as those materials whose structural elements - clusters, crystallites or molecules - have dimensions in the 1-100 nm range. The explosion in both academic and industrial interest over the past 20 years arises from the remarkable variations in fundamental electrical, optical and magnetic properties that occur as one progresses from an "infinitely extended" solid to a particle of material consisting of a countable number of atoms. In this work the attention was laid on

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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

LiF films have been grown on silicon substrate, irradiated with soft x-rays to create fluorescent regular micrometric-spaced arrays based on colour centres, and studied by Scanning Near-field Optical Microscope (SNOM). Strong variations in the local reflectivity have been observed in the infrared region between 6.1 and 9.2 mum and tentatively ascribed to a modulated variation of the refractive index of the coloured zone with respect to that of the uncoloured LiF matrix. (C) 2003 WILEY-VCH Verlag GmbH & Co.

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The Laboratory of Industrial Energy systems has evaluated a series of high performance air-water heat pump concepts with the aim to retrofit existing fuel fired boilers for residential hydronic heating systems. The results are published within the framework of the Swiss Retrofit Heat Pump project, which is conducted by the Swiss Federal Office of Energy. The two-stage heat pump cycle has shown the best efficiency prospects. Oil migration between the upper stage and lower stage compressors is the main obstac

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 demonstrate edge-emitting lasers based on self-assembled InAs quantum dots (QDs) on GaAs substrates. The InAs QDs are embedded in an InGaAs quantum well (QW) to red-shift the lasing transition. The lasers emit at lambda=1.2 mum with threshold current densities approximate to100 A/cm(2). Maximum modal gains on the order of 5 cm(-1) are deduced for a single QD sheet.

Mid-Infrared Modulation of Quantum Emitters in Hexagonal Boron Nitride

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