Comparison of the coherence properties of superradiance and laser emission in semiconductor structures

The coherence properties of a transient electron-hole state developing during superradiance emission in semiconductor laser structures have been studied experimentally using a Michelson interferometer and Young's classic double-slit configuration. The results demonstrate that, in the lasers studied, the first-order correlation function, which quantifies spatial coherence, approaches unity for superradiant emission and is 0.2-0.5 for laser emission. The supercoherence is due to long-range ordering upon the superradiant phase transition. © 2012 Kvantovaya Elektronika and Turpion Ltd.

Optical properties of silicon rich oxides

Thermally treated silicon rich oxides (SRO) used as starting material for the fabrication of silicon nanodots represent the basis of tunable bandgap nanostructured materials for optoelectronic and photonic applications. The optical modelization of such materials is of great interest, as it allows the simulation of reflectance and transmittance (R&T) spectra, which is a powerful non destructive tool in the determination of phase modifications (clustering, precipitation of new phases, crystallization) upon thermal treatments. In this paper, we study the optical properties of a variety of as-deposited and furnace annealed SRO materials. The different phases are treated by means of the effective medium approximation. Upon annealing at low temperature, R&T spectra show the precipitation of amorphous silicon nanoparticles, while the crystallization occurring at temperatures higher than 1000 °C is also clearly identified, in agreement with structural results. The existing literature on the optical properties of the silicon nanocrystals is reviewed, with attention on the specificity of the compositional and structural characteristics of the involved material. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Nature of the electronic band gap in lanthanide oxides

Accurate electronic structures of the technologically important lanthanide/rare-earth sesquioxides (Ln2O3, with Ln=La, ⋯,Lu) and CeO2 have been calculated using hybrid density functionals HSE03, HSE06, and screened exchange (sX-LDA). We find that these density functional methods describe the strongly correlated Ln f electrons as well as the recent G0W0@LDA+U results, generally yielding the correct band gaps and trends across the Ln period. For HSE, the band gap between O 2p states and lanthanide 5d states is nearly independent of the lanthanide, while the minimum gap varies as filled or empty Ln 4f states come into this gap. sX-LDA predicts the unoccupied 4f levels at higher energies, which leads to a better agreement with experiments for Sm2O 3, Eu2O3, and Yb2O3. © 2013 American Physical Society.

How to achieve ultra high photoconductive gain for transparent oxide semiconductor image sensors

We present quantitative analysis of the ultra-high photoconductivity in amorphous oxide semiconductor (AOS) thin film transistors (TFTs), taking into account the sub-gap optical absorption in oxygen deficiency defects. We analyze the basis of photoconductivity in AOSs, explained in terms of the extended electron lifetime due to retarded recombination as a result of hole localization. Also, photoconductive gain in AOS photo-TFTs can be maximized by reducing the transit time associated with short channel lengths, making device scaling favourable for high sensitivity operation. © 2012 IEEE.

Modeling bipolar power semiconductor devices gachovska

This book presents physics-based models of bipolar power semiconductor devices and their implementation in MATLAB and Simulink. The devices are subdivided into different regions, and the operation in each region, along with the interactions at the interfaces which are analyzed using basic semiconductor physics equations that govern their behavior. The Fourier series solution is used to solve the ambipolar diffusion equation in the lightly doped drift region of the devices. In addition to the external electrical characteristics, internal physical and electrical information, such as the junction voltages and the carrier distribution in different regions of the device, can be obtained using the models. Table of Contents: Introduction to Power Semiconductor Device Modeling/Physics of Power Semiconductor Devices/Modeling of a Power Diode and IGBT/IGBT Under an Inductive Load-Switching Condition in Simulink/Parameter Extraction. © 2013 by Morgan & Claypool.

Superradiant emission in semiconductor diode laser structures

This paper reviews recent advances in superradiant (SR) emission in semiconductors at room temperature, a process which has been shown to enable the generation on demand of high power picosecond or subpicosecond pulses across a range of different wavelengths. The different characteristic features of SR emission from semiconductor devices with bulk, quantum-well, and quantum-dot active regions are outlined, and particular emphasis is placed on comparing the characteristic features of SR with those of lasing. Finally, potential applications of SR pulses are discussed. © 1995-2012 IEEE.

Ultrafast dynamics of exciton formation in semiconductor nanowires.

The dynamics of free electron-hole pairs and excitons in GaAs-AlGaAs-GaAs core-shell-skin nanowires is investigated using femtosecond transient photoluminescence spectroscopy at 10 K. Following nonresonant excitation, a bimolecular interconversion of the initially generated electron-hole plasma into an exciton population is observed. This conducting-to-insulating transition appears to occur gradually over electron-hole charge pair densities of 2-4 × 10(16) cm(-3) . The smoothness of the Mott transition is attributed to the slow carrier-cooling during the bimolecular interconversion of free charge carriers into excitons and to the presence of chemical-potential fluctuations leading to inhomogeneous spectral characteristics. These results demonstrate that high-quality nanowires are model systems for investigating fundamental scientific effects in 1D heterostructures.

III-V semiconductor nanowires for optoelectronic device applications

Semiconductor nanowires have recently emerged as a new class of materials with significant potential to reveal new fundamental physics and to propel new applications in quantum electronic and optoelectronic devices. Semiconductor nanowires show exceptional promise as nanostructured materials for exploring physics in reduced dimensions and in complex geometries, as well as in one-dimensional nanowire devices. They are compatible with existing semiconductor technologies and can be tailored into unique axial and radial heterostructures. In this contribution we review the recent efforts of our international collaboration which have resulted in significant advances in the growth of exceptionally high quality IIIV nanowires and nanowire heterostructures, and major developments in understanding the electronic energy landscapes of these nanowires and the dynamics of carriers in these nanowires using photoluminescence, time-resolved photoluminescence and terahertz conductivity spectroscopy. © 2011 Elsevier Ltd. All rights reserved.