A study of temperature-related non-linearity at the metal-silicon interface

In this paper, we investigate the temperature dependencies of metal-semiconductor interfaces in an effort to better reproduce the current-voltage-temperature (IVT) characteristics of any Schottky diode, regardless of homogeneity. Four silicon Schottky diodes were fabricated for this work, each displaying different degrees of inhomogeneity; a relatively homogeneous NiV/Si diode, a Ti/Si and Cr/Si diode with double bumps at only the lowest temperatures, and a Nb/Si diode displaying extensive non-linearity. The 77–300 K IVT responses are modelled using a semi-automated implementation of Tung's electron transport model, and each of the diodes are well reproduced. However, in achieving this, it is revealed that each of the three key fitting parameters within the model display a significant temperature dependency. In analysing these dependencies, we reveal how a rise in thermal energy “activates” exponentially more interfacial patches, the activation rate being dependent on the carrier concentration at the patch saddle point (the patch's maximum barrier height), which in turn is linked to the relative homogeneity of each diode. Finally, in a review of Tung's model, problems in the divergence of the current paths at low temperature are explained to be inherent due to the simplification of an interface that will contain competing defects and inhomogeneities

Optical properties of multi-layer type II InP/GaAs quantum dots studied by surface photovoltage spectroscopy

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)We present a low-temperature (73 K) study of the optical properties of multi-layer type II InP/GaAs self-assembled quantum dots by means of surface photovoltage (SPV) spectroscopy, taking advantage of its high sensitivity and contactless nature. The samples contain 10 periods of InP quantum dot planes separated by 5 nm GaAs spacers. The SPV amplitude spectra reveal two major broad peaks, situated at low and high energies, respectively. These features are analyzed taking into account the type II character of the structure, the quantum coupling effects, the spectral behavior of the SPV phase, and the photoluminescence spectra. As a result they have been attributed to optical transitions in the quantum dots and the wetting layers, respectively. The main mechanism for carrier separation in the SPV generation process is clarified via the analysis of the SPV phase spectra. The influence of the substrate absorption on the SPV spectra is discussed in details. (C) 2011 American Institute of Physics. [doi:10.1063/1.3638705]1106Bulgarian National Science Fund [D01-463/12.7.06]Alexander von Humboldt FoundationCoordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Bulgarian National Science Fund [D01-463/12.7.06

Experimental study of the effect of local atomic ordering on the energy band gap of melt grown InGaAsN alloys

We present a study of melt grown dilute nitride InGaAsN layers by x-ray photoelectron spectroscopy (XPS), Raman and photoluminescence (PL) spectroscopy. The purpose of the study is to determine the degree of atomic ordering in the quaternary alloy during the epitaxial growth at near thermodynamic equilibrium conditions and its influence on band gap formation. Despite the low In concentration (~3%) the XPS data show a strong preference toward In–N bonding configuration in the InGaAsN samples. Raman spectra reveal that most of the N atoms are bonded to In instead of Ga atoms and the formation of N-centred In3Ga1 clusters. PL measurements reveal smaller optical band gap bowing as compared to the theoretical predictions for random alloy and localised tail states near the conduction band minimum

Photochemical Charge Separation in Poly(3-hexylthiophene) (P3HT) Films Observed with Surface Photovoltage Spectroscopy

Surface photovoltage spectroscopy (SPS) was used to probe photon induced charge separation in thin films of regioregular and regiorandom poly(3-hexylthiophene) (P3HT) as a function of excitation energy. Both positive and negative photovoltage signals were observed under sub-band-gap (<2.0 eV) and super-band-gap (>2.0 eV) excitation of the polymer. The dependence of the spectra on substrate work function, thermal annealing, film thickness, and illumination intensity was investigated, allowing the identification of interface, charge transfer (CT), and band-gap states in the amorphous and crystalline regions of the polymer films. The ability to probe these states in polymer films will aid the development and optimization of organic electronic devices such as photovoltaics (OPVs), light-emitting diodes (OLEDs), and field effect transistors (OFETs). The direction and size of the observed photovoltage features can be explained using the depleted semiconductor model. © 2013 American Chemical Society

Treatment of tracheal stenosis - our experience

In cases of tracheal stenosis, tracheal resection and anastomosis is widely accepted as the procedure of choice. It has excellent results, reported in many large series. When the subglottis is involved, surgical treatment is more difficult and complex laryngotracheal techniques are necessary.Our aim is to discuss the indications for laryngotracheal surgey, provide step-by-step explanation of the technique and share our results in cases with benign tracheal stenosis. An algorithm for laryngotracheal technique selection according to different criteria (stenosis location, vocal cords status and tracheal mucosa and/or cartilaginous larynx involvement) is depicted. A review of the most important reported series in tracheal surgery is presented.In experienced hands the gold standard in laryngotracheal stenosis surgery is reconstruction with temporary laryngotracheal stent placement for prevention of airway collapse. This treatment has good results in 79% of the patients.Der Erstautor gibt keinen Interessenkonflikt an

Validation of FDS for the prediction of medium-scale pool fires

Fire dynamics simulator (FDS) has been applied to simulate a medium-scale methanol pool fire. The simulation used predominantly the existing features in FDS except that an additional sub-grid-scale combustion model based on the laminar flamelet approach of Cook AW and Riley JJ [Combust and Flame 1998;112:593–606] was used alongside the default mixture fraction combustion model for comparison. The predictions of the two different combustion models for temperature and axial velocity distributions were found to be in reasonably good agreement with each other and the experimental data. The pulsating nature of air entrainment was demonstrated by the air entrainment velocity fluctuations and the instantaneous velocity vectors, which revealed formation and shedding of vortices and the well-known “neck-in” at a distance of approximately one diameter from the pool surface. The predicted variations of air entrainment at different heights agreed well with some published data and correlation. Although the limitation of the code in predicting the puffing frequency was noticed as the spectra of temperature fluctuations failed to demonstrate any dominant frequency, the present study has demonstrated the capability of FDS to deliver reliable predictions on most important parameters of pool fires