Single photon counting, based on single photon sources and detectors, is a key ingredient for certain applications aiming at new quantum information technologies. Quantum cryptography, quantum radiometry, distributed quantum computing, as well as adjacent technologies such as biomedical and astronomical imaging, and low power classical communication also rely on single-photon technology. This paper reviews the present status of single photon sources and related counting measurement techniques, based on correlated (or heralded) photons in parametric down-conversion, and their possible impact on the above mentioned technologies, as well as an assessment for photon standards in the future.

Design of integrated power systems requires prototype-less approaches. Accurate simulations are necessary for analysis and verification purposes. Simulation relies on component models and associated parameters. This paper focuses on an implementation of a physic-based analytical PIN diode model [Power Electron. 8, 342 (1993)] with the very high description language VHDL-AMS [IEEE Computer Society, IEEE Draft Standard VHDL-AMS Language Reference Manual, 1997]. The Lumped Charge (LC) concept of Linvill is employed. The state-of-art of parameter extraction methods is briefly recalled and a step-by-step extraction procedure for the model parameters is described. Due to poor agreement between simulation results and experimental data, an improvement is added to the model. Finally, our improved model is validated with a confrontation of the simulated and the experimental curves for both current and voltage at different range of the operating conditions. All this operation was made under the Free version of the “SIMPLORER©-SV 7.0” environment.

Sulfosalt SnSb2S4 films for optical and electrical applications have been prepared on glass substrates by thermal evaporation and subsequently thermally annealed in vacuum at temperatures from 100 to 200 °C. The optical and structural properties of the films were studied as a function of the annealing temperature. The SnSb2S4 films exhibit a polycrystalline structure and undergo abrupt changes in electrical and optical properties at a transition temperature of 140 °C. After annealing below the transition temperature, the films are highly resistive with a dominant amorphous component, but when annealed above this temperature, the samples exhibit p+-type semiconductor behaviour with a dominant crystalline component

For a uniform distribution we have theoretically studied the subband structure of p-type δ-doped GaAs inserted into a quantum well at T = 0 K. We will investigate the influence of the δ-doping concentration and the layer thickness. The electronic properties such as the depth of confining potential, the density profile, the Fermi level, the subband energies and the subband populations have been calculated by solving the Schrödinger and Poisson equations self consistently. In this study, we have seen that the heavy-hole subbands contain many more energy states than the light-hole ones, the population of the heavy-hole levels represent approximately 91% of all the carriers.

The films of 1-(3-hydroxypropylamino)-9,10-anthraquinone (1) obtained by Hot Wall Epitaxy technique (HWE) have been studied for their morphological and electrical properties. The films were deposited on to the glass substrate at different temperatures kept at pressure of ~1.33 × 10−3 Pa. The powder X-ray diffraction (XRD) spectra show the polycrystalline nature of the films. The crystallanity of the films increases with the increase in film deposition temperature. Scanning electron microscope (SEM) shows that the molecules of 1 undergo uniform aggregation to form blade type crystallites with width 5.2–11.8 μm and length 32.6–90 μm at substrate temperature 348 K. The conduction in these films is ohmic in nature and both the increase in substrate temperature during film deposition and increase in absolute temperature of the films during conductivity measurement resulted in increased conductivity. The band gap lies in the range 1.25–1.44 eV

Effect of Pb substitution on the amorphous-crystalline transformation temperature, optical band gap and crystalline structure of Ge2Sb2Te5 has been studied. In Pb:GeSbTe chalcogenide films prepared by thermal evaporation, an amorphous to crystallization transition is observed at 124, 129, 136 and 138 °C in Pb0Ge20Sb24Te56, Pb1.6Ge19Sb26Te54, Pb3Ge17Sb28Te53 and Pb5Ge12Sb28Te55 respectively. XRD investigations of annealed samples reveal that Pb substitution retains NaCl type crystalline structure of GST but expands the lattice due to large atomic radii. The increase in amorphous-crystalline transformation temperature is followed with the increase in phase segregation. The optical gap shows marginal variations with composition.

Ge nanocrystals (NCs) are produced by a dewetting process during annealing of an amorphous Ge layer deposited on an ultra thin SiO2 layer. We have investigated the characteristics of the resulting NCs as a function of the nominal Ge layer thickness. Thanks to transmission electron microscopy images, we have extracted both the wetting angle and the NCs aspect ratio. We found that these characteristics remain constant whatever is the nominal thickness in the range of 1.5 to 10 nm. These results suggest that NCs have reached their equilibrium shape. We also experimentally determined the evolution of the NCs with the nominal thickness of the amorphous layer and found a linear relation. These results are in agreement with mass conservation and energetical considerations. Moreover a memory effect was evidenced in all the samples by C − V measurements. At last, we demonstrate that the use of a patterned SiO2 surface improves considerably the ordering of NCs and reduces their size distribution. Such a process is promising for future integration of NCs in memory devices.

A theoretical study (by using the Nonequilibrium Statistical Operator Method) is performed on the ultrafast transient transport properties of photoexcited carriers in ZnSe subjected to electric fields up to 35 kV/cm. The electron and hole drift velocity evolution towards the steady state present maxima in subpicosecond scale.

Light effect on electrical properties of a pentacene-based transistor was studied. We showed that under optical excitation, the phenomenon of photoconductivity can modify both carrier density and mobility; these changes depend on the wavelength, on the carrier photogeneration rate and on the material absorption coefficient. At first, we examined structural, optical and electrical properties of pentacene films; a thickness of 50 nm is the good compromise to obtain optimal performances. Then we observed the effect of illumination on the drain current in the accumulation regime: at 365 nm, we obtained a maximum ratio of photocurrent to dark current (Idsillumination/Idsdark) of about 2 × 103 when the gate is turned off, mobility and threshold voltage values around 0.02 cm2 V−1 s−1 and 7.5 V respectively. Moreover the dynamics study (off-state) showed sufficiently fast response times with large current gains to envisage applications in the area of light activated memory components. Finally, we examined the performances of a new component based on the coupling of an organic light emitting diode (with an emission peak at 550 nm) as an input unit with an organic transistor as an output unit. This last study enabled to underscore an increase in mobility without modifying the carrier density for low carrier photogeneration rates.

Formation of CoSi2 in Co implanted Si sample has been studied using glancing incidence X-ray diffraction and depth resolved positron annihilation techniques. The implanted sample exhibits near-surface amorphization in the temperature range between 300 K and 670 K. It is found that recrystallization of Si occurs at 870 K which inturn, triggers the formation of the CoSi2 phase at lower temperatures as compared to that obtained in thin film systems. The results are discussed in the light of enhanced intermixing brought by defect migration, associated with recrystallization.

This study reports highly efficient green multilayer polymer light-emitting diodes (PLEDs). The fluorescent polymer is poly[(9,9-dioctyl-2,7-divinylene-fluorenylene)-alt-co-{2-methoxy-5-(2-ethyl-hexyloxy)-1,4-phenylene}] end capped with dimethylphenyl (ADS108GE). This emissive polymer has been found to behave as an electron transport emitter. A poly(N-vinylcarbazole) (PVK) layer has been introduced as both hole transporting layer/electron blocking layer. Thicknesses of both ADS108GE and PVK layers have been optimized. 3.1 lm/W have been achieved which corresponds to an improvement by a factor 2 comparing to devices without PVK. Luminances as high as 25 000 Cd/m2 at low operating voltage are reported.

In this paper we discuss and model the effects of the density of defects in hydrogenated amorphous silicon from an electronics point of view. To this end, we have created a SPICE model that accounts for the two main field effects, Poole-Frenkel and tunnel, responsible for the leakage current. The comparison between our model and the experimental data shows that our approach allows a quick evaluation of the quality of the device with no need to run a complete steady state measurement. Also, we have validated our SPICE photodiode model by implementing it into a three CMOS simple pixel structure.

Structural and optical properties of thermally evaporated methylene blue trihydrate thin films up to a film thickness of 165 nm have been investigated. The lattice constants and the crystallite size were calculated. The optical parameters were obtained using spectrophotometric measurements of the transmittance and reflectance at normal incidence of light in the wavelengths range 200–2500 nm. Below the absorption edge, subgap absorption in the energy range 0.75–1.4 eV was observed and interpreted in terms of defect states induced absorption phenomena and act as deep traps for charge carriers. The type of optical transition was found to be an indirect allowed transition. The values of the optical gap Eopt, the transport gap Et, the exciton binding energy EB, the Urbach's energy Eu and the dispersion parameters for as-deposited, annealed and irradiated films with different doses of γ-irradiation were estimated and discussed their influenced by heat treatment and irradiation.

An infinite regular three-dimensional network is composed of identical resistors each of resistance R joining adjacent nodes. What is the equivalent resistance between the lattice site $\mathaccent"017E{r}_i $ and the lattice $\mathaccent"017E{r}_j $ site, when two bonds are removed from the perfect network? Three cases are considered here, and some numerical values are calculated. Finally, the asymptotic behavior of the equivalent resistance is studied for large distances between the two sites.

The complex permittivity of carbon black/epoxy composites containing different amounts of conductive carbon black particles was reported in the frequency range 100 Hz–15 MHz and over the temperature range 23–80 °C. The shape of experimental spectra of these heterogeneous media gives evidence of a typical dielectric relaxation process below the threshold percolation. The temperature dependence of the dielectric response has been analysed below and at near the epoxy glass transition temperature (Tg≅ 80 °C), for various carbon concentrations. Jonscher's phenomenological model has been used for modelling this relaxation process. The activation energy, deduced from Arrhenius equation, is found to be insensitive to the carbon black concentration. This behavior is discussed in term of the interfacial interaction between the carbon particles and the polymer. Besides, the increase of both parts of the complex permittivity with increasing the carbon black concentration and the temperature is compared to the recently proposed Shin's mixture law.

Concentrators use reflection or refraction of light, or a combination of both, but concentration of light leads to a crucial heating of the cell, which involves degradation of its performance. However, solar cells especially conceived for concentration can support very intense illuminations as far as an active cooling is assured. In this work, a GaAs solar cell with AlxGa$_{1-x}$As window layer, operating under low injection conditions, has been studied with temperature and solar concentration. The temperature corresponding to each concentration was calculated, and then used in the calculation of photovoltaic parameters. The study was carried out under free mode conditions (without heat sink) and then under forced conditions (with a cooling system) in order to demonstrate the importance of cooling in the concentrator solar cells. The effect of series resistance on solar cell characteristics has also been studied. The simulation was carried out using SCAPS-1D simulator. The results were compared with those obtained theoretically; a good agreement was found between the two models.

In this paper, the effect of temperature of operation on the turn-on time delay, td, of semiconductor laser has been re-studied theoretically. We derived a full analytical and exact expression to determine td in terms of nonradiative, radiative, Auger recombination coefficients, cavity dimensions, threshold carrier density (and in turn threshold current density), injected current and temperature of operation. The temperature dependence (TD) of td was calculated through the TD of threshold carrier density. The TD of threshold carrier density was calculated according to the TD of cavity parameters and not by the well-known exponential Pankove relation via the use of characteristics temperature and current. A complete agreement between the values of td calculated by our proposed model and the numerical method, was shown through the simulation results.

Zinc telluride thin films have been deposited on glass and silicon wafers substrates at room temperature by thermal evaporation technique in a vacuum of 10−5 Torr. The thickness dependence of both the dc electrical resistivity and thermoelectric power of ZnTe were carried out at room temperature and after being annealed over a thickness range from 22 nm to 170 nm. The type of conduction, the carriers concentration and the conduction mechanisms were revealed. The average thermal activation energy ΔE equals to 0.324 eV for the as deposited films and 0.306 eV for annealed films, it is found to correspond with the ionization energy reported for intrinsic defect levels in ZnTe. Seebeck coefficient measurements showed that ZnTe thin films behave as p-type semiconductor and the average value of the free charge carrier concentration is found to be 1.6 × 1019 cm−3. The built-in voltage, the widt of the depletion region, the diode quality factor and the operating conduction mechanisms have been determined from dark current-voltage (I − V) and capacitance-voltage (C − V) characteristics of p-ZnTe/ n-Si heterojunctions.

Orthorhombic tungsten bronze Pb$_{1-x}$K$_{2x-3y}$SmyNb2O6 (where x = 0.29 and y = 0.145) ceramic has been synthesized by the conventional sintering technique. Preliminary X-ray diffractogram analysis of crystal structure showed that a single phase compound has been formed with orthorhombic system. Frequency and temperature dependences of impedance, modulus, conductivity and dielectric permittivity have been performed in the frequency and temperature range 45 Hz–5 MHz and 35–595 °C respectively. Impedance spectroscopy study showed the presence of both bulk and grain boundary effects in the materials. The complex impedance spectra above 440 °C have been fitted by the superposition of two Cole-Cole types of relaxations. The ac conductivity spectrum obeyed the Jonscher's power law. Modulus analysis indicated the possibility of hopping mechanism for electrical process in the system.

The two-dimensional percolation problem with elliptical objects was studied theoretically using Monte Carlo simulation. The percolation-threshold number of ellipses was compared for the lattice model and the random-position (continuum) model, and a semi-lattice model was also introduced as a bridge between the two limiting models. The results showed a gradual transition from the lattice model to the random-position model when the positional disorder of the particles was increased. A similar transition was observed when the lattice was refined and the site-occupation probability was simultaneously decreased.