Search results

In this paper, we present the results of submicron pseudomorphic AlGaAs/InGaAs/ GaAs HEMT simulations. Our main interest is the study of electronic temperature behavior in the device and improvement of the current‐voltage characteristic curves. Three types of models are being used. The first is the well known drift‐diffusion model. The second is of the hydrodynamic type and the third is a combination of the two preceding models. The numerical treatment is based on the discretization by the Galerkin finite element method for both Poisson and continuity equations with the streamline‐diffusion method being used for the energy equation. A comparison of the different approaches have been realized and a synthesis on the validity of each of these models is being drawn.

The purpose of this paper is to develop a generalized model of the nonlinear conductivity of varistor ceramic suitable for solving problems of prediction and control of ceramic nonlinearity, stability of varistor properties.

The modeling of current-voltage characteristic of the intergranular barrier in metal oxide varistor ceramics is based on the development of the algorithm. It includes all the known mechanisms of electrotransfer in a wide range of voltages and currents of the current-voltage characteristics, and also takes into account the deviation of the barrier form the Schottky barrier.

The models of double Schottky barrier and double barrier of arbitrary form, as well as the algorithms for calculating the current-voltage characteristics of a single intergranular potential barrier and a separate “microvaristor” with the use of the most well-established understanding of the main mechanisms of electrical are developed. The results of current-voltage characteristics modeling correspond to the existing understanding of the nonlinear electrical conductivity varistor ceramics are based on zinc oxide. The model of double barrier of arbitrary form takes into account the deviation of the barrier form the Schottky barrier which is important in predicting the deformation of the current-voltage characteristics of the varistor products in the process of degradation.

The relation between the form of the current-voltage characteristic and the distribution profile of the donor concentration in the surface regions of the semiconductor crystallites constituting the intergranular potential barrier is established. The accumulation of donors in the space charge region leads to the increase in the current on the prebreakdown region of the current-voltage characteristic and the reduction of voltage corresponding to the breakdown region beginning of the current-voltage characteristic. The significant role of the interlayer in the formation of current-voltage characteristic of the intergranular potential barrier is shown.

The purpose of this paper is to design and construct a low‐cost current‐voltage tester, bearing in mind the short falls of the existing testers and the ever‐increasing price of the testers currently on the market. The I‐V tracer presented in this paper uses a variable external power supply unit (PSU) as the load, in order to obtain the entire operating range of a PV module from open circuit through maximum power to short circuit condition.

The I‐V tracer presented in this paper was divided into three main sections, mainly the data acquisition system (DAS), which comprises an A/D computer card, temperature card, electromechanical relays, current and voltage transducers, aluminum housed resistors and power MOSFETS, the variable load (programmable variable PSU) and finally the signal processing unit. These components were integrated and finally interfaced to a PC.

The results obtained using this system compared with the capacitive tester show a low percentage difference of <1 from the comparative I‐V curves measured. The results measured by the PSU tester are also of high accuracy. The findings also demonstrated the fact that most of the components found in most university laboratories can be used to build the PSU tester and still obtain highly accurate results.

Since some components are semiconductors, which have a limited lifetime, they need to be changed if they fail. Mostly the MOSFETS should be replaced when no switching signal is sent.

This low‐cost PSU tester is suitable for researchers in disadvantaged institutions whose research capabilities are limited due to the high cost of this equipment.

The PSU tester uses a variable power supply as the load to measure PV module I‐V curves. The system is capable of measuring up to eight modules at the same time, making it possible to analyze PV modules within the same time frame.

The purpose of this paper is to investigate electrical properties of eutectic In8Sb8Te84 and In10Sb51Te39 as made thin films to evaluate their potential for non-volatile phase-change memories, once the thermal measurements are very optimistic.

The films were deposited by pulse laser deposition technique. By using a very simple home-made cell, transversal current-voltage curves films were measured involving both voltage controlled-pulses generator and current controlled-pulses generator, employing different pulse shapes: triangular and sine shaped.

The memory effect, characteristic of a typical phase-change memory material, was observed in both materials under research. For higher tellurium content in the film, lower is the value of threshold voltage.

Further studies on endurance, scaling and SET/RESET operations are needed.

The values of the key parameters, threshold voltage and hold voltage are comparable with those of Ge2Sb2Te5, GeTe and Sb2Te being considered to date as the main compounds for PCM devices.

The conduction mechanism in the amorphous regime is agreed with Poole–Frenkel effect in deep traps.

GERMANY Inhibition of hydrogen corrosion of iron by phenyl thiourea. In de‐aerated acid solutions the corrosion of iron is much reduced by very small additions of phenyl thiourea. For a quantitative study of this, stationary current/voltage curves were studied at potentials close to the open‐circuit potential of carbonyl iron in NaClO‐HClO4 solution of pH 2. By control measurements of various kinds it was thus shown that it is possible to obtain the partial current/voltage curves of both iron dissolution and hydrogen deposition with high accuracy. Therefore a quantitative estimation of the anodic and cathodic components of the total inhibition efficiency is possible. With phenyl thiourea it was found that, under the experimental conditions, inhibition was nearly exclusively cathodic up to 10−6 mol/1. inhibitor, with gradually increasing anodic inhibition at higher concentration.—(H. Kaesche, Werks. u. Korr., 1959, 10 (10), 622–624.)

The purpose of this paper is to investigate the structure and electrical properties of eutectic Sb_7.4Te_92.6 as made thin films to evaluate their potentiality for application to non-volatile phase-change memories.

The films were prepared by the pulsed laser deposition technique. The films were characterized by using X-ray diffraction in grazing-incident geometry, differential scanning calorimetry, Raman spectroscopy and transversal current–voltage curves.

The memory effect state, characteristic of a typical phase-change memory material, was observed. The temperature of crystallization was about 100ºC.

Further studies on endurance, scaling and SET/RESET operations are needed.

One of the main characteristic values, the hold voltage and the threshold voltage values, were about 0.85 and 1.2 V, respectively, in a line with those of Ge₂Sb₂Te₅, GeTe and Sb₂Te being considered to date as the main compounds for phase-change memory devices.

The conduction mechanism in the amorphous regime is highly agreed with the Poole–Frenkel effect in deep traps.

This paper aims to achieve accurate maximum power from solar photovoltaic (PV), its five parameters need to be estimated. This study proposes a novel optimization technique for parameter estimation of solar PV.

To extract optimal parameters of solar PV new optimization technique based on the Jellyfish search optimizer (JSO). The objective function is defined based on two unknown variables and the proposed technique is used to estimate the two unknown variables and the rest three unknown variables are estimated analytically.

In this paper, JSO is used to estimate the parameters of a single diode PV model. In this study, eight different PV panels are considered. In addition, various performance indices, such as PV characteristics, such as power-voltage and current-voltage curves, relative error (RE), root mean square error (RMSE), mean absolute error (MAE) and normalized mean absolute error (NMAE) are determined using the proposed algorithm and existing algorithms. The results for different solar panels have been obtained under varying environmental conditions such as changing temperature and constant irradiance or changing irradiance and constant temperature.

The proposed technique is new and provides better results with minimum RE, RMSE, NMAE, MAE and converges fast, as depicted by the fitness graph presented in this paper.

The purpose of this paper is to investigate and classify the defects on silicon-based power devices under extreme conditions.

Electrical characterization was performed on MOS devices to study their interface defects. The devices were subjected to a voltage or a current constraint to induce defects, and then measurements were done to detect the effects of those defects. Measurements include current voltage, capacitance and conductance characterization. The Hill–Coleman method was used to calculate the interface states density in each case.

It was found that most of the defects have energies within the upper band gap of the semiconductor.

The method used in this paper allows the determination of any interface defects on a Si/SiO₂ structure.

The purpose of this paper is to investigate the optoelectronic properties of the multichannel ZnO UV photodetectors.

ZnO nanowires were assembled by dielectrophoresis for the UV photodetectors. Different ZnO channels were adjusted by different alternating current voltages and investigated for UV optoelectronic properties.

The number of the ZnO channels increases with the enhancing alternating current voltage. Optimum performance of the UV photodetectors is obtained with more channels.

Dielectrophoresis is a promising method for controllable assembly of multichannel ZnO photodetectors. ZnO photodetectors with more channels demonstrate a good response to 380-nm UV light, which shows great potential application in UV photodetector.

The study aims to carry out the production of a bulk heterojunction organic solar cell in a laboratory scale using a blend of poly (3-hexylthiopene) (P3HT) and [6, 6]-phenyl (C61) butyric acid methyl ether (PCBM).

Four inverted geometry organic solar cells were prepared based on 1:1 ratio of P3HT to PCBM and subjected to post annealing at different temperatures of 32, 120, 130 and 140°C. Solar cells were fabricated with structure glass/ITO/P3HT:PCBM/PEDOT:PSS/Au and characterized using Keithley 2400 series sourcemeter and a multimeter interfaced to a computer system with a LabVIEW software, which showed both dark and illumination current–voltage characteristic curves. Four reference cells were also fabricated with structure soda lime glass/P3HT:PCBM and annealed at different temperatures of 32, 120, 130 and 140°C.

The third organic solar cell prepared, Sample CITO, had the best performance with power conversion efficiency (PCE) of 2.0281 per cent, fill factor (FF) of 0.392, short circuit current of −0.0133 A and open circuit voltage of 0.389 V. Annealing of active layer was found to improve cell morphology, FF and PCE. Annealing of the active layer at 140°C resulted in a decrease of the PCE to 2.01 per cent.

These findings are in good agreement with previous investigation in literature which reported that best annealing temperature for a 1:1 ratio blend of active material is 130°C. Ultraviolet–visible spectra on reference cells showed that sample CITO had wider absorption spectra with peak absorbance at a wavelength of 508 nm.

This research is purely original.