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EN
Optical properties of transition metal dichalcogenides monolayer of MoS₂ are analyzed using multi-orbital tight-binding models with only Mo d-orbitals (three-band model) and with an inclusion of S p-orbitals (six-band model). We look at band structures, momentum matrix elements between valence and conduction band, and joint optical density of states. Good agreement between the two models is shown in a vicinity of K point of the Brillouin zone. On line connecting K and Γp points, a local conduction band minimum at Q point is recovered only by six-band model in agreement with density functional theory and experimental results. We show that optical transitions at this point are active for both light polarizations. A peak in joint optical density of states is also seen at this point suggesting its potentially important role in a proper description of excitonic effects.
EN
Au/polymer P2ClAn(H₃BO₃)/n-GaAs Schottky barrier diodes, where P2ClAn stands for poly(2-chloroaniline), have been fabricated. To fabricate Schottky diodes with polymer interface, n-type GaAs wafer was used. The P2ClAn polymer solution was applied on the front face of the n-GaAs wafer by a pipette. The P2ClAn emeraldine salt was chemically synthesized by using boric acid (H₃BO₃). Schottky diode parameters, such as ideality factor, barrier height and series resistance have been measured, as functions of hydrostatic pressure, using the current-voltage technique. The ideality factor values of Au/P2ClAn/n-GaAs Schottky barrier diodes have decreased from 3.38 to 3.01, the barrier height has increased from 0.653 to 0.731 eV at 0.36 kbar and series resistances were ranging from 14.95 to 14.69. The results obtained from I-V characteristics of Au/P2ClAn/n-GaAs Schottky barrier diodes show that pressure treatment improves the rectifying properties of the diodes. These diodes can be used as pressure-sensitive capacitors, due to pressure-dependence of diode parameters.
EN
This paper presents an analytical model calculating the threshold voltage in nanocrystalline silicon (nc-Si) thin film transistors by considering a granular morphology of silicon nanocrystallites forming the channel and using the two-dimensional the Poisson equation. The numerical calculations demonstrate that, according to the quantum size effects on both dielectric constant and band gap, the threshold voltage values are strongly related to the silicon crystallites structure. To justify the validity of our model suitable for implementation in circuit simulators such as SPICE, the simulation results obtained are compared with the available research data and they shows a satisfactory match, thus, demonstrating the validity of our model.
EN
On textured n-type silicon substrates for solar cell manufacturing, the relation between light trapping behavior, structural imperfections, energetic distribution of interface state densities and interface recombination losses were investigated by applying surface sensitive techniques. The field-modulated surface photovoltage (SPV), in-situ photoluminescence (PL) measurements, total hemispherical UV-NIR-reflectance measurements and electron microscopy (SEM) were employed to yield detailed information on the influence of wet-chemical treatments on preparation induced micro-roughness and electronic properties of polished and textured silicon substrates. It was shown that isotropic as well as anisotropic etching of light trapping structures result in high surface micro-roughness and density of interface states. Removing damaged surface layers in the nm range by wet-chemical treatments, the density of these states and the related interface recombination loss can be reduced. In-situ PL measurements were applied to optimise HF-treatment times aimed at undamaged, oxide-free and hydrogen-terminated substrate surfaces as starting material for subsequent solar cell preparations.
EN
Methods to modify gate dielectrics of MIS structures by irradiation treatments and high-field electron injection into dielectric are considered. In addition, distinctive features of these methods used to correct parameters of MIS devices are studied. It was found out that negative charge, accumulating in the thin film of phosphosilicate glass (PSG) of the MIS structure having a two-layer gate dielectric SiO_2-PSG under the high-field injection or during the irradiation treatment can be used to correct the threshold voltage to improve the charge stability and raise the voltage of breakdown for the MIS devices. It is proved that the density of electron traps rises with the increasing thickness of the PSG film. In this paper a method to modify electrophysical characteristics of MIS structures by the high-field tunnel injection of electrons into the gate dielectric under the mode of controlled current stress is proposed. The method allows to monitor changing of MIS structure parameters directly during the modification process.
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