Electrical Conductivity and Complex Impedance Analysis of Ba<Subscript>2</Subscript>CrMo<Subscript>0.8</Subscript>W<Subscript>0.2</Subscript>O<Subscript>6</Subscript> Double Perovskite

Electrical properties of Ba ₂CrMo_0.8W_0.2O₆ double perovskite were investigated using admittance spectroscopy technique. According to impedance analysis, the material was modeled by an electrical equivalent circuit. Such analysis proves the presence of relaxation phenomenon in the compound. We also found that ac conductivity follows the Jonscher universal power law. Conduction process is found to be dominated by the thermally activated small polaron (SPH). The activation energy values, inferred from dc conductivity and from the temperature dependence of relaxation time, are closed to each other. Such result indicates that conduction process and relaxation phenomenon are related to the same defect.     

Structural,morphological and optoelectronic properties of porous silicon combined alumina coating film deposited by PLD

Pulsed laser deposition of Al₂O₃ onto porous silicon (PS) is shown to provide excellent passivation of multi-crystalline silicon surfaces intended for solar cells applications. Surface passivation and reflectivity are investigated before and after the deposition of various nominal thicknesses of Al₂O₃ ranging from isolated nanoparticles to ~80 nm-thick films. The level of surface passivation is determined by techniques based on photoconductance and FTIR. As a result, the effective minority carrier lifetime increase from 1 to 130 μs at a minority carrier density (Δn) of 1?×?10¹³ cm^?3. However, passivation scheme provide a significant decrease in the reflectivity; it’s reduced from 28% to about 5% after Al₂O₃/PS coating.     

Structural,dielectric and electrical properties of Sol–gel auto-combustion technic of CuFeCr0.5Ni0.5O4 ferrite

Journal of Materials Science - The CuFeCr0.5Ni0.5O4 (CFO) compound was synthesized using sol–gel reaction combustion technic. The structural analysis showed that the obtained composites have...     

Analysis of the electrical transport,conductivity, and dielectric relaxation behavior of La0.75 Ba0.10 Sr0.15 Fe O2.875-δ (δ = 0.375 and 0.50) brownmillerite oxides

The topotactic reduction of La_0.75Ba_0.10Sr_0.15FeO_2.875 with titanium metal leads to a new isostructural material of the composition La_0.75Ba_0.10Sr_0.15FeO_2.875-δ (δ?=?0.375 and 0.50). XRD analysis of phases confirms that the obtained compound adopts a brownmillerite-type structure. A slight distorted monoclinic P2/m was found to describe the crystal structure. The transport properties have been investigated by current–voltage (I–V). The electric and dielectric measurements were carried out covering a wide range of temperature (300–600 K). Our materials display semiconducting properties as well as mixed ionic and electronic conductivity. At high temperatures, the activation energy values proved to be around 907–630 meV, which refers basically to oxygen vacancies conduction. The analysis of dielectric properties and dielectric losses (ε’, tanδ) of both compounds vs temperature at different frequencies demonstrates two relaxer attitudes. A low dielectric loss and low electrical conductance were displayed. Relying upon these values, these materials stand for perfect candidates for micro-electronics devices.

     

Modelization of epitaxial GaAs X-ray detectors

X-ray detectors are fabricated with non-intentionally doped thick epitaxial GaAs layers grown by a chemical technique. They are p⁺/i/n⁺ structures in which the highly doped p- and n-type layers are made by ion implantation on both faces of the i epilayers. In order to understand the behaviour of charge collection, we modelize the capacitance–voltage characteristics of such structures, which are then compared with experimental data.     

Electronic characterization of several 100 μm thick epitaxial GaAs layers

Non intentionally doped thick epitaxial GaAs layers, grown by chemical vapour phase epitaxy using a high growth rate, are characterized by different electrical techniques applied on a junction (forward and reverse Current–Voltage characteristics, Current versus time and temperature, Deep Level Transient Spectroscopy, Capacitance–Voltage measurements) in order to detect the defects they contain. Experimental data are coupled with theoretical modelling to determine the electrical characteristics of the layers: type and concentration of the carriers, energy levels and concentrations of the defects, associated minority carrier lifetime. The results obtained indicate that i) the concentration of the residual impurities is in the order of 10¹³ to 10¹⁴ cm⁻³, ii) the layers contain two shallow defects (at 0.12 and 0.21 eV below the conduction band Ec) slightly compensated by a deep defect (at Ec-0.5 eV) and iii) the deep defect is in low concentration (10¹² cm⁻³), resulting in a minority carrier lifetime still limited by the radiative recombination process. Therefore, epilayers obtained using high growth rates exhibit electronic properties very similar to the ones obtained using conventional epitaxial techniques. The good and uniform electronic properties of these layers coupled with the low yield of the fluorescence of GaAs is interesting for high resolution X-ray detection.     

Zinc oxide incorporating iron nanoparticles with improved conductance and capacitance properties

Iron nanoparticles were incorporated into zinc oxide powders by an in situ dispersion method. The products were fully characterized by X-ray diffractometry, diffuse reflectance, FTIR spectrophotometry and complex impedance spectroscopy. The XRD patterns agreed with that of the ZnO typical wurtzite structure, the sharp diffraction peaks indicating good crystallinity of ZnO and ZnO-Fe nanoparticles. The average particle size determined by the Scherrer equation showed an increase from 20 to 25 nm for ZnO and ZnO-Fe respectively. The UV peak positions of the modified samples shifted to a longer wavelength compared to pure ZnO, providing evidence of changes in the acceptor level induced by iron nanoparticles. The optical band gap of the samples was found to be 3.14 eV for ZnO and 3.04 eV for ZnO-Fe. The electrical properties were investigated between 273 and 413 K, at several frequencies. Besides, a detailed analysis of the impedance spectrum showed an appreciable improvement of the conductivity due to the addition of iron nanoparticles. The incorporation of Fe-NPs appears to be responsible for conductance variations, charge transfer and capacitance improvement. The above properties make these materials to be regarded as very promising electrode materials for high-efficiency energy storage.     

Khaya gum – a natural and eco-friendly biopolymer dielectric for low-cost organic field-effect transistors (OFETs)

Journal of Materials Science: Materials in Electronics - Nature provides a wide range of dielectric biopolymers that can be used in electronic devices. In this work, organic field-effect...