This paper studies the dc and ac impedance behaviour of undoped ZnO thin films produced by spray pyrolysis and rf magnetron sputtering under UV light illumination, at room temperature, emphasising the role that the crystallite size, structure, surface morphology and the state of surface have on the electrical responsivities obtained. The results achieved show that the sputtered films with crystal sizes of about 4 nm exhibit dc electrical UV responsivities of 108. On the other hand, the spray pyrolysis films exhibit the lowest dc responsivities, due the high crystal sizes and state of surface contamination, to which very good capacitance responses were obtained, mainly due to the degree of porosity exhibit by these films when produced at low temperatures. Based on that, a two-phase electrical model is proposed to explain the set of behaviours observed. © 2005 Elsevier B.V. All rights reserved.

Space charge in electrically aged cross-linked polyethylene (XLPE) was studied using a procedure combining isothermal and non-isothermal measurements of charge and discharge currents. Aging is carried out using an AC field while immersing the disk-shaped samples in an ionic aqueous solution at constant temperature. After aging the samples were isothermally DC charged and discharged. Next a non-isothermal experiment with constant heating rate was performed (FTSDC). Finally the sample was kept at the highest temperature in order to completely discharge the polymer. The space charge introduced in the XLPE during aging can be analyzed from the study of the FTSDC spectra. The thermogram (FTSDC) shows a very broad peak. The peak is attributed to trapped space charge in traps with long relaxation times. It is possible to decompose it into three or four individual peaks and obtain the corresponding activation energies. The results were compared with previous ones obtained for LDPE (low density polyethylene) aged under similar conditions.

High-quality SrBi2Nb2O9 (SBN) single crystals were grown from a melt using a high-temperature self-flux solution method and Bi2O3 added with B2O3 as a flux. A suitable thermal profile involving slow cooling rates allowed growing large and translucent SBN crystals exhibiting platelet morphology with typical size ∼5 × 5 mm2 and thickness approximately 400 μm. X-ray diffraction revealed a dominant (001)-orientation of the major face of the platelet crystals and edges oriented parallel to the [110] directions. The dielectric properties were evaluated along the ab-plane and in the c-axis direction. The ferro-paraelectric phase transition was observed at TC = 440°C with Curie-Weiss relationship above TC. The anisotropy of dielectric permittivity, i.e., the ratio between permittivity in the ab-plane and along c-axis was about 10 at TC-The obtained results are used to discuss the observed correlations between anisotropy, crystalline orientation, and electrical properties.

This work deals with the study of the role of the buffer layers thickness on the TCO/p-a-SiC:H/buffer1/buffer2/i(nc-Si/a-Si:H)/n-a- Si:H/Al solar cell I-V and impedance performances. The aim was to improve the p/i interface region, which has a large influence on the solar cell characteristics and stability. In order to match the difference between the p and i layers optical gaps, the buffer layers were deposited using, for each layer, different methane to silane mixtures, aiming to obtain a gradual match of the corresponding optical gaps. The intrinsic layer was deposited at high hydrogen dilution rates at 27.12 MHz in conditions that allowed the incorporation of nanoparticles/nanoclusters. Solar cells with fill factor of 0.63; open circuit voltage of 0.93 Volts; short circuit current density of 16.13 mA/cm2 and an efficiency of 9.4% were produced with buffer layers around 1.3 nm thick. When comparing these solar cells with conventional amorphous silicon solar cells we notice that the quantum efficiency from ultraviolet to green regions is improved up to 13%, in average. Concerning solar cell capacitance, the data show that the best solar cells exhibit the highest capacitance, meaning that the films are compact and dense, in-line with the other electrical characteristics obtained. ©2005 IEEE.

This work reports on the fabrication process and performances presented by metal insulator semiconductor (MIS) linear position sensitive detectors (PSD) with an active length of 6 cm. The use of long sensitive areas allows the PSD to achieve higher resolution without the need of a highly accurate light spot integration mechanism. The PSD is built in a multilayered structure consisting of Cr/a-Si:H (n+ doped)/a-Si:H (intrinsic)/SiOx (passivation layer)/Au, where the active a-Si:H layers were deposited by a modified triode plasma enhanced chemical vapour deposition (MTPECVD), which allows the deposition of highly electronic grade material with a low (≈ × 1015 cm-3) defect density inferred by CPM. The sensor linearity and sensitivity shows dependence on the sensor width to length ratio and on the value of load resistance. Sensitivities of more than 30 mV/cm were achieved with linearity near 99%. Besides that, this type of MIS structure allows an improved spectral response near the UV region and has the maximum response at 540 nm. © 2004 Published by Elsevier B.V.

The experimental results obtained in a wide range of temperatures, for polyethylene terephthalate, demonstrate that the apparent activation energy changes when the charging (polarization) time or the isothermal discharging time, prior to the final thermally stimulated discharge current measurement, are used as variable parameters. Consequently, the charging and/or discharging time can be used as a variable parameter to investigate the landscape of the apparent thermal activation energies. A continuous distribution of the traps in the range from 0.4 to 3 eV was observed. The experimental results demonstrate that there is a range of experimental conditions for which the thermal activation energy is independent of the experimental parameter values. This is the activation energy value which should be used to characterize a certain mechanism.

The experimental results obtained in a wide range of temperatures, for polyethylene terephthalate, demonstrate that the apparent activation energy changes when the charging (polarization) time or the isothermal discharging time, prior to the final thermally stimulated discharge current measurement, are used as variable parameters. Consequently, the charging and/or discharging time can be used as a variable parameter to investigate the landscape of the apparent thermal activation energies. A continuous distribution of the traps in the range from 0.4 to 3 eV was observed. The experimental results demonstrate that there is a range of experimental conditions for which the thermal activation energy is independent of the experimental parameter values. This is the activation energy value which should be used to characterize a certain mechanism.

This paper discusses the electron transport in the n-type amorphous indium-zinc-oxygen system produced at room temperature by rf magnetron sputtering, under different oxygen partial pressures. The data show that the transport is not band tail limited, as it happens in conventional disordered semiconductors, but highly dependent on its ionicity, which explains the very high mobilities (≥ 60 cm 2 V -1 s -1) achieved. The room temperature dependence of the Hall mobility on the carrier concentration presents a reverse behaviour than the one observed in conventional crystalline/polycrystalline semiconductors, explained mainly by the presence of charged structural defects in excess of 4 × 10 10 cm -2 that scatter the electrons that pass through them. © 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.