Abstract: The transport properties of Zn0.88-xMgxMn0.12O/ZnO modulation-doped heterostructures (x≤0.15) were investigated. The heterostructures were fabricated on ZnO single-crystal substrates by a pulsed laser deposition system. Atomic force microscope observation and X-ray diffraction analysis suggested that Zn0.88-xMgxMn0.12O layers have atomically flat surface and excellent crystallinity. The results of Hall measurement for Zn0.88-xMgxMn0.12O/ZnO modulation-doped heterostructure with x=0.075 revealed that the carrier concentration and the electron mobility were 5.1×1012cm-2 and 800 cm2/Vs at 10 K, respectively, suggesting that the carrier confinement effect exits at the heterointerface between Zn0.88-xMgxMn0.12O barrier layer and ZnO channel layer. In the magnetoresistance (MR) measurement at 1.85 K, a positive MR behavior was observed below 0.5 T, while a negative MR behavior was recognized above 0.5 T. The slope of the positive MR decreased with increasing the temperature and was well fitted to the Brillouin function with S=5/2. The electrical and magneto-transport properties were very similar to those of Zn0.88Mn0.12O/ZnO heterostructures without doping Mg.
Abstract: The paper will present a review of different solutions for transparent conducting electrodes on flexible substrates. The analysis of the present situation reveals a gap for low sheet resistance electrodes.
Two new approaches to the problem will be presented. The first one is a novel technology for the deposition of zinc oxide on polyethylene terephtalate film. The intention for this process is the establishment of a low cost coating in a roll-to-roll machine. Silicon was used as the dopant material with a concentration varying in different samples between 1 and 4 %. The optimum parameters provided a transparent layer with a sheet resistance of 16 Ωsqu. Metal grids are a second promising approach for achieving low sheet resistance electrodes. The combination of these grids with transparent conducting oxides (TCO) will be presented. The TCO were deposited under vacuum in a roll-to-roll coating machine. The grids were applied by aerosol jet printing and subsequent tempering of the film.
Abstract: State of the art optoelectronic applications such as thin film solar cells, flat panel displays, and light emitting diodes suffer from the non-availability of p-type oxide materials on the industrial scale. Novel technologies such as transparent electronics, UV light emitting diodes, and improved thin film solar cells using wide band gap p-type oxide layers as front contact will be available once p-type oxide layers with proper layer and interface properties can be obtained on an industrial scale.
In this paper, we report on our progress towards p-type oxide layers for industrial applications. We address the first principles density functional theory modeling of ZnO based layers where a pathway towards p-conductivity is seen taking the nitrogen doping of grain boundaries into account.
The second part of the paper is on the synthesis of p-type Delafossite layers such as
CuCr1-xAlxO2:Mg by Sol-Gel and CuCrO2 by hollow cathodes gas flow sputtering. We report on the deposition processes and film properties obtained. Both methods reveal p-type conductivity by means of Seebeck-coefficient measurements.
Abstract: Thin films of Au were made by sputter deposition onto glass substrates with and without transparent and electrically conducting layers of SnO2:In. The Au films were up to ~11 nm in thickness and covered the range for thin film growth from discrete islands, via large scale coalescence and formation of a meandering conducting network, to the formation of a more or less “holey” film. Scanning electron microscopy and atomic force microscopy showed that the SnO2:In films were considerably rougher than the glass itself. This roughness influenced the Au film formation so that large scale coalescence set in at a somewhat larger thickness for films on SnO2:In than on glass. Measurements of spectral optical transmittance and electrical resistance could be reconciled with impeded Au film formation on the SnO2:In layer, leading to pronounced “plateaus” in the near infrared optical properties for Au films on SnO2:In and an accompanying change from such two-layer films having a lower resistance than the single gold film at thicknesses below large scale coalescence to the opposite behavior for larger film thicknesses.
Abstract: Melanin doped zinc oxide thin films were obtained using a process of soft chemistry with pH in the basic region. The electric and structural properties of these films were compared with films of un-doped ZnO obtained using the same process. Undoped films show the characteristic diffraction pattern of polycrystalline ZnO wurtzite type, while the doped films also present other signals associated to the melanin or some derived present phase of this. It is relevant because melanin is reported as amorphous material. Differences of grain size were detected and attributed to the presence of at least two existent phases in the films. Resistivity data were analyzed from the obtained values of films of un-doped ZnO and associated to the structural changes. The films have turned out to be stable in bio-generating systems of useful energy.
Abstract: Powders of tin dioxide (SnO2) have been prepared by two different modifications of wet chemical synthesis, i.e. (i) by conventional hydrolysis of tin chloride dissolved in aqueous ammonia solution and (ii) by precipitation from tin chloride dissolved in aqueous hydrazine monohydrate (N2H4*H2O) solution. The prepared gels were dried and then annealed at different temperatures varied from 300 to 700 oC in order to form nanocrystals. Structure and optical properties of the samples were investigated by using X-ray diffraction, transmission electron microscopy, thermoprogrammable hydrogen reduction, low temperature nitrogen adsorption method, photoluminescence, infra-red absorption, Raman spectroscopy, and X-ray photoelectron spectroscopy. The samples prepared by hydrazine-based method are characterized by surface area about 127-188 m2/g with high sintering resistance. The optical spectroscopy data revealed pure crystallinity and high defect concentration for the samples prepared by hydrazine-based method. The experimental results are discussed in view of different states of chemisorbed oxygen on SnO2 nanocrystal surfaces, which determine electronic and optical properties of the prepared samples.
Abstract: Transparent zinc oxide (ZnO) films on flexible copper-coated polyethylene terephthalate (PET) sheet have been grown by a potentiostatic cathodic deposition technique using aqueous zinc nitrate as electrolyte. ZnO films were fabricated using different deposition parameters such as applied potential, electrolyte concentration and bath temperature. Their structural and optical properties were characterized by X-ray diffractometer, scanning electron microscope, diffuse reflectance UV-VIS spectrophotometer and photoluminescence spectrometer. The effects of these deposition parameters on the structural and optical properties of the fabricated ZnO films have been investigated. On the basis of our results, we demonstrate that high quality ZnO films have been successfully grown on flexible polymeric substrates using a low temperature potentiostatic cathodic deposition technique.
Abstract: Both a low and a high resistance stateｓ which were written by the voltage application in a
local region of NiO/Pt films by using conducting atomic force microscopy (C-AFM) were observed
by using scanning electron microscope (SEM) and electron probe micro analysis (EPMA). The
writing regions are distinguishable as dark areas in a secondary electron image and thus can be
specified without using complicated sample fabrication process to narrow down the writing regions
such as the photolithography technique. In addition, the writing regions were analyzed by using
energy dispersive X-ray spectroscopy (EDS) mapping. No difference between the inside and outside
of the writing regions is observed for all the mapped elements including C and Rh. Here, C and Rh are
the most probable candidates for contamination which affect the secondary electron image. Therefore,
our results suggested that the observed change in the contrast of the secondary electron image is
related to the intrinsic change in the electronic state of the NiO film and a secondary electron yield is
correlated to the physical properties of the film.