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- Photoconductivity kinetics of indium sulfofluoride thin films starPublication . Vygranenko, Yuri; Fernandes, Miguel; Vieira, Manuela; Lavareda, Guilherme; CARVALHO, CARLOS; Brogueira, Pedro; Amaral, AnaIndium sulfofluoride is an amorphous wide-gap semiconductor exhibiting high sensitivity to UV radiation. This work reports on the kinetics of photoconductivity in indium sulfofluoride thin films along with their electrical and optical properties. The films were deposited by radio-frequency plasma-enhanced reactive thermal evaporation. The film characterization includes electrical, optical, and photoconductivity measurements. The films are highly transparent in the visible-infrared range due to an indirect bandgap of 2.8 eV. The spectral response measurements have revealed existence of the band tail states. The synthesized compound is highly resistive (similar to 200 M ohm-cm at 300 K) and exhibits extremely slow photocurrent relaxations. Photoconductivity kinetics was studied under various excitation conditions. A dependence of the photocurrent on the incident photon flux was also determined.
- Conducting indium oxide films on plastic substrates by plasma enhanced reactive thermal evaporationPublication . Vygranenko, Yuri; Fernandes, Miguel; Vieira, Manuela; Lavareda, Guilherme; CARVALHO, CARLOS; Brogueira, P.; Amaral, AnaThis work reports on low temperature deposition of conducing indium oxide films by a radio-frequency plasma enhanced reactive thermal evaporation (rf-PERTE) technique. The films were deposited on polyethylene terephthalate (PET) without intentional heating of the substrate and at elevated temperatures up to 150 degrees C. The material stoichiometry was accurately controlled by adjusting deposition conditions including the oxygen flow, process pressure, pumping speed, and RF-power. Besides, fine turning of the critical deposition parameters during the deposition was implemented by measuring the variation of film conductance in-situ. The film morphology was analyzed by scanning electron microscopy. Hall effect measurements were also performed to determine the relation between the deposition conditions and the electrical properties of the films. A resistivity of 4 x 10(-4) Omega-cm was reached under optimized deposition conditions. A 250 nm-thick coating with 16 Omega/sq sheet resistance shows an 82% peak value of transmittance in the visible spectral range.
- Etchability dependence of InOx and ITO thin films by plasma enhanced reactive termal evaporation on structural properties and deposition conditionsPublication . Amaral, Ana; Lavareda, Guilherme; Carvalho, Carlos Nunes de; Andre, Vania; Vygranenko, Yuri; Fernandes, Miguel; Brogueira, PedroIndium oxide (InOx) and indium tin oxide (ITO) thin films were deposited on glass substrates by plasma enhanced reactive thermal evaporation (PERTE) at different substrate temperatures. The films were then submitted to two etching solutions with different chemical reactivity: i) HNO3 (6%), at room temperature; ii) HCl (35%): (40 °Be) FeCl3 (1:1), at 40 °C. The dependence of the etchability of the films on the structural and deposition conditions is discussed. Previously to etching, structural characterization was made. X-ray diffraction showed the appearance of a peak around 2θ=31° as the deposition temperature increases from room temperature to 190 °C, both for ITO and InOx. AFM surface topography and SEM micrographs of the deposited films are consistent with the structural properties suggested by X-ray spectra: as the deposition temperature increases, the surface changes from a finely grained structure to a material with a larger-sized grain or/and agglomerate structure of the order of 250-300 nm. The roughness Rq varies from 0.74 nm for the amorphous tissue to a maximum of 10.83 nm for the sample with the biggest crystalline grains. Raman spectra are also presented.
- InOx thin films deposited by plasma assisted evaporation: application in light shuttersPublication . Merino, E. G.; Almeida, Pedro L.; Carvalho, Carlos Nunes de; Brogueira, P.; Amaral, A.; Lavareda, GuilhermeAn integration of undoped InOx and commercial ITO thin films into laboratory assembled light shutter devices is made. Accordingly, undoped transparent conductive InOx thin films, about 100 nm thick, are deposited by radiofrequency plasma enhanced reactive thermal evaporation (rf-PERTE) of indium teardrops with no intentional heating of the glass substrates. The process of deposition occurs at very low deposition rates (0.1-0.3 nm/s) to establish an optimized reaction between the oxygen plasma and the metal vapor. These films show the following main characteristics: transparency of 87% (wavelength, lambda = 632.8 nm) and sheet resistance of 52 Omega/sq; while on commercial ITO films the transparency was of 92% and sheet resistance of 83 Omega/sq. The InOx thin film surface characterized by AFM shows a uniform grain texture with a root mean square surface roughness of Rq similar to 2.276 nm. In contrast, commercial ITO topography is characterized by two regions: one smoother with Rq similar to 0.973 nm and one with big grains (Rq similar to 3.617 nm). For the shutters assembled using commercial ITO, the light transmission coefficient (Tr) reaches the highest value (Tr-max) of 89% and the lowest (Tr-min) of 1.3% [13], while for the InOx shutters these values are 80.1% and 3.2%, respectively. Regarding the electric field required to achieve 90% of the maximum transmission in the ON state (E-on), the one presented by the devices assembled with commercial ITO coated glasses is 2.41 V/mu m while the one presented by the devices assembled with InOx coated glasses is smaller, 1.77 V/mu m. These results corroborate the device quality that depends on the base materials and fabrication process used. (C) 2014 Elsevier Ltd. All rights reserved.