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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.
- Optical and photoconductive properties of indium sulfide fluoride thin filmsPublication . Vygranenko, Yuri; Vieira, Manuela; Lavareda, G.; Carvalho, C. Nunes de; Brogueira, Pedro; Amaral, A.; Pessoa Barradas, Nuno; Alves, E.This work reports on transparent semiconducting indium sulfide fluoride (ISF) thin-films exhibiting high sensitivity to ultraviolet radiation. The films were deposited on fused silica and silicon substrates using a radiofrequency plasma-enhanced reactive thermal evaporation system. The deposition was performed evaporating pure indium in SF6 plasma at a substrate temperature of 423 K. Rutherford backscattering measurements were used to determine the chemical composition of the films deposited on silicon substrates. The surface morphology was studied using scanning electron microscopy technique. The film characterization includes electrical, optical, and photoconductivity measurements. The synthesized compound is highly-resistive (similar to 700 M Omega-cm at 300 K) and exhibits an evident semiconducting behavior. The activation energy of 0.88 eV is deduced from the temperature dependence of electrical resistivity. The indirect band energy gap of 2.8 eV is determined from transmittance spectra of the ISF films. The photoconductivity band is centered at 345 nm wavelength. The photoconductivity spectrum also shows the Urbach tail with a characteristic energy of 166 meV. ISF is a promising candidate for a buffer layer in chalcogenide-based solar cells.
- An indium-oxide electrode with discontinuous Au layers for plasmonic devicesPublication . Vygranenko, Yuri; Lavareda, G.; André, V.; Brogueira, Pedro; Amaral, A.; Fernandes, M.; Fantoni, Alessandro; Vieira, ManuelaIn this contribution we report on a low cost plasmonic electrode for light-sensing applications. The electrode combines a conducting nonstoichiometric indium oxide (InOx) layer with an ultrathin (~5 nm) discontinuous Au layer. The InOx and Au layers were deposited on glass substrates by plasma enhanced reactive thermal evaporation and thermal evaporation, respectively. Several device configurations with one or two Au layer(s) sandwiched between InOx layers were fabricated and characterized. The morphological and structural properties of both Au and InOx layers were analyzed using AFM and XRD techniques. In particular, the effect of thermal annealing (673 K, 15 min) on the surface morphology of Au layers grown on bare glass and InOx-coated substrate was investigated. It has been also found that the oxide film grown above an underlying nanostructured Au layer is amorphous, while a reference InOx film on glass is nanocrystalline with a smooth surface. The electrical properties of InOx grown on the Au surface are worsened due to Au-induced structural disorder. The observed difference in transmission spectra of the glass/InOx/Au and glass/Au/InOx structures indicates the difference in the morphology of the metal layer. Thus, the optical and morphological properties of the InOx electrode can be varied in a wide range by incorporating several Au layers.
- 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.