Ferreira, I.M.M., Martins Cabrita Fortunato Vilarinho R. F. P. A. "
Nanocrystalline undoped silicon films produce by hot wire plasma assisted technique."
Materials Research Society Symposium - Proceedings. Vol. 609. 2000. A2241-A2246.
AbstractIn this work, we show results concerning electro-optical properties, composition and morphology of nanocrystalline hydrogenated undoped silicon (nc-Si:H) films produced by hot wire plasma assisted chemical vapour deposition process (HWPA-CVD) and exhibiting a compact granular structure, as revealed by SEM micrographs. This was also inferred by infrared spectra, which does not present the SiO vibration band located at 1050-1200 cm-1, even when samples have long atmospheric exposition. The photoconductivity measured at room temperature also does not change when samples have a long time exposition to the air or to the light irradiation. The influence of hydrogen dilution on the properties of the films was also investigated.
Ferreira, I., Aguas Mendes Fernandes Fortunato Martins H. L. F. "
Performances of nano/amorphous silicon films produced by hot wire plasma assisted technique."
Materials Research Society Symposium - Proceedings. Vol. 507. 1999. 607-612.
AbstractThis work reports on the performances of undoped and n doped amorphous/nano-crystalline silicon films grown by hot wire plasma assisted technique. The film's structure (including the presence of several nanoparticles with sizes ranging from 5 nm to 50 nm), the composition (oxygen and hydrogen content) and the transport properties are highly dependent on the filament temperature and on the hydrogen dilution. The undoped films grown under low r.f. power (≈4 mWcm-2) and with filament temperatures around 1850 °K have dark conductivities below 10-10 Scm-1, optical gaps of about 1.5 eV and photo-sensitivities above 105, (under AM1.5), with almost no traces of oxygen content. N-doped silicon films were also fabricated under the same conditions which attained conductivities of about 10-2 Scm-1.
Ferreira, I., Raniero Fortunato Martins L. E. R. "
Electrical properties of amorphous and nanocrystalline hydrogenated silicon films obtained by impedance spectroscopy."
Thin Solid Films. 511-512 (2006): 390-393.
AbstractNanocrystalline hydrogenated silicon (nc-Si:H) thin films are generally accepted to be a two phase material-Si crystalline and Si:H amorphous. This work reports the use of impedance spectroscopy to determine the amorphous and crystalline electrical conductivity of a/nc-Si:H films obtained by hot wire chemical vapour deposition. Different relaxation time or time constants are detected, if the film is composed by inhomogeneous material, by measuring ac impedance in a wide range of frequencies. Relating the conduction mechanism of the film to a series of two RC circuits constituted by a resistance and a capacitor in parallel, we may determine distinct ac conductivities and correlate that to the crystalline, amorphous and interface components. The amorphous films analysed exhibit one ac conductivity component while for nanocrystalline films two ac conductivity components are observed. The average value of ac conductivities is in agreement with that of dc conductivity. © 2006.
Ferreira, I., Vilarinho Fernandes Fortunato Martins P. F. E. "
Influence of hydrogen gas dilution on the properties of silicon-doped thin films prepared by the hot-wire plasma-assisted technique."
Key Engineering Materials. 230-232 (2002): 591-594.
AbstractP- and n-type silicon thin films have been produced using a new hot wire plasma assisted deposition process that combines the conventional plasma enhanced chemical vapor deposition and the hot wire techniques. The films were produced in the presence of different hydrogen gas flow and their optoelectronic, structural and compositional properties have been studied. The optimized optoelectronic results achieved for n-type Si:H films are conductivity at room temperature of 9.4(Ωcm)-1 and optical band gap of 2eV while for p-type SiC:H films these values are 1 × 10-2(Ωcm)-1 and 1.6eV, respectively. The films exhibit the required optoelectronic characteristics and compactness for device applications such as solar cells.
Fortunate, E., Gonçalves De Carvalho Pimentel Lavareda Marques Martins A. C. N. "
Enhancement of the electrical properties of ITO deposited on polymeric substrates by using a ZnO buffer layer."
Materials Research Society Symposium Proceedings. Vol. 814. 2004. 231-236.
AbstractIn this paper we present the effect of the insertion of a non-doped nanocrystalline zinc oxide/buffer layer on the electrical, optical and structural properties of indium tin oxide produced at room temperature by radio frequency plasma enhanced reactive thermal evaporation on polymeric substrates. The electrical resistivity of the ITO films is reduced by more than two orders of magnitude (4.5×10-1 to 2.9×10-3 Ωcm). From the Hall effect measurements it is observed that the large decrease associated to the electrical resistivity, is due to the increase associated to the Hall mobility. Concerning the optical properties no effect was observed, being the transmittance in the visible and near the infra red region always higher than 80%.
Fortunate, E., Assunção Marques Ferreira Águas Pereira Martins V. A. I. "
Characterization of transparent and conductive ZnO:Ga thin films produced by rf sputtering at room temperature."
Materials Research Society Symposium - Proceedings. Vol. 763. 2003. 225-230.
AbstractGallium-doped zinc oxide films were prepared by rf magnetron sputtering at room temperature as a function of the substrate-target distance. The best results were obtained for a distance of 10 cm, where a resistivity as low as 2.7×10-4 Ωcm, a Hall mobility of 18 cm2/Vs and a carrier concentration of 1.3×1021 cm-3 were achieved. The films are polycrystalline presenting a strong crystallographic c-axis orientation (002) perpendicular to the substrate. The films present an overall transmittance in the visible part of the spectra of about 85 %, in average. The low resistivity, accomplished with a high growth rate deposited at RT, enables the deposition of these films onto polymeric substrates for flexible applications.
Fortunate, E.a, Ferreira Giuliani Wurmsdobler Martins I. a F. a. "
New ultra-light flexible large area thin film position sensitive detector based on amorphous silicon."
Journal of Non-Crystalline Solids. 266-269 B (2000): 1213-1217.
AbstractIn this paper we report on large area one dimensional (1D) amorphous silicon position sensors deposited on flexible polymer foil substrate. The pin sensor structure was deposited by rf plasma enhanced chemical vapour deposition (PECVD). For the electrical and optical characterisation the sensors have been mounted on a convex holder with a 14-mm radius-of-curvature, since the main goal of this work is to develop a flexible position sensor to be incorporated in a micromotor in order to measure its angular velocity continuously. The obtained sensors present adequate performances concerning the position non-linearity (±1% in 20 mm length), comparable to those fabricated on glass substrates. © 2000 Elsevier Science B.V. All rights reserved.
Fortunato, E.M.C., Brida Ferreira Águas Nunes Cabrita Giuliani Nunes Maneira Martins D. I. M. M. "
Large area flexible amorphous silicon position sensitive detectors."
Materials Research Society Symposium - Proceedings. Vol. 609. 2000. A1271-A1276.
AbstractLarge area thin film position sensitive detectors based on amorphous silicon technology have been prepared on polyimide substrates using the conventional plasma enhanced chemical vapour deposition technique. The sensors have been characterised by spectral response, illuminated I-V characteristics and position detectability measurements. The obtained one dimensional position sensors with 5 mm wide and 60 mm long present a maximum spectral response at 600 nm, an open circuit voltage of 0.6 V° and a position detectability with a correlation of 0.9989 associated to a standard deviation of 1 × 10-2, comparable to those ones produced on glass substrates. The surface of the sensors at each stage of fabrication was investigated by Atomic Force Microscopy.
Fortunato, E., Nunes Marques Costa Águas Ferreira Costa Martins P. A. D. "
Highly conductive/transparent ZnO:Al thin films deposited at room temperature by rf magnetron sputtering."
Key Engineering Materials. 230-232 (2002): 571-574.
AbstractTransparent conducting ZnO:Al thin films have been deposited on polyester (Mylar type D, 100 μm thickness) substrates at room temperature by r.f. magnetron sputtering. The structural, optical and electrical properties of the deposited films have been studied. The samples are polycrystalline with a hexagonal wurtzite structure and a strong crystallographic c-axis orientation (002) perpendicular to the substrate surface. As deposited ZnO:Al thin films have an 85% transmittance in the visible and infra-red region and a resistivity as low as 3.6×10-2 Ωcm. The obtained results are comparable to those ones obtained on glass substrates, opening a new field for low cost, light weight, small volume, flexible and unbreakable large area optoelectronic devices.