Pereira, L.a, Aguas Beckers Martins Fortunato Martins H. a M. b. "
Characterization of nickel induced crystallized silicon by spectroscopic ellipsometry."
Materials Research Society Symposium Proceedings. Vol. 910. 2007. 529-534.
AbstractIn this work Spectroscopic Ellipsometry (SE) was used to study metal induced crystallization (MIC) on amorphous silicon films in order to analyze the influence of different annealing conditions on their structural properties. The variation of the metal thickness has shown to be determinant on the time needed to full crystallize silicon films. Films of 100 nm thickness crystallize after 2h at 500°C using 1 nm of Ni deposited on it. When reducing the average metal thickness down to 0.05 nm the same silicon film will need almost 10 hours to be totally crystallized. Using a new approach on the modelling procedure of the SE data we show to be possible to determine the Ni remaining inside the crystallized films. The method consists in using Ni as reference on the Bruggeman Effective Medium Approximation (BEMA) layer that will simulated the optical response of the crystallized silicon. Silicon samples and metal layers with different thicknesses were analyzed and this new method has shown to be sensible to changes on the initial metal/silicon ratio. The nickel distribution inside the silicon layers was independently measured by Rutherford Backscattering Spectroscopy (RBS) to check the data obtained from the proposed approach. © 2006 Materials Research Society.
Zhang, S., Raniero Fortunato Pereira Martins Canhola Ferreira Nedev Águas Martins L. E. L. "
Characterization of silicon carbide thin films prepared by VHF-PECVD technology."
Journal of Non-Crystalline Solids. 338-340 (2004): 530-533.
AbstractA series of hydrogenated amorphous silicon carbide films were prepared by plasma enhanced chemical vapor deposition (PECVD) using a gas mixture of silane, methane, and hydrogen as the reactive source and an excitation frequency of 27.12 MHz. Compared to the typical radio frequency deposition technique, the very high plasma excitation frequency increases the density of the electrons and decreases the electron temperature, which helps the dissociation of the SiH4 and CH4, and reduces the energetic ion impact on the growth surface of the thin film. Thus, dense-films with lower bulk density of states and higher growth rate are expected, as confirmed by spectroscopic ellipsometry data. Apart from that, a substantial reduction of bulk defects is achieved, allowing an improvement of the valence controllability (widening of the optical gap from about 1.9 to 3.6 eV). In this work results concerning the microstuctural and photoelectronic properties of the silicon carbide films will be discussed in detail, correlating them with the deposition process conditions used as well as with the gas phase composition of the mixtures used. © 2004 Elsevier B.V. All rights reserved.
Raniero, L., Pereira Zhang Ferreira Águas Fortunato Martins L. S. I. "
Characterization of the density of states of polymorphous silicon films produced at 13.56 and 27.12 MHz using CPM and SCLC techniques."
Journal of Non-Crystalline Solids. 338-340 (2004): 206-210.
AbstractThe aim of this paper is to compare the density of bulk states (DOS) of polymorphous silicon (pm-Si:H) films produced by plasma enhanced chemical vapor deposition at 13.56 and 27.12 MHz using the constant photocurrent method and the space charge limited current (SCLC) technique. The data achieved revealed that the set of films produced present similar DOS. Apart from that, data concerning the correlation of the deposition conditions that lead to the production of pm-Si:H as well as their characteristics, such as the hydrogen content and how hydrogen is bonded, will be discussed, giving special emphasis to the set of mechanical stresses developed. By doing so we could get a better understanding of the nature of hydrogen bonding in pm-Si:H films as well as to determine the role of the excitation frequency on the film's performances, where films with amounts of hydrogen around 20 at.% can have DOS as low as 8 × 10 14 cm-3 with Urbach energies in the range of 41-50 meV. © 2004 Elsevier B.V. All rights reserved.
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.
Fortunato, E., Nunes Marques Costa Águas Ferreira Costa Martins P. A. D. "
Characterization of zinc oxide thin films deposited by rf magnetron sputtering on Mylar substrates."
Materials Research Society Symposium - Proceedings. Vol. 666. 2001. F3211-F3216.
AbstractAluminium doped zinc oxide thin films (ZnO:Al) have been deposited on polyester (Mylar type D, 100 μm thickness) substrates at room temperature by r.f. magnetron sputtering. The structural, morphological, 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. The ZnO:Al thin films with 85% transmittance in the visible and infra-red region and a resistivity as low as 3.6×10-2 Ωcm have been obtained, as deposited. The obtained results are comparable to those ones obtained on glass substrates, opening a new field of low cost, light weight, small volume, flexible and unbreakable large area optoelectronic devices.
i Martins, R.a, Águas Ferreira Fortunato Raniero Roca Cabarrocas H. a I. a. "
Composition, structure and optical characteristics of polymorphous silicon films deposited by PECVD at 27.12 MHz."
Materials Science Forum. 455-456 (2004): 100-103.
AbstractThis paper presents data concerning the composition structure and optical characteristics of polymorphous silicon films produced by plasma enhanced chemical vapour deposition at 27.12 MHz and determined respectively by infrared spectrometry, micro Raman, exodiffusion and spectroscopic ellipsometry measurements. When compared to the pm-Si:H films produced at 13.56 MHz, the films produced at 27.12 MHz present hydrogen contents in the range of 21 at%, the sharp peak ascribed to the exodifusion measurements is shifted towards high temperatures and the imaginary part of the dielectric function 〈ε2〉 is larger and shifted to high energies. Apart from that the peaks of the infrared spectra ascribed to the stretching modes shift towards high wave numbers and the half width of the micro Raman peaks shrinks, meaning that the films produced at 27.12 MHz are more compact and dense.