Prabakaran, R., Aguas Pereira Elangovan Fortunato Martins Ferreira H. L. E. "
Optical and microstructural investigations of porous silicon coated with a-Si:H using PECVD technique."
Materials Science Forum. 587-588 (2008): 308-312.
AbstractIn the present work, the spectroscopic ellipsometry (1.5 - 5.5 eV) was used to investigate the effects of current density induced microstructural variations and their influence on the electronic states of as-prepared and a-Si:H coated porous silicon (PS). The pseudodielectric responses of the low and high current densities (5 and 40 mA/cm2) were analyzed using a multilayer model within the effective medium approximation. The FTIR investigation reveals me enhancement of surface oxide (Si-Ox) layer with current density and the improvement of the Si-Hx band after a-Si:H coating.
Pimentel, A.C., Gonçalves Marques Martins Fortunato A. A. R. "
Zinc oxide thin films used as an ozone sensor at room temperature."
Materials Research Society Symposium Proceedings. Vol. 915. 2006. 243-248.
AbstractIn this paper we present results of intrinsic/non doped zinc oxide films deposited at room temperature by rf magnetron sputtering able to be used as a truly semiconductor on electronic devices like ozone gas sensors and ultra-violet detectors. The produced films are polycrystalline with a c-axis preferential orientation parallel to the substrate. The films' resistivity varies from 4.0×10-2 Ωcm to 1.0×10-9 Ωcm, depending on the deposition conditions used (rf power density and oxygen partial pressure), which turns not affecting the optical properties (in average a transmittance of around 85 % and an optical band gap of about 3.44 eV, independent of the deposition conditions used). When exposed to UV light the sensor response based on these films may exceed more than 5 orders of magnitude, recovering to the initial state in the presence of ozone. The sensitivity of the films is improved when the oxygen partial pressure increases and the rf power density used decreases, due to changes on the structural properties of the films. © 2006 Materials Research Society.
Pereira, L., Águas Raniero Martins Fortunate Martins H. L. R. "
Role of substrate on the growth process of polycrystalline silicon thin films by low-pressure chemical vapour deposition."
Materials Science Forum. 455-456 (2004): 112-115.
AbstractThis paper deals with the role the substrate on the structure of undoped and n-doped polycrystalline silicon (poly-Si) films produced by Low Pressure Chemical Vapour Deposition (LPCVD). The structural and electrical properties of the films deposited on glass, glass covered with molybdenum (Mo), oxidised crystalline silicon and oxidised crystalline silicon covered with Mo were analysed using X-ray diffraction and Spectroscopic Ellipsometry, dark conductivity and Hall effect measurements. Undoped poly-Si films deposited over Mo present modifications in the crystalline structure relatively to those deposited on the other substrates. The presence of Mo changes the preferential growth orientation, enhancing the Si {111} grains orientation, leading to more compact films. The electrical measurements also confirm that the films grown on Mo substrates present better characteristics. Some differences are also observed during the initial growth stages when using glass or oxidised silicon. Very thin n-doped films present a less effective doping effect when deposited on oxidised silicon than the ones deposited on glass substrates.
Pereira, L., Águas Martins Fortunato Martins H. R. M. "
Polycrystalline silicon obtained by gold metal induced crystallization."
Journal of Non-Crystalline Solids. 338-340 (2004): 178-182.
AbstractThe aim of this paper is to study the role of gold (Au) induced crystallization on amorphous silicon (a-Si) films produced by low pressure chemical vapor deposition (LPCVD) at low process temperatures (550 °C) to allow the use of glass substrates. Concerning the crystallization process Au was deposited by e-beam thermal evaporation over the silicon (Si), using different metal thickness, from 5 to 100 Å. The samples were then annealed at 450, 500 and 550 °C and the crystallization time was changed from 5 up to 30 h. The structure of the films was analyzed by X-ray diffraction (XRD) and spectroscopic ellipsometry (SE) while electrical conductivity measurements were performed to obtain the electrical properties of the films produced, namely the activation energy (EA) and how it changes with the Au thickness used. The data achieved show that the increase of the metal layer thickness decreases the time needed to get full crystallization. However this leads to lower conduction activation energy (EA) meaning that there is also an increase of Au incorporation that leads to the production of doped films. © 2004 Elsevier B.V. All rights reserved.
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.