Raniero, L.a, Martins Águas Zang Ferreira Pereira Fortunato Boufendi R. a H. a. "
Growth of polymorphous/nanocrystalline silicon films deposited by PECVD at 13.56 MHz."
Materials Science Forum. 455-456 (2004): 532-535.
AbstractThis paper aims to characterize the growth process of polymorphous/ nanocrystalline silicon (pm-Si:H) films produced by PECVD at 13.56 MHz. The emphasis is in determining the plasma parameters that allow to control the conditions where pm/nc-Si:H can be obtained under high hydrogen dilution, where the only varied parameter is the silane gas flow, fixing rf power, deposition pressure and substrate temperature. The data achieved show that good pm/nc-Si:H films are produced at 240 Pa using a silane gas flow of 5sccm (dilution 1:70) to which it corresponds films with photosensitivities exceeding 106, optical gaps close to 1.80 eV and 18 at% hydrogen contents. The data also show that under certain deposition conditions the pm-Si:H films peel-off.
Fortunato, E., Pimentel Pereira Gonçalves Lavareda Águas Ferreira Carvalho Martins A. L. A. "
High field-effect mobility zinc oxide thin film transistors produced at room temperature."
Journal of Non-Crystalline Solids. 338-340 (2004): 806-809.
AbstractIn this paper we present the first results of thin film transistors produced completely at room temperature using ZnO as the active channel and silicon oxynitride as the gate dielectric. The ZnO-based thin film transistors (ZnO-TFT) present an average optical transmission (including the glass substrate) of 84% in the visible part of the spectrum. The ZnO-TFT operates in the enhancement mode with a threshold voltage of 1.8 V. A field effect mobility of 70 cm2/Vs, a gate voltage swing of 0.68 V/decade and an on-off ratio of 5×105 were obtained. The combination of transparency, high field-effect mobility and room temperature processing makes the ZnO-TFT very promising for the next generation of invisible and flexible electronics. © 2004 Elsevier B.V. All rights reserved.
Fortunato, E., Pimentel Gonçalves Marques Martins A. A. A. "
High mobility nanocrystalline indium zinc oxide deposited at room temperature."
Materials Research Society Symposium Proceedings. Vol. 811. 2004. 437-442.
AbstractIn this paper we present results of indium doped zinc oxide deposited at room temperature by rf magnetron sputtering, with electron mobility as high as 60 cm2/Vs. The films present a resistivity as low as 5×10 -4 Ωcm with an optical transmittance of 85%. The structure of these films look-like polymorphous (mixed of different amorphous and nanocrystalline phases from different origins) as detected from XRD patterns (no clear peak exists) with a high smooth surface, as detected from SEM micrographs, highly important to ensure long life time when used in display devices.
Fortunato, E.a, Assunção Gonçalves Marques Águas Pereira Ferreira Vilarinho Martins V. a A. a. "
High quality conductive gallium-doped zinc oxide films deposited at room temperature."
Thin Solid Films. 451-452 (2004): 443-447.
AbstractTransparent and highly conducting gallium-doped zinc oxide films were successfully deposited by rf sputtering at room temperature. The lowest resistivity achieved was 2.6×10-4 Ω cm for a thickness of 1100 nm (sheet resistance ≈1.6 Ω/sq), with a Hall mobility of 18 cm2/Vs and a carrier concentration of 1.3×1021 cm-3. The films are polycrystalline with a hexagonal structure and a strongly preferred orientation along the c-axis. A linear dependence between the mobility and the crystallite size was obtained. The films present a transmittance in the visible spectra between 80 and 90% and a refractive index of approximately 2, which is very close to the value reported for bulk material. © 2003 Elsevier B.V. All rights reserved.
b c Nedev, N.a b, Beshkov Fortunato Georgiev Ivanov Raniero Zhang Martins G. a E. b. "
Influence of the rapid thermal annealing on the properties of thin a-Si films."
Materials Science Forum. 455-456 (2004): 108-111.
AbstractThe variation of the structure, morphology and the electrical properties of thin amorphous silicon films caused by Rapid Thermal Annealing is studied. The films annealed at 1200°C for 2 minutes change their structure to polycrystalline and as a result their resistivity decreases by 4 orders of magnitude. Due to the small thickness of the as deposited amorphous silicon the obtained poly-Si is strongly irregular and has many discontinuities in its texture.
Alendouro, M.S.J.G.a, Monteiro Figueiredo Martins Silva Ferro Fernandas R. C. C. a. "
Microstructural characterization and properties of a glass and a glassceramic made from municipal incinerator bottom ash."
Materials Science Forum. 455-456 (2004): 827-830.
AbstractA glass was made using bottom ash produced by a Portuguese municipal solid waste (MSW) incinerator. The bottom ash was the single batch material used in the formation of the glass, which was obtained through a conventional melt-quenching method. The glass was then converted to glass-ceramic for further recycling to construction materials. After submitting the glass samples to several heat treatments, between 820 and 1050°C and during different times, it was verified that the optimum heat treatment schedule for the ceramization of the glass was at 1000°C for 10h, as confirmed by microstructural observation and by X-ray diffraction. The major crystalline phases precipitated in the glass-ceramic were wollastonite (CaSiO3) and diopside (Ca(Mg,Al)(Si,Al)2O6). Microstructural analysis of the glass-ceramic revealed that the crystalline phases were present as dendrites and fiber-like structures that were homogeneously distributed in the material. The glassceramic showed good mechanical properties with a hardness of 5.6 MPa and a bending strength of 101 MPa. This material had a density of 2.8 gcm-3 and a thermal expansion coefficient of 9.10-6°C-1. The glass and the glass-ceramic showed an excellent chemical stability against leaching in acidic solution and in alkaline solution. In summary, both the glass and the glass-ceramic have good chemical and mechanical properties and can, therefore, be applied as construction materials.
Fortunato, E., Barquinha Pimentel Gonçalves Pereira Marques Martins P. A. A. "
Next generation of thin film transistors based on zinc oxide."
Materials Research Society Symposium Proceedings. Vol. 811. 2004. 347-352.
AbstractWe report high performance ZnO thin film transistor (ZnO-TFT) fabricated by rf magnetron sputtering at room temperature with a bottom gate configuration. The ZnO-TFT operates in the enhancement mode with a threshold voltage of 19 V, a field effect mobility of 28 cm2/Vs, a gate voltage swing of 1.39 V/decade and an on/off ratio of 3×105. The ZnO-TFT present an average optical transmission (including the glass substrate) of 80% in the visible part of the spectrum. The combination of transparency, high field-effect mobility and room temperature processing makes the ZnO-TFT a very promising low cost optoelectronic device for the next generation of invisible and flexible electronics.
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, Águas Martins Vilarinho Fortunato Martins H. a R. M. "
Polycrystalline silicon obtained by metal induced crystallization using different metals."
Thin Solid Films. 451-452 (2004): 334-339.
AbstractThe aim of this paper is to study the role of different metals (aluminium, molybdenum, nickel and titanium) in inducing crystallization in films produced by LPCVD at high and low temperature processes and to compare the structural, morphological, optical and electrical properties of the various films produced. This work envisages the use of the most suitable conditions that lead to the production of films for optoelectronic applications such as solar cells. © 2003 Elsevier B.V. All rights reserved.
Ferreira, I., Águas Pereira Fortunato Martins H. L. E. "
Properties of a-Si:H intrinsic films produced by HWPA-CVD technique."
Thin Solid Films. 451-452 (2004): 366-369.
AbstractIn this paper, we investigate the optoelectronic properties and the photodegradation of amorphous silicon films produced by the hot wire plasma assisted technique (HWPA-CVD). We observed that hydrogen dilution in the gas phase plays an important role in the time dependence of the photoconductivity, which is correlated with an enhancement of defect density. We also compare the degradation of these films with those produced by plasma enhanced and by hot wire chemical vapour deposition techniques (PECVD and HW-CVD) and we found lower time dependence for the photodegradation of the films produced by HWPA-CVD technique © 2003 Elsevier B.V. All rights reserved.
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.
Águas, H.a, Raniero Pereira Viana Fortunato Martins L. a L. a. "
Role of the rf frequency on the structure and composition of polymorphous silicon films."
Journal of Non-Crystalline Solids. 338-340 (2004): 183-187.
AbstractIn this work we present results of structural composition and morphological characteristics of polymorphous silicon (pm-Si:H) films deposited by PECVD at 13.56 and 27.12 MHz. In addition, the role of the excitation frequency on the growth rate will be also analyzed. The results show that by using the 27.12 MHz excitation frequency the hydrogen dilution in the plasma needed to produce pm-Si:H can be reduced by more than 50% as well as the rf power density, leading to an increase on the growth rate to values higher than 3 Å/s. Spectroscopic ellipsometry and Raman spectroscopy show that the 27.12 MHz pm-Si:H films are more ordered than the pm-Si:H films produced at 13.56 MHz, while the infrared spectroscopy show that the SiH2 concentration in the films is strongly reduced. AFM measurements reveal that the films produced at 27.12 MHz films are more structured, presenting also higher roughness. © 2004 Elsevier B.V. All rights reserved.
Silva, A., Raniero Ferreira Águas Pereira Fortunato Martins L. E. H. "
Silicon etching in CF4/O2 and SF6 atmospheres."
Materials Science Forum. 455-456 (2004): 120-123.
AbstractThe aim of this work is to present a process able to allow a fast method to clean plasma enhanced chemical vapour deposition (PECVD) systems used to produce amorphous silicon films and their alloys, and a proper device patterning when required. In this work we propose to study CF4/O2 or SF6 as etchant gases at room temperature to perform cleaning and films patterning. The aim is to select the process that leads to a faster cleaning process without formation of residual contaminants or to anisotropic patterning of very thin layers. The influence of some plasma parameters, such as pressure (p), power (P) and flow (f) for the etchant gases used will be also analysed.