Maçarico, A.a, Vieira Fantoni Louro Sêco Martins Hollenstein M. a A. a. "
On the a-Si:H film growth: The role of the powder formation."
Journal of Non-Crystalline Solids. 198-200 (1996): 1207-1211.
AbstractResults are presented which are geared towards an understanding of the influence of powder formation during film growth. Plasma chemistry is correlated with the morphology, structure (inferred through infrared spectroscopy, scanning electron microscopy and X-ray diffraction) electro-optical and density of states of intrinsic films deposited under continuous and power modulated operation. Results show that for modulation frequencies where no powder formation occurs and low substrate temperatures T (150°C), silane decomposition gives rise to the growth of inhomogeneous films while in the high modulation frequency regime, at the same temperature, the anions and powder are trapped resulting in films with high deposition rates and low defect density.
Malik, A., Nunes Martins R. R. "
Cubic to hexagonal phase transition in spray deposited tin-doped indium oxide films."
Materials Research Society Symposium - Proceedings. Vol. 481. 1998. 599-605.
AbstractThis work's aim is to report for the first time the cubic to hexagonal phase transition in tin-doped In2O3 films with a Sn/In atomic ratio of 0.03, fabricated at low temperature and normal pressure from alcoholic solution of InCl3 and SnCl4. The performed X-ray diffraction measurements show a difference between crystallographic symmetry of thin (100 nm) and thick (400 nm) films prepared in the same conditions: the structure of thick films can be related to high pressure In2O3 hexagonal system with a preferred orientation of c-axis parallel to the substrate surface, while thin films present a cubic symmetry with columnar (400) grain orientation. Phase transition nature is connected with non-axial tensile deformation of indium oxide grid due to insertion of chlorine ions in the position of two diagonally opposite oxygen vacancies in In2O3 network.
Malik, A.a, Sêco Fortunato Martins A. c E. b. "
Microcrystalline thin metal oxide films for optoelectronic applications."
Journal of Non-Crystalline Solids. 227-230 (1998): 1092-1095.
AbstractWe report the properties and optoelectronic applications of transparent and conductive indium and tin oxide films prepared by the spray pyrolysis method and doped with Sn or F, respectively. The film properties have been measured using X-ray diffraction, optical and electrical absorption. As examples of applications we produced a set of selective optical detectors for different spectral regions, covering the wavelength range from 0.25 to 1.1 μm, based on metal oxide-semiconductor heterostructures and using different substrates such as: GaP, GaSe, AlxGa1-xAs, GaAs and Si. The fabricated devices exhibit several features such as: production simplicity, high quantum efficiency, uniform sensitivity over the entire active area and a high response speed. Finally, we present a high quantum efficiency and solar blind monocrystalline zinc sulphide optical sensor fabricated by spray deposition as an alternative to the ultraviolet-enhanced SiC and GaN photodetectors and the performances of a solar cell. © 1998 Elsevier Science B.V. All rights reserved.
Malik, A., Martins R. "
Light-controlled switching transients in MIS silicon structures with multichannel insulator: physical processes and new device modelling."
Materials Research Society Symposium - Proceedings. Vol. 490. 1998. 257-262.
AbstractWe present the modelling of a new two-terminal and low-voltage operating optoelectronic device based on MIS silicon structure with multichannel insulator and having as gate a transparent metallic tin-doped indium oxide (ITO) layer deposited by spray pyrolysis technique over the insulator layer. ITO layer has a multiple non-rectifier electrical contact with silicon substrate, in the SiO2 channel's region. Construction details of the process, together with its operating characteristics are given. The devices developed do not require external active electronic components (transistors, microschemes) to execute their functions and to transform analogue input optical signals to digital output form, highly important for a wide range of optoelectronic applications.
Malik, A., Martins R. "
UV enhanced and solar blind photodetectors based on large-band-gap materials."
Materials Science Forum. 258-263 (1997): 1425-1430.
AbstractHigh quantum efficiency, UV-enhanced monocrystalline zinc sulphide optical sensors for precise radiometric and spectroscopic measurements have been developed by spray deposition of heavy fluorinedoped tin oxide thin films with carrier concentration near 1021 cm-3 onto the surface of zinc sulphide monocrystals as an alternative to the UV-enhanced silicon photodetectors as well as to new detectors based on SiC and GaN. The fabricated sensors have an unbiased internal quantum efficiency that was nearly 100% from 250 to 320 nm, and the typical sensitivity at 290 nm is 0.15 A/W. The sensors were insensitive to solar radiation in earth's conditions and can be used as solar blind photodetectors for precision UV-measurements under direct solar illumination, both terrestrial and space applications.
Malik, A., Martins R. "
Metal oxide/silicon heterostructures: New solutions for different optoelectronic applications."
Materials Research Society Symposium - Proceedings. Vol. 487. 1998. 375-380.
AbstractIn this paper we report the success in fabricating FTO/Si surface-barrier photodiodes produced by spray pyrolysis deposition technique, under ambient conditions. Three types of photodetectors for low-voltage-bias operation were developed based on high-resistivity silicon: 1. X-Ray detectors with energy resolution of 16.5% at 661.5 keV (137Cs source), consisting of surface-barrier PIN photodiode with an active area of 50 mm2 operating at 5 V reverse bias, scintillator based on monocrystalline Bi4Ge3O12 and preamplifier (noise of 250 e- RMS.); 2. Fast-response surface-barrier FTO/n–n+ silicon epitaxial photodiodes, operating at 10 V bias with rise times of 2 ns at λ = 0.85 μm; 3. Radiation-resistant drift epitaxial surface-barrier PIN photodiodes for unbiased operating conditions, with an exponential impurity distribution in a 8 μm thick epitaxial layer. A built-in electrical field due to the carrier concentration distribution in the epitaxial layer provides a considerable improvement in the `critical fluence' value (3×1014 cm-2) for neutron irradiation.
Martins, R., Fortunato E. "
Static and dynamic resolution of 1D thin film position sensitive detector."
Journal of Non-Crystalline Solids. 198-200 (1996): 1202-1206.
AbstractThe aim of this work is to present a model to interpret the static and the dynamic detection and resolution limits of 1D thin film position sensitive detectors based on p-i-n a-Si:H devices. The model can determine the device characteristics that influence the spatial limits and the response time of the device.
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.
Martins, Rodrigo, Lavareda Guilherme Fortunato Elvira Soares Fernando Fernandes Luis Ferreira Luis. "
Linear thin-film position-sensitive detector (LTFPSD) for 3D measurements."
Proceedings of SPIE - The International Society for Optical Engineering. Vol. 2415. 1995. 148-158.
AbstractA linear array thin film position sensitive detector (LTFPSD) based on hydrogenated amorphous silicon (a-Si:H) is proposed for the first time, taking advantage of the optical properties presented by a-Si:H devices we have developed a LTFPSD with 128 integrated elements able to be used in 3-D inspections/measurements. Each element consists on a one-dimensional LTFPSD, based on a p.i.n. diode produced in a conventional PECVD system, where the doped layers are coated with thin resistive layers to establish the required device equipotentials. By proper incorporation of the LTFPSD into an optical inspection camera it is possible to acquire information about an object/surface, through the optical cross-section method. The main advantages of this system, when compared with the conventional CCDs, are the low complexity of hardware and software used and that the information can be continuously processed (analogue detection).