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1995
Martins, Rodrigo, Fortunato Elvira. "Simulation of the lateral photo effect in large-area 1D a-Si:H p-i-n thin-film position-sensitive detectors." Proceedings of SPIE - The International Society for Optical Engineering. Vol. 2397. 1995. 745-756. Abstract

The aim of this work is to provide the basis for the interpretation, under steady state, of the lateral photoeffect in p-i-n a-Si:H 1D Thin Film Position Sensitive Detectors (1D TFPSD) through an analytical model. The experimental data recorded in 1D TFPSD devices with different performances are compared with the predicted curves and the obtained correlation's discussed.

Fantoni, Alessandro, Vieira Manuela Martins Rodrigo. "Spatial microscopic/macroscopic control and modeling of the p.i.n devices stability." Proceedings of SPIE - The International Society for Optical Engineering. Vol. 2397. 1995. 695-702. Abstract

The introduction into a traditional p.i.n. structure of two defective buffer layers near the p/i and i/n interfaces can improve the device stability and efficiency through an enhancement of the electric field profile at the interfaces and a reduction of the available recombination bulk centers. The defectous layer (`i-layer'), grown at a higher power density, present a high density of the defects and acts as `gettering centers' able to tailor light induced defects under degradation conditions. If the i-layer density of states remains below 1016 eV-1 cm-3 and assuming a Gaussian distribution of defect states, the gettering center distribution will not affect significantly the carrier population but only its spatial distribution. We report here about a device numerical simulation that allows us to analyze the influence of the `i- layer' position, thickness and density of states on the a-Si:H solar cells performances. Results of some systematic simulation rom the ASCA program (Amorphous Solar Cell Analysis), and for different configurations will be presented.

Martins, R., Fortunato E. "Static behaviour of thin-film position-sensitive detectors based on p-i-n a-Si:H devices." Sensors and Actuators: A. Physical. 51 (1995): 143-151. AbstractWebsite

The aim of this work is to provide the basis for the interpretation of the lateral photoeffect in p-i-n a-Si:H one-dimensional thin-film position-sensitive detectors (1D TFPSDs) under steady state, through an analytical model. The experimental data recorded in 1D TFPSD devices with different characteristics are compared with the predicted curves and the obtained correlations are discussed. © 1996.

Martins, R., Vieira Ferreira Fortunato M. I. E. "Structure and composition of doped silicon oxycarbide microcrystalline layers produced by spatial separation techniques." Materials Research Society Symposium - Proceedings. Vol. 358. 1995. 787-792. Abstract

This work presents experimental data concerning the role of the oxygen partial pressure used during the preparation process, on the structure, composition and optoelectronic properties of wide band gap doped microcrystalline silicon oxycarbide films produced by a TCDDC system [1].

Meng, L., Macarico Martins A. R. "Study of annealed indium tin oxide films prepared by rf reactive magnetron sputtering." Materials Research Society Symposium - Proceedings. Vol. 388. 1995. 379-384. Abstract

Tin doped indium oxide (ITO) films were deposited on glass substrates by rf reactive magnetron sputtering using a metallic alloy target (In-Sn, 90-10). The post-deposition annealing has been done for ITO films in air and the effect of annealing temperature on the electrical, optical and structural properties of ITO films was studied. It has been found that the increase of the annealing temperature will improve the film electrical properties. The resistivity of as-deposited film is about 1.3×10-1 Ω* cm and decreases down to 6.9×10-3 Ω* cm as the annealing temperature is increased up to 500°C. In addition, the annealing will also increase the film surface roughness which can improve the efficiency of amorphous silicon solar cells by increasing the amount of light trapping.

Meng, L.-j., Maçarico Martins A. R. "Study of annealed indium tin oxide films prepared by rf reactive magnetron sputtering." Vacuum. 46 (1995): 673-680. AbstractWebsite

Tin doped indium oxide (ITO) films were deposited on glass substrates by rf reactive magnetron sputtering using a metallic alloy target (In-Sn, 90-10). The post-deposition annealing has been done for ITO films in air and the effect of annealing temperature on the electrical, optical and structural properties of ITO films was studied. It has been found that the increase of the annealing temperature will improve the film electrical properties. The resistivity of as deposited film is about 1.3 × 10-1 gW*cm and decreases down to 6.9 × 10-3 Ω*cm as the annealing temperature is increased up to 500 °C. In addition, the annealing will also increase the film surface roughness which can improve the efficiency of amorphous silicon solar cells by increasing the amount of light trapping. © 1995.

1996
b Vieira, M.a, Fantoni Koynov Cruz Maçarico Martins A. a S. a. "Amorphous and microcrystalline silicon p-i-n optical speed sensors based on the flying spot technique." Journal of Non-Crystalline Solids. 198-200 (1996): 1193-1197. AbstractWebsite

From the flying spot technique (FST) the ambipolar diffusion length and the effective-lifetime of the carriers photogenerated by a moving light spot that strikes a p-i-n junction can be inferred. In this paper, those properties of a p-i-n junction are used together with an optical triangulation principle to determine the velocity of an object that is moving in the direction of a light source. The light reflected back from the object is analysed through an amorphous or a microcrystalline p-i-n structure. Its transient transverse photovoltage is dependent on the velocity of the object. A comparison between the performances of both kinds of devices is presented.

Martins, R., Macarico Ferreira Nunes Bicho Fortunato A. I. R. "Correlation between electrical-optical and structural properties of microcrystalline silicon N type films." Materials Research Society Symposium - Proceedings. Vol. 420. 1996. 807-812. Abstract

Wide band gap microcrystalline silicon films have aroused considerable interest since they combine some electro-optical advantages of amorphous and crystalline materials highly important to produce electro-optical devices such as TFTs and solar cells. In this paper we present results concerning the electro-optical characteristics of highly transparent and conductive n-type μc-Si based films. Here, emphasis is given to the production of n-type μc-films with optical gaps of 2.3 eV and dark conductivity's of 6.5 Scm-1.

Topic, M., Smole Furlan Fortunato Martins F. J. E. "Examination of 1-D position sensitive detector performance through analysis of front contact heterojunction." Materials Research Society Symposium - Proceedings. Vol. 420. 1996. 171-176. Abstract

The influence of different TCOs (SnO2 and ITO) on the photoelectrical properties of 1-D position sensitive detectors based on p-i-n structures was studied. A strong cross-contamination in the p-layer and contamination in the i-layer reduce the quality of the device. Numerical analysis of TCO/p-i-n structure also revealed a strong increase in defect states at the p-layer surface which can be attributed to the reduction of TCO. ITO seems to be less appropriate for a front TCO, although the spectral response of the p-i-n structure under reverse bias is not significantly affected by the conditions at the TCO/p heterojunction.

Fortunato, Elvira, Lavareda Guilherme Martins Rodrigo Soares Fernando Fernandes Luis. "From intelligent materials to smart sensors." Proceedings of SPIE - The International Society for Optical Engineering. Vol. 2779. 1996. 269-274. Abstract

A 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 3D inspections/measurements. Each element consists on a 1D 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 will be 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).

Fortunato, E., Fernandes Soares Lavareda Martins M. F. G. "From intelligent materials to smart sensors: a-Si:H position sensitive detectors." Materials Research Society Symposium - Proceedings. Vol. 420. 1996. 165-170. Abstract

This work presents the main static and dynamic performances showed by one dimensional thin film position sensitive detectors (1D TFPSD), based on a-Si:H technology, with a size of 80 mm × 5 mm. The results obtained show that the TFPSD is able to respond to light powers as low as 2μ W/cm2, presenting a detection accuracy, linearity and response frequency better than 10 μm, 2% and 2 KHz, respectively. These results are quite promising regarding the application of these sensors to a wide variety of optical inspection systems where continuous quality control is required.

Lavareda, G., Fortunato Carvalho C.Nunes Martins E. R. "Improved a-Si:H TFT performance using a-Six-Ni1-x/a-SixC1-x stack dielectrics." Materials Research Society Symposium - Proceedings. Vol. 424. 1996. 59-64. Abstract

In this paper we present a study on the electrical characteristics (conductivity, σ and relative dielectric constant, εr) of amorphous silicon nitride (a-SixN1-x) and carbide (a-SixC1-x) films deposited by PECVD, used as dielectric materials in TFT devices, aiming to select the most adequate alloy that lead to improve device performances. Besides that, double stack a-SixN1-x/a-SixC1-x structures were developed and applied as dielectric layers on TFTs, whose performances show to be superior to those ones using single silicon nitride or silicon carbide as dielectric.

de Nunes de Carvalho, C., Nijs Ferreira Fortunato Martins J. M. M. I. "Improvement of the ITO-p interface in a-Si:H solar cells using a thin SiO intermediate layer." Materials Research Society Symposium - Proceedings. Vol. 420. 1996. 861-865. Abstract

The use of ITO thin films on glass/ITO/p-i-n/metal amorphous silicon solar cells is reviewed. It is suggested a new application for silicon monoxide thin films on the ITO-p interface, as an intermediate layer, to minimize the ITO thin film deterioration process, during the early stage of exposure to a silane plasma rich in hydrogen. The thickness of the silicon monoxide thin films is chosen not to worsen the optical and electrical properties of the ITO thin films. The ITO-p interface is optimized (due to impurities diffusion decrease), leading to an overall improvement of the device performance.

dede Carvalho, C.Nunes, Nijs Ferreira Fortunato Martins J. M. M. I. "Improvement of the ITO-P interface in a-Si:H solar cells using a thin SiO intermediate layer." Materials Research Society Symposium - Proceedings. Vol. 426. 1996. 25-29. Abstract

The use of ITO films on glass/ITO/p-i-n/metal amorphous silicon solar cells is reviewed. It is suggested a new application for silicon monoxide thin films on the ITO-p interface, as an intermediate layer, to minimize the ITO thin film deterioration process, during the early stage of exposure to a silane plasma rich in hydrogen. The thickness of the silicon monoxide thin films is chosen not to worsen the optical and electrical properties of the ITO thin films. The ITO-p interface is optimized (due to impurities diffusion decrease), leading to an overall improvement of the device performance.

Martins, R.F.P., Fortunato E. M. C. "Interpretation of the static and dynamic characteristics of 1-D thin film position sensitive detectors based on a-Si:H p-i-n Diodes." IEEE Transactions on Electron Devices. 43 (1996): 2143-2152. AbstractWebsite

In this work, we present a model to interpret the steady-state and the dynamic detection limits of 1-D Thin Film Position Sensitive Detectors (1-D TFPSD) based on p-i-n a-Si:H devices. From this, an equivalent electric circuit is derived and the predicted values are compared with the experimental results obtained in 1-D TFPSD devices, with different sizes. The model is also able to determine the device characteristics that influence the spatial limits and the response time of the device. © 1996 IEEE.

Martins, R., Fortunato E. "Lateral effects in amorphous silicon photodiodes." Optical Materials. 5 (1996): 137-144. AbstractWebsite

The objective of this work is to provide a basis for the interpretation of the a-Si:H photodiode behaviour under low illumination level conditions, where a lateral leakage current plays an important role on the devices' performances when the doped collecting layer can not be considered a true equipotential. To determine this effect, a-Si:H p.i.n devices with small metal dot contacts, matrix distributed, were produced and analysed before and after etching the surrounding doped region of the metal collecting contact. The experimental data fit a model that includes the contribution of a lateral leakage current influencing the J-V characteristics, responsivity and the apparent light degradation behaviour of the device.

Fortunato, E., Soares Lavareda Martins F. G. R. "A linear array thin film position sensitive detector for 3D measurements." Journal of Non-Crystalline Solids. 198-200 (1996): 1212-1216. AbstractWebsite

A novel compact linear thin film position sensitive detector with 128 elements, based on p-i-n a-Si:H devices was developed. The proper incorporation of this sensor into an optical inspection camera makes possible the acquisition of three dimension information of an object, using laser triangulation methods. The main advantages of this system, when compared with the conventional charge-coupled devices, are the low complexity of hardware and software used and that the information can be continuously processed (analogue detection).

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. AbstractWebsite

Results 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.

Courteille, C.a, Hollenstein Ch.a Dorier Gay Schwarzenbach Howling Bertran Viera Martins Macarico J. - L. a. "Particle agglomeration study in in silane plasmas: In situ study by polarization-sensitive laser light scattering." Journal of Applied Physics. 80 (1996): 2069-2078. AbstractWebsite

To determine self-consistently the time evolution of particle size and their number density in situ multi-angle polarization-sensitive laser light scattering was used. Cross-polarization intensities (incident and scattered light intensities with opposite polarization) measured at 135° and ex situ transmission electronic microscopy analysis demonstrate the existence of nonspherical agglomerates during the early phase of agglomeration. Later in the particle time development both techniques reveal spherical particles again. The presence of strong cross-polarization intensities is accompanied by low-frequency instabilities detected on the scattered light intensities and plasma emission. It is found that the particle radius and particle number density during the agglomeration phase can be well described by the Brownian free molecule coagulation model. Application of this neutral particle coagulation model is justified by calculation of the particle charge whereby it is shown that particles of a few tens of nanometer can be considered as neutral under our experimental conditions. The measured particle dispersion can be well described by a Brownian free molecule coagulation model including a log-normal particle size distribution. © 1996 American Institute of Physics.

Fortunato, E., Lavareda Scares Martins G. F. R. "Performances presented by large-area thin film position-sensitive detectors based on amorphous silicon." Thin Solid Films. 272 (1996): 148-156. AbstractWebsite

This paper presents a low-cost technology for the realisation of large-area thin film position-sensitive detectors using the a-Si:H technology. The obtained results are quite promising regarding the application of these sensors to a wide variety of optical inspection systems, such as: machine tool alignment and control; angle measuring; rotation monitoring; surface profiling; medical instrumentation; targeting; remote optical alignment; guidance systems; etc., to which automated inspection control is needed.

Fortunato, E., Martins R. "Role of the collecting resistive layer on the static characteristics of a 1D a-Si:H thin film position sensitive detector." Review of Scientific Instruments. 67 (1996): 2702-2707. AbstractWebsite

The aim of this work is to present an analytical model able to interpret the role of the thin collecting resistive layer on the static performances exhibited by 1D amorphous silicon hydrogenated p-i-n thin film position sensitive detectors. The data obtained show that the devices present a linearity and a spatial resolution, of respectively, better than 99% and 20 μm for a spatial detection limit of about 80 mm, highly dependent on the characteristics exhibited by the collecting resistive layer that should have sheet resistivities in the range of 10 to 103 Ω/sq, as predicted by the model proposed. © 1996 American Institute of Physics.

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. AbstractWebsite

The 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.

Martins, R.a, Vieira Ferreira Fortunato Guimarães M. b I. a. "Transport properties of doped silicon oxycarbide microcrystalline films produced by spatial separation techniques." Solar Energy Materials and Solar Cells. 41-42 (1996): 493-517. AbstractWebsite

This paper presents results of the role of the oxygen partial pressure used during the deposition process on the transport properties exhibited by doped microcrystalline silicon oxycarbide films produced by a Two Consecutive Decomposition and Deposition Chamber system, where a spatial separation between the plasma and the growth regions is achieved. This paper also presents the interpretative models of the optoelectronic behaviour observed in these films (highly conductive and transparent with suitable properties for optoelectronic applications) as well as the interpretation of the growth process that leads to film's microcrystallization.

Fantoni, A.a, Vieira Cruz Schwarz Martins M. a J. a. "A two-dimensional numerical simulation of a non-uniformly illuminated amorphous silicon solar cell." Journal of Physics D: Applied Physics. 29 (1996): 3154-3159. AbstractWebsite

We present here a two-dimensional numerical simulation of a hydrogenated amorphous silicon p-i-n solar cell non-uniformly illuminated through the p-layer. This simulation is used to show the effect of the presence of dark regions in the illuminated surface on the electrical behaviour of the device. The continuity equations for holes and electrons together with Poisson's equation, implemented with a recombination mechanism reflecting the amorphous structure of the material, are solved using standard numerical techniques over a rectangular domain. The results obtained reveal the appearance of a lateral component of the electric field and current density vectors inside the structure. The effect of such components is a lateral carrier flow of electrons inside the intrinsic layer and of holes inside the p-layer, resulting in leakage of the transverse current collected at the contacts and an increase in the series resistance.

1997
Topič, M.a, Smole Furlan Fortunato Martins F. a J. a. "Analysis of front contact heterojunction in a-Si:H one-dimensional position sensitive detectors." Review of Scientific Instruments. 68 (1997): 1377-1381. AbstractWebsite

The influence of different transparent conducting oxides (TCO) on the transverse photoelectrical properties of one-dimensional position sensitive detectors based on p-i-n amorphous silicon structures was studied. For both SnO 2 and indium tin oxide, poor quality of the p layer was revealed by secondary ion mass spectroscopy measurements. Good agreement between experimental and simulation characteristics of TCO/p-i-n structure was additionally conditioned by a strong increase in defect states at the p layer surface which can be attributed to the reduction/ oxidation process at the TCO/p interface. However, the analysis showed that under reverse bias the spectral response of the p-i-n structure is not significantly affected by different TCO layers and conditions at the TCO/p heterojunction. Nevertheless, indium tin oxide is less appropriate for a front TCO layer due to the poor reverse dark current-voltage characteristic, i.e., higher leakage current component leading to lower signal to noise ratio. © 1997 American Institute of Physics.