Rodrigo Martins

This work deals with the study of the role of intra-gap density of states on the colour selection of the collection spectrum of glass/ITO/a-Six:C1-x:H/Al Schottky photodiodes. In order to optimise the voltage colour selection and to study the influence of intragap density of states in the final device performances, different undoped a-Six:C1-x:H films (1 μm thick) have been produced in a conventional Plasma Enhanced Chemical Vapour Deposition (PECVD) system using silane and a controlled mixtures of silane and methane as gas sources. The properties of the films were analysed by dark conductivity measurements, infrared spectroscopy, visible spectroscopy and constant photocurrent method (CPM), to determine the valence controllability and to correlate the silicon carbide layer composition with the performances of the devices. The performances obtained concerning the spectral response of the devices were correlated with the carbon content and the density of states of the a-Six:C1-x:H films.

This paper presents the role of the deposition pressure and the rf power density on the optimization of the electrical, optical and structural properties of large area (30×40 cm2) indium-tin oxide films produced by rf magnetron sputtering, with growth rates exceeding 30 nm/min. The films were produced at room temperature under reactive plasma, followed by a thermal annealing in air or formic gas. The best films' uniformity (≤±5%), compactness and surface smoothness (preferential growth orientation along (222)); and electro-optical properties (resistivity and mobility, respectively, of about 7×10-4 Ω cm and 19.6 cm2 V -1 s-1, with transmittance of about 92%) were achieved using a rf power density of 0.92 W cm-2 and a pressure of 8.5×10-2 Pa, followed by its annealing in air by about 2 h at 773 K. © 2005 Elsevier B.V. All rights reserved.

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.

In this paper we present results concerning the influence of laser energy and shot density on the electrical resistance, X-ray diffraction pattern, and structure obtained by SEM, on recrystallized a-Si:H thin films produced by using a Nd-YAG laser, working in a wavelength of 532 nm. The base material (undoped and doped a-Si:H) was obtained by Plasma Enhanced Chemical Vapour Deposition (PECVD). The structure and electrical characteristics of the recrystallized thin films are dependent on the laser beam energy density, beam spot size and the number of shots applied to the base a-Si:H thin film used. Overall, the data show recrystallized material with grain sizes larger than 1μm, where the electrical resistance of both, undoped and doped materials, can be varied up to 5 orders of magnitude, by the proper choice of the recrystallization conditions.

Reduction in the accumulation capacitance value was more in Si metal-oxide-semiconductor devices than that of Ge metal-oxide-semiconductor devices after a thermal treatment irrespective of the annealing environment. Relatively, thermal treatment in oxygen environment improves the interface quality of HfO2/Ge stacks considerably, when compared with HfO 2/Si stacks. Whereas, the forming gas annealing at a temperature of 400 °C was not so effective in improving the interface quality at HfO 2/Si stack. The presence of induced negatively charged hydrogen atom in Ge lessens the Fermi level pinning at HfO2 and Ge interface. © 2011 Elsevier B.V. All rights reserved.

Doped zinc oxide with aluminium are attractive alternative material as transparent conducting electrode because they are nontoxic and inexpensive compared with indium tin oxide (ITO) for diffrent applications: solar cells, tft. Transparent aluminumdoped zinc oxide (AZO) thin films were deposited on glass substrates by RF magnetron sputtering at room temperature and 100W from ceramic target ZnO-Al2O3 (98:2 weight percent). The structural, electrical and optical properties of these films were characterized as a function of deposition pressure. AZO films with low resistivity 2.02×10-3 Ωcm and high transmittance (over 80% in vizible range) were thus prepared with a deposition pressure of 3 mTorr.

AMATLAB/SIMULINK software simulation model (structure and component blocks) has been constructed in order to view and analyze the potential of the PSD (Position Sensitive Detector) array concept technology before it is further expanded or developed. This simulation allows changing most of its parameters, such as the number of elements in the PSD array, the direction of vision, the viewing/scanning angle, the object rotation, translation, sample/scan/simulation time, etc. In addition, results show for the first time the possibility of scanning an object in 3D when using an a-Si:H thin film 128 PSD array sensor and hardware/software system. Moreover, this sensor technology is able to perform these scans and render 3D objects at high speeds and high resolutions when using a sheet-of-light laser within a triangulation platform. As shown by the simulation, a substantial enhancement in 3D object profile image quality and realism can be achieved by increasing the number of elements of the PSD array sensor as well as by achieving an optimal position response from the sensor since clearly the definition of the 3D object profile depends on the correct and accurate position response of each detector as well as on the size of the PSD array. © 2015 by the authors; licensee MDPI, Basel, Switzerland.

The movement of a micro cantilever was detected via a self constructed portable data acquisition prototype system which integrates a linear array of 32 1D amorphous silicon position sensitive detectors (PSD). The system was mounted on a microscope using a metal structure platform and the movement of the 30 μm wide by 400 μm long cantilever was tracked by analyzing the signals acquired by the 32 sensor array electronic readout system and the relevant data algorithm. The obtained results show a linear behavior of the photocurrent relating X and Y movement, with a non-linearity of about 3%, a spatial resolution of less than 2μm along the lateral dimension of the sensor as well as of less than 3μm along the perpendicular dimension of the sensor, when detecting just the micro-cantilever, and a spatial resolution of less than 1μm when detecting the holding structure. © 2010 by the authors.

A 32/128 linear array of 1-D amorphous silicon position sensitive detectors (PSD) was integrated into a self constructed suitable and portable data acquisition prototype system. The system is comprised by a commercially available existing electronics module suitable for photodiode data acquisition operations and by another adapter module, which allows for removal and replacement of the 32/128 PSD based sensor. This system is applied for imaging 3-D objects using the triangulation principle with a sheet-of-light laser. The sensor array response obtained from the reflected light of the object was fed into an electronic readout system and the corresponding signals were analyzed using the relevant data algorithm. The obtained results show a sensor nonlinearity of about 4%-7%, a wide sensor/system dynamic range and a 3-D profile spatial resolution supplied by each sensor strip of 339 μm, which can easily be reduced to 8.5 μm and even further with appropriate software modifications. © 2011 IEEE.

The position of a 40 μm wide by 400 μm long cantilever in a microscope was detected by a 32 lines array of 1D amorphous silicon position sensitive detectors (PSD). The sensor was placed in the ocular used for the CCD camera of a microscope and the alignment, focusing and positioning of the cantilever was achieved using the X-Y-Z translation table of the microscope that has a micrometer resolution controller. In this work we present results concerning the micro positioning of a cantilever and its holding structure through the reflected light that is detected by 1D/3D psd and converted to an analog signal proportional to the movement. The signal given by the 32 sensor array was analyzed directly without any electronic readout system or data algorithm. The obtained results show a linear behavior of the photovoltage relating X and Y movement, a non-linearity less than 2% and spatial resolution of 600 μV/μm. © 2006 Elsevier B.V. All rights reserved.

The color sensing ability of a data acquisition prototype system integrating a 32 linear array of 1D amorphous silicon position sensitive detectors (PSD) was analyzed. Besides being used to reproduce a 3D profile of highly reflective surfaces, here we show that it can also differentiate primary red, green, blue (RGB) and derived colors. This was realized by using an incident beam with a RGB color combination and adequate integration times taking into account that a color surface mostly reflects its corresponding color. A mean colorimetric error of 25.7 was obtained. Overall, we show that color detection is possible via the use of this sensor array system, composed by a simpler amorphous silicon pin junction. © 2013 Elsevier B.V. All rights reserved.

The 3D scanning electro-optical characteristics of a data acquisition prototype system integrating a 32 linear array of 1D amorphous silicon position sensitive detectors (PSD) were analyzed. The system was mounted on a platform for imaging 3D objects using the triangulation principle with a sheet-of-light laser. New obtained results reveal a minimum possible gap or simulated defect detection of approximately 350 μm. Furthermore, a first study of the angle for 3D scanning was also performed, allowing for a broad range of angles to be used in the process. The relationship between the scanning angle of the incident light onto the object and the image displacement distance on the sensor was determined for the first time in this system setup. Rendering of 3D object profiles was performed at a significantly higher number of frames than in the past and was possible for an incident light angle range of 15 ° to 85 °. © 2012 Optical Society of America.

This paper presents a low-offset comparator based on n-type amorphous indium gallium zinc oxide thin-film transistors (TFTs). An a-Si:H TFT model was adapted to fit the electrical characterization data obtained for these devices. The proposed comparator comprises three pre-amplification stages, a positive-feedback analog latch and a fully dynamic digital latch. Simulation results show that the proposed circuit can work at several tens of kHz, with an accuracy of the order of 10 mV, considering a supply voltage of 10 V and a current consumption of 380 μA. Monte-Carlo simulations exhibit a 1-sigma random offset voltage smaller than 10 mV and 40 mV, respectively, with and without using autozeroing techniques. © 2015 IEEE.

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.

Large-area electronics for applications in environments with radioactive contamination or medical X-ray detectors require materials and devices resistant to continuous ionizing radiation exposure. Here the superior X-ray radiation hardness of oxide thin film transistors (TFTs) based on gallium-indium-zinc oxide is demonstrated, when compared to organic ones. In the experiments both TFTs are subjected to X-ray radiation and their performances are monitored as a function of total ionizing dose. Flexible oxide TFTs maintain a constant mobility of 10 cm2 V−1 s−1 even after exposure to doses of 410 krad(SiO2), whereas organic TFTs lose 55% of their transport performance. The exceptional resistance of oxide semiconductors ionization damage is attributed to their intrinsic properties such as independence of transport on long-range order and large heat of formation. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Electrochromic coatings are used in a wide range of technical fields. This paper refers to the properties of amorphous Indium-tin-oxide (ITO) and WO 3 thin films obtained by dc-magnetron reactive sputtering in different oxygen partial pressures (PO2) at room temperature (RT). SEM, XRD and UV-Vis-NIR spectroscopy characterized the films prepared in terms of morphology, structure, and optical and electrical properties. The maximum of the optical transmittance in the visible range for the ITO and WO3 films was above 97% and 98%, respectively. These films were incorporated into ECDs (electrochromic devices) whose performance was assessed by optical methods.

Transparent conductive oxides (TCOs) such as indium tin oxide (ITO) thin films onto glass substrates are widely used as transparent and conductive electrodes for a variety of technological applications including flat panel displays, solar cells, smart windows, touch screens, etc. ITO films on glass and polycarbonate (PC) substrates were prepared at room temperature (RT) and at different PO2. The films were characterized in terms of the surface roughness (δ), sheet resistance, the refractive index (n) and extinction coefficient (k). The free carrier density (nc) and the carrier mobility (μ) of the ITO (In2O3:Sn) films were measured and studied. The nc and μ values vary in different ratio of oxygen partial pressure (PO2) of ITO deposition. The observed changes in the ITO film resistivity are due to the combined effect of different parameter values for nc and μ. From AFM analysis and spectra calculations, the surface roughness values of the ITO films were studied and it was observed that the δ values were lower than 15 nm. The energy band gap Eg ranges from 3.26 eV to 3.66 eV as determined from the absorption spectrum. It was observed an increase on the energy band gap as the PO2 decrease in the range of 20-2% PO2. The Lorentz oscillator classical model has also been used to fit the ellipsometric spectra in order to obtain both refractive index n and extinction coefficient κ values. © 2008 Elsevier Ltd. All rights reserved.

In obtaining uniform array of ZnO 1D nanostructures, especially using solution based methods, the thickness and the morphology of the epitaxial seeds layer are very important. The paper presents the effect of the thickness and the morphology of the Al:ZnO seeds layer on the morphology and properties of ZnO nanowires array grown by hydrothermal method. Compact and vertically aligned ZnO 1D nanostructures were obtained. Concentration of 0.02 M of zinc nitrate was found to be optimal for growing nanowires with diameters up to 50 nm and lengths between 1.5 and 2.5 microns. Using 0.04 M solution, nanorods with diameter between 50 and 100 nm were obtained. The correlation between the crystal structure and optical properties of ZnO nanowires is discussed. From electrical measurements on single nanowire, resistivity value of 9×10?2 cm was obtained. The I-V curves of single ZnO NWs show quasi diode characteristic when an e-beam is irradiating the NWs, and a typical semiconductive behaviour when the e-beam is turned off. Copyright © 2013 American Scientific Publishers.

High conductivity in the off-state and low field-effect mobility compared to bulk properties is widely observed in the p-type thin-film transistors of Cu2O, especially when processed at moderate temperature. This work presents results from in situ conductance measurements at thicknesses from sub-nm to around 250 nm with parallel X-ray photoelectron spectroscopy. An enhanced conductivity at low thickness is explained by the occurrence of Cu(II), which is segregated in the grain boundary and locally causes a conductivity similar to CuO, although the surface of the thick film has Cu2O stoichiometry. Since grains grow with an increasing film thickness, the effect of an apparent oxygen excess is most pronounced in vicinity to the substrate interface. Electrical properties of Cu2O grains are at least partially short-circuited by this effect. The study focuses on properties inherent to copper oxide, although interface effects cannot be ruled out. This non-destructive, bottom-up analysis reveals phenomena which are commonly not observable after device fabrication, but clearly dominate electrical properties of polycrystalline thin films. © 2016 Author(s).

The reduction of aCu2O layer on copper by exposure toTMAduring the atomic layer deposition of Al2O3 has recently been reported. (Gharachorlou et al 2015 ACS Appl. Mater. Interfaces 7 16428-16439). The study presented here analyzes a similar process, leading to the reduction of a homogeneous Cu2O thin film, which allows for additional observations. Angle-resolved in situ X-ray photoelectron spectroscopy confirms the localization of metallic copper at the interface. The evaluation of binding energy shifts reveals the formation of aCu2O/Cu Schottky barrier, which gives rise to Fermi level pinning in Cu2O. An initial enhancement of the ALD growth per cycle (GPC) is only observed for bulk Cu2O samples and is thus related to lattice oxygen, originating from regions lying deeper than just the first few layers of the surface. The oxygen out-take from the substrate is limited to the first few cycles, which is found to be due to a saturated copper reduction, rather than the oxygen diffusion barrier of Al2O3. © 2016 IOP Publishing Ltd.

The aim of the present work was to study the optical properties of amorphous hydrogenated silicon films produced by capacitive and inductive r.f. glow discharge in a 3%SiH4-Ar gas mixture. The effect of the application of static electric and magnetic fields during the film formation on the photoconductivity, photoactivation energy, recombination mechanisms and optical gap was thoroughly investigated. Films prepared in a capacitively or inductively coupled discharge show bias-dependent photoconductivities, which reach about 10-4 Ω-1 cm-1 for an inductive discharge with a negative bias and about 10-5 Ω-1 cm-1 for a capacitive discharge with a positive bias. The optical gap is of the order of 1.55 eV for capacitive films and is bias dependent for inductive films (1.45-1.85 eV). A superimposed magnetic field (of about 1 kG) increases the photoconductivity by one order of magnitude for both deposition methods. The optical gap is field dependent for inductive films (1.6-1.8 eV) and is about 1.6 eV for capacitive films. The main recombination mechanism at a moderate photon flux (less than 1014 cm-2 s-1) is monomolecular for all deposition conditions. The photoactivation energy lies between 0.1 and 0.2 eV for capacitive films and is about 0.1 eV for inductive films. It was also found that, by using suitable crossed electric and magnetic fields, it was possible to control the density and nature of the defect states in the films. These are correlated with the type of hydrogenated silicon species and with the amount of hydrogen incorporated into the films, which markedly influence the film properties. © 1982.

Microcrystalline phosphorus-doped hydrogenated silicon alloy films were deposited in a remote plasma CVD (chemical vapor deposition) system. The film properties were studied as a function of RF power density and hydrogen concentration in the reaction gas mixture. The properties of the deposited films are extremely sensitive to the RF power density in the studied range of 250 mW/cm2 to 625 mW/cm2. Very low values of electrical resistivity were obtained. For an RF power density of 500 mW/cm2, ρ = 3 × 10-2 Ω-cm, while ρ = 1.9 × 103 Ω-cm for 625 mW/cm2, indicating the predominance of the amorphous tissue over the microcrystalline phase. High doping efficiencies which can be correlated to large grain size are indicated by the very low values of the activation energy as low as 30 meV for 500 mW/cm2, that were obtained.

Indium molybdenum oxide (IMO) thin films were radio-frequency (RF) sputtered at room temperature (RT) and studied as a function of base pressure (BP). The crystallinity of the films is decreased with the increase in BP. A maximum mobility (μ) of 49.6 cm 2 V -1 s -1 was obtained from the IMO films deposited at RT without any post-annealing treatment. The electronic behaviour of the deposited films was investigated by temperature-dependent (100-550 K) Hall measurements. Study on the scattering mechanisms based on the experimental data and theoretical models show that the ionized scattering centres are dominating. The films possess wide work function (4.91 eV) and high transmittance (> 70%) over visible and near infrared (NIR) range. The obtained results, especially the high work function and NIR transmittance, are very promising particularly in applications such as optical detectors and solar cells. Copyright © EPLA, 2012.

Thin films of indium molybdenum oxide (IMO) were rf sputtered onto glass substrates at room temperature. The films were studied as a function of sputtering power (ranging 40-180 W) and sputtering time (ranging 2.5-20 min). Thickness of the films found varied between 50-400 nm. The films were characterized for their structural (XRD), electrical (Hall measurements) and optical (Transmittance spectra) properties. XRD studies revealed that the films are amorphous for the sputtering power ≤ 100 W and deposition time ≤ 5 min. All the other films are polycrystalline and the strongest refection along (222) plane showing a preferential orientation. A minimum bulk resistivity of 2.65 × 10-3 Ω-cm and a maximum carrier concentration of 4.16 × 1020 cm-3 have been obtained for the films sputtered at 180 W (10 min). Whereas maximum mobility (19.5 cm2 V-1 s-1) has been obtained for the films sputtered at 80 W (10 min). A maximum visible transmittance of 90% (500 nm) has been obtained for the films sputtered at 80 W (10 min) with a minimum of 27% for those sputtered at 180 W. The optical band gap of the films found varying between 3.75 and 3.90 eV for various sputtering parameters. © 2006 Materials Research Society.

Indium molybdenum oxide thin films radio-frequency sputtered at room temperature on glass were studied as a function of oxygen volume percentage. The as-deposited films were post-annealed in the temperature range of 300-500 °C in oxidizing (open air) and reducing (N2:H2 gas) atmospheres for 1 h. The as-deposited amorphous films become crystalline on post-annealing irrespective of the annealing conditions. In most cases, the (2 2 2) diffraction line is emerged as the high intensive peak. The films annealed at ≥400 °C in N2:H2 show a carrier concentration >1020 cm-3. The better electrical properties are obtained for the films post-annealed at 300 °C. The optical transmittance of the as-deposited films varies between 10% and 85% depending on the deposition and annealing conditions. Atomic force microscope analysis reveal that the films annealed at 300 °C are composed of closely packed crystallites (size of which varies between 5 nm and 150 nm) whose size varies noticeably when the annealing temperature is raised to 400 °C. On the other hand, the surface of the films annealed at 500 °C becomes rougher, with the RMS roughness varying between 2.00 nm and 16.97 nm. The surface of the films deposited in the presence of oxygen shows metal like features when annealed at ≥400 °C in N2:H2 that is attributed to the segregation of indium. Further, the segregation of In is substantiated from the scanning electron microscope analysis of these samples. © 2008 Elsevier B.V. All rights reserved.