This study presents annealing experiments conducted on near-stoichiometric hydrogenated amorphous silicon nitride (a-SiNx:H) thin films deposited via Plasma Enhanced Chemical Vapor Deposition. The heat treatment was carried out under an inert atmosphere within a temperature range of 400-1000 degrees C, with increments of 100 degrees C. After each annealing step, a-SiNx:H films were subjected to characterization using visible and FTIR spectros-copies, evaluating their optical and structural properties, as well as hydrogen concentration. The infrared analysis reveals a significant reduction in Si-H bond concentration within the temperature range of 400-700 degrees C, becoming virtually undetectable at higher annealing temperatures. Conversely, the N-H bond concentration primarily decreases at elevated temperatures, persisting at 23% of its initial value at 1000 degrees C. Optical constants were determined from transmittance spectra using a dispersion model that combines two unbounded Tauc-Lorentz oscillators. The refractive index experiences an increase up to 600 degrees C due to material densification, followed by a decrease at higher temperatures attributed to optical gap widening. Dispersion curves of the extinction coefficient reveal a wide sub-gap absorption band, which vanishes after a 900 degrees C annealing step, rendering the material suitable for waveguide applications.

This article reports on blue-enhanced a-Si:H-based n-i-p photodiodes with protocrystalline silicon (pc-Si:H) players by plasma-enhanced chemical vapor deposition. Microstructure of p-layers was studied by Raman spectroscopy. An optical model has been developed to analyze the device performance. The Transfer Matrix Method was applied to simulate light propagation in the glass/Cr/n-i-p/ZnO:Al stack, while modified Tauc-Lorentz model including the Urbach tail was used to obtain the dispersive optical constants for each semiconductor layer. Two photodiodes with a-Si:H and pc-Si:H p-layers were fabricated, characterized, and modeled for comparison. The deduced optical gaps are 1.8 and 2.33 eV for p-type a-Si:H and pc-Si:H, respectively. Observed band gap widening is the quantum confinement effect due to Si nanocrystals in pc-Si:H. Modeling reveals that incorporation of pc-Si:H leads to a significant reduction of absorption and reflection losses. The optimized heterojunction photodiode exhibits a quantum efficiency up to 92% at 510 nm wavelength. The achieved quantum efficiency of 66% at 400 nm wavelength almost triples that for the homojunction photodiode.

This work reports on undoped and Sn-doped indium sulfofluoride thin-films deposited by radio-frequency plasma-enhanced reactive thermal evaporation. The deposition was performed evaporating pure indium or indium-tin alloy in SF6 plasma at substrate temperatures ranging from 373 to 423 K. Rutherford backscattering analysis and secondary-ion mass spectrometry were used to determine the chemical composition of the films. The film characterization includes electrical, optical, and photoconductivity measurements. The resistivity of undoped material varies in a wide range of 1 G Omega-cm to 2 T Omega-cm depending on deposition conditions. Sn doping leads to a decrease in the resistance down to 8 M Omega-cm. The films are highly transparent in the visible-infrared region due to an indirect bandgap of 2.7-3 eV. Moreover, the doped material is highly photosensitive in the blue -UV region. Photoconductivity kinetics under various excitation conditions was also studied. The synthesized material is a promising candidate for a buffer layer in chalcogenide-based solar cells.

a-SiCN:H thin films were deposited at 150°C by PECVD using silane, methane and ammonia as precursor gases, with a SiH4:H2 dilution of 1:9. RBS and ERDA were used for determining material composition. The concentration of silicon, carbon and nitrogen in the deposited films was correlated with the respective precursor gas concentration and the incorporation yield of each atomic species was determined and related to the molecular bond energies of precursor gases. Chemical bonding type and density determined by FTIR were also related to the chemical composition of the films. Optical transmission was measured to estimate the optical gap (Eop) and refractive index (n) in the transparent region. Stoichiometric a-SiN has the lowest n (1.74) and highest Eop (4.12 eV) while a-Si:H presents the highest n (3.37) and lowest Eop (1.85 eV). A trade-off between the Eop and n is presented to show the applicability of this ternary material in optical devices.

This work reports on low temperature deposition of conducing indium oxide films by a radio-frequency plasma enhanced reactive thermal evaporation (rf-PERTE) technique. The films were deposited on polyethylene terephthalate (PET) without intentional heating of the substrate and at elevated temperatures up to 150 degrees C. The material stoichiometry was accurately controlled by adjusting deposition conditions including the oxygen flow, process pressure, pumping speed, and RF-power. Besides, fine turning of the critical deposition parameters during the deposition was implemented by measuring the variation of film conductance in-situ. The film morphology was analyzed by scanning electron microscopy. Hall effect measurements were also performed to determine the relation between the deposition conditions and the electrical properties of the films. A resistivity of 4 x 10(-4) Omega-cm was reached under optimized deposition conditions. A 250 nm-thick coating with 16 Omega/sq sheet resistance shows an 82% peak value of transmittance in the visible spectral range.

The structure and electrical properties of transparent indium-oxide thin films produced by plasma-enhanced reactive thermal evaporation at different substrate temperatures are studied. It is found that the films have a grained structure. An increase in the substrate temperature yields a considerable increase in the conductivity of the films and a decrease in the photoconductivity-relaxation time. An interpretation of the effect of the substrate temperature on the observed changes in the electrical and photoelectric properties of the indium-oxide films under study is proposed.

This paper reports about a study of the local plasmonic resonance (LSPR) produced by metal nanoparticles embedded in a dielectric or semiconductor matrix. It is presented an analysis of the LSPR for different nanoparticle metals, shapes, and embedding media composition. Metals of interest for nanoparticle composition are Aluminum and Gold. Shapes of interest are nanospheres and nanotriangles. We study in this work the optical properties of metal nanoparticles diluted in water or embedded in amorphous silicon, ITO and ZnO as a function of size, aspect-ratio and metal type. Following the analysis based on the exact solution of the Mie theory and DDSCAT numerical simulations, it is presented a comparison with experimental measurements realized with arrays of metal nanospheres. Simulations are also compared with the LSPR produced by gold nanotriangles (Au NTs) that were chemically produced and characterized by microscope and optical measurements.

This work reports on transparent semiconducting indium sulfide fluoride (ISF) thin-films exhibiting high sensitivity to ultraviolet radiation. The films were deposited on fused silica and silicon substrates using a radiofrequency plasma-enhanced reactive thermal evaporation system. The deposition was performed evaporating pure indium in SF6 plasma at a substrate temperature of 423 K. Rutherford backscattering measurements were used to determine the chemical composition of the films deposited on silicon substrates. The surface morphology was studied using scanning electron microscopy technique. The film characterization includes electrical, optical, and photoconductivity measurements. The synthesized compound is highly-resistive (similar to 700 M Omega-cm at 300 K) and exhibits an evident semiconducting behavior. The activation energy of 0.88 eV is deduced from the temperature dependence of electrical resistivity. The indirect band energy gap of 2.8 eV is determined from transmittance spectra of the ISF films. The photoconductivity band is centered at 345 nm wavelength. The photoconductivity spectrum also shows the Urbach tail with a characteristic energy of 166 meV. ISF is a promising candidate for a buffer layer in chalcogenide-based solar cells.

AbstractThe structure and electrical properties of transparent indium-oxide thin films produced by plasma-enhanced reactive thermal evaporation at different substrate temperatures are studied. It is found that the films have a grained structure. An increase in the substrate temperature yields a considerable increase in the conductivity of the films and a decrease in the photoconductivity-relaxation time. An interpretation of the effect of the substrate temperature on the observed changes in the electrical and photoelectric properties of the indium-oxide films under study is proposed.

In this research we present a Visible Light Communication (VLC) system for indoor positioning and navigation. The viability of this methodology was demonstrated in previous work for indoor positioning within the unit navigation cell. In this paper it is proposed to extend this concept for navigation in wider spaces that demand more than one navigation unit. The proposed system uses white RGB LEDs of wide divergence angle and a specific photodetector dedicated to the selective wavelengths detection of red, green and blue light. The photodetector is a multilayered pin-pin heterostructure based on a-SiC: H/a-Si: H, such that the spectral sensitivity can be controlled externally by steady state background light. The RGB emitters of the white LED were modulated with specific bit sequences and frequency to assign different optical excitations to each spatial region. The measurement of the induced photocurrent signal by the detector allows the identification of the position. For this purpose the decoding algorithm for the photocurrent signal processing uses the filtering properties of the photodetector for the recognition of the navigation cell word code, and detection of the wavelength and Fourier analysis for recognition of the signal frequency.

We propose the development and realization of a plasmonic structure based on the LSP interaction of metal nanoparticles with an embedding matrix of amorphous silicon. This structure need to be usable as the basis for a sensor device applied in biomedical applications, after proper functionalization with selective antibodies. The final sensor structure needs to be low cost, compact and disposable. The study reported in this paper aims to analyze different materials for nanoparticles and embedding medium composition. Metals of interest for nanoparticles composition are Aluminum, Gold and Alumina. As a preliminary approach to this device, we study in this work the optical properties of metal nanoparticles embedded in an amorphous silicon matrix, as a function of size, aspect-ratio and metal type. Following an analysis based on the exact solution of the Mie theory, experimental measurements realized with arrays of metal nanoparticles are compared with the simulations.

In this work we present a fully automated plasma-enhanced reactive thermal evaporation system (rf-PERTE) that can be used for the deposition of transparent metal oxide films without intentional heating of the substrate. The system and developed software enables the full control over critical deposition conditions such as mass flow of oxygen, process pressure, current flowing through crucible and rf-power. These parameters are automatically adjusted during the deposition thus keeping them in a narrow process window. This way, highly transparent and conductive coating can be deposited with a high degree of reproducibility of the optical and electrical characteristics. The resistivity of 9×10-4 Ω-cm and the peak transmittance of 90% in the visible spectral range were achieved for indium oxide films deposited on glass substrates. This technique is also suitable for the deposition of transparent conducting coatings in a wide range of plastic materials for flexible solar cells. In particular, we have successfully deposited indium oxide on PEN (polyethylene naphthalate) sheets with electrical and optical properties approaching the ones for films on glass.

This paper reports on device-quality silicon-carbon alloy (a-SiC:H) application as an absorber material in semi-transparent solar cells. Films with an optical bandgap ranging from 2 to 2.3 eV were prepared by plasma enhanced chemical vapour deposition (PECVD). The n-i-p structures with undoped SiC:H layers deposited under the same experimental conditions were also fabricated and characterized. The optimized devices showed forward current-voltage characteristics with a diode ideality factor in the range from 1.4 to 1.8, and an open circuit voltage up to 0.92 V. The density of deep defect states in a SiC:H was estimated from the transient current measurements and correlated with the optical bandgap.

This work reports a theoretical study aimed to identify the plasmonic resonance condition for a system formed by metallic nanoparticles embedded in an a-Si:H matrix. The study is based on a Tauc-Lorentz model for the electrical permittivity of a-Si:H and a Drude model for the metallic nanoparticles. It is calculated the The polarizability of an sphere and ellipsoidal shaped metal nanoparticles with radius of 20 nm. We also performed FDTD simulations of light propagation inside this structure reporting a comparison among the effects caused by a single nanoparticles of Aluminium, Silver and, as a comparison, an ideally perfectly conductor. The simulation results shows that is possible to obtain a plasmonic resonance in the red part of the spectrum (600-700 nm) when 20-30 nm radius Aluminium ellipsoids are embedded into a-Si:H.

This article reports on characterization of hydrogenated amorphous silicon (a-Si:H) photovoltaic modules fabricated on 100μm thick PEN plastic films. Experimental results show that the shunt leakage is one of the factors reducing the device performance. Current-voltage characteristics of individual a-Si:H p-i-n cells were analysed to estimate a variation of shunt resistances. A SPICE model of the a-Si:H p-i-n cell with local shunt leakage was also developed to analyse the impact of leakage currents on the device performance. Using the LBIC technique, the presence of multiple shunts in the cell was detected. They are attributed to surface defects in plastic foils, which are thermally induced during the device fabrication.

Conventional film based X-ray imaging systems are being replaced by their digital equivalents. Different approaches are being followed by considering direct or indirect conversion, with the later technique dominating. The typical, indirect conversion, X-ray panel detector uses a phosphor for X-ray conversion coupled to a large area array of amorphous silicon based optical sensors and a couple of switching thin film transistors (TFT). The pixel information can then be readout by switching the correspondent line and column transistors, routing the signal to an external amplifier.In this work we follow an alternative approach, where the electrical switching performed by the TFT is replaced by optical scanning using a low power laser beam and a sensing/switching PINPIN structure, thus resulting in a simpler device.The optically active device is a PINPIN array, sharing both front and back electrical contacts, deposited over a glass substrate. During X-ray exposure, each sensing side photodiode collects photons generated by the scintillator screen (560 nm), charging its internal capacitance. Subsequently a laser beam (445 nm) scans the switching diodes (back side) retrieving the stored charge in a sequential way, reconstructing the image.In this paper we present recent work on the optoelectronic characterization of the PINPIN structure to be incorporated in the X-ray image sensor. The results from the optoelectronic characterization of the device and the dependence on scanning beam parameters are presented and discussed. Preliminary results of line scans are also presented. (C) 2014 Elsevier B.V. All rights reserved.

Solar cells on lightweight and flexible substrates have advantages over glass- or wafer-based photovoltaic devices in both terrestrial and space applications. Here, we report on development of amorphous silicon thin film photovoltaic modules fabricated at maximum deposition temperature of 150 °C on 100 μm thick polyethylene-naphtalate plastic films. Each module of 10 cm × 10 cm area consists of 72 a-Si:H n-i-p rectangular structures with transparent conducting oxide top electrodes with Al fingers and metal back electrodes deposited through the shadow masks. Individual structures are connected in series forming eight rows with connection ports provided for external blocking diodes. The design optimization and device performance analysis are performed using a developed SPICE model.

This paper reports a fully automated plasma-enhanced plasma chemical vapor deposition (PECVD) system for thin-film deposition. This system can be used for the deposition of hydrogenated amorphous silicon (a-Si:H) and nanocrystalline silicon for devices like solar cells or optical sensors with good film homogeneity and material properties reproducibility. The control software enables two modes of system operation: semi-manual and full-auto. In the semi-manual mode the user sets all process parameters and controls all depositions steps. In the full-auto mode, the program performs the process steps according to script commands in a recipe file. This way, complex multilayered devices can be fabricated, with a high degree of reproducibility of the device characteristics.

This article reports on amorphous silicon solar cells on plastic foils in the substrate configuration having a front metal grid. A two-dimensional distributed circuit model of the photovoltaic cell has been developed for performance analysis and device design optimization. The circuit simulator SPICE is used to calculate current and potential distributions in a network of sub-cell circuits. This approach enables a realistic device model that predicts output current-voltage characteristics and maps Joule losses in the TCO electrode and the metal grid. As an example of usage, the optimization of contact grid geometry at various TCO sheet resistances has been performed.