We introduce a novel method for the analysis of the dependence of the optical parameters of Hydrogenated Silicon-rich Carbide (SRC:H) on the alloy composition by using a ternary-3D diagram. The SRC:H samples were fabricated using the very high frequency (VHF) plasma enhanced chemical vapour deposition technique. The composition is given as Si-% + C-% + H-% = 100, with the carbon fraction C-f = C%AC% + Si%) varying between 0.18 and 0.72. The actual composition was determined by Rutherford Back Scattering analysis. The optical constants are determined by means of Reflectance and Transmittance UV-visible spectroscopy, and are modelled by means of the Jellison-Tauc-Lorentz-with Gaussian Band Tail model. The unique properties of the ternary-3D diagram give unexpected insight on the origin of the dependence of optical properties on composition. It is shown that the wavelength position of the Lorentz oscillator is governed by Cf with virtually no influence of H-%. Conversely, the refractive index is strongly affected by H-%, besides C-f. We show that using the ternary-3D diagram approach it is possible to separate the contributions of the different components, and derive the analytical dependence between optical parameters and composition. In the second part of the paper such findings are used for a reversed analysis, that is, we employ the obtained analytical formulations in order to retrieve the SRC:H composition within better than +/- 4% absolute error for all components.

This paper reports on the structural evolution of the silicon–rich SiC/c–Si interface upon 1100°C, 30min thermal treatment, which is typically used when fabricating c–Si based devices that incorporate Si–nanocrystals in an SiC matrix. The onset of local interfacial epitaxy is revealed and analyzed. The inhibitory effect of a thin SiC interfacial buffer layer is reported. The investigation is based on Transmission Electron Microscopy and UV–Visible Reflectance spectroscopy. We show that a minimum thickness is required for the SiC buffer layer to preserve the presence and quality of the interface. The investigation also indicates that the epitaxial regrowth occurs in competition with random nucleation, which turns out to be the dominant crystallization mechanism in silicon rich SiC. A value 3÷10nm is given for the diffusion distance of carbon in silicon upon 1100°C, 30min thermal treatment, which confirms previously reported results. The investigation shows that qualitative as well as quantitative structural information can be rapidly and routinely obtained by careful analysis of UV–Visible Reflectance spectral data.

The use of graphene as transparent conducting layer in devices that require high temperature processing is proposed. The material shows stability upon thermal treatments up to 1100°C if capped with a sacrificial silicon layer. The use of Cu foil or evaporated Cu as catalysts in Catalytic-Chemical Vapor Deposition growth gives rise to graphene of similar properties, which represents a promising result in view of its direct integration in microelectronic devices. Photovoltaic p–i–n thin film devices were fabricated on the as-deposited or annealed graphene membranes and compared with similar devices that incorporate as-deposited Indium Tin Oxide. No degradation in series resistance is observed for the annealed device. A 3.7% and 2.8% photovoltaic conversion efficiency is observed on the devices fabricated on as-transferred and on annealed graphene respectively. The major limitation derives from the high sheet resistance of the as-transferred state-of-the-art material. The results opens the way to the use of graphene in applications that require transparent conducting layers resistant to high temperature processing.

Thermally treated silicon rich oxides (SRO) used as starting material for the fabrication of silicon nanodots represent the basis of tunable bandgap nanostructured materials for optoelectronic and photonic applications. The optical modelization of such materials is of great interest, as it allows the simulation of reflectance and transmittance (R&T) spectra, which is a powerful non destructive tool in the determination of phase modifications (clustering, precipitation of new phases, crystallization) upon thermal treatments. In this paper, we study the optical properties of a variety of as-deposited and furnace annealed SRO materials. The different phases are treated by means of the effective medium approximation. Upon annealing at low temperature, R&T spectra show the precipitation of amorphous silicon nanoparticles, while the crystallization occurring at temperatures higher than 1000 degrees C is also clearly identified, in agreement with structural results. The existing literature on the optical properties of the silicon nanocrystals is reviewed, with attention on the specificity of the compositional and structural characteristics of the involved material.

Amorphous silicon solar cells were deposited on porcelain stoneware tiles in order to develop a fully integrated PV building element. In a previous work we demonstrated the feasibility of adopting porcelain stoneware tiles as thin-film solar cell substrates and we fabricated 1×1cm2 solar cells on “industrial-level” ceramic substrates showing more than 4% efficiency. In this study we focus our attention on larger area (7cm2) devices deposited on 100cm2 tiles. As the active area increases additional problems arise from the surface of the substrate. In particular we find that short-circuit paths originate from the unfavorable properties of the substrate tiles (roughness, porosity, etc.) having dramatic consequences on the performance of larger area devices. With the assumption that spot-like regions, in which the back layer and the front layer are in electrical contact (local short-circuits), are present all over the device, we propose a new device structure to overcome the substrate drawbacks. A new contacts arrangement was designed in order to minimize the shunting effect of short-circuit paths. As a result an initial efficiency of 2.5% has been obtained using the new device structure for 7cm2 devices deposited on a 100cm2 PV mini-module tile.

The influence of the chamber residual pressure level in the radio frequency magnetron sputtering process on the electrical, optical and structural properties of indium thin oxide (ITO) is investigated. Several ITO films were deposited at various residual pressure levels on Corning glass using In2O3:SnO2 target in argon atmosphere and without the addition of oxygen partial pressure. It is found that a very good vacuum is associated to metallic films and results in less transparent ITO films, with some powder formation on the surface. On the contrary highly transparent and conducting films are produced at a higher residual pressure. The best deposition conditions are addressed for ITO films as transparent conducting oxide layers in silicon heterojunction solar cells. Using the optimal vacuum level for ITO fabrication, a maximum short circuit current of 36.6 mA/cm2 and a fill-factor of 0.78 are obtained for solar cells on textured substrates with a device conversion efficiency of 16.2%.

A generalized matrix method to treat multilayer systems with mixed coherent and incoherent optical behavior is presented. The method is based on the calculation of the light energy flux inside the multilayer, whose internal light absorption is straightforwardly derived. The Poynting vector is used to derive the light energy flux in the case of a layer with coherent behavior. Multilayer structures with any distribution of layers with coherent or incoherent behavior can be treated, including the case of oblique incidence. Use of the light energy flux instead of the more commonly used light intensity permits the calculation of light absorption with a better accuracy and a much shorter computation time.

APEmille is a SIMD parallel processor under development at the Italian National Institute for Nuclear Physics (INFN). It is the third machine of the APE family, following Ape and Ape100. APEmille is well suited for Lattice QCD applications, climate modelling, neural networks, computational chemistry, numerical wind tunnels, seismic and combustion simulation. APEmille is a tridimensional array of custom processors each with peak performance of 528Mflop and 8-32 Mbytes of locally addressable RAM. The 2048-processor machine reaches the performance of 1.081Tflops. APEmille is interfaced to the external world through a PCI interface. A powerful programming language named TAO is provided. A C++ compiler is foreseen.

A fast and simple experimental method for the electrical characterisation (current–voltage curve) of metal/semiconductor interfaces is presented, discussed and experimentally tested. The sample preparation is reduced at minimum, no ohmic contacts are needed. The method can be used to characterize Schottky diodes and metallic contacts.

In the framework of plasma deposition of silicon heterojunction solar cells, the issue of depositing by very high frequency, a microcrystalline emitter, without affecting the passivating properties of the underlying amorphous buffer layer, is addressed. The sequence, deposition–exposure to H2 plasma–deposition, was used to fabricate the microcrystalline emitter. Using high-resolution transmission electron microscopy, we give microscopic evidence of the long-range effects of hydrogen, already inferred by large area optical techniques. Upon exposure to H2 plasma, it is observed that silicon nanocrystallites are formed within the amorphous layer. Thinner amorphous layers undergo etching, and epitaxial growth takes place from the substrate. Photovoltaic devices with open circuit voltage up to 638 mV were fabricated.

Microcrystalline n-type emitters, that, compared to a-Si:H ones, ensure better electronic properties and better transparency in the visible, were used to fabricate heterojunction solar cells on crystalline silicon. The substrate surface was passivated by the deposition of a very thin intrinsic a-Si:H buffer layer. The microcrystalline n-type emitters were deposited by radio-frequency (rf) plasma enhanced chemical vapor deposition, using a high hydrogen diluted gas mixture. The simulation of optical spectra of n/i double layers on c-Si gives a preliminary evidence that the continuity of the intrinsic a-Si:H buffer layer is preserved after the rf deposition. The photovoltaic devices incorporating microcrystalline emitters exhibit a remarkable increase of short circuit current (Jsc) and efficiency (a factor 1.24 and 1.38 respectively) compared to the case of a-Si:H emitters. Noticeable improvements are observed if the structure is applied to textured substrates.

Very-high-frequency plasma enhanced chemical vapor deposition was used to fabricate microcrystalline silicon p–i–n photodetectors. Optical simulation of reflectance measurements was used to monitor the crystalline fraction, which determines the quantum efficiency in the near infrared range, relevant for telecommunication applications. To improve the i/p interface quality, a variable silane concentration was used in the early stages of the i-layer deposition. It is observed that a 50% large-grain fraction in the initial (200 nm) region of the i-layer results in a microcrystalline material well beyond the transition region between the amorphous and microcrystalline phase. The large-grain concentration in such initial layer is correlated with the open circuit voltage of the final p–i–n device. We suggest that the total elimination of the amorphous component in the heterophase transition region would result in excessive crystallization of the i-layer in the p–i–n device, which is to be technologically hindered by an on-time modulation of the deposition parameters.

Random pyramidal texturing of silicon solar cell substrates allows to increase the short-circuit current of the device, and it is usually achieved, in commercial solar cells, by chemical anisotropic etching using a potassium hydroxide and isopropyl alcohol solution. Due to some drawbacks of these chemicals, alternative chemical etching solutions are required. Our successful results on the tetramethyl ammonium hydroxide (TMAH), (CH3)4NOH, solution for silicon random texturing are reported. Heterojunction solar cells were deposited on textured substrates, indicating the feasibility of TMAH texturing for solar cell fabrication.