On the choice of the test structure for the electrical characterization of dielectrics for silicon solar cells

Surface passivation of Si solar cells is typically achieved by deposition of a dielectric layer. Via the investigation of Al₂O₃ passivation layers, we show that care must be taken when performing capacitance–voltage (C –V) measurements in order to obtain results that are meaningful at solar cell level. The passivation properties of a dielectric are not only affected by post‐deposition treatments but also by the presence and the nature of a metal covering the dielectric. Consequently, this Letter emphasizes how important it is to perform C –V measurements on a device structure that resembles as closely as possible that of the finished solar cell, using the same metal, deposition technique and thermal budget. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Two‐Phase Flow Characterization by Automated Digital Image Analysis. Part 2: Application of PDIA for Sizing Sprays

A series of experiments were conducted in order to assess the robustness and accuracy of a recently developed digital image analysis technique (PDIA). This paper investigates the application of the PDIA technique to the sizing of relatively small fuel droplets of diameters in the range 5 to 30 μm produced by a pressure‐swirl atomizer. The measurement performance of the PDIA system has been assessed in terms of individual object diameters and also number and volume probability density functions of diameter in comparison to phase Doppler anemometry (PDA) data obtained under identical conditions. PDIA measurements revealed good agreement with spray data obtained by PDA at a measurement location 36 diameters downstream from the nozzle orifice with differences in the arithmetic mean diameter, D₁₀ and volume mean diameter, D₃₀ of approximately 5 and 3% respectively. The PDIA technique was shown to detect the presence of very large, predominantly non‐spherical droplets whose diameters were in excess of 100 μm. These droplets, although few in number constitute a significant proportion of the total spray volume and would have otherwise been either erroneously measured or have passed through the probe volume undetected using PDA due to non‐sphericity. Smaller objects may also be measured correctly by both methods although sensitivity to signal‐to‐noise ratio, for both methods can generate spurious and contradictory errors.     

A study of electrodeposition of CuInSe2 thin films with triethanolamine as the complexing agent

In this article, the electrochemistry of CuInSe₂ and its compositional ingredients CuCl₂, InCl₃ and SeO₂ in aqueous solution were investigated. Triethanolamine was added in the single-step electrodeposition of CuInSe₂ from aqueous solution as the complexing agent in order to improve the crystallinity and uniformity of the layer. The stoichiometry, crystal structure and grain sizes of CuInSe₂ thin films of various deposition conditions were compared. The deposition parameters such as the concentration of complexing agent, deposition potential, deposition time and annealing temperature are found to be important factors in the processes of electrical deposition of CuInSe₂ thin films.     

Effective surface passivation of crystalline silicon using ultrathin Al2O3 films and Al2O3/SiNx stacks

We measure surface recombination velocities (SRVs) below 10 cm/s on p‐type crystalline silicon wafers passivated by atomic–layer–deposited (ALD) aluminium oxide (Al₂O₃) films of thickness ≥10 nm. For films thinner than 10 nm the SRV increases with decreasing Al₂O₃ thickness. For ultrathin Al₂O₃ layers of 3.6 nm we still attain a SRV < 22 cm/s on 1.5 Ω cm p‐Si and an exceptionally low SRV of 1.8 cm/s on high‐resistivity (200 Ω cm) p‐Si. Ultrathin Al₂O₃ films are particularly relevant for the implementation into solar cells, as the deposition rate of the ALD process is extremely low compared to the frequently used plasma‐enhanced chemical vapour deposition of silicon nitride (SiN_x). Our experiments on silicon wafers passivated with stacks composed of ultrathin Al₂O₃ and SiN_x show that a substantially improved thermal stability during high‐temperature firing at 830 °C is obtained for the Al₂O₃/SiN_x stacks compared to the single‐layer Al₂O₃ passivation. Al₂O₃/SiN_x stacks are hence ideally suited for the implementation into industrial‐type silicon solar cells where the metal contacts are made by screen‐printing and high‐temperature firing of metal pastes. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Force Constants,Coriolis Coupling Constants,and Mean Amplitudes of Vibration of InCl6 3-

Abstract

The general quadratic force constants, coriolis coupling constants and mean amplitudes of vibration have been evaluated for InCl₆ ^3- using recent vibrational data. The results are employed to study the trend of variation in the isoelectronic sequences e.g. InCl₆ ^3-, SnCl₆ ^2- and SbCl₆ ^?.

In the present communication we report the force constants, coriolis coupling constants and mean amplitudes of vibration for InCl₆ ^3- which have not been reported so far. The results are used to study the trend of variation of the molecular parameters in the isoelectronic sequence e.g. InCl₆ ^3-, SnCl₆ ^2- and SbCl₆ ^?. The fundamental frequencies of InCl₆ ^3-, employed in this computation, have been reported on the basis of octahedral symmetry, from infrared and Raman Spectral Studies¹.     

Studies of single-step electrodeposition of CuInSe2 thin films with sodium citrate as a complexing agent

The influences of various parameters in a single-step electrodeposition of CuInSe₂ from aqueous solution containing CuCl₂, InCl₃, and SeO₂, with sodium citrate as the complexing agent, are investigated. Co-deposition of CuInSe₂ from a room temperature, aqueous bath of these electrolytes is accomplished by the aid of sodium citrate. In this work the optimum potential for deposition of CuInSe₂ is found to be −0.5 V vs. Ag/AgCl, the deposition time is 800 s, the concentration ratio of CuCl₂, InCl₃, and SeO₂ is 9 mM:22 mM:22 mM in aqueous solution, and the annealing temperature is 225 °C. Under the optimum conditions, crystalline layers of CuInSe₂ having the chalcopyrite structure can be successfully synthesized. Cyclic voltammetry (CV), scanning electron microscope (SEM), X-ray diffractometer (XRD), and energy dispersive X-ray spectrometer (EDX) were used to examine the electrochemistry, morphologies, structures, and compositions of CuInSe₂ thin films deposited on ITO glass.     

Synthesis of ultrafine single crystals and nanostructured coatings of indium oxide from solution precursor

Indium oxide (In₂O₃) has been widely used in sensors, solar cells and microelectronics. There are several techniques available for making In₂O₃ such as vapor, electrochemical and atomic layer deposition, which are not only expensive but also time consuming processes. In this study, an inexpensive and straightforward synthesis approach is being presented to make micron/submicron size single crystals as well as nanostructured adherent coatings of In₂O₃ using Indium Chloride (InCl₃) powders and InCl₃ solution precursor. Both the powders and the solution precursor were calcined in a furnace to obtain the crystals; however, the liquid precursor was also treated by a DC plasma jet to obtain the nanostructured coatings. The phase transformations during thermal decomposition of InCl₃ powders and solution precursor were investigated via differential scanning calorimetry studies. The phase structure and crystallinity of the crystals and coatings were confirmed by X-ray diffraction. Microstructural characterization of the crystals and coatings was done by scanning electron microscopy, transmission electron microscopy and atomic force microscopy techniques. Size of the crystals was observed to be dependent on the heating schemes adapted during calcination. Solution precursor plasma sprayed In₂O₃ coatings showed porosity and ultrafine particulates with grain size ranging between 10 and 75 nm. Resistivity was determined to be ∼0.553 ± 0.337 kΩ cm. Optical transmittance of In₂O₃ coatings was ∼60-78% in the visible region and it was observed to decrease with increasing the number passes or the thickness of the coatings. Based on the optical transmission data, direct band gap of 3.57 eV was determined.     

Electrochemical deposition and characterization of cadmium indium telluride thin films for photovoltaic application

Cd–In–Te films were electro-deposited potentiostatically over SnO₂:F coated glass substrates from aqueous acidic solutions containing CdSO₄, InCl₃ and TeO₂ at 85 °C. Cyclic voltammetric studies were carried out to study the growth process and the potential range for ternary Cd–In–Te thin film deposition. Crystalline structure and surface morphological studies were carried out and correlated with the deposition potential. The deposited film showed cubic structure having a high degree of (1 1 1) orientation. Optical transmission studies showed a direct band structure and the band gap of the deposited film change with the deposition potential. A typical decrease from 1.2 to 1.1 eV in the optical band gap was observed on increasing the cathodic deposition potential from −0.5 to −0.54 V (SCE).     

ZrO2-based thin films synthesized by electrostatic spray deposition: Effect of post-deposition thermal treatments

Cubic and tetragonal Y₂O₃-doped ZrO₂ thin films were deposited with a dense surface morphology by electrostatic spray deposition. Four dependent process parameters – substrate temperature, precursor solution flow rate, nozzle to substrate distance and the deposition time – have been used to control the process. Temperature dependent Raman spectroscopy and X-ray diffraction were performed in order to investigate the crystallization behavior and structural properties.     

Extremely low surface recombination in 1 Ω cm n‐type monocrystalline silicon

A key requirement in the recent development of highly efficient silicon solar cells is the outstanding passivation of their surfaces. In this work, plasma enhanced chemical vapour deposition of a triple layer dielectric consisting of amorphous silicon, silicon oxide and silicon nitride, charged extrinsically using corona, has been used to demonstrate extremely low surface recombination. Assuming Richter's parametrisation for bulk lifetime, an effective surface recombination velocity S_eff = 0.1 cm/s at Δn = 10¹⁵ cm^–3 has been obtained for planar, float zone, n ‐type, 1 Ω cm silicon. This equates to a saturation current density J_0s = 0.3 fA/cm², and a 1‐sun implied open‐circuit voltage of 738 mV. These surface recombination parameters are among the lowest reported for 1 Ω cm c‐Si. A combination of impedance spectroscopy and corona‐lifetime measurements shows that the outstanding chemical passivation is due to the small hole capture cross section for states at the interface between the Si and a‐Si layer which are hydrogenated during nitride deposition. (© 2016 The Authors. Phys. Status Solidi RRL published by WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Modular deposition chamber for in situ X‐ray experiments during RF and DC magnetron sputtering

A new sputtering system for in situ X‐ray experiments during DC and RF magnetron sputtering is described. The outstanding features of the system are the modular design of the vacuum chamber, the adjustable deposition angle, the option for plasma diagnostics, and the UHV sample transfer in order to access complementary surface analysis methods. First in situ diffraction and reflectivity measurements during RF and DC deposition of vanadium carbide demonstrate the performance of the set‐up.     

Determination of the optimal parameters for the fabrication of ZnO thin films prepared by spray pyrolysis method

In this work, ZnO thin films have been prepared by spray pyrolysis deposition method on the glass substrates. The effect of deposition parameters, such as deposition rate, substrate temperature and solution volume has been studied by X-ray diffraction (XRD) method, UV–Vis–NIR spectroscopy, scanning electron microscopy (SEM), and electrical measurements. The XRD patterns indicate polycrystalline wurtzite structure with preferred direction along (0 0 2) planes. Thin films have transparency around 90% in the visible range. The optical band gap was determined at 3.27 eV which did not change significantly. Evolution of electrical results containing the carriers’ density, sheet resistance and resistivity are in agreement with structural results. All the results suggest the best deposition parameters are: deposition rate, R = 3 ml/min, substrate temperature, T _s = 450°C and thickness of the thin films t = 110–130 nm.     

Application of glancing‐emergent‐angle fluorescence for polarized XAFS studies of single crystals

X‐ray absorption fine‐structure (XAFS) data were obtained for the V K‐edge for a series of anisotropic single crystals of (Cr_xV_1–x)₂O₃. The data and the results were compared for the as‐prepared bulk single crystals (measured in fluorescence in two different orientations) and those ground to powder (measured in transmission). For the bulk single crystals, the glancing‐emergent‐angle (GEA) method was used to minimize fluorescence distortion. The reliability of the GEA technique was tested by comparing the polarization‐weighted single‐crystal XAFS data with the experimental powder data. These data were found to be in excellent agreement throughout the entire energy range. Thus, it was possible to reliably measure individual V–V contributions parallel and perpendicular to the c axis of the single crystals, i.e. those unavailable by powder data XAFS analysis. These experiments demonstrate that GEA is a premiere method for non‐destructive high‐photon‐count in situ studies of local structure in bulk single crystals.     

An original approach for Raman spectroscopy analysis of radioactive materials and its application to americium‐containing samples

An approach for Raman measurements of highly radioactive samples is presented here. The innovative part of this approach lies in the fact that no single part of the Raman equipment is in direct contact with the radioactive sample, as the sample is sealed in an alpha‐tight capsule. Raman analysis is effectively performed through the optical‐grade quartz window closing the capsule. This allows performing micro‐Raman measurements on radioactive samples with no limitations on the laser source wavelength, polarisation mode, spectrometer mode and microscope mode (provided the focal length of the microscope objective is greater than the thickness of the quartz window and with sub mg samples). Some example results are shown and discussed. In particular, some spectral features of americium‐containing oxide nuclear fuel specimens are presented. Raman spectra clearly reveal in these specimens the presence of abundant oxygen defects induced in the fcc fluorite lattice by trivalent americium. In order to complete the analysis the Raman spectrum of pure americium dioxide was also measured with a lower energy excitation source compared with previous research. The current results seem to be consistent with the possible occurrence of a photolysis process induced by the Raman laser, resulting in the formation of hyperstoichiometric americium sesquioxide Am₂O_{3 + z}. Such a photolytic process is deemed to be unavoidable when visible lasers are used as excitation sources for the Raman analysis of americium dioxide. © 2015 The Authors Journal of Raman Spectroscopy Published by John Wiley & Sons, Ltd.     

Preparation of well-structured organosilane layers on silica

An efficient grafting process of monofunctional alkylchlorosilanes (general formula: CH₃-(CH₂) _n-1-Si(CH₃)₂Cl with n varying from 4 to 30) onto silica nanoparticules was developed by varying the surface preparation and the solvent used for the deposition process. A vapor phase deposition method was considered as reference and silicon wafers with a native SiO₂ layer were used as a model surface of the silica particles. The grafting method was evaluated by studying the wettability and the grafting densities of the resulting monolayers. The chain conformation of the monolayers was determined by comparing the thickness measured by SE ellipsometry and AFM. By comparing the solvent and vapor phase deposition methods, it was demonstrated that the deposition process had a large influence on the structure of the grafted monolayers. The same structure as from a vapor phase method can be obtained from a solvent deposition process by a suitable choice of the solvent and by a strict cleaning of the surface before deposition. The grafting of much longer chains of such silane-terminated polyethylenes with different molar mass on the silica surface was also investigated in order to study the effects of the chain length on the grafting density and the layer structure. For both the short alkylchlorosilanes and polymeric grafted chains, the proposed organization of the grafted chains at the silica surface is found to be strongly dependent on the length of the alkyl chains.     

Cadmium–carbon wavenumber analysis using B3LYP level theory calculations in investigations of dimethylcadmium decomposition

Computational chemistry has been widely used to understand homogeneous reactions and to support spectroscopy analysis. Thus, it is a useful tool to understand gas‐phase dynamics of metal organic chemical vapor deposition (MOCVD). In this study, we report that the basis set selection possibly results in unequivocal peak assignment in Raman spectroscopy, especially when an effective core potential (ECP) is employed. The basis set selection for the decompositionof dimethylcadmium (DMCd), for example, was examined using five different ECPs (i.e. CRENBS, CRENBL, SDD, LanL2DZ and SBKJC for Cd atom combined with STO‐3G, 3‐21G, 6‐31G(d), 6‐311G(d) and 6‐311++G(2d,2p) for C and H atoms). The analyses demonstrated that the SDD/STO‐3G/3‐21G combination for Cd/C/H atoms best reproduce the experimentally reported Cd C vibrational stretching modes of Cd(CH₃)₂ (DMCd) and •CdCH₃ (MMCd). Although the SDD/STO‐3G/3‐21G combination consists of simple and basic basis sets, we found that a good potential balance between metal (Cd) and auxiliary (C) atoms is essential to estimate frequencies suitable for spectroscopy analysis computationally. The same combination of basis set was then used to examine other possible reaction steps, and Raman experiments successfully detected one of the suggested intermediates of (CdCH₃)₂. Copyright © 2009 John Wiley & Sons, Ltd.     

Plasma enhanced atomic layer deposition of gallium oxide on crystalline silicon: demonstration of surface passivation and negative interfacial charge

Herein we report on the passivation of crystalline silicon by gallium oxide (Ga₂O₃) using oxygen plasma as the oxidizing reactant in an atomic layer deposition (ALD) process. Excess carrier lifetimes of 2.1 ms have been measured on 1.75 Ω cm p‐type silicon, from which a surface recombination current density J₀ of 7 fA cm^–2 is extracted. From high frequency capacitance‐voltage (HF CV) measurements it is shown that, as in the case of Al₂O₃, the presence of a high negative charge density Q_tot/q of up to –6.2 × 10¹² cm^–2 is one factor contributing to the passivation of silicon by Ga₂O₃. Defect densities at midgap on the order of ～5 × 10¹¹ eV^–1 cm^–2 are extracted from the HF CV data on samples annealed at 300 °C for 30 minutes in a H₂/Ar ambient, representing an order of magnitude reduction in the defect density compared to pre‐anneal data. Passivation of a boron‐diffused p⁺ surface (96 Ω/□) is also demonstrated, resulting in a J₀ of 52 fA cm^–2. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Absorptionsspektren von Er3+ in InCl3 und in ScCl3

The optical absorption spectra of Er³⁺ in single crystals of InCl₃ and ScCl₃ have been obtained between 14,000 and 29,000 cm^?1. The observed crystal field splittings are interpreted in terms of crystal potential of symmetry 3m for ScCl₃ and of symmetry 2m for InCl₃. There is however found, that for both cases the splittings will be approximately explained by a crystal potential of cubic symmetry. The employed hostlattices are of special interest, because the ions of the iron series can occupy the same sites as the rare earth ions.     

A layered antiferromagnetic semiconductor EuMTe3 (M = Bi,Sb)

We synthesized ternary tellurides EuMTe₃ (M = Bi, Sb) using a low‐temperature flux method. These compounds crystallize in the P_mmn space group with layered structure. A superstructure modulation along the b‐axis was observed. Physical property measurements revealed that these compounds are antiferromagnetic semiconductors. Finally, a strong spin–orbit coupling with possible novel quantum interference between localization and weak antilocalization effects was suggested in the present system. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Low‐temperature atomic layer deposition of MoOx for silicon heterojunction solar cells

The preparation of high‐quality molybdenum oxide (MoO_x) is demonstrated by plasma‐enhanced atomic layer deposition (ALD) at substrate temperatures down to 50 °C. The films are amorphous, slightly substoichiometric with respect to MoO₃, and free of other elements apart from hydrogen (&11 at%). The films have a high transparency in the visible region and their compatibility with a‐Si:H passivation schemes is demonstrated. It is discussed that these aspects, in conjunction with the low processing temperature and the ability to deposit very thin conformal films, make this ALD process promising for the future application of MoO_x in hole‐selective contacts for silicon heterojunction solar cells. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)