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ZnO/Ag/ZnO nanolaminate structures were deposited by consecutive RF sputtering at room temperature.The optical transparency, sheet resistance, and figure of merit are determined in relation to the deposition time of Ag and to the film thickness of the ZnO top layer. An improved transmittance has been found in the visible spectral range of the ZnO/Ag/ZnO structure compared to ZnO multilayers without Ag. High transmittance of 98% at 550 nm, sheet resistance of 8 Ω/sq, and figure of merit (FOM) of 111.01 × 10−3 Ω−1are achieved for an optimized ZnO/Ag/ZnO nanolaminate structure. It is suggested that the good optical and electrical properties are due to the deposition of the discontinuous Ag layer. The electrical metallic type conductivity is caused by planar located silver metal granules. The deposition of a discrete layer of Ag nano-granules is confirmed by atomic force microscopy (AFM) and cross-section high-resolution transmission electron microscopy (HRTEM) observations.

Thin films of copper (I) bromide deposited by Physical Vapor Deposition (PVD) were investigated for their potential application as inorganic hole transport layer in perovskite solar cells with standard architecture. The CuBr layers with different thicknesses were prepared on monocrystalline silicon substrates or on quartz plates for optical investigations. Ellipsometric characterization, performed for the layers deposited on mono silicon have given a thickness about 330–370 nm with Rout Mean Square (RMS) roughness near 10 nm. The optical spectra of the films have shown more than 80% transparency in the visible range and estimated band gap of as deposited CuBr layers were about 2.98 eV with a split off band above the valence band edge, observed for all samples. In the sandwich structure with In:SnO2 (ITO) covered soda lime glass substrates – ITO/CuBr/Cu the volt – amperometric characteristics are linear indicating formation of ohmic contact with the copper top electrode.

In our study, transparent and conductive films of NiOx were successfully deposited by sol-gel technology. NiOx films were obtained by spin coating on glass and Si substrates. The vibrational, optical, and electrical properties were studied as a function of the annealing temperatures from 200 to 500 °C. X-ray Photoelectron (XPS) spectroscopy revealed that NiO was formed at the annealing temperature of 400 °C and showed the presence of Ni+ states. The optical transparency of the films reached 90% in the visible range for 200 °C treated samples, and it was reduced to 76–78% after high-temperature annealing at 500 °C. The optical band gap of NiOx films was decreased with thermal treatments and the values were in the range of 3.92–3.68 eV. NiOx thin films have good p-type electrical conductivity with a specific resistivity of about 4.8 × 10−3 Ω·cm. This makes these layers suitable for use as wideband semiconductors and as a hole transport layer (HTL) in transparent solar cells.

The era of flexible optoelectronics demands development of wearable and bendable structures, foldable touch screens, paper-like displays, and curved and flexible solid-state lighting devices. Here, we demonstrate the fabrication of highly flexible light valves using polymer-dispersed liquid crystal (PDLC) and TiO

Wide band gap metal oxide semiconductors are an important material base in optoelectronic industry. Dye sensitized solar cells and especially the organometallic perovskite ones present a new way of application of these materials with specific requirements for their properties. Therefore the reduction of production costs in relation to the efficiency is an important factor for its commercialization. In this work we present sol-gel approach to form dense, uniform and voids free electron selective layers of intrinsic SnO2 for application in nano-sized organometallic photovoltaics. The purpose is to find conditions for deposition at lowest temperatures of compact and well crystallized SnO2 thin films with effective electron blocking ability with perspective to apply on polymer substrates. The process of pyrolysis of the precursors into expected SnO2 was investigated by Differential Scanning Calorimetry. The results were used to have an insight for main reaction steps and to define an adequate annealing regime. The films were characterized by X – ray – photoelectron spectroscopy XPS, diffractometry, UV – Vis spectrophotometry and Scanning Electron Microscopy. Different solvents for the precursor SnCl4.5H2O were investigated in order to minimize their influence onto polymeric substrates. In the row between ethanol, methanol and isopropanol the last ones yielded compact layers without pinholes and cracks. The level of electrical leakage was estimated by cyclic voltammetry measurements of residual current in aqueous redox solution. The quality of the coverage depends on the concentration of the precursor solution but at over 0.5 M SnCl4 the root mean squares (RMS) roughness of the films increases.

In the present study, thermally evaporated thin copper (I) bromide films were investigated as a potential hole-transport material for hybrid perovskite solar cells in a standard configuration. The films were deposited on top of glass substrates; the measured transparency was 80 %. The structural and morphological analyses revealed a dense polycrystalline structure of γ-CuBr. The analysis of the surface chemical composition demonstrated that copper was in a Cu1+ state and the films were stoichiometric. Electrical measurements were performed with deposited planar silver or copper electrodes. The layers were highly resistive; however, a current increasing with the time was observed when the samples were biased by a dc voltage of 20 V for two hours, which we speculate might be due to a possible new conduction mechanism.

In this paper, TiO2/Ag/TiO2 multilayers, deposited by magnetron sputtering technique at room temperature are used as transparent conductive layers for Liquid Crystal (LC) devices fabrication. The measured electro-optical modulation characteristics and phase retardation of LC cell based on TiO2/Ag/TiO2 electrode show improved electro-optic performances in comparison with LC reference cell using commercial Indium Tin Oxide (ITO). Low sheet resistance and high transparency of TiO2/Ag/TiO2 multilayers open a great potential for next generation ITO-free liquid crystals electro-optical modulators.

Results obtained at integration of nano-laminated Dielectric-Metal-Dielectric (DMD) resistors in silicon MEMS sensors are presented in this paper. Fabrication technology with significantly reduced thermal budged for integration of DMD resistors in four-cantilever device has been developed. The ultrathin layers have been deposited in a consecutive RF sputtering process, without exposure to air, exploiting a lift-off patterning technique. The results proved that: i) very good stability of the DMD resistors was achieved, and ii) strain-sensing behavior of nano-laminated structures has been demonstrated.

This paper presents the comparison of nitrogen incorporation in GaAsN and InGaAsN layers grown on GaAs substrate from Ga- and In-rich solution, respectively, by liquid-phase epitaxy. Polycrystalline GaN has been used as a source of nitrogen in two cases. The initial epitaxy temperature has been varied in the temperature range 600-550 °C. Nitrogen content in Ga1-xAsNx grown layers has been determined to be in the range 0.1-0.5%. Higher nitrogen incorporation efficiency has been found for quaternary InGaAsN layers grown under carefully chosen lattice matched conditions. The incorporation of nitrogen into GaAsN and InGaAsN layers has been study by vibrational mode absorption spectroscopy. Nitrogen-induced vibration mode near 472 cm-1 has been registered in GaAsN samples. Preferential In-N bonds and the formation of N-centred In3Ga1 clusters have been identified for lattice matched to GaAs epitaxial InGaAsN layers. Electrical properties of the samples have been characterized by temperature-dependent Hall effect measurements. Nominally undoped GaAsN and InGaAsN grown layers are n-type with Hall concentration about one order of magnitude higher in comparison to layers not containing nitrogen. Thermally activated increase in the free carrier concentration at temperatures higher than 150 K is observed which indicates the presence of N-related deep donor levels below dilute nitride conduction band edge. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

In this work chemical liquid deposition from sol–gel solutions has been used to obtain thin (Al2O3)x(B2O3)1 − x dielectric films. Passivation of Si surfaces using these films has been studied. Morphological properties of thin films deposited on polished Si surfaces have been investigated by scanning electron microscopy (SEM) and atomic force microscopy (AFM) technique. Their chemical composition, structural and optical features have been analysed by X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR) and ultraviolet-visible (UV–VIS) spectroscopy. Results, obtained in this work, show that silicon surfaces can be effectively passivated by thin dielectric layers deposited from chemical solutions. The thin dielectric layers developed in his work, can be recommended as back side passivation coating for Si-based solar cells.

Crystallographic and transport properties of nominally undoped and Sn-doped InGaAsN layers grown by low-temperature LPE have been studied and related to the growth conditions. In the case of lattice matching, flat and uniform mirror-like layers of 8–10 μm in thickness are obtained. The compositions of the layers under study have been determined by combination of X-ray microanalysis and X-ray diffraction methods to be In 0.035 Ga 0.065 As 0.086 N 0.014 . The lattice mismatch between layer and substrate Δ a l / a s calculated from X-ray diffraction curves is less than−7×10 −4 for all samples. The layers grown at lower epitaxy temperatures exhibit the highest crystalline quality, better lattice match and better homogeneity. This is in good agreement with the results of morphological study by atomic force microscopy which show root mean-square surface roughness of 0.18 nm for the best layers. CV and Hall measurements reveal that intentionally undoped InGaAsN layers are n-type with free carrier concentration about one order of magnitude higher in comparison to layers not containing nitrogen and high electron mobility values over 2000 cm 2 /Vs. A dramatic reduction in the free carrier concentration and slightly increase in mobility are observed for Sn-doped InGaAsN layers.

This work demonstrates the possibility for low-temperature Liquid-Phase Epitaxy (LPE) growth of lattice matched to GaAs substrate dilute nitride InGaAsN layers with good crystalline quality and high Hall electron mobility. X-ray microanalysis and X-ray diffraction methods have been used to determine the composition and crystalline quality of the grown InGaAsN layers. Surface roughness is examined by atomic force microscopy. N-related local vibration modes are observed by Raman scattering. The Hall electron mobility and free carrier concentration have been measured in the temperature range 80-300K by conventional Van der Pauw method.

International audience; The present work demonstrates the possibility to use liquid phase epitaxy to incorporate nitrogen in epitaxial GaAsN/GaAs and GaInAsN/GaAs heterostructures, including nanoscaled ones. The structures are grown from Ga - and GaIn - melts containing polycrystalline GaN as a nitrogen source. The red shift of the absorption spectra corresponds to nitrogen content in the epitaxial layers near or less than 0.2 at %. Photoluminescence spectra of dilute nitride GaAsN and GaInAsN show emission from localized nitrogen states - N-nanoclusters of more than two N atoms. These studies show that the melt grown dilute GaAsN and GaInAsN nanostructures can be used for solar cells with extended long wavelength edge. (C) 2010 Published by Elsevier Ltd

GaSb based III-V heterostuctures are attractive for optoelectronic devices such as midin- frared lasers, detectors, and thermophotovoltaics (TPVs). In this paper the growth and characterization of GaInAsSb and GaAlAsSb quaternary layers, lat-tice-matched to GaSb substrate, are reported, with a particular focus on these alloys for TPV devi-ces. High-quality with a mirror-like surface morphology epilayers Ga1-x InxAsy Sb1-y with In content x in the range 0.1-0.22 and Ga1-xAlxAsySb1-y layers with Al content up to 0.3 in the solid are grown by Liquid-Phase Epitaxy (LPE) from In- and Ga-rich melt, respectively. The compositions of the quaternary compounds are determined by X-ray microanalysis. The crystalline quality of GaInAsSb/ GaSb and GaAlAsSb/GaSb heterostuctures is studied by X-ray diffraction (XRD) and transmission electron microscopy (TEM) measurements.

Currently, the conventional dielectric, SiO2 or SiON is being replaced by alternative materials to suppress high leakage currents observed at low film thickness. In this work, thin layers of ZrO2 and (ZrO2)x(Al2O3)1−x, deposited on Si substrates are obtained by sol–gel method. The structural and electrical properties as a function of the annealing temperature are studied. Usually, the post-annealing temperature of 700 °C leads to re-crystallization in ZrO2 layers, which can induce high leakage current and severe mass transport along the grain boundaries. The purpose is to amorphisize the films by adding aluminium oxide and in this way improve their electrical behaviour. Structural analysis shows that ZrO2 films are crystallized, meanwhile the mixed oxide films remain in amorphous state even after high temperature annealing. The obtained results are encouraging and determine the (ZrO2)x(Al2O3)1−x films as a promising material with good dielectric properties.

Uniform Al2O3 films were deposited on silicon substrates by the sol–gel process from stable coating solutions. The technological procedure includes spin coating deposition and investigating the influence of the annealing temperature on the dielectric properties. The layers were studied by Fourier transform infrared spectroscopy and Scanning Electron Spectroscopy. The electrical measurements have been carried out on metal–insulator–semiconductor (MIS) structures. The C–V curves show a negative fixed charge at the interface and density of the interface state, Dit, 3.7 × 1011 eV− 1cm− 2 for annealing temperature at 750 °C.

We report the fabrication of buried contact solar cells using porous silicon as sacrificial layer to create well-defined channels (for buried contacts) in silicon. In this paper, the salient features of the technology have been presented. No detrimental effect was found in the performance of buried contact solar cell with partially filled contact area compared to the solar cells having conventional planar contacts. However, a marked difference in the short circuit current density was seen when channel was fully filled with metal by screen printing, without degradation in the open-circuit voltage. It is expected that improved processing in combination with optimized buried metallic contact parameters may yield higher efficiencies that may result in substantial decrease in solar cell cost.

Surface recombination velocities as low as 10 cm/s have been obtained by treated atomic layer deposition (ALD) of Al 2 O 3 layers on p-type CZ silicon wafers. Low surface recombination is achieved by means of field induced surface passivation due to a high density of negative charges stored at the interface. In comparison to a diffused back surface field, an external field source allows for higher band bending, that is, a better performance. While this process yields state of the art results, it is not suited for large-scale production. Preliminary results on an industrially viable, alternative process based on a pseudo-binary system containing Al 2 O 3 are presented, too. With this process, surface recombination velocities of 500–1000 cm/s have been attained on mc-Si wafers.

This paper presents new results on the deposition technique and the characterization of thin (ZrO 2 ) x (Al 2 O 3 ) 1 - x layers on silicon. The layers were deposited using the chemical solution deposition method on silicon substrates, and they were then subjected to different temperature treatments. For comparison, pure ZrO 2 layers were deposited, too. The chemical composition of (ZrO 2 ) x (Al 2 O 3 ) 1-x layers is determined by Rutherford Back Scattering. The morphology was studied by HRSEM. The addition of Al 2 O 3 makes the layers structurally more homogeneous as compared to those of pure ZrO 2 . The electric properties of MIS structures were studied. A fixed negative charge and the high dielectric constants are characteristic for these layers. The experimental results are discussed in the context of using them as high-k dielectrics.

An interesting opportunity arises when two or more oxides are used as alloys in an attempt to combine the desirable properties of several materials. These systems are predominantly non-stoichiometric, and in the case of two oxides, they are called pseudobinary alloys. Varying the ratio of the two oxides, thin films with certain preset characteristics can be obtained-refractive index, energy band gap, dielectric constants etc. Our investigations were focussed on spin-coated (Al 2 O 3 ) x (TiO 2 ) 1-x films. The electrical properties of (Al 2 O 3 ) x (TiO 2 ) 1-x were studied forming MIS structures. For accurate determinations of the dielectric constant various measurement methods were used: classical C-V, impedance spectroscopy and CV map B instrument. The effect of adding Al 2 O 3 to TiO 2 is to produce an amorphous dielectric film, which is thermodynamically stable on Si.

The sorption properties of TiO2 thin films are investigated, in order to detect ammonium vapor existence. For the purpose mass-sensitive quartz resonators covered by TiO2 film are used. TiO2 thin films are prepared using a new method called liquid phase deposition (LPD). By this method metal oxide layers are deposited on surfaces dipped in solutions. The layers are obtained as a result of a balance reaction, which happens between the metal fluorocomplex and metal oxide in aqueous solution. By this process substances with complex morphology are easily coated using no special equipment. The main advantage of this method is its low synthesis temperature–up to 200 °C. The sorption sensitiveness of the created structure is registered by the Quartz Crystal Microbalance (QCM) method. An interval of ammonium concentration (from 100 to 10,000 ppm) is investigated. A dependence is obtained between relative change of resonator frequency (Δf/f) and ammonium solution concentration. The obtained initial results show that this sort of systems could be used for creating sensor elements aiming the detection of ammonium contamination in the air.

The investigation of MIS structures with thin metal oxide films by the classical C – V methods is impeded because of the specific properties of the dielectric material: high dielectric permittivity, electronic polarization, high dielectric losses, thermodynamic reaction with the silicon surface and formation of multi-phased systems. Complex impedance spectroscopy has been used for investigation of MIS structures with films of (Al 2 O 3 ) x (TiO 2 ) 1− x . The dielectric films were deposited on Si substrates by spin-on-coating from sol solution and underwent additional thermal treatment. Using the spectroscopic plot of the imaginary part of the impedance versus frequency, the different capacitance components of the MIS structure were evaluated. The correct value of the relative dielectric constant e r and interface states can be determined from the capacitance components.

(Al 2 O 3 ) x (TiO 2 ) 1− x thin films obtained from sol solutions by spin coating technique have been studied. The chemical composition and stoichiometry of the films have been determined by X-ray photoelectron spectroscopy (XPS) and Rutherford backscattering spectroscopy (RBS). The peaks at 461.48 eV for Al2p and Ti2p at 74.4 eV are characteristic for the respective metal oxides and indicate the presence of Al 2 O 3 and TiO 2 . The refractive index, dielectric constant and optical band gap for direct transitions have been determined for varying Al:Ti ratios in the starting solution.

The optical constants (refractive index, n and absorption coefficient, k) in the visible and near-UV spectral range of (Al2O3)x(TiO2)1−x films, deposited by the sol–gel method on polished single-crystalline silicon wafers, was studied at varied ratios of the components Al2O3 :TiO2. The thickness was determined by ellipsometry at 632.8 nm and a multiwavelength curve fitting method was applied to calculate the refractive index dispersion. The absorption coefficient α and optical band gap E g were determined from the transmission and reflection spectra when a sapphire substrate was used.

BaTiO 3 (BTO) and Ba 1− x Sr x TiO 3 (BSTO) thin films (15–45 nm) were obtained with good dielectric properties on Si wafer using the sol–gel method. The films are coated with the sol solution by spin coating technique and additional thermal annealing. The results from XPS and XRD measurement show that, at high thermal annealing at 700–800°C, there is a penetration of the Si atoms from the substrate into the layer, forming silicon oxide. In this way, formation of solid solution BTO+SiO 2 and BSTO+SiO 2 takes place, leading to an improvement of the film dielectric properties: small leakage current and high breakdown voltage, but the dielectric constant decreases.

High dispersed TiO 2 powders with specific surface area up to 220 m 2 /g have been obtained. The nanosized particles with average dimensions from 8.7 to 31.3 nm have been measured. The sol–gel samples are treated from 80 to 700°C. The results obtained by DTA and XRD show that DTA-, TG- and DTG-stability curves exist in the region from 400 to 700°C. An anatase phase formation in the region up to 420–440°C has been checked. Pure rutile phase is detected at 700°C. IR spectroscopy study confirms DTA and XRD data for phase evolution from low crystalline phase via anatase to rutile one. According to optical measurements AcAc precursor used leads to a high dispersion level of the particles; the band gap is 3.9 eV measured on the TiO 2 thin films.

The influence of the emitter thickness on the photovoltaic properties of monocrystalline silicon solar cells with porous silicon was investigated. The measurements were carried out on n + p silicon junction whose emitter depth was varied between 0.5 and 2.2 μm. A thin porous silicon layer (PSL), less than 100 nm, was formed on the n + emitter. The electrical properties of the samples with PS were improved with decrease of the n + p junction depth. Our results demonstrate short-circuit current values of about 35–37 mA/cm 2 using n + region with 0.5 μm depth. The observed increase of the short-circuit current for samples with PS and thin emitter could be explained not only by the reduction of the reflection loss and surface recombination but also by the additional photogenerated carriers within the PSL. This assumption was confirmed by numerical modeling. The spectral response measurements were performed at a wavelength range of 0.4–1.1 μm. The relative spectral response showed a significant increase in the quantum efficiency of shorter wavelengths of 400–500 nm as a result of the PS coating. The obtained results point out that it would be possible to prepare a solar cell with 19–20% efficiency by the proposed simple technology.

One of the most important and costly aspects of solar cell manufacture, besides the silicon itself, is the way of contact metallization which provides electrically conducting paths on the surface of the cell. This work shows that the selective electrode-deposition process for nickel and electroplated copper can be used for solar cell metallization without sacrificing the efficiency but reducing the total price. The basic technological steps for the metallization process are discussed. Terrestrial solar cells with NiCu system are fabricated without compromising their electrical performance.

Transparent and conductive oxide/ metal/ oxide nanolaminate structures were deposited on glass and polymer substrate by RF magnetron sputtering without substrate heating. The Ag nanoparticles with different size and distance between neighboring particles were located on the interface of two thin oxide layers. This sputtering configuration allows obtaining thin films with homogeneous thickness. The three targets give the opportunity to deposit successively three different layers without opening the chamber. The developed process for transparent conducting coating is a low temperature and it is suitable for application on organic materials as substrate and foils. The experiment with different substrates manifest that the optical transparency of the conducting coating depends on substrate material. The obtained results have demonstrated that the nanolaminate structures oxide/metal/oxide (OMO) as TCO coating are especially suitable for applications in flexible electronics and optoelectronics

Thin films of molybdenum oxide were deposited by radio frequency (RF) magnetron sputtering in Ar from a MoO3 target at different deposition power on glass and silicon substrates. The thickness of the films was determined by profilometer measurements and by ellipsometry. The films were annealed in air at temperatures between 200 and 400°C in air. The optical transmission and reflection spectra were measured. The conductivity of the as deposited and annealed films was determined. The crystal structure was probed by Raman spectroscopy. The oxidation state of the surface was studied by X-ray photoelectron spectroscopy (XPS) spectroscopy. The deposition technique described above was used to experiment with MoOx as a hole transport layer (HTL) in polymer solar cells with bulk hetrojunction active layer, deposited by spin coating. The performance of these layers was compared with poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS), which is the standard material used in this role. The measured current-voltage characteristics of solar cells with the structure glass/ITO/HTL/Poly(3-hexyl)thiophene (P3HT):[6,6]-phenyl-C61- butyric acid methyl ester (PCBM)/Al demonstrate that the studied MoOx layer is a good HTL and leads to comparable characteristics to those with PEDOT:PSS. On the other hand the deposition by magnetron sputtering guarantees reliable and repeatable HTLs.

A solution based deposition method to form nano-sized thin films of molybdenum oxide suitable for photovoltaic device applications is presented. The samples were deposited by spin-coating from molybdenum metal organic precursor solution on soda lime glass substrates. The influence of the process parameters such as spinning regime and concentration of the precursor solutions on the thickness and morphology of the films were investigated. The thermal decomposition of the molybdenum precursor and oxide formation were investigated by differential scanning calorimetry and characteristic patterns showed transitions up to 300oC followed by a zone of stability. Optical spectroscopy measurements in the wavelength range from 300 to 1800 nm presented an increase in transparency when temperature of annealing was raised up to 400oC. Raman scattering analysis revealed the presence of mixed molybdenum oxides. Measurements of the electrical conductivity were performed by the 4-point method.

Two types of polymer solar cells with active layers of P3HT:PCBM and PCDTBT:PCBM in a standard configuration were deposited by spin-coating the polymer layers and sputtering the Ag back contacts. After encapsulation, they were subjected to post-deposition annealing and were studied by measuring their current-voltage characteristics and quantum efficiency spectra. Their stability was examined by exposing them to solar radiation in open-circuit conditions for several hours every day for a total of 80 hours. Their characteristics were measured regularly throughout this period. The performance of the two types of cells are compared and discussed.

The aim of this study was formation of a multilayered transparent conductive nanolaminate structure with optimized conductivity vs. transparency parameters. The nanolayered structure comprised one or two thin layers of dielectric materials. The overall electrical conductivity was modified by tuning the size of the planar metal granules. Magnetron sputtering system with three different targets was used for layers deposition. The advantages are: the good reproducibility of a low-temperature process allows for effective process control and, optionally, selective formation of conductive areas in a dielectric structure. Our studies revealed that the relation between the sheet resistance and the maximum transparency in the visible spectral range depends on the size of the metal granules and the film thickness of the dielectric coating. The technology provides transparent conductive coatings with well-controlled optical and electrical properties.

Thin films of tin sulfide (SnS) were prepared by thermal evaporation technique on glass substrates and on n-type Si substrate and their physical properties were studied. The phase of the obtained thin films before and after thermal treatment was confirmed by X-ray diffraction analysis and Raman spectra. Optical transmission and reflection spectra were measured in the wavelength range 300-1800 nm, and the data were used to determine the direct and indirect optical band gaps. Four-point measurements have revealed that SnS thin film exhibits p-type conduction. Current-voltage characteristics of the SnS/ n-Si structures demonstrate strong photosensitivity and photovoltaic effect. However, in order to be able to evaluate the potential applicability of this heterojunction for photovoltaic or electronic devices, further study and technological optimization has to be conducted.

In this paper we present experimental results that indicate the possibility of observing individual interface traps energetically located near the conduction band edge. By employing sub-μm MOSFETs operating at 4.2 K we were able to achieve a sufficient spatial and energetic resolution to make the change in charge state of an interface trap visible by studying the gate and drain voltage dependence of the drain current I d and the transconductance g m in the weak-inversion regime. The drain current exhibits a step like structure in its dependence on the gate voltage and hence one finds sharp peaks in the transconductance.

A critical goal for photovoltaic energy conversion is the development of high-efficiency, low cost photovoltaic structures which can reach the thermodynamic limit of solar energy conversion. New concepts aim to make better use of the solar spectrum than conventional single-gap cells currently do. In multijunction solar cells based on III-V heterostructures, better spectrum utilization is obtained by stacking several solar cells. These cells have achieved the highest efficiency among all other solar cells and have the theoretical potential to achieve efficiencies equivalent to or exceeding all other approaches. Record conversion efficiencies of 40.7 % (King, 2008) and 41,1 (Guter at al., 2009) under concentrated light for triplejunction allows hoping for practical realization of gianed values of efficiency in more multiplejunction structures. The expectations will be met , if suitable novel materials for intermediate cascades are found, and these materials are grown of an appropriate quality. Models indicate that higher efficiency would be obtained for 4-junction cells where 1.0 eV band gap cell is added in series to proven InGaP/GaAs/Ge triple-junction structures. Dilute nitride alloys such as GaInAsN, GaAsSbN provide a powerful tool for engineering the band gap and lattice constant of III-V alloys, due to their unique properties. They are promising novel materials for 4and 5-junction solar cells performance. They exhibit strong bowing parameters and hold great potential to extend the wavelength further to the infrared part of the spectrum. The incorporation of small quantity of nitrogen into GaAs causes a dramatic reduction of the band gap (Weyeres et al., 1992), but it also deteriorates the crystalline and optoelectronic properties of the dilute nitride materials, including reduction of the photoluminescence intensity and lifetime, reduction of electron mobility and increase in the background carrier concentration. Technologically, the incorporation probability of nitrogen in GaAs is very small and strongly depends on the growth conditions. GaAsNbased alloys and heterostructures are primarily grown by metaloorganic vapor-phase epitaxy (MOVPE) (Kurtz et all, 2000; Johnston et all, 2005)) and molecular-beam epitaxy (MBE) (Kurtz et al. 2002; Krispin et al, 2002; Khan et al, 2007), but the material quality has been inferior to that of GaAs. A peak internal quantum efficiency of 70 % is obtained for the solar cells grown by MOCVD (Kurtz et al. 1999). Internal quantum values near to unit are reported for p-i-n

International audience; Dilute III-nitrides, such as GaAsN and GaInAsN, are of considerable current interest both from a fundamental point of view and for applications in solar cells, GaAs-based long-wavelength photodetectors and diode lasers. The addition of nitrogen leads to material properties that deviate strongly from those expected for conventional III-V solid solutions. The possibility was investigated to use liquid phase epitaxy to incorporate nitrogen in epitaxial GaAsN/GaAs and GaInAsN/GaAs heterostructures. The structures were grown from Ga- and Ga-In- melts containing powder GaN as a nitrogen source. The initial growth temperature was varied in the range 560°C − 660°C. The low temperature growth favors nitrogen incorporation in the epilayers. The optical transmission and photoluminescence spectra of a set of structures grown at different temperatures were studied showing ternary and quaternary dilute nitride solid solutions with nitrogen content about 0.2 at.%. The photoluminescence spectra show emission from localized nitrogen states as well.

A simple capacitance method for determination of feature sizes in LDD devices is presented. It is based on direct measurement of the intrinsic MOS capacitances using a suitable multitransistor test structure. Experimental results for conventional and inverse T , lightly-doped drain MOSTs with 1.5 μm drawn channel length are shown.

Methods for measuring the intrinsic capacitances of small geometry MOS transistors are described. The influence of short- and narrow-channel effects on the capacitance characteristics of MOS transistors is evaluated. The results are compared with long-channel devices. It is shown that the presented capacitance methods can be used to study the physics of short-channel transistors.

To scale MOS transistors beyond 100 nm, it is imperative to find a dielectric of high permittivity (high-k dielectric) to replace the current SiO/sub 2/ as a gate insulator. In principle, a high dielectric can deliver an equivalent SiO/sub 2/ thickness of 1 nm with a greater physical thickness (20 nm if k=80) and, hence lower leakage current. Realizing the promise of high-k dielectrics in the ULSI technology is an enormously challenging task. There are several classes of dielectric, such as oxides and fluorides. The simplest such oxides have one metallic element, e.g. HfO/sub 2/, ZrO/sub 2/, Y/sub 2/O/sub 3/ with rare earth metals. Their dielectric constant range is from 10-30. More complex such oxides have two different metallic elements such as BaTiO/sub 3/ and SrTiO/sub 3/. They can form solid-state solutions with each other at all ratios, because of their identical crystal structures. That is why thin films of barium titanate (BTO) and barium strontium titanate (BSTO) of a permittivity in the range of 100-400 and greater specific capacitance, have emerged as a leading contender as a gate dielectric for sub - 0.1 mm MOS transistors. In this study results are reported of the structural and dielectric properties of several thin films prepared by the sol-gel method. The electrical properties are investigated on MIS structures and the results are related to the effect of reaction with the silicon substrate upon thermal annealing.

This paper presents the state of the art of photovoltaics in the new member and candidate states of the European Union, namely, Bulgaria, the Czech Republic, Estonia, Hungary, Latvia, Lithuania, Poland, Romania, the Slovak Republic, and Slovenia. A brief survey of the research, including its organization and potentials, and the development, industry, markets, demonstration installations, education, policies, support mechanisms, barriers, challenges, and needs is given.

In hot climates, the use of PV modules is sometimes problematic, since their efficiency normally decreases with increasing solar cell temperature. The temperature behavior of PV modules is thus important when considering their application for large-scale economical power generation.

The present paper reports the incorporation of Si nanoparticles (NPs) in (Al2O3)x (B2O3)1-x films. A new approach for involving Si NPs (20 nm) p+ doped into sol solution was used. After spin coating deposition and additional annealing at 850°C, (Al2O3)x (B2O3)1-x films with Si NPs have been obtained with thickness of 75 and 120 nm. The (Al2O3)x (B2O3)1-x films were deposited on p-type and n-type Si wafers. The optical study reveals that Si NPs embedded in (Al2O3)x(B2O3)1-x leads to higher absorption in the visible spectral range compared to dielectric layer without nanoparticles. AFM studies show that the incorporated Si nanoparticles into the dielectric layer have probably a uniform distribution on film surface. This conclusion is confirmed by SEM observation. The current - voltage (I-V) characteristics of a structure (Al2O3)x(B2O3)1-x layer with Si NPs on p- type Si shows an ohmic type of conductivity. The sheet resistance is 480 Ohm/sq respectively, when the same layer is deposited on quartz substrate. This work presents a new technological approach for integration of Si NPs in dielectric matrix of (Al2O3)x (B2O3)1-x. The results can find applications for formation of ultra thin emitter for photodiodes and Si solar cells.

The performance of bulk heterojunction P3HT :PCBM polymer solar cells is studied using current-voltage and spectral sensitivity measurements. Front transparent contacts of either ITO or a sputtered multilayer TiO2/Ag/TiO2 transparent conductive electrode are applied. Thin PEDOT:PSS and P3HT:PCBM polymer layers are deposited on these substrates by spin coating. The degradation of the solar cells is studied by subjecting them to UV irradiation. The obtained spectral sensitivity curves are analyzed in comparison with the optical absorption spectra of the transparent electrodes and active layers employed. It is observed that there is a pronounced dependence of the spectral sensitivity curves on the thermal treatment and UV irradiation applied to the solar cells. The performance of the multilayer TiO2/Ag/TiO2 transparent conductive electrodes is also studied in comparison with that of the ITO ones.

We present a detailed investigation of the properties of silicon dioxide deposited at a low temperature. The advantages of this process include its low thermal requirements (about 200 °C), the absence of corrosive by-products and the lack of need of vacuum equipment. Sol solutions were prepared for the deposition of ultrathin SiO2 films by spin-coating at the low annealing temperature of 200 °C. The layers' thickness was 24 nm and 5 nm. We describe in detail the material properties of this novel low-temperature SiO2 layers obtained by extensive characterization using Fourier transform infrared spectroscopy (FTIR), atomic force microscopy (AFM), XPS spectroscopy, capacitance-voltage (C-V) and current-voltage (I-V) measurements. The ultrathin oxide layers on Si substrates show good dielectric properties.

ZrO2 and (ZrO2)x(Al2O3)1-x films were deposited by the sol-gel technique on Si substrates. The effect of the Al2O3 additive on the film surface morphology was studied by atomic force microscopy (AFM). The mixed oxide films showed a smoother morphology and lower values of the root-mean-square (RMS) roughness compared to ZrO2. Further, FTIR spectra indicated that ZrO2 underwent crystallization. The electrical measurements of the MIS structure revealed that the presence of Al2O3 and the amorphization affects its dielectric properties. The MIS structure with (ZrO2)x(Al2O3)1-x showed a lower fixed charge (~ 6×1010 cm−2) and an interface state density in the middle of the band gap of 6×1011 eV−1 cm−2). The dielectric constant measured was 22, with the leakage current density decreasing to 2×10−8 A cm−2 at 1×106 V cm−1.