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We compute the thermal conductivity of amorphous SiO 2 combining density functional theory calculations and lifetime models. The supercell we use to represent amorphous SiO 2 is small, 78 atoms. We show that this rudimentary model is nevertheless sufficient to reproduce the temperature dependence of the thermal conductivity from 0.1 K to 1000 K if we use a lifetime model at low frequencies accounting for Rayleigh scattering, the absorption of phonons by two levels systems and structural relaxations. The necessary conditions needed to observe the plateau in the thermal conductivity around 10 K are also discussed according to this model. • Ab initio calculation of the thermal conductivity of amorphous silica. • Intraband and interband contributions to the thermal conductivity. • The calculations are performed using small sample of amorphous silica. [ABSTRACT FROM AUTHOR]

The indium and aluminum nitride (In x Al 1-x N) semiconductor material was postulated in 2008 as an excellent candidate to produce solar cells. In this research, amorphous layers of In x Al 1-x N (0.55 ≤ x ≤ 0.60) were synthesized using the RF sputtering magnetron technique, and then studied for their possible use in photovoltaic applications. Physical, structural, morphological, optical, and electrical properties were studied. The amorphousness was checked by XRD difractograms. Samples have very smooth surfaces, with very low roughness values, according to AFM and SEM techniques. Electrical properties of the InAlN films were studied using Van Der Pauw technique and Hall Effect parameters. The volumetric carrier concentration decreases when InN fraction mole increases. The mobility values range between 6 × 10 −2 and 5 × 10 −1  cm 2  V −1  s −1 , which are lower than those obtained for crystalline and polycrystalline samples. The obtained band gap values could be used in both the absorbing layer and the window layer in solar cells (1.9 eV–2.3 eV). Interestingly, this figures of Eg are very close to the previously obtained values for polycrystalline samples. The optical absorption coefficients were high compared to the materials currently used in solar cells (~10 5  cm −1 ). This implies the possibility of using thinner layers in photovoltaic devices based on In x Al 1-x N. [ABSTRACT FROM AUTHOR]

Under its crystalline form, the ZnGeN 2 alloy is promising for optoelectronic devices such as LEDs because of its large, direct and adjustable band gap. Nevertheless, data are scarce, more especially for the amorphous form. We report here on the study of zinc germanium nitride amorphous thin films obtained by reactive co-sputtering. The samples are elaborated by PVD and analyzed by physical and chemical methods to determine their composition, structure and optical properties. We observe a clear evolution of these properties with composition. The shape of the complex refractive index reveals changes in the electronic structure. Furthermore, the optical gap and Urbach energy decrease with increasing zinc content. [ABSTRACT FROM AUTHOR]

A time-resolved pump-probe method is used for the evaluation of non-linear optical coefficients of chalcogenide glasses from the As-S-Se and Ge-Se systems near their fundamental absorption band edges. The results are analyzed via comparison with the spectral dependencies of the non-linear optical coefficients of crystalline semiconductors; the role of electron transitions through the gap states of chalcogenide glasses is discussed. [ABSTRACT FROM AUTHOR]

We propose and optimize theoretically a supercontinuum (SC) laser source in the mid-IR based on using As-Se-Te/As-S core/clad step-index fibers and a femtosecond all-fiber laser system at 2 μm. Numerically simulated spectra extending from ~ 1 μm to > 8 μm are demonstrated for pump energy of order 100 pJ in a fiber with a core diameter of 2 μm. To the best of our knowledge, the possibility of such long-wavelength spectral conversion of pump pulses at the wavelength of 2 μm in optical fibers is demonstrated for the first time. The theoretical calculations are performed on the base of real low loss step-index As-Se-Te/As-S glass fibers with various core-clad diameter ratios. [ABSTRACT FROM AUTHOR]

We report the detailed thermal, structural, microstructural and electrical transport studies on Pb x Ge 42 − x Se 58 with (0 ≤ x ≤ 20) glasses. The influence of Pb content on thermal and local atomic structure and its qualitative consequences on the electronic properties has been elucidated. The composition dependent variation of glass transition temperature (T g ), change in specific heat capacity at the glass transition (ΔC p ) and non-reversing enthalpy change (ΔH NR ) complement with each other for enabling the role of Pb content on structural relaxation behavior of these glasses. The Raman spectroscopic studies reveal the presence of different structural species and its variation with Pb content, i.e. pronounced decrease in the amount of ethane-like structural units with the incorporation of Pb content. The addition of Pb content into Ge 42 Se 58 glass, the network connectivity becomes loosened due to the depolymerization. The observed Raman band position of ethane-like structural units show noticeable blue shift with an increase of Pb content, which dictates the development of stress in the network structure caused by the predominant ionic character. The microstructural studies by positron annihilation life-time spectroscopy reveal the nature of defect states and its variation with Pb content. The composition dependent dc conductivity and its activation energy shows marked change across the p-n transition threshold due to the change in the charged defect concentration. The influence of local atomic structure and nature of defect states responsible for the carrier type reversal (CTR) has been discussed. [ABSTRACT FROM AUTHOR]

We report on the investigation of morphology, magnetic and conductive properties of the mutilayered nanostructures [(Co 40 Fe 40 B 20 ) 34 (SiO 2 ) 66 ]/[C] 47 consisting of the contacting magnetic (Co 40 Fe 40 B 20 ) 34 (SiO 2 ) 66 nanocomposite and amorphous semiconductor carbon C layers. It is shown by Grazing-Incidence Small-Angle X-ray Scattering method that the ordering and the size of nanoparticles in the magnetic layers do not change profoundly with increasing of carbon layer thickness. Meanwhile, the electrical conductance and the magnetic properties are significantly varied: resistance of the samples changes by four orders of magnitude and superparamagnetic blocking temperature changes from 15 K to 7 K with the increment of carbon layer thickness h c from 0.4 nm to 1.8 nm. We assume that the formation of the homogeneous semiconductor interlayer leads to modification of the metal-insulator growth process that drives the changes in the magnetic and conductive properties. [ABSTRACT FROM AUTHOR]

A physics-based model for electron and hole mobility in an amorphous semiconductor is developed to estimate the mobility limits of an amorphous semiconductor. The model involves band tail state trapping of a diffusive (Brownian motion) mobility and accounts for both drift- and diffusion-induced transport, as normally encountered in the operation of a thin-film transistor. Employing this model leads to a predicted maximum mobility of ~70 cm 2 V -1 s -1 (~10 cm 2 V -1 s -1 ) for electrons (holes). [ABSTRACT FROM AUTHOR]

We have in depth analyzed the refractive-index behavior and optical absorption of below-band-gap light, in order to calculate the basic parameters of the energy-band structure of thin layers of non-crystalline semiconductors. By carrying out a semi-empirical determination of the influence of the finite (non-zero) width of the valence and conduction electronic bands, we find the dependence of the index of refraction upon the photon energy, n (E) , which goes just one order beyond the Wemple–DiDomenico two-level single-oscillator expression, and we simultaneously obtain the spectral dependence of the absorption coefficient, α (E). By model fitting the measured normal-incidence transmittance spectrum, we demonstrate that with a highly-sensitive double-beam spectrophotometer, it can be accurately determined the energy distance, E M,Sol , between the corresponding 'centers of mass' of the bonding and anti-bonding electronic bands, and also a reasonable estimate of the so-called effective width, Δ eff , of both valence and conduction bands. We have used this devised optical approach with a series of uniform and non-uniform thin layers of unhydrogenated fully a -Si, grown by RF-magnetron-sputtering deposition, onto room-temperature transparent glass substrates. The advantages of our novel approach are mainly due to the additional attention paid to the roles of the weak-absorption Urbach tail and the thickness non-uniformity of the studied a -Si films. We have also used a universal normal-incidence transmission expression reported by the authors in an earlier paper, which can be applied even to strongly-wedge-shaped semiconductor layers. Together with the use of the improved Solomon formula for the normal optical dispersion of the refractive index, the complete approach with all its elements constitutes the main novelty of the present paper, in comparison with other existing works. [Display omitted] • Amorphous silicon thin layers have been prepared by radio-frequency magnetron sputtering on room-temperature glass substrates. • The film thickness and optical constants have been determined by a novel inverse-synthesis approach. • The refractive-index dispersion has been analyzed by using the Solomon model. • Structural characterization of the amorphous silicon specimens has been carried out by Raman spectroscopy and X-ray diffraction. • The void volume fraction of the a -Si films has been found by using effective-medium theories. [ABSTRACT FROM AUTHOR]

The composition dependence of optical and electrical of amorphous unirradiated and γ-irradiated thin films of Pb x Ge 42-x Se 48 Te 10 (5 ≤ x ≤ 16) deposited by thermal evaporation was measured as a function of wavelength (0.3 μm ≤ λ ≤ 2.5 μm). The optical transition was found to be indirect. The optical energy gap (E opt ) decreases with increasing concentration of Pb at.wt.% and exhibits a minimum value for the composition with 9 at.wt.% Pb and the results have been interpreted in terms of the average bond energy. The band tail (E c ) obeys Ubarch's empirical relation. The d.c. electrical resistance was measured in a temperature range of (300–455 K). The activation energy for electrical conduction decreased with increasing Pb concentration. The electronic conduction in the temperature range has been attributed to band transport mechanism. The effect of γ-radiation on the optical constants (n, k), band tail (E c ) and E elect energies as a function of composition has been determined. The results show that, the radiation causes increase in optical and electrical energies as γ-doses increase. [ABSTRACT FROM AUTHOR]

Morphology, microstructure and phase evolution of nanocrystalline Ce 0.5 Gd 0.5 O 1.75 mixed oxide supported on amorphous SiO 2 were studied in oxidizing and reducing atmosphere by XRD, TEM and SEM-EDS. The Ce 0.5 Gd 0.5 O 1.75 /SiO 2 samples were prepared by two methods: impregnation of the support with an aqueous solution of nitrates and deposition of homogeneous Ce 0.5 Gd 0.5 O 1.75 nanoparticles synthesized using the microemulsion method. The latter system is structurally and chemically stable in the oxidizing atmosphere up to 1000 °C, exhibiting only a small increase of the mean crystallite size of the mixed oxide from 2 to 3 nm. Prolonged heating at 1100 °C for 24 h caused partial decomposition of the mixed oxide and formation of small amount of B-Gd 2 Si 2 O 7 . In the reducing atmosphere the Ce 0.5 Gd 0.5 O 1.75 underwent amorphization and spreading over SiO 2 already at 900 °C to form an amorphous silicate. Most of the silicate remained amorphous even after reduction at 1100 °C, but certain amount crystallized into particles with strongly defected structure. The system prepared by impregnation exhibited significantly worse thermal stability due to chemical inhomogeneity. The complex systems synthesized in this work, containing nanocrystalline particles of mixed silicate with high concentration of Ce 3 + ions, may be interesting as scintillating materials. [ABSTRACT FROM AUTHOR]

Abstract: We investigate temperature dependence of electric conductivity and photoconductivity of hydrogenated amorphous silicon (a-Si:H) thin films due to energetic proton irradiation and clarify the change in dominant electric conduction mechanism. We also investigate variations of the temperature dependence after proton irradiation at different temperatures and the recovery from radiation damage due to thermal annealing. The results show that the high fluence proton irradiation changes the dominant electric conduction mechanism from the band transport of thermally excited carriers through the extended states to the hopping transport based on the carrier transport via localized states near the Fermi level. The hopping conduction has the weak temperature dependence which disappears at elevated temperature and the strong temperature dependence based on the band conduction appears again. Also, the proton irradiation at high temperature never provoke the hopping conduction. However, the band conduction after irradiation is not completely restored even after thermal annealing, indicating that thermally stable radiation defects remain. We conclude that these dominant electric conduction mechanism changes originated from proton irradiation and thermal annealing, and are simply caused by the increase or decrease in localized density of states. [Copyright &y& Elsevier]

Abstract: Optical properties of amorphous Se80− x Te20Bi x thin films with different compositions (x =0, 2, 4, 6 and 8at.%) deposited by evaporation technique have been investigated by optical spectrophotometry measurements in the wavelength range of 400–2500nm. An optical characterization method for uniform films based on Swanepoel's ideas (envelope method) has been employed to extract the refractive index n and film thickness d, with accuracies better than 1%. It was found that the refractive index increases with increasing the concentration of Bi at the expense of Se content. The increasing in refractive index n is interpreted in terms of polarizability and the mean coordination number. The dispersion of the refractive index is discussed in terms of the single oscillator Wemple–DiDomenico model. The fundamental parameters for the investigated semiconducting thin films Se80− x Te20Bi x e.g. absorption coefficient and band gap are calculated in the strong absorption region of transmittance and reflectance spectra. The possible optical transition in these films is found to be allowed indirect transition with energy gap E g optdecreases from 1.467 to 1.035eV with increasing Bi content at expense of Se. Finally, the decrease in the optical band gap with increasing Bi content in Se80− x Te20Bi x has been explained in terms of the chemical bond approach. [Copyright &y& Elsevier]

Abstract: This paper contributes to a series of work analyzing the Meyer–Neldel compensation rule (MNCR) for various binary Se-based amorphous semiconductor systems. These systems are classified into two groups relying on the coordination number of the stoichiometric compound in each of the binary systems (〈r〉=2.4 and 2.4〈r〉≤2.67). The estimated shift in the Fermi level of the investigated materials declares the physical basis of the MNCR behavior for DC conductivity where the activation energies (ΔE) are commonly measured around and above room-temperature. Also, the obtained MN energy (E MN ) values, supporting the electronic polaron hopping model resulted from the carrier-induced softening vibrations, provide a clearer physical picture for origin of the rule. In this consensus, one can realize the concept of multiple excitations entropy, that reserved for the large vibrations accompanied large ΔE, dominates the correlation between the two MNCR parameters (true pre-factor σ 00 and E MN ) for all investigated systems in both groups. [Copyright &y& Elsevier]

Abstract: Optical and electrical properties of the (Se80Te20)100− x Ag x (0≤ x ≤4) ultra-thin films have been studied. The ultra-thin films were prepared by thermal evaporation of the bulk samples. Thin films were annealed below glass transition temperature (328K) and in between glass transition temperature and crystallization temperature (343K). Thin films annealed at 343K showed crystallization peaks for Se–Te–Ag phases in the XRD spectra. The transmission and reflection of as-prepared and annealed ultra-thin films were obtained in the 300–1100nm spectral region. The optical band gap has been calculated from the transmission and reflection data. The refractive index has been calculated by the measured reflection data. It has been found that the optical band gap increases, but the refractive index, extinction coefficient, real and imaginary dielectric constant decrease with increase in Ag content. The optical band gap and refractive index show the variation in their values with increase in the annealing temperature. The extinction coefficient increases with increasing annealing temperature. The surface morphology of ultra-thin films has been determined using a scanning electron microscope (SEM). The measured dc conductivity, under a vacuum of 10−5 mbar, showed thermally activated conduction with single activation energy in the measured temperature range (288–358K) and it followed Meyer–Neldel rule. The dc activation energy decreases with increase in Ag content in pristine and annealed films. The results have been analyzed on the bases of thermal annealing effects in the chalcogenide thin films. [Copyright &y& Elsevier]

Abstract: The paper reviews our understanding of the conduction, localisation, instability and doping properties of amorphous oxide semiconductors. Amorphous oxide semiconductors (AOSs) are characterized by a larger Bohr radius than a-Si:H, so that the density of states at the mobility edge is much lower than in a-Si:H. Combined with a sharper conduction band tail, this leads to a much small total density of tail states in AOSs, leading to a sharper turn-on characteristic for their thin film transistors. The band gaps of most semiconducting oxides are wide, which is valuable for transparent electronics, but means that they are unlikely to be bipolar dopable, reducing their prospects for solar cells. [Copyright &y& Elsevier]

Abstract: We have studied the epitaxial-like growth of germanium (Ge), due to solid phase crystallization (SPC) from amorphous Ge (a-Ge) deposited on single crystal silicon (Si) substrate. The crystalline growth of Ge following the orientation of Si substrates was successfully obtained by the SPC at 400°C or higher. The preferential growth on Si (111) substrates continues up to 10,000Å. Different orientations from the substrate orientation in XRD patterns are slightly observed in the growth on Si (100) substrates at 450°C, but the preferential growth of (100) orientation continued in the whole film thickness in TEM images. The epitaxial-like growth of Ge may be more preferable on the Si (111) substrate than the (100) one. [Copyright &y& Elsevier]

Abstract: The anomalous sign of the Hall coefficient in amorphous semiconductors is still poorly understood. It seems accepted, however, that an anomalous sign of the Hall coefficient indicates a different charge transport mechanism compared to free carrier motion on which the Lorentz force is acting. We find anomalous Hall coefficient signs in phosphorus-doped microcrystalline silicon films after irradiation with high energy electrons and subsequent annealing. These films are mixtures of amorphous and crystalline phases. We analyze measurements of Hall effect, electrical conductivity, and thermopower on such samples prior to and after electron irradiation and annealing, and use the anomalous Hall effect sign as a phenomenological indication of electronic transport in the amorphous phase. We deduce that the material consists of crystalline particles embedded in an amorphous matrix. [Copyright &y& Elsevier]

Abstract: The change in the surface morphology of amorphous Sb2Se3 thin films during the electron beam irradiation has been studied mainly by atomic force microscopy (AFM). Electron beam at accelerating voltages 30kV is focused onto the surface of the specimens of 100-μm thickness, and then the surface morphology of each specimen has been observed by AFM in air. The modification of the film surface includes lateral and vertical resizing which is typically in the micrometer and sub-micrometer range. Protrusions above the surface as high as 90nm are observed at 180pA electron beam current, whilst trenches as deep as 97nm are observed at 800pA electron beam current (total thickness of thin film is 100nm). The dependence of patterns characteristics on irradiation parameters such as exposure time and beam current has also been studied. Physical mechanisms for trench and mound formation are proposed. [Copyright &y& Elsevier]

Abstract: The origin of the compensation Meyer–Neldel rule (MNR) for an Arrhenius dc conductivity behavior has been elucidated via comparative analytical studies on non-crystalline and crystalline groups of Se-like structure semiconductors (i.e., mixed isoelectronic chalcogens: Se–S, Se–Te and Se–S–Te systems) with a comparison with those of Si:H. Findings and results disclosed a clear appearance of the MNR in all non-crystalline forms and a common deviation for the crystalline structures. The presence (EMN >0) or absence (EMN <0) of the MNR does not depend entirely on the quantity of the activation energy of conduction process, whether it is small or large. This surveillance brings about a fact that defects associated with disorder do behave in a monotonic similar mode in the two non-crystalline semiconductors types. In this consensus, one can realize that the concept of the multiple excitations entropy stimulated by phonon energy is strongly authenticating the correlation between the two MN parameters (true-prefactor σ 00 and MN-energy E MN ) for both lone-pair (mixed chalcogens) as well as for tetrahedrally bonded (Si:H) semiconductors. [Copyright &y& Elsevier]

Abstract: One of the most important parameters which determine the performance of many modern devices based on amorphous semiconductors is the drift mobility-lifetime product, μτ. There has been much interest in determination of charge-carrier ranges in amorphous semiconductors by various measurement techniques. Although the mobility, μ, can be measured by the conventional time-of-flight transient photoconductivity technique, the determination of the lifetime, τ, is often complicated by both experimental and theoretical limitations. The present article provides an overview of xerographic measurements as a tool for studying the electrical properties of amorphous semiconductors. First, details of the experimental set-up are discussed. Thereafter, the analysis and interpretation of dark discharge, the first cycle residual potential, cycled-up saturated residual potential are considered. It is shown that from such measurements the charge-carrier lifetime, τ, the range of the carriers, μτ, and the integrated concentration of deep traps in the mobility gap can be readily and accurately determined. Xerographic measurements on Se-rich amorphous photoconductors have indicated the presence of relatively narrow distribution of deep hole traps with integrated density of about 1013 cm−3. These states are located at ~0.85eV from the valence band. A good correlation was observed between residual potential and the hole range, in agreement with the simple Warter expression. The capture radius is estimated to be r c =2–3Å. Since r c for pure a-Se and a-AsxSe1−x is comparable to the Se–Se interatomic bond length in a-Se, it can be suggested that deep hole trapping centers in these chalcogenide semiconductors are neutral-looking defects, possibly of intimate valence-alternation pair (IVAP) in nature. The absence of any electron spin resonance signal (ESR) at room temperature seemed to be a strong argument in favor of this suggestion. Finally, photoinduced effects on xerographic parameters are discussed. It has been shown that photoexcitation of a-AsxSe1−x amorphous films with band-gap light alters deep hole and electron states. During room-temperature annealing photosensitized states relax to equilibrium. Recovery process becomes slower with increasing As content. Qualitative explanation of the observed behavior may be based on associating the deep states with C3 + and C1 −intimate-valence-alternation–pair (IVAP) centers. [Copyright &y& Elsevier]

Abstract: Local structures of the hydrogenated (Ni0.6Nb0.4)1-xZrx (x=0.3–0.4) amorphous alloys attract much attention for the sake of their epoch-making electronic transport behaviors. We investigated the local structures by XAFS for the as-quenched (Ni0.6Nb0.4)0.65Zr0.35 and hydrogenated [(Ni0.6Nb0.4)0.65Zr0.35]0.922H0.078 amorphous alloys, in which ballistic conductivity has been observed. XAFS results of the Ni K-edge are analyzed based on the structure model deduced by the first principle calculation. The analysis suggests that highly distorted icosahedral Ni5Nb3Zr5 cluster, which has a centered-Ni and a surrounding Nb triangle, is a main structural unit of (Ni0.6Nb0.4)0.65Zr0.35 and the [(Ni0.6Nb0.4)0.65Zr0.35]0.922H0.078 amorphous alloys. This distorted icosahedral Ni5Nb3Zr5 cluster can be associated with the occurrence of the singular electronic transport behaviors of the hydrogenated (Ni0.6Nb0.4)0.65Zr0.35 alloy. [Copyright &y& Elsevier]

Abstract: We have experimentally measured the current–voltage and capacitance–voltage characteristics of Au/amorphous As x Se1− x (x ≤0.05)/Zr trilayer structures at temperatures from 4 to 295K. The observed capacitance of structures with an amorphous As x Se1− x (a-As x Se1− x ) thickness of ~0.4 to ~2.8μm does not significantly change over the entire range of applied bias (−5V to 5V), indicating that the a-As x Se1− x films are fully depleted and thus the structures are Mott barriers. The current–voltage (I–V) characteristics of the a-As0.03Se0.97 device at low (< 3000V/cm) to moderate fields (3000V/cm–10000V/cm) follow the predictions of trap limited space charge conduction theory, as they exhibit Ohmic behavior at low fields and trap limited space charge current at moderate fields. According to the trap limited space charge current model of Lampert, the a-As0.03Se0.97 film has an effective hole mobility, Θμ (with Θ<1), of ~5×10−7 cm2/V-sec at 295K. This value is similar to, but consistently lower than previously reported mobilities inferred from time of flight measurements. The current at high fields (>104 V/cm) increases rapidly with applied field as a result of carrier emission from localized states and is consistent with transport by the Poole–Frenkel mechanism. A permanent transition to a high conductance state (~10−3 S) is observed after exposure to very high electric fields (~4×105V/cm). [Copyright &y& Elsevier]

Abstract: Amorphous GeSx (x=2, 4, 6) films were prepared by the pulsed laser deposition (PLD) technique. The optical band gaps (E g opt ) and refractive indices of the films were obtained from the optical absorption spectra and transmission spectra, respectively. The short-wave absorption edges of the films were described using the ‘non-direct transition’ model proposed by Tauc. The dispersion of the refractive index was analyzed in terms of the single-oscillator Wemple–Di Domenico model. The structural units of the films were characterized using Raman spectroscopy. In addition to the basic structural units of edge-sharing and corner-sharing [GeS4] tetrahedra, there are S–S homopolar bonds in S-rich GeS4 and GeS6 films while Ge–Ge bonds exist in stoichiometric GeS2 film. The results show that the index of refraction decreases while E g opt increases with the sulphur content in the GeSx films. The changes of E g opt were discussed in relation to the structure of GeSx films, which were confirmed by the Raman spectra analysis. [Copyright &y& Elsevier]

Abstract: Exposure with above band gap light and thermal annealing at a temperature near to glass transition temperature, of thermally evaporated amorphous (As2S3)0.85Sb0.15 thin films were found to be accompanied by structural effects, which in turn, lead to changes in the optical properties. The optical properties of thin films induced by illumination and annealing were studied by Fourier Transform Infrared spectrometry, X-ray Photoelectron Spectroscopy and Raman Spectroscopy. Photodarkening or photobleaching was observed in the film depending upon the conditions of the light exposure or annealing. These changes of the optical properties are assigned to the change of homopolar bond densities. The photodarkening in the as-prepared film was seen at low temperature (4.2K). [Copyright &y& Elsevier]

Abstract: Hydrogenated amorphous silicon (a-Si:H) films show considerable potential for the fabrication of thin film solar cells. In this study, the a-Si:H thin films have been deposited in a parallel-plate radio frequency (RF) plasma reactor fed with pure SiH4. The plasma diagnostics were performed simultaneously during the a-Si:H solar cell deposition process using an optical emission spectrometer (OES) in order to study their correlations with growth rate and microstructure of the films. During the deposition, the emitting species (SiH*, Si*, H*) was analyzed. The effect of RF power on the emission intensities of excited SiH, Si and H on the film growth rate has been investigated. The OES analysis revealed a chemisorption-based deposition model of the growth mechanism. Finally, the a-Si:H thin film solar cell with an efficiency of 7.6% has been obtained. [ABSTRACT FROM AUTHOR]

Abstract: We have fabricated a dielectric reflector and a passband filter, both with first order photonic bandgaps in the middle-infrared region around λ =4μm. The devices were made from alternating amorphous Ge25S75 and Ge15Te85 chalcogenide films with high transparency in the middle infrared region stacked in multilayers. Due to high thickness accuracy and periodicity of prepared multilayers we also observed second order photonic bandgaps at λ ~1.4μm. The experimental data were in good agreement with theoretical predictions. The work focused on investigation of compositional homogeneity, surface roughness, thermal and optical properties of individual amorphous Ge25S75 and Ge15Te85 films. We confirmed chalcogenide materials as being of suitable choice for designing middle-infrared quarter wave stack devices. FT-IR reflectance spectra confirmed occurrence of 99.4% stopband near λ =4μm for fabricated reflector and narrow ~50% passband of prepared filter near λ =3.934μm. [ABSTRACT FROM AUTHOR]

Abstract: Feasibility of producing high purity silicon from amorphous silica fume, using a low temperature magnesiothermic reduction was demonstrated. Commercial silica fume containing 97.5% amorphous silica was first purified by acid leaching and roasting to remove large quantities of transition metals and carbon. The product was then reduced using magnesium as the reductant. The effect of the amount of reductant, initial temperature, and dwell time were investigated on the quantity and type of the reaction products. The optimum reduction conditions were decided based on the maximum yield of the Si metal. These corresponded to Mg/SiO2 molar ratio of 2.0, preheating temperature of 750 °C, and holding time of 2h. High purity silicon (>99wt.%) containing <3 ppmw B and 12 ppmw P was obtained after leaching purification of the reduction products, showing that the material is superior to metallurgical grade silicon, for use as solar-grade silicon feedstock. [ABSTRACT FROM AUTHOR]

Abstract: Photoconductivity (PC) variations of device-grade a-Si:H thin films due to proton irradiation are investigated in this paper. We performed in-situ measurements of the PC variations induced by 0.10, 1.0 and 10MeV proton irradiations. The irradiation initially caused an increase in PC in all sample. However, continued irradiation resulted in a dramatic decrease as the irradiation fluence increased. The results obtained in this study suggest that the PC increment is caused not by accumulation of displacement damage. We also found that the dark conductivity (DC) was drastically increased in the same manner as the PC increment, whereas the photosensitivity had a minimum value at the peak of the PC increment. The results of the temperature dependence of PC for a-Si:H before and after 10MeV proton irradiation showed that such a proton-induced PC increment consisted of two components: one thermally stable and one metastable. The thermally metastable component disappeared in the temperature region of 300 to 340K. On the contrary, radiation-induced defects were annealed above 340K. [Copyright &y& Elsevier]

Abstract: Optical properties and structural aspects of As x S100-x glasses from visible to terahertz wavelengths were explored. A series of annealed, bulk As x S100-x glasses (x =30 to 42) were made and their refractive indices determined at terahertz, infrared, and visible frequencies using a quasi-optical backwards wave oscillator spectrometer for terahertz measurements combined with a prism coupler for visible and infrared measurements. It was found that the refractive index at all frequencies increases with arsenic composition up to 40at.% arsenic and then decreases with additional arsenic. The structure in X-ray diffraction patterns supports the notion of a minimum volume at 40at.%, while the average covalent coordination number indicates that the rigidity percolation threshold is reached there. At arsenic concentrations >40at.%, the network becomes over-constrained, and the molar volume increases. [Copyright &y& Elsevier]

Abstract: A novel process is employed in the fabrication of porous anodic aluminum oxide film in neutral electrolyte. A titration technique which involves titration of acid–base neutralization process is used as the electrolyte source in the anodization of the aluminum substrate. Freshly prepared 10% phosphoric acid at pH1 is titrated with 1M of sodium hydroxide until it reaches pH7 in a neutral environment. The growth of the porous anodic film was made possible by 60V dc applied potential from an in-house electrochemical cell to the aluminum substrate in the neutral electrolyte. The diameter of the pores produced is in the range of 40–200nm. [Copyright &y& Elsevier]

Abstract: We study the vibrational properties of amorphous germanium at high pressures using a constant pressure ab initio technique. With the application of pressure, the low-frequency modes gradually soften with a decrease in their acoustic-like nature while the high-frequency modes shift to larger frequencies. The acoustic-like vibrations are found to have negative Grüneisen parameters whereas the optic-like ones have positive values of about +1. A negative thermal expansion is produced below 200K. Furthermore, we find that pressure reduces the number of localized states. Accompanied by the phase transition into a metallic high-density amorphous state, the nature of the low-frequency vibrations is changed from acoustic-like to optic-like and from bond bending to bond stretching. [Copyright &y& Elsevier]

Abstract: Phase transition triggered by picosecond (ps) single-shot laser pulse in as-deposited AgInSbTe films was achieved with appropriate laser fluence. Structure transition is further conformed by micro-area X-ray diffraction measurement. Current–voltage curves of the amorphous and the picosecond laser-crystallized area were measured by conductive atomic microscopy. Ultrafast laser pulse recording and electrically reading will be very promising for phase change data storage due to high data transfer rate and high readout signal-to-noise ratio. These results will be helpful to make ultrafast optical–electrical hybrid phase change data storage feasible. [Copyright &y& Elsevier]

Abstract: Oxide glass with a starting composition of 40P2O5–40V2O5–20Fe2O3 (mol%) is prepared by the usual melt quenching technique. The prepared sample is heat treated at 500K for 4, 6 and 8h. The effect of heat treatment on the hyperfine structure and dielectric properties is studied in more details. The hyperfine structure of these glasses is investigated using Mössbauer spectroscopy. The measured isomer shifts showed that, the ferric ions (Fe3+) are in octahedral and tetrahedral coordinations. The infrared spectra of these glasses is recorded over a continuous spectral range (400–1400cm−1) as an attempt to study their structure systematically. The structure of these glasses has investigated by means of IR studies which shows the presence of ν(VO3) single chains, VO4 octahedral and VO5 trigonal bipyramids. Unmonotonic variation in the ac conductivity, σ ac(ω), the dielectric constant, ε 1(ω), and the dielectric loss, ε 2(ω), is found with increasing the HT time. The room temperature ac conductivities at a fixed frequency (10kHz) of the as quenched and the heat treated for 4, 6 and 8h samples are 1.4×10−4, 4.1×10−4, 1.7×10−5 and 4.15×10−6 (Scm−1), respectively. The ferroelectric transition temperature is shifted to lower temperature with increasing the HT time. [Copyright &y& Elsevier]

Abstract: Boron-doped hydrogenated microcrystalline silicon thin films (p-μc-Si:H) have been deposited by RF-PECVD method at different temperature, and the temperature dependence of growth kinetics and optoelectronic properties of p-μc-Si:H thin films have been studied. Both the deposition rate and the dark-conductivity of the p-μc-Si:H thin films drop down when the substrate temperature decreases. XRD and Raman measurements are used to characterize the micro-structure of p-μc-Si:H thin films prepared at different substrate temperature. Grain size of p-μc-Si:H thin films with different thickness as a function of substrate temperature has been investigated. Amorphous silicon thin film solar cells with p–i–n structures were fabricated on deposited boron doped μc-Si:H layers. The best cells performance is obtained for p-layers processed at 90°C. [Copyright &y& Elsevier]

Abstract: Amorphous indium tin oxide (ITO) thin films have been deposited on silicon and Corning 7059 glass substrates at room temperature (RT) and at 75°C by direct-current magnetron sputtering method. After exposure of the two kinds of samples to the temperature–humidity (T–H) test, we find that there are two different types of circular structures are formed. RT ITO films are composed of granules, and 75°C ITO films are composed of several different parts which have different Sn and In concentrations. Metallic ion concentration corrosion cells are used to explain the phenomena. [Copyright &y& Elsevier]

Abstract: New quaternary chalcogenide Ge x Sb40− x S50Te10 (x =10, 20 and 27at.%) and Ge x Sb40− x S55Te5 (x =20 and 27at.%) glasses have been synthesized and the compositions have been characterized applying prompt gamma-ray activation analyses, neutron diffraction, and material density measurements. Using the experimental data, the basic physical parameters, such as average atomic volume, packing density, compactness, average coordination number, number of constrains, average heat of atomization and cohesive energy, of the synthesized glasses are evaluated and the results are discussed in a function of glass composition. [Copyright &y& Elsevier]

Abstract: Chalcogenide glasses are interesting materials due to their infrared transmitting properties and photo-induced effects exhibited by them. Thin films of the glasses Sn10Sb20− x Bi x Se70 (0⩽ x ⩽8) prepared by melt quenching technique were evaporated in a vacuum better than 10−5 mbar. Optical transmission spectra of all the deposited films were obtained in a range 400–2500nm. The optical band gap and the absorption coefficient were calculated from the transmission data and refractive index was calculated using the swanepoel method. The optical band gap initially increases with increase in Bi content (for x =2) and then decreases sharply for higher Bi concentrations. The refractive index as well as absorption coefficient decrease with increase in wavelength. The dark activation energy initially increases with increase in Bi content and then decreases with further addition. [Copyright &y& Elsevier]

Abstract: Silicon thin films are deposited using plasma enhanced chemical vapor deposition (PECVD) of silane, argon, hydrogen mixture at various pressures in the range of 2–8Torr. Raman scattering shows these to be amorphous in the pressure range 6–8Torr, and nanocrystalline in the range 2–4Torr. The volume fraction of nanocrystals is estimated by fitting the Raman data to three peaks and is found to be ∼75% for the films deposited at low pressure, density of states of these films was measured. It is observed that the electrical conduction in these films depends on the crystalline volume fraction (ρ), estimated from the laser Raman Spectroscopy. Temperature dependence electrical conductivity shows that at lower temperatures thermionic emission dominates for the films with lower ρ, whereas, hopping is the main conduction mechanism for the films having high ρ. The density of states is estimated from the space charge limited currents (SCLC) observed at high fields. Photoconductivity at room temperature is also measured. The amorphous films are found to be more photosensitive than the nanocrystalline one. In the context of these findings, changes in the properties of silicon from amorphous to nanocrystalline are described. [Copyright &y& Elsevier]

Abstract: Large-scale synthesis of clustered one-dimensional amorphous silica nanowires was achieved by simple thermal pyrolysis of an amorphous preceramic powder from perhydropolysilazane on alumina wafers coated with catalyst FeCl2. Scanning electron microscopy and transmission electron microscopy observations showed that the silica nanowires had smooth surface, and lengths of hundreds of micrometers and diameters in the range of 30–40nm. Energy dispersive X-ray spectroscopy revealed that these nanowires consisted of Si and O elements in an atomic ratio of approximately 1:2, consistent with the stoichiometric formula SiO2. The two amorphous bulges in Raman spectrum at the centers of around 260cm−1 and 800cm−1 were identified to be those of amorphous silica. The growth mechanism of the as-produced silica nanowires could be attributed to vapor–liquid–solid mechanism. These results provide an alternative and simple preparation procedure for nanostructures with controlled morphology, and it will be helpful to understand the growth mechanism of one-dimensional SiO2 nanostructures. [Copyright &y& Elsevier]

Abstract: The influence of crucibles (Au or Pt) on the structure, electrical, dielectric and optical properties of 70TeO2·30PbCl2 glasses doped with Pr3+ added as a metal, chloride, or oxide, in concentrations of 500–1500wt-ppm, is reported. The dc conductivity of ‘pure’ glasses prepared in Au crucibles is two orders of magnitude higher than that of those prepared in Pt crucibles. Upon doping, the dc conductivity of glasses prepared in Pt and Au crucibles increases or decreases, respectively. The static relative permittivity is equal to 33±2. In the range of 640–700nm, six photoluminescence (PL) peaks were observed, at 641.5, 647.1, 652.4, 660.8, 662.9, and 664.5nm. In the range of 200–1200cm−1, seven Raman scattering (RS) peaks were observed at 184, 217, 321, 468, 654, 735cm−1, and a small peak at 650cm−1. Both spectra were deconvoluted using symmetrical Gaussian functions. Relative intensities of PL and RS bands depend on the concentration and chemical form of Pr3+ and on the material of the crucible. However, positions of these bands are independent of these conditions. [Copyright &y& Elsevier]

Abstract: Thermal properties and structure of As x Se100− x and Sb x Se100− x glass-forming systems (x =0, 1, 2, 4, 8 and 16) were studied by conventional and StepScan DSCs and Raman spectroscopy. Compositional dependence of the glass transition temperature, T g, was determined from reversible part of StepScan DSC records and discussed. The attention was also focused on the crystallization of undercooled melts of these systems. It was found that only selenium crystallizes from undercooled melts of As–Se system and its tendency to crystallize decreases markedly with increasing As content, for arsenic content higher than 4at.% no crystallization was observed. In the case of Sb–Se system Sb2Se3 crystallizes in the first step followed by trigonal selenium crystallization from non-stoichiometric undercooled melt. Sb2Se3 crystallizes from incongruent melt with crystallization enthalpy ΔH c(Sb2Se3)=−52±2J/(g of Sb2Se3), Johnson–Mehl–Avrami kinetics of crystallization and kinetic exponent close to 3 was found. Raman spectra were measured to obtain basic information on the structure of both glassy systems. [Copyright &y& Elsevier]

Abstract: In Ge–As–Te system, the glass forming region determined by normal melt quenching method has two regions (GFR I and GFR II) separated by few compositions gap. With a simple laboratory built twin roller apparatus, we have succeeded in preparing Ge7.5As x Te92.5− x glasses over extended composition ranges. A distinct change in T g is observed at x =40, exactly at which the separation of the glass forming regions occur indicating the changes in the connectivity and the rigidity of the structural network. The maximum observed in glass transition (T g) at x =55 corresponding to the average coordination number (Z av)=2.70 is an evidence for the shift of the rigidity percolation threshold (RPT) from Z av =2.40 as predicted by the recent theories. The glass forming tendency (K gl) and ΔT (=T c−T g) is low for the glasses in the GFR I and high for the glasses in the GFR II. [Copyright &y& Elsevier]

An original light-assisted approach for optical-material deposition is introduced, and preliminary results concerning the properties of the deposits, in the case of As–S binary glass alloys, are reported for the first time. Such approach uses a continuous-wave laser source and on-axis geometry, to grow a semiconducting glass alloy onto a transparent substrate under the concurrent actuation of a given light-intensity distribution. Significant differences are observed when the material is prepared by using this technique, in comparison with those reported for similar alloys prepared by both physical- and chemical-vapor based techniques. [Copyright &y& Elsevier]

Abstract: Thin amorphous films of Ge–Sb–Te were deposited from Ge2Sb2Te5 target by RF (f =13.56MHz) magnetron sputtering in argon plasma. Composition and chemical homogeneity of target and prepared thin films were traced by Energy Dispersive X-ray Analysis coupled with Scanning Electron Microscope (SEM-EDX). SEM technique was also used for surface morphology observation. Crystallinity of target and prepared thin films was studied by X-ray Diffraction (XRD). Optical parameters of prepared thin films (spectral dependence of refractive index, optical band gap energy ) and film thicknesses were established via Variable Angle Spectroscopic Ellipsometry (VASE) supported by UV–Vis–NIR spectroscopy. Influence of deposition conditions (RF power, Ar pressure, angle divergency from normal direction) to composition, crystallinity, optical properties and deposition rate was established. [Copyright &y& Elsevier]

Abstract: Erbium doped chalcogenide glasses are of great interest in the integrated optoelectronic technology due to their Er3+ intra-4f emission at the standard telecommunication wavelength of 1.54μm. In this paper, the photoluminescence (PL) of a series of (GeS2) x (Ga2S3)100− x (x =75 and 67) glasses doped with high amounts of Er2S3 (1.8, 2.1, 2.4 and 2.7mol%) under excitation with 1064nm light has been studied. A quenching PL effect at 1.22аt.% Er-doped (GeS2)75(Ga2S3)25 and 1.39аt.% Er-doped (GeS2)67(Ga2S3)33 glasses has been established. The relative changes in PL line-shape at around 1540nm have been estimated by deconvoluting the spectra to Gaussian sub-bands centered at 1519±1, 1537±1, 1546±1, 1555±1 and 1566±4nm, which correspond to F21, F11, F22, F12 and F13 transitions in the and energy levels and have intensity and manifestation that are strongly depend on the Er-doping level. The influence of gallium on the PL efficiency has been evaluated with a view to enhanced emission cross-section. [Copyright &y& Elsevier]

Abstract: X-ray photoelectron spectroscopy and depth profile analysis were used to investigate the X-ray-induced silver photodiffusion into an amorphous As50Se50 thin film. At the initial stages of irradiation an induction period was observed while core level spectra analysis revealed the existence of a mixed As–Se–Ag interlayer between the metal and the chalcogenide matrix. It was found that during the induction period this interlayer is enriched in silver and the existing As–Se–Ag intermediate species are transformed to Ag–Se–Ag that form the metal source for the effective silver photodiffusion. With further irradiation photodiffusion proceeds by the disruption of Ag–Se bonds and the recombination of As atoms with Se to stable As–Se units. Ultimately, silver concentration reaches a plateau when the diffusion stops. A separated Ag2Se phase on the film’s surface is identified at this stage. Depth profile analysis shows that silver has been homogenously diffused into the chalcogenide matrix and the Ag2Se phase exists only at the top surface layers probably in the form of quasi-crystalline clusters that prohibit further Ag diffusion. [Copyright &y& Elsevier]

Abstract: Transitions into, and out of intermediate phases (IPs) with minimal strain have been identified to date by Boolchand and co-workers, in bulk glasses, primarily by the extraordinary low values of the change in enthalpy, ΔH nr, associated with non-reversible heat flow, and by Lucovsky and coworkers in deposited thin films, and at dielectric–semiconductor interfaces by combining spectrographic characterizations, primarily synchrotron X-ray absorption and X-ray photoemission, and electrical measurements. This paper emphasizes chemical bonding self-organizations that minimize macroscopic strain within the IP windows, and identifies for the first time the necessary and sufficient conditions for IP windows to open, and to close, as a function of changes in the alloy composition. Percolation theory, and in particular competitive and synergistic double percolation provide a quantification of IP window first and second transition compositions that account for many of the experimentally determined IP window threshold transitions and IP window widths identified to date. [Copyright &y& Elsevier]

Abstract: We report on the study of the slow dynamics of supercooled and molten Selenium by means of dynamic light scattering. To achieve this in the present case, where the opaqueness of Se prevents visible light scattering measurements, we have developed a novel experimental setup using infrared radiation as the light source. By measuring the scattered intensity autocorrelation function we have been able to extract the average size of the Se clusters in the liquid state and determine the temperature dependence of the related diffusion coefficient which was found to exhibit Arrhenius behavior. [Copyright &y& Elsevier]

Abstract: Three sets of boron nitride (BN) thin films are deposited with different N2/B2H6 flow ratios (r =4, 10 and 25) by plasma enhanced chemical vapor deposition (PECVD). The variations of physical properties in different deposition sets are analyzed by optical (XPS, FTIR, UV–visible spectroscopies), mechanical and electrical measurements. The films are considered to be deposited in a turbostratic phase (t-BN). Evolution of bonding configurations with increasing r is discussed. Relatively higher nitrogen flow rate in the source gas mixture results in lower deposition rates, whereas more ordered films, which tend to reach a unique virtual crystal of band gap 5.93eV, are formed. Anisotropy in the film structure and film inhomogeneity along the PECVD electrode radial direction are investigated. [Copyright &y& Elsevier]