Search

SnO 2 thin films are considered cheap transparent electrodes, interesting for scalable electronic applications, with intrinsic n-type conductivity related to donor defects like tin interstitials and oxygen vacancies. Besides, SnO 2 allows n-type extrinsic doping by pentavalent cations such as Ta or Sb. In the present work, SnO 2 and SnO 2 :Sb films were deposited on unheated soda lime glass substrates by reactive DC sputtering from Sn and Sn:Sb(5%) targets. Their structural, optical and electrical properties have been analyzed comparatively for the layers prepared at different oxygen partial pressures in the sputtering atmosphere, as-grown and after heating in air at several temperatures. Sb doping is proven effective to improve the electrical conductivity of sputtered tin dioxide samples. The contribution of oxygen vacancies is found dependent on the reactive deposition environment, in both pure and Sb-doped films, but subsequent heating can change the proportion and nature of the donor defects. For operation at temperatures above 400 °C, SnO 2 :Sb shows the best electrical performance and good thermal behavior is also achieved with pure SnO 2 layers by adjusting the oxygen content in the sputtering atmosphere. Image 1 • SnO 2 and SnO 2 :Sb are prepared by reactive sputtering on unheated substrates. • Conductivity in amorphous SnO 2 is dominated by oxygen vacancies. • Optimal Sb Sn incorporation is achieved by crystallization above 400 °C. • Coexistence with intermediate oxides allows the formation of cation interstitials. • Sb-doping and intermediate oxides reduce the average visible transmittance. [ABSTRACT FROM AUTHOR]

Starting from evaporated Cu layers, oxidation and sulfurization processes were developed by reaction at 250 °C with O 2 or elemental sulfur to obtain Cu 2 O and CuS thin films, respectively, with p-type conductivity and visible transparency. With the aim of achieving mixed compounds that combine the best properties of oxides (transparency) and sulfides (metal-like conductivity), different methods were tested, including Cu 2 O sulfurization, CuS oxidation and direct Cu sulfoxidation. The crystalline structure, morphology and optical and electrical characteristics of the various samples were studied comparatively. CuSO 4 crystals with a mean size above 40 nm were obtained by sulfoxidation, showing higher transmittance and lower resistance than the Cu 2 O film shaped by crystallites of ∼13 nm. Moreover, a superior electrode quality was achieved after CuS oxidation, which produces a mixture of small Cu 2 O and larger Cu 2 S nanocrystals with visible transmittance as high as the pure oxide and a hole density close to the sulfide. [ABSTRACT FROM AUTHOR]

The optical and electrical characteristics of copper oxide thin films are greatly dependent on the preparation procedure, which determines the crystallite size and the density of native defects. Minimization of the synthesis temperature is in general desirable to reduce the thermal budget and extend the deposition on sensitive substrates. Here, copper oxide layers have been prepared by heating evaporated copper in air at low temperatures (≤350 °C). The crystalline structure, optical and electrical properties of the oxidized films have been analyzed as a function of the evaporated copper thickness and the heating temperature. Single-phase Cu 2 O and CuO layers have been obtained by adjusting the preparation parameters, which allow to change the visible transmittance and gap energy of the films according to the specific application. Both copper oxide phases exhibit p-type conduction and photosensitivity. The analysis of photoconductivity transients and the optical absorption coefficients made possible to identify the sub-gap defect levels present in these compounds. [ABSTRACT FROM AUTHOR]

Copper chalcogenide materials are interesting for multiple applications due to the feasibility of suiting their optical absorption and electrical conduction by the creation of copper vacancies. Here, CuS and CuSe nanocrystalline films with p-type conductivity have been obtained by heating evaporated copper layers of various thicknesses with elemental sulfur or selenium, at temperatures ranging from 250 to 400 °C. These preparation parameters determine the composition and the crystalline structure of the samples, which in turn control their morphology, optical and electrical properties. Thus, the surface roughness increases with the mean crystallite size, whereas the hole concentration increases as the copper atomic proportion (or x value) decreases. Owing to the high carrier densities achieved, around 10 cm, the samples show a metallic behavior with plasmonic absorption in the near infrared and electrical transport dominated by phonon scattering. Apart from such common behavior, some differences have been established between the sulfide and selenide films. One is the superior thermal stability of hexagonal CuS, present in all the temperature range, with respect to hexagonal CuSe, which evolves to cubic CuSe above 300 °C. Other is about the bandgap, wider for the sulfide than selenide samples. [ABSTRACT FROM AUTHOR]

TiO 2 layers with crystalline anatase structure have been attained on unheated glass substrates, by reactive sputtering from a metallic target, using the sputtering pressure to change the energy of the particles arriving to the film surface. Such energy and the time of plasma exposure also influence the morphology and other physical properties of the sputtered films. The deposition time has been ranged to obtain TiO 2 coatings with different thicknesses from 0.24 to 1.08 μm and at various total pressures from 0.2 to 1.0 Pa. Overall characterization of the samples has been performed by X-ray diffraction, atomic force microscopy and spectrophotometry. The effects of the sputtering pressure and the film thickness on the crystalline structure (interplanar distance and mean crystallite size), the morphology (roughness and surface area) as well as the optical properties (refractive index, extinction coefficient) have been established. A direct relation between optical and morphological characteristics, and the calculated film porosity has been proven. Such porosity is well controlled by the deposition parameters; these allow tuning the optical and morphological properties of the sputtered TiO 2 coatings as required for different applications. [ABSTRACT FROM AUTHOR]

Tin sulfide thin films on soda-lime glass substrate were prepared by co-evaporation. This technique uses a vapor phase procedure involving chemical reactions between the precursor species evaporated simultaneously. The influence of the substrate temperature in the crystal structure and chemical composition were determined by X-ray diffraction and energy dispersive analysis of X-rays, showing that thin films crystallized in SnS, SnS, and SnS phases. Scanning electron microscope shows thin films with homogenous and uniform surface. Some of the samples were annealed to study the variation of structural, chemical, and optical properties. The variation of refractive index ( n), extinction coefficient ( k), and dielectric constant ( ε) with wavelength and photon energy are reported. The energy band gap was calculated from optical transmittance and reflectance measurements in the range 300-1500 nm. The calculated energy band gap values were between 1.75 and 2.3 eV, depending on the phase in which crystallized the different thin films. [ABSTRACT FROM AUTHOR]

Indium sulfide thin films were successfully deposited on soda lime glass substrates by modulated flux deposition (MFD) at significantly lower substrate temperatures than in previous experiments. The influence of both experimental parameters sulfur source temperature ( TS) and substrate temperature ( T) on the optical, structural, and chemical properties were studied. Amorphous indium sulfide layers were obtained at T = 100 °C and crystallized as β-In2S3 for T ≥ 150 °C. Quite high values were required for the TS parameter in order to ensure the formation of transparent β-In2S3 thin films. No other polycrystalline phases were detected. Direct optical bandgaps of 2.58 eV (amorphous In2S3) and 2.73 eV (β-In2S3) were estimated for film thicknesses of around 100 nm. [ABSTRACT FROM AUTHOR]

Cu(In,Ga)Se thin films have been prepared by selenization of the evaporated metallic precursors on transparent and conductive ITO-coated as well as uncoated glass substrates, by starting from slightly Cu-rich or Cu-poor overall metallic proportions. The objective is to determine the influence of the Cu availability on the constituents distribution achieved after selenization, by means of data obtained at several film depths by grazing incidence X-ray diffraction and X-ray photoelectron spectroscopy that have been related to the overall optical and structural characteristics of the material. This study points out the possibility of achieving homogeneous or graded absorber layers, showing for homogeneous samples an ITO/Cu(In,Ga)Se interface with ohmic electrical characteristics suitable to act as back contact for semitransparent photovoltaic devices. [ABSTRACT FROM AUTHOR]

Abstract: CuInSe2 thin films with typical 1.0eV gap energy and tetragonal chalcopyrite structure have been obtained on soda–lime glass substrates by the reaction of sequentially evaporated Cu and In layers with elemental selenium vapor, at 500°C in flowing Ar. When analogous deposition and reaction processes were performed on Al:ZnO coated glasses, some increment in the band gap energy and diminution in the crystalline interplanar spacings have been detected for the resulting films with an extent that depends on the Cu/In atomic ratio of the evaporated precursor layers. This fact has been related to Zn incorporation into the selenized film, with quaternary (CuIn)1−x Zn2x Se2 compound formation that is influenced by the presence of copper selenide phases during the reaction process. Such deductions are supported by the optical, structural and compositional characterizations that have been performed comparatively on samples prepared by selenization of evaporated metallic precursors with two different Cu/In ratios (0.9 and 1.1) on bare and Al:ZnO coated glass substrates. [Copyright &y& Elsevier]

Abstract: Transparent and conductive Al-doped ZnO (AZO) films have been grown with various thicknesses between 0.3 and 1.1 μm by magnetron sputtering at room temperature onto soda lime glass substrates. After deposition, the samples have been annealed at temperatures ranging from 150 to 450 °C in air or vacuum. The optical, electrical, and structural characteristics of the AZO coatings have been analyzed as a function of the film thickness and the annealing parameters by spectrophotometry, Hall effect measurements, and X-ray diffraction. As-grown layers are found polycrystalline, with hexagonal structure that shows some elongation of the unit cells along the c-axis, having visible transmittance ∼85–90% and resistivity ∼1.6–2.0 mΩ cm, both parameters slightly decreasing when the film thickness increases. Heating in air or vacuum produces further elongation of the crystalline lattice together with some increase of the visible transmittance and a decrease of the electrical resistance that depends on the heating temperature and atmosphere. The best characteristics have been obtained after treatment in vacuum at 350 °C, where the highest carrier concentrations are achieved, giving visible transmittance ∼90–95% and resistivity ∼0.8–0.9 mΩ cm for the AZO layers with various thicknesses. Some relationships between the analyzed properties have been established, showing the dependence of the lattice distortion, the band gap energy and the mobility on the carrier concentration. [Copyright &y& Elsevier]

Abstract: Transparent conducting oxides (TCOs) have a wide range of applications in several optoelectronic devices but beyond the conventional characteristics of transparency and conductivity different characteristics are required by each different technology. This constitutes a promising stimulation of the present research of TCO films. In order to investigate the possible application of antimony doped tin oxide (ATO) thin films as a TCO electrode for new concepts in solar cells and other optoelectronic devices, ATO thin films with adequate properties in terms of light transparency and conductivity were obtained using room temperature processes by oxygen-reactive DC magnetron sputtering, then the films were annealed in nitrogen atmosphere at a temperature of 350°C. The effect of O2/(Ar+O2) ratio in the sputter flow gas mixture has been studied. Results regarding to optical and electrical properties, microstructure and composition measurements are reported. [Copyright &y& Elsevier]

Abstract: ITO/Ag/ITO multilayers have been prepared onto conventional soda lime glass substrates by sputtering at room temperature. The optical and electrical characteristics of single layer and multilayer structures have been investigated as a function of the Ag and ITO film thicknesses. Transmittance and sheet resistance values are found mainly dependent on the Ag film thickness; whereas the wavelength range at which the maximum transmittance is achieved can be changed by adjusting the ITO films thickness. ITO/Ag/ITO electrodes with sheet resistance below 6Ω/sq have been obtained for Ag film thickness above 10nm and ITO layers thickness in the 30–50nm range. These multilayers also show high transmittance in the visible spectral region, above 90% by discounting the glass substrate, with a maximum that is located at higher wavelengths for thicker ITO. [Copyright &y& Elsevier]

Abstract: Indium tin oxide (ITO) thin films were deposited by sputtering at room temperature on glass and different polyester substrates; namely polyarylate (PA), polycarbonate (PC) and polyethylene terephtalate (PET). The influence of the substrate on the structural, optical and electrical characteristics of the ITO layers was investigated. The sputtered films exhibited crystallization in the (222) orientation, with higher mean crystallite size and lower structural distortion onto PET than onto PA, PC or glass substrates. ITO films deposited onto PET showed also higher band gap energy, higher carrier concentration and lower resistivity than the ITO layers onto the other tested substrates. These optical and electrical characteristics have been related to the structural distortion that was found dependent on the specific polyester substrate. [Copyright &y& Elsevier]

Abstract: Transparent conductive indium tin oxide (ITO)/metal/ITO multilayer electrodes have been prepared by sputtering at room temperature. Ag and Cu thin films with thickness ranging from 5 to 35nm have been used as intermediate metal layer, between ITO coatings of about 30nm thickness. Evolution of the optical and electrical characteristics of the multilayers as a function of each metal film thickness has been analyzed. High-quality transparent electrodes have been obtained, with sheet resistance below 6Ω/sq for Ag film thickness above 10nm or Cu film thickness above 16nm. These multilayers also showed high transmittance in the visible spectral range, above 90% by discounting the glass substrate, with a maximum that is located at lower wavelength for Ag-based electrodes than for the Cu-based ones. After heating at 350°C in flowing nitrogen, some improvement in the optoelectronical characteristics of the multilayer electrodes has been achieved that is related to the structural improvement of the ITO components. [Copyright &y& Elsevier]

Abstract: Aluminium-doped zinc oxide (AZO) thin films have been prepared by pulsed magnetron sputtering from a ceramic oxide target in pure argon atmosphere. Sputtering processes were performed in current or voltage regulation modes at different pulsing frequencies up to 200kHz. Several growth parameters (discharge power, substrate temperature and growth rate) as well as AZO film properties (crystalline structure, optical transmittance and electrical characteristics) have been measured and analysed as a function of the current or voltage applied, the pulsing frequency and the operation time. By adjusting these deposition parameters, AZO layers with resistivity as low as 1.0×10−3 Ωcm and average visible transmittance above 85% have been obtained at growth rate in the range 70–80nm/min, at substrate temperatures below 150°C. [Copyright &y& Elsevier]

Abstract: Indium tin oxide (ITO) thin films have been grown onto glass substrates by sputtering at room temperature with various controlled oxygen and argon ratios used as reactive and sputter gases, respectively. After deposition, the samples have been annealed at 350°C in the same sputtering chamber in vacuum or in air. The structure, morphology and electro-optical characteristics of the ITO coatings have been analyzed as a function of the oxygen added during deposition and of the annealing atmosphere by X-ray diffraction, atomic force microscopy, four points electrical measurements and spectrophotometry. It has been found that the as-deposited amorphous samples crystallize in the cubic structure by annealing. The optical transmittance and the electrical resistance decrease when the oxygen content in the deposition and the annealing atmosphere is reduced. [Copyright &y& Elsevier]

Abstract: Indium tin oxide (ITO) thin films have been grown simultaneously onto glass and polymer substrates at room temperature by sputtering from ceramic target. The structure, morphology and electro-optical characteristics of the ITO/glass and ITO/polymer samples have been analyzed by X-ray diffraction, atomic force microscopy, four-point electrical measurements and spectrophotometry. In the selected experimental conditions, the polycrystalline ITO coating shows higher average grain size and higher conductivity, with similar visible transmittance, onto the polymer than onto the glass substrate. [Copyright &y& Elsevier]

Abstract: The structure, morphology and optical properties of copper indium sulfide thin films prepared by a novel modulated flux deposition procedure have been investigated for layers from 200 to 400 nm thickness. These polycrystalline CuInS2 films grown onto glass substrates showed CuAu-like structure, similar to epitaxial CuInS2 films grown onto monocrystalline substrates, and direct band gap values Eg=1.52–1.55 eV, optimum for single-junction photovoltaic applications. The increase in the layer thickness leads to growth of the average crystallite size and increases slightly the surface roughness and the absorption coefficient. [Copyright &y& Elsevier]

Here we present experimental evidence of the strong modification of the CdS photoluminescence when it is embedded in a SiO[sub 2] colloidal photonic crystal. When the emitted light matches a forbidden photonic band in the matrix, inhibition of the semiconductor photoluminescence is achieved. In this work we prove the effective control of this effect by means of the photonic lattice parameter of the host. CdS was grown by chemical bath deposition and its quality has been checked employing Raman spectroscopy and x-ray diffraction. Scanning electron microscopy is used to study the morphology of the composite. © 1998 American Institute of Physics. [ABSTRACT FROM AUTHOR]

N-doped TiO 2 thin films have been grown over glass substrates without intentional heating by DC sputtering of a metallic Ti target immersed in a reactive gas mixture of argon, oxygen and nitrogen. The oxygen partial pressure has been adjusted to achieve effective N-doping, intended to decrease the band gap energy with respect to analogous undoped layers. These N-doped TiO 2 films are found amorphous by X-ray analysis, even after post-deposition heating in air up to 550 °C, whereas the analogous intrinsic TiO 2 layers exhibit rutile crystalline structure before and after heating. The obtained results agree with the localized level model that has been developed for titania crystals and applies here for amorphous TiO 2 :N layers, which show an effective redshift of 0.88 eV with respect to the undoped samples. Nevertheless, the widest gap value of 3.22 eV is achieved for the several TiO 2 and TiO 2 :N thin films after annealing in air at the highest temperature. This is attributed to the suppression of oxygen vacancies and Ti 3+ oxidation states during such thermal treatment. [ABSTRACT FROM AUTHOR]

Abstract: During the fabrication of a thin film photovoltaic device the transparent conducting oxide (TCO), which constitutes an integral part of its basic structure, could be exposed at high temperature processes; in addition, a TCO which could be grown at ambient temperature can be useful in order to minimize possible damages caused to other previously deposited components. Aluminum doped zinc oxide (AZO) is a well known TCO with good properties in terms of light transparency and conductivity, however its electrical properties deteriorate after subsequent high temperature processes in air atmosphere. On the other hand antimony doped tin oxide (ATO) has poorer conductivity than AZO but has good light transparency and better thermal stability. In the present work, ATO layers with a thickness ranging from 30nm to 210nm were deposited over a 600nm thick AZO layer. These AZO/ATO bilayers, which have been developed at ambient temperature by DC magnetron sputtering, were subsequently annealed at high temperatures in order to study their thermal stability. An ATO optimal thickness of 130nm is found to improve the bilayer thermal stability at temperatures over 350°C in air atmosphere, keeping good optical properties. [Copyright &y& Elsevier]

Abstract: Antimony doped tin oxide (ATO) is a transparent conducting oxide (TCO), which has been the focus of intensified study due to its wide range of technological applications and low cost. In the present work ATO films have been prepared by reactive DC magnetron sputtering from a metallic target at different discharge power densities without direct substrate heating. Then a post-deposition annealing at 350°C in N2 during 20min was performed. There is a process window for the optimal sputter deposition of ATO with a minimum resistivity of about 3.3×10−3 Ωcm observed in samples deposited at a power density of 1.13W/cm2. These samples, which present a (211) preferential orientation, have good electrical conductivity and good transparency in the visible range. Higher values of sputtering discharge power density (1.24W/cm2) change the preferential orientation to (101) because of the formation of oxygen vacancy planes. These samples are less conductive and transparent because their layered structure reduces the free charge mobility and allows the formation of Sb in its unusual oxidation state 4+ (between Sb3+ and Sb5+), which produces a sample blue darkening. Higher discharge power densities, above 1.41W/cm2, produce amorphous samples and an abrupt resistivity increase. The aim of the present work is to go into more depth in the knowledge of ATO in order to develop thin films with optimal electrical and optical properties. [Copyright &y& Elsevier]

Abstract: In this work ITO thin films have been grown onto glass, polyethylene terephthalate (PET) and Arylite polymer substrates by sputtering at room temperature. The In2S3 films were chemically deposited on ITO during different times, forming bilayers for subsequent photovoltaic applications. Optical properties of the films were investigated from the transmittance and the structural properties by XRD. Transmittance of the films varies with deposition time and the different substrates used, the same as the adherence and the homogeneity of the films. [Copyright &y& Elsevier]

Abstract: We have deposited Cu–In–S films by an innovative modulated flux deposition (MFD) procedure performed in a static physical evaporation chamber in compositional ranges as diverse as: [In] ranging 10–70%, [Cu]=2–43% and [S]=20–50%. We propose optical absorption (A%=100− R%− T%) in the near-IR (about 0.5 eV or 2500 nm) as a non-contact measurement which could be indirectly correlated with chemical composition. The films, characterized by spectrophotometry (A%) and sheet resistance (R) by four-terminal sensing measurement, were classified in compositional groups by the use of the two-dimensional parameter (R, A%). Interestingly, the optical absorption A% was linearly correlated with Cu content in our compositional range while R presents a jump back related with the variation of S concentration. The independence of R and A% in this case is discussed in terms of different conduction mechanisms. [Copyright &y& Elsevier]

Abstract: In this paper, we study the optical properties of indium sulfide thin films to establish the best conditions to obtain a good solar cell buffer layer. The In2S3 buffer layers have been prepared by chemical bath deposition (CBD) and thermal evaporation (PVD). Optical behavior differences have been found between CBD and PVD In2S3 thin films that have been explained as due to structural, morphological and compositional differences observed in the films prepared by both methods. The resultant refractive index difference has to be attributed to the lower density of the CBD films, which can be related to the presence of oxygen. Its higher refractive index makes PVD film better suited to reduce overall reflectance in a typical CIGS solar cell. [Copyright &y& Elsevier]

Cu 2 ZnSnS 4 (CZTS) thin films have been grown by sulfurization of Cu 2 SnS 3 (CTS) and ZnS layers evaporated on glass substrates. Four CTS precursor films have been tested, with two different atomic compositions (Cu/Sn = 1.7 and Cu/Sn = 2.1) and substrate temperatures (350 and 450 °C), together with analogous ZnS layers deposited by maintaining the substrate at 200 °C. The sulfurization of the CTS and ZnS stacked layers was performed at 500 °C during 1 h. The evolution of the crystalline structure, morphology, optical and electrical properties from each CTS precursor to the CZTS compound has been studied, especially the influence of the ternary precursor features on the quaternary film characteristics. The kesterite structure has been identified after sulfurization of the various samples, with main (112) orientation and mean crystallite sizes S 112 = 40–56 nm, being higher for the Cu-poor compositions. The CZTS average roughness has varied in a wide interval R a = 8–66 nm, being directly related to the CTS precursor layer, which becomes rougher for a higher deposition temperature or Cu content. Besides, the band gap energy and the electrical resistivity of the CZTS films have changed in the ranges E g = 1.54–1.64 eV and ρ = 0.2–40 Ωcm, both decreasing when the Cu content and/or the surface roughness increase. [ABSTRACT FROM AUTHOR]

Copper tin sulfide thin films have been grown on soda-lime glass substrates from the elemental constituents by co-evaporation. The synthesis was performed at substrate temperatures of 350 °C and 450 °C and different Cu/Sn ratios, adjusting the deposition time in order to obtain thicknesses above 1000 nm. The evolution of the morphological, structural, chemical, optical and electrical properties has been analyzed as a function of the substrate temperature and the Cu/Sn ratio. For the samples with Cu/Sn ⩽ 1, Cu 2 Sn 3 S 7 and Cu 2 SnS 3 have been observed by XRD. Increasing the Cu/Sn to 1.5, the Cu 2 SnS 3 phase was the majority, being the formation completed at Cu/Sn ratio around 2. The increment of the substrate temperature leads to a change of cubic structure to tetragonal of the Cu 2 SnS 3 phase. The chemical treatment with KCN was effective to eliminate CuS excess detected in the samples with Cu/Sn > 2.2. The samples with Cu 2 SnS 3 structure show a band gap energy increasing from 0.9 to 1.25 eV and an electrical resistivity decreasing from 7 ∗ 10 −2 Ω cm to 3 ∗ 10 −3 Ω cm when the Cu/Sn atomic ratio increases from 1.5 to 2.2. [ABSTRACT FROM AUTHOR]

Abstract: In2S3 films have been chemically deposited on ITO coated glass substrates by chemical bath deposition, using different deposition times and precursor concentrations. The bilayers are intended for photovoltaic applications. Different characterization methods have been employed: optical properties of the films were investigated from transmittance measurements, structural properties by XRD and micro-Raman, and surface morphology by SEM microscopy analysis. Also, the direct and indirect band-gaps and the surface gap states were studied with surface photovoltage spectroscopy (SPS). We proposed that electronic properties of the In2S3 samples are controlled by two features: shallow tail states and a broad band centred at 1.5eV approximately. Their relation with the structure is discussed, suggesting that their origin is related to defects created on the S sub-lattice, and then both defects are intrinsic to the material. [ABSTRACT FROM AUTHOR]