Effect of annealing and composition on crystal structure,surface morphology and optical absorption of chemically deposited Cd1‐xSnxS films

Cd_1‐xSn_xS thin films were successfully deposited on suitably cleaned glass substrate by chemical bath deposition method at 74 °C. Hydrated Stannous Chloride (SnCl₂.2H₂O) in aqueous solution was added to the CdS growing solution in different proportions. The experimental results indicate, a successful doping for lower concentration of Sn, saturation for intermediate doping levels, and a degradation of the doping process for higher concentration of Sn. Indirect (X‐ray diffraction) and Direct (Scanning electron microscopy) measurements were performed to characterize the growth and the nature of crystallinity of the different Cd_1‐xSn_xS films. The effect of annealing on the crystal structure and morphology of the deposited films has also been discussed. The X‐ray diffraction spectra show that the thin films are polycrystalline and have both cubic and hexagonal structure. The Interplanar spacing, lattice constant, grain size, strain, and dislocation density were calculated for as‐deposited and annealed films. The grain size was found to decrease from 5 nm to 0.89 nm with doping concentration of Sn. The grain size further decreased due to annealing at 400 °C. SEM studies show layered growth and long needle like structures along with some voids. After annealing the densification and smaller size of the particles was also observed. The optical absorption spectra show shifting of absorption peaks towards lower wavelength side (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effect of Thermal Annealing on Structural Properties,Morphologies and Electrical Properties of TiO2 Thin Films Grown by MOCVD

TiO₂ thin films, were deposited on Si(100) and Si(111) substrates by metalorganic chemical vapor deposition at 500 °C, and have been annealed for 2 min, 30 min and 10 hours at the temperature from 600 °C to 900 °C, in oxygen and air flow, respectively. XRD and atomic force microscopy characterized the structural properties and surface morphologies of the films. As‐deposited films show anatase polycrystalline structure with a surface morphology of regular rectangled grains with distinct boundaries. Rutile phase formed for films annealed above 600 °C, and pure rutile polycrystalline films with (110) orientation can be obtained after annealing under adequate conditions. Rutile annealed films exhibit a surface morphology of equiaxed grains without distinct boundaries. The effects of substrate orientation, annealing time and atmosphere on the structure and surface morphology of films have also been studied. Capacitance‐Voltage measurements have been performed for films deposited on Si(100) before and after annealing. The dielectric properties of TiO₂ films were greatly improved by thermal annealing above 600 °C in oxygen.     

Fabrication and characterization of transparent conductive ZnO:Al thin films prepared by direct current magnetron sputtering with highly conductive ZnO(ZnAl2O4) ceramic target

Using a highly conductive ZnO(ZnAl₂O₄) ceramic target, c-axis-oriented transparent conductive ZnO:Al₂O₃ (ZAO) thin films were prepared on glass sheet substrates by direct current planar magnetron sputtering. The structural, electrical and optical properties of the films (deposited at different temperatures and annealed at 400°C in vacuum) were characterized with several techniques. The experimental results show that the electrical resistivity of films deposited at 320°C is 2.67×10⁻⁴ Ω cm and can be further reduced to as low as 1.5×10⁻⁴ Ω cm by annealing at 400°C for 2 h in a vacuum pressure of 10⁻⁵ Torr. ZAO thin films deposited at room temperature have flaky crystallites with an average grain size of ∼100 nm; however those deposited at 320°C have tetrahedron grains with an average grain size of ∼150 nm. By increasing the deposition temperature or the post-deposition vacuum annealing, the carrier concentration of ZAO thin films increases, and the absorption edge in the transmission spectra shifts toward the shorter wavelength side (blue shift).     

Photorefractive features of non‐stoichiometry codoped Hf:Fe:LiNbO3 single crystals

Hf(2mol%):Fe(0.05wt%):LiNbO₃ crystals with various [Li]/[Nb] ratios of 0.94, 1.05, 1.2 and 1.38 have been grown. The photorefractive resistant ability increases with the accretion of [Li]/[Nb] ratio. When the ratio of [Li]/[Nb] is 1.20 or 1.38, the OH^‐ absorption band shifts to about 3477cm^‐1. The mechanisms of the photorefractive resistant ability increase and the absorption band shift have been discussed. The exponential gain coefficient (Γ) of the crystals was measured with two‐beam coupling method and the effective charge carrier concentration (N_eff) was calculated. The results show that Γ and N_eff increase with the accretion of [Li]/[Nb] ratio. The temperature effect of codoped Hf:Fe:LiNbO₃ crystals was also studied, it was found that the exponential gain coefficient increase dramatically at about 55°C, 70°C and 110°C, this is due to the inner electric field which is resulted from structure phase change. (© 2007 WILEY ‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Isochronal Studies of α‐Si:H Crystallization and the Performance of it's Schottky Barriers

Hydrogenated amorphous silicon films (α‐Si:H) were crystallized employing a metal induced crystalline (MIC) technique. Structural changes during annealing these films at 300 °C for different periods (0‐300 minutes) were obtained by XRD. Al was used as a metal induced crystalline for α‐Si:H produced by ultra high vacuum (UHV) plasma enhanced chemical vapor deposition (PECVD). XRD shows that crystallization of the interacted α‐Si:H film underneath Al initiates at 300 °C for 15 minutes. A complete crystallization was obtained after annealing for 60 minutes. A gold dot was evaporated onto α‐Si:H films, which annealed for different periods to form Schottky barriers. Electrical properties of Au/α‐Si:H were calculated such as the ideality factor, n, barrier height, Φ_B, donor concentration, N_D, and the diffusion voltage, V_d, as a function of the annealing time of α‐Si:H films. All these parameters were carried out through the current voltage characteristics (J‐V) and the capacitance voltage measurements (C‐V). The results were presented a discussed on the basis of XRD performance and the thermionic emission theory.     

Textural properties of AISb films

Textural studies have been carried out in AlSb films deposited by coevaporation method under high vacuum at different substrate temperatures between 450° to 625 °C. The films have been examined by X-ray and electron diffraction techniques. It was observed that the films deposited around 550 °C were found to exhibit [110] and [111] textures and the films deposited at higher substrate temperatures (above 600 °C) were found to exhibit only [111] textures.     

Morphology,composition, structure and optical properties of thermally annealed Cu2O thin films prepared by reactive DC sputtering method

Abstract

Thin films copper oxides are perspective materials for many optoelectronic applications, including photovoltaics. The samples were deposited on glass and silicon substrates by magnetron sputtering method using Modular Platform PREVAC. After deposition the samples were thermally treated by annealing in oxygen atmosphere for 60?min at 450?°C. Morphology confirms that all the films have crystalline structure. Optical measurements show that the films have wide band gap within the range 2.20÷2.48?eV before and 2.03÷2.40?eV after annealing. The article presents the discussion about the influence of annealing on Cu₂O thin film parameters.     

Structural investigation and electronic band transitions of nanostructured TiO2 thin films

Titanium dioxide (TiO₂) thin film was deposited on n‐Si (100) substrate by reactive DC magnetron sputtering system at 250 °C temperature. The deposited film was thermally treated for 3 h in the range of 400‐1000 °C by conventional thermal annealing (CTA) in air atmosphere. The effects of the annealing temperature on the structural and morphological properties of the films were investigated by X‐ray diffraction (XRD) and atomic force microscopy (AFM), respectively. XRD measurements show that the rutile phase is the dominant crystalline phase for the film annealed at 800 °C. According to AFM results, the increased grain sizes indicate that the annealing improves the crystalline quality of the TiO₂ film. In addition, the formation of the interfacial SiO₂ layer between TiO₂ film and Si substrate was evaluated by the transmittance spectra obtained with FTIR spectrometer. The electronic band transitions of as‐deposited and annealed films were also studied by using photoluminescence (PL) spectroscopy at room temperature. The results show that the dislocation density and microstrain in the film were decreased by increasing annealing temperature for both anatase and rutile phases. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Preparation and optical properties of AgGaS2 nanofilms

In this paper, AgGaS₂ nanofilms have been prepared by a two‐step process involving the successive ionic layer absorption and reaction (SILAR) and annealing method. Using AgNO₃, GaCl₃ and Na₂S₂O₃ as reaction sources, the mixture films were firstly deposited on quartz glass substrates at room temperature, and then annealed in Ar environment at 200–500 °C for 4 h, respectively. The effects of annealing temperature on structural and optical properties were investigated by XRD, UV‐Vis, EDS and photoluminescence (PL) spectra. It was revealed in XRD results that α‐Ag₉GaS₆ was contained in the samples annealed at 200 °C, and this phase was decreased with increase of the annealing temperatures. When the sample was annealed at above 400 °C, the chalcopyrite AgGaS₂ nanofilm was obtained. The preferred orientation was exhibited along the (112) plane. It was shown in atomic force microscopy (AFM) results that the grain sizes in AgGaS₂ nanofilms were 18‐24 nm and the thin films were smooth and strongly adherent to the substrates. When the annealing temperature was higher than 400 °C, it is an optimum condition to improve the structural and optical properties of the AgGaS₂ thin films. The room temperature PL spectra of AgGaS₂ nanofilms showed prominent band edge emission at 2.72 eV. Based on all results mentioned above, it can be concluded that the SILAR‐annealing method is preferable to preparing high‐quality AgGaS₂ nanofilms. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

MOCVD and characterization of Hf-silicate thin films using HTB and TEMAS

Hafnium silicate (HfSi_xO_y) films were deposited by metal-organic chemical vapor deposition (MOCVD) using a combination of precursors: hafnium tetra-tert-butoxide [Hf(OC(CH₃)₃)₄, HTB] and tetrakis-ethylmethylamino silane [Si(N(C₂H₅)(CH₃))₄, TEMAS]. The activation energy was independent on the ratio of precursor amounts in the surface reaction regime. The grown films showed Hf-rich characteristics and the impurity concentrations were less than 1 at.% (below detection limits). Hafnium silicate films were amorphous up to 700 °C annealing. Hf/(Hf + Si) composition ratio and dielectric constant (k) of the Hf-silicate films decreased by increasing the growth temperature above 270 °C.     

Modification of the CuInSe2 Crystal Surface during Polishing and Annealing

The RBS/channelling technique was used to study the near-surface damage characteristics of CuInSe₂ crystals after polishing with 0.05 μm grade alumina and subsequent annealing up to temperatures of 600 °C. A comparative RUMP and damage density depth profile analysis of the channelling spectra revealed a polish-induced near-surface disordered layer with a thickness close to 40 nm. Up to annealing temperatures of about 400 °C a gradual overall decrease of the defect density in the damaged layer is observed without detectable changes in its thickness. An indium-rich surface layer is formed after vacuum annealing at 600 °C.     

Growth of epitaxial TmFeCuO4 thin films by pulsed laser deposition

Epitaxial thin films of TmFeCuO₄ with a two-dimensional triangular lattice structure were successfully grown on yttria-stabilized-zirconia substrates by pulsed laser deposition and ex situ annealing in air. The films as-deposited below 500 °C showed no TmFeCuO₄ phase and the subsequent annealing resulted in the decomposition of film components. On the other hand, as-grown films deposited at 800 °C showed an amorphous nature. Thermal annealing converted the amorphous films into highly (0 0 1)-oriented epitaxial films. The results of scanning electron microscopic analysis suggest that the crystal growth process during thermal annealing is dominated by the regrowth of non-uniformly shaped islands to the distinct uniform islands of hexagonal base.     

Electrochemical Deposition of CdTe Layers. Their Structure and Electrical Properties

CdTe layers have been deposited catodically on nickel substrates from an aqueous solution of CdSO₄ and TeO₂. The degree of erystallinity increases with increasing temperature and decreasing deposition potential. The structure of the layers is cubic with 〈111〉 or 〈110〉 texture which is determined by TeO₂ concentration predominantly. Amorphous phase is found in deposits prepared at higher deposition potential or at lower temperatures of bath (60 °C). After annealing at 200 °C the amorphous deposits crystallized and pure tellurium appeared in diffraction spectra. The resistivity of the films was determined by means of I—V characteristics. Films with deposition potentials (−500 to −400) mV vs SCE are p-type conductivity whereas at lower potentials (down to − 700 mV vs. SCE) the n-type material is formed.     

Nanostructural and optical features of amorphous AlxSi0.45−xO0.55 (0 ⩽ x ⩽ 0.05) thin films prepared by RF-magnetron sputter techniques

The nanostructural, chemical, and optical features of Al_xSi_0.45−xO_0.55 (0 ⩽ x ⩽ 0.05) thin films were investigated in terms of Al concentration and post-deposition annealing conditions; the films were prepared by co-sputtering a Si main target and Al-chips, and the annealing was carried out at temperatures of 400–1100 °C. The a-Si_0.45O_0.55 films prepared without Al-chips and annealed at 800 °C contain ∼3.5 nm-sized Si nanocrystallites. The photoluminescence (PL) intensity as well as the volume fraction of Si nanocrystallites increased with increasing the concentration of Al to a certain level. In particular, the intensity of the PL spectra of the Al_0.025Si_0.425O_0.550 films which were annealed at 800 °C increased significantly at wavelengths of ∼580 nm. It is highly likely that the observed increase in the PL intensity is caused by the raise in the total volume of the ∼3.5 nm-sized nanocrystallites in the films. The addition of Al as well as the post-deposition annealing allow adjustment and control of the nanostructural and light-emission features of the a-SiO_x films.     

Studies on optical properties of polycrystalline SnO2:Sb thin films prepared using SnCl2 precursor

Optical properties of spray deposited antimony (Sb) doped tin oxide (SnO₂) thin films, prepared from SnCl₂ precursor, have been studied as a function of antimony doping concentration. The doping concentration was varied from 0‐4 wt.% of Sb. All the films were deposited on microscope glass slides at the optimized substrate temperature of 400 °C. The films are polycrystalline in nature with tetragonal crystal structure. The doped films are degenerate and n‐type conducting. The sheet resistance of tin oxide films was found to decrease from 38.22 Ω/□ for undoped films to 2.17 Ω/□ for antimony doped films. The lowest sheet resistance was achieved for 2 wt.% of Sb doping. To the best of our knowledge, this sheet resistance value is the lowest reported so far, for Sb doped films prepared from SnCl₂ precursor. The transmittance and reflectance spectra for the as‐deposited films were recorded in the wavelength range of 300 to 2500 nm. The transmittance of the films was observed to increase from 42 % to 55 % (at 800 nm) on initial addition of Sb and then it is decreased for higher level of antimony doping. This paper investigates the variation of optical and electrical properties of the as‐deposited films with Sb doping. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Characteristics of ITO films fabricated on glass substrates by high intensity pulsed ion beam method

Transparent conductive oxides such as indium tin oxide (ITO) are interesting materials due to their wide-band gaps, high visible light transmittance, high infrared reflectance, high electrical conductivity, hardness and chemical inertness. ITO films were fabricated on soda lime glass substrates by using high-intensity pulsed ion beam (HIPIB) technique. The as-deposited films comprised of partially crystallized In₂O₃ and after annealing at 500 °C for 1 h the film changed to polycrystalline phase. After annealing carrier concentration and Hall mobility increased while specific resistance and sheet resistance decreased quickly; and this trend was also observed when film thickness increased up to 300 nm for the post-annealed samples. Further increase in thickness of the film changed the electrical properties slightly. Atomic force microscopy (AFM) revealed that roughness decreased after 500 °C annealing for 1 h in air, except for the film of 65 nm thick. The thickness of the film which relates to the carrier concentration and mobility, degree of crystallization, size of the grain, and connections among grains in film are main factors to determine film’s electrical properties.     

Effects of CdCl2 treatment on properties of CdTe thin films grown by evaporation at low substrate temperatures

The structural, morphological and optical properties of vacuum‐evaporated CdTe thin films were investigated as a function of substrate temperature and post‐deposition annealing without and with CdCl₂/treatment at 400°C for 30 min. Diffraction patterns are almost the same exhibiting higher preferential orientation corresponding to (111) plane of the cubic phase. The intensity of the (111) peak increased with the CdCl₂/annealing treatment. The microstructure observed for all films following the CdCl₂/annealing treatment are granular, regardless of the as‐deposited microstructure. The grain sizes are increased after the CdCl₂/annealing treatment but now contain voids around the grain boundaries. The optical band gaps, E_g, were found to be 1.50, 1.50 and 1.48 eV for films deposited at 200 K and annealed without and with CdCl₂/treatment at 400°C for 30 min respectively. A progressive sharpening of the absorption edge upon heat treatment particularly for the CdCl₂/treated was observed. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Plasma enhanced chemical vapor deposition of ZnO thin films

Zinc oxide thin films were deposited on silicon and corning-7059 glass substrates by plasma enhanced chemical vapor deposition at different substrate temperatures ranging from 36 to 400 °C and with different gas flow rates. Diethylzinc as the source precursor, H₂O as oxidizer and argon as carrier gas were used for the preparation of ZnO films. Structural and optical properties of these films were investigated using X-ray diffraction, reflection high energy electron diffraction, atomic force microscopy and photoluminescence. Highly oriented films with (0 0 2) preferred planes were obtained on silicon kept at 300 °C with 50 ml/min flow rate of diethylzinc without any post annealing. Reflection high energy electron diffraction pattern also showed the crystalline nature of these films. A textured surface with rms roughness ∼28 nm was observed by atomic force microscopy for the films deposited at 300 °C. A sharp peak at 380 nm in the PL spectra indicated the UV band-edge emission.     

Effect of annealing on the properties of chemical bath deposited nanorods of CdSe thin films

Cadmium selenide (CdSe) thin films have been deposited by chemical bath deposition (CBD) on a glass substrate and they are annealed at 450 °C for 1 h. Scanning electron microscopic (SEM) image of as‐deposited CdSe shows the spherical shaped grains distributed over entire glass substrate. When it is annealed at 450 °C, clusters of nano‐rods with star shaped grains are formed. The X‐ray diffraction (XRD) study of the as‐deposited films exhibits a polycrystalline nature and it undergoes a structural phase transition from the metastable cubic to the stable hexagonal phase when annealed at 450 °C. Optical band gap of as‐deposited films (2.0 eV) has a blue shift with respect to the bulk value (1.7 eV) due to quantum confinement. The band gap energies of the films are decreased from 2.0 eV to 1.9 eV due to annealing at the temperature of 450 °C. The electrical resistivity, Hall mobility and carrier concentration of as‐deposited and annealed films are determined.     

Effects of post-annealing on electrical properties of amorphous Ga-doped Zn–Sn–O semiconductor films

We investigated the effect of post-annealing on the electrical properties of amorphous gallium-zinc-tin oxide (a-GZTO) films with different Ga contents. The films were deposited at room temperature by sputtering and annealed in air for 1 h. It was found that the doping with Ga, which acts as the carrier suppressor, contributes to the thermal stability of characteristic properties of a-GZTO thin films. The film with a small amount of Ga showed significant variations in carrier concentration according to the annealing temperature. Increases in carrier concentration and mobility can be ascribed to the reduction of subgap density of states by annealing. After annealing at 400 °C, however, the enrichment of Zn cations in surface region resulted in considerable changes in chemical bonding states and consequently, the carrier concentration decreased by two orders of magnitude for the low Ga-doped ZTO film.