Structural and optical properties of ZnO thin films deposited onto ITO/glass substrates

ZnO films were prepared by post deposition thermal oxidation in the ambient atmosphere of metallic Zn films (d = 100–170 nm) vacuum evaporated onto unheated indium tin oxide (ITO)-coated glass substrates. To study the effect of the substrate position during the Zn film deposition on the microstructure and optical properties (transmittance, reflectance and absorbance) of as obtained ZnO films, two set of Zn samples simultaneously deposited onto horizontally and obliquely arranged substrates were prepared. The as obtained ZnO films had a polycrystalline wurtzite structure, those obtained from normally deposited Zn films having a higher c-axis preferred orientation and a lower optical transmittance in the visible wavelength range. The optical band-gap was found to be of 3.14 eV for oxidized normally deposited virgin Zn films and of 3.16 eV for those obliquely deposited.     

Growth and characterization of nanostructured CdS/Polyaniline/CuInSe2 thin films for solar cell applications

In the present paper, we report about synthesis of nanostructured organic–inorganic heterojunction of CdS/Polyaniline/CuInSe₂ thin films by cost effective chemical route at room temperature, for solar cell application. As such obtained thin films are characterized for structural, compositional, morphological, optical and electrical properties by X-ray diffraction (XRD) pattern, energy dispersive X-ray (EDAX) analysis, scanning electron microscopy (SEM), optical absorbance spectra and I–V response respectively. The XRD reveals the polycrystalline nature of the thin films having tetragonal crystal structure and a crystallite size of 19 nm. The presence of observed and expected elements in the EDAX spectra confirms the elemental compositions in CdS/Polyaniline/CuInSe₂ thin films. From SEM images it can be inferred that the surface morphology of the Polyaniline thin films exists like clothing fibers, while CdS/CuInSe₂ shows granular shape particles distributed over the substrate and the SEM of CdS/Polyaniline/CuInSe₂ represents mixing and attachment of circular particles to fiber like structure. The optical absorbance spectra have shown red shift in absorbance strength and energy band gap value of CdS/CuInSe₂ from ~ 1.36 eV to ~ 1.62 eV upon formation of CdS/Polyaniline/CuInSe₂ thin film. The I–V response of CdS/CuInSe₂ and CdS/Polyaniline/CuInSe₂ measured under dark and illumination to 100 mW/cm² light, exhibited the solar characteristics from these graphs and the conversion efficiency calculated is observed to be 0.26 and 0.55% for CdS/CuInSe₂ and CdS/Polyaniline/CuInSe₂ thin films respectively.     

Growth of pure ZnO thin films prepared by chemical spray pyrolysis on silicon

Structural, morphological, optical and electrical properties of ZnO thin films prepared by chemical spray pyrolysis from zinc acetate (Zn(CH₃COO)₂ 2H₂O) aqueous solutions, on polished Si(1 0 0), and fused silica substrates for optical characterization, have been studied in terms of deposition time and substrate temperature. The growth of the films present three regimes depending on the substrate temperature, with increasing, constant and decreasing growth rates at lower, middle, and higher-temperature ranges, respectively. Growth rate higher than 15 nm min⁻¹ can be achieved at T_s=543 K. ZnO film morphological and electrical properties have been related to these growth regimes. The films have been characterized by X-ray diffraction, scanning electron microscopy and X-ray photoelectron spectroscopy.     

The effect of different oriented sapphire substrates on the growth of polar and non-polar ZnMgO by MOCVD

Polar and non-polar ZnMgO were synthesized on different crystallographic planes (C-, R- and M-planes) of sapphire (Al₂O₃) substrates by metal organic chemical vapor deposition, respectively. Under the same experimental condition, polar ZnMgO nanorods were obtained on C-Al₂O₃ substrate whereas non-polar ZnMgO thin films were obtained on R- and M-Al₂O₃ substrates. The surface morphology was significantly influenced by the competition of the preferable growth directions on different sapphire substrates. On C-Al₂O₃ substrate, ZnMgO nanorods were vertically well-aligned with typical lengths in the range 330–360 nm. On R- and M-Al₂O₃ substrates, however, ZnMgO thin films with flat surfaces were obtained, whose thickness were 150 and 20 nm, respectively. Under the same condition, the C-ZnMgO deposited on C-Al₂O₃ substrate has the maximum growth velocity (11 nm/nim), followed by A-ZnMgO deposited on R-Al₂O₃ substrate (5 nm/min), and the M-ZnMgO deposited on M-Al₂O₃ substrate has the minimum one (0.67 nm/min). The Near-Band-Edge (NBE) emission in Photoluminescence (PL) spectra shows a clear blueshift and a slight broadening compared with that of pure ZnO samples, which suggest that the Mg content has successfully incorporated into ZnO. The different energy blueshifts (67 meV and 98 meV) of the NBE emission demonstrate that A-ZnMgO deposited on R-Al₂O₃ substrate has higher Mg incorporation efficiency than C-ZnMgO on C-Al₂O₃ substrate.     

Influence of amorphous buffer layers on the crystallinity of sputter-deposited undoped ZnO films

Undoped ZnO films were deposited by radio frequency (RF) magnetron sputtering on amorphous buffer layers such as SiO_x, SiO_xN_y, and SiN_x prepared by plasma enhanced chemical vapor deposition (PECVD) for dielectric layer in thin film transistor (TFT) application. ZnO was also deposited directly on glass and quartz substrate for comparison. It was found that continuous films were formed in the thickness up to 10 nm on all buffer layers. The crystallinity of ZnO films was improved in the order on quartz>SiO_x >SiO_xN_y>glass>SiN_x according to the investigated intensities of (0 0 2) XRD peaks. The crystallite sizes of ZnO were in the order of SiO_x～glass >SiN_x. Stable XRD parameters of ZnO thin films were obtained to the thickness from 40 to 100 nm grown on SiO_x insulator for TFT application. Investigation of the ZnO thin films by atomic force microscope (AFM) revealed that grain size and roughness obtained on SiN_x were larger than those on SiO_x and glass. Hence, both nucleation and crystallinity of sputtered ZnO thin films remarkably depended on amorphous buffer layers.     

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.     

Characterization of pure ZnO thin films prepared by a direct photochemical method

In this paper, amorphous ZnO thin films were obtained by direct UV irradiation of β-diketonate Zn(II) precursor complexes spin-coated on Si(1 0 0) and fused silica substrates. ZnO films were characterized by means of XPS, X-ray diffraction (XRD) and Atomic Force Microscopy (AFM). These analyses revealed that as-deposited films are amorphous and have a rougher surface than thermally treated films. Optical characterization of the films showed that these are highly transparent in the visible spectrum with an average transmittance of up to 95% over 400 nm, and an optical band-gap energy of 3.21 eV for an as-deposited film, and 3.27 eV for a film annealed at 800 °C. Low resistivity values were obtained for the ZnO films (1.0 × 10⁻² Ω cm) as determined by Van der Pauw four-point probe method.     

Dopant concentration dependence of structure,optical, and magnetic properties of ZnO:Fe thin films

The effects of Fe-dopant concentration on the structure, optical, and magnetic properties of ZnO thin films were investigated by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), optical transmittance, absorption, photoluminescence (PL), and magnetic measurements. XRD spectra indicated that the doping of Fe atoms could not only change the lattice constant of ZnO but also improve the crystalline quality of ZnO thin films. And the Zn (0 0 2) diffraction peak at round 36.34°(2θ) was detected with increasing Fe content for the substitution of the Zn in the ZnO film. The band gap edge shifted toward longer wavelength with increase in Fe doping. Moreover, near band edge emission gradually increased with increase in Fe content (up to about 0.82 wt%), and then abruptly decreased due to the concentration quenching effect. Magnetic measurements confirmed that the ferromagnetic behavior of Fe-doped ZnO was correlated with the dopant concentration.     

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).     

Precipitation of zinc ferrite nanoparticles in the Fe2O3–ZnO–SiO2 glass system

Glass materials in the ZnO–Fe₂O₃–SiO₂ system, containing zinc ferrite nanoparticles, were prepared by the sol–gel method and characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), Mössbauer spectroscopy, AC- and DC-magnetization techniques. The gel samples, dried at 130 °C, were further heat treated in air at 500 and 800 °C. At 500 °C zinc ferrite and hematite nanoparticles, with an average size of approximately 24 nm, were precipitated in the brown and opaque 10ZnO–10Fe₂O₃–80SiO₂ and in the ruby colored transparent 5ZnO–5Fe₂O₃–90SiO₂ and 2.5ZnO–2.5Fe₂O₃–95SiO₂ glass matrices. In the 5ZnO–5Fe₂O₃–90SiO₂ sample the nanoparticles exhibited ferro or ferrimagnetic interactions combined with superparamagnetism with a blocking temperature of approximately 14 K. Heating at 800 °C seems to cause partial dissolution of the zinc ferrite and hematite particles in all the investigated compositions. Accordingly at 800 °C the 5ZnO–5Fe₂O₃–90SiO₂ glass shows a paramagnetic behavior down to 2 K.     

Synthesis and photoluminescence of Eu3+-doped ZnO–Ga2O3–SiO2 nano-glass-ceramics

Transparent rare-earth Eu³⁺-doped ZnO–Ga₂O₃–SiO₂ nano-glass-ceramics were obtained by a sol–gel method. X-ray diffraction and transmission electron microscopy were used to characterize the as-synthesized materials. Results showed that ZnGa₂O₄ nanocrystals with the size of 5 nm were precipitated from ZnO–Ga₂O₃–SiO₂ system and dispersed in the SiO₂-based glass when the heat-treatment temperature was up to 800 °C. Photoluminescence characterization of Eu³⁺-doped ZnO–Ga₂O₃–SiO₂ nano-glass-ceramics was carried out and the results show that the as-synthesized material display intense emission at 615 nm belonging to ⁵D₀ → ⁷F₂ transition.     

Effect of TiO2 addition on the chemical durability of Bi2O3–SiO2–ZnO–B2O3 glass system

The effect of the substitution of ZnO for TiO₂ on the chemical durability of Bi₂O₃–SiO₂–ZnO–B₂O₃ glass coatings in hot acidic medium (0.1 N H₂SO₄ at 80 °C) for different times was studied. The thick films produced by a screen-printing method and heat treated at 700 °C/5 min were analyzed by X-ray diffraction, scanning electron microscopy, and energy dispersive spectroscopy. The glass from the Bi₂O₃–SiO₂–ZnO–B₂O₃ system developed Zn₂SiO₄ and a glassy phase that were readily attacked by hot 0.1 N sulfuric acid, whereas the heat treated coating from the Bi₂O₃–SiO₂–TiO₂–ZnO–B₂O₃ system presented a finer microstructure with thin interconnected Bi₄Ti₃O₁₂ crystals and a glassy phase more resistant to hot 0.1 N sulfuric acid attack etching.     

Structural study of undoped and (Mn, In)-doped SnO2 thin films grown by RF sputtering

Undoped and 5%(Mn, In)-doped SnO₂ thin films were deposited on Si(1 0 0) and Al₂O₃ (R-cut) by RF magnetron sputtering at different deposition power, sputtering gas mixture and substrate temperature. X-ray reflectivity was used to determine the films thickness (10–130 nm) and roughness (～1 nm). The combination of X-ray diffraction and Mössbauer techniques evidenced the presence of Sn⁴⁺ in an amorphous environment, for as-grown films obtained at low power and temperature, and the formation of crystalline SnO₂ for annealed films. As the deposition power, substrate temperature or O₂ proportion are increased, SnO₂ nanocrystals are formed. Epitaxial SnO₂ films are obtained on Al₂O₃ at 550 °C. The amorphous films are quite uniform but a more columnar growth is detected for increasing deposition power. No secondary phases or segregation of dopants were detected.     

Dissolution behavior of ZnO–P2O5 glasses in water

Bulk binary ZnO–P₂O₅ glasses with 50–70 mol% ZnO were immersed in distilled water at 30–90 °C for up to 72 h. The immersed samples were characterized by weight loss, the change in solution pH, X-ray diffraction (XRD) analysis, scanning electron microscopy and Raman spectroscopy. Weight loss decreased with ZnO concentration for all immersion temperatures. Dissolution behavior was classified into two types in terms of weight loss and macroscopic appearance. Type I was primarily recognized in 50–60 mol% ZnO glasses. In type I, the weight loss for 72 h was relatively large (>1.0 × 10⁻⁷ kg mm⁻², >10% of initial sample weight). Raman spectra of the type I glasses indicated that the depolymerization of phosphate glass network occurred during the dissolution process. Crystalline Zn₂P₂O₇ · 3H₂O was precipitated in the water solution after immersion. Type II dissolution behavior was recognized in the 65 and 70 mol% ZnO glasses except for the 65ZnO–35P₂O₅ glass immersed at 90 °C. In the type II behavior, the weight loss for 72 h was relatively-small (<1.0 × 10⁻⁸ kg mm⁻², <1% of initial sample weight). The microstructure of the type II glass indicated selective dissolution. The dissolution process of the type II glass is discussed.     

Crystallization behavior of e-beam evaporated Ga5Ge15Te80 thin films

Ga₅Ge₁₅Te₈₀ thin films have been deposited by e-beam evaporation method. The chemical composition of the deposited films was identified using energy dispersive X-ray spectrometry. The electrical conductivity, σ of the deposited films during heating/cooling cycles was investigated in the temperatures 298–570 K. The conductivity curve showed two sudden upward trends during the first heating cycle. The first upward trend occurs in the temperature range 408–430 K and was attributed to the amorphous-to-crystalline phase transformation. While the second is in the temperature range 470–495 K, and can be attributed to the crystallization process. However, for second heating cycle the conductivity curve becomes reversible. The optical band gap of the as-deposited and annealed film at annealing temperature 423 K was determined from the recorded transmittance and reflectance spectra. The obtained results were confirmed throughout the X-ray and transmission electron microscope studies.     

Sol–gel derived yttrium doped ZnO nanostructures

Yttrium doped ZnO nanostructures were synthesized at room temperature by sol–gel technique. The sols were prepared using zinc acetate di-hydrate and ethanol as the precursors with yttrium nitrate hexahydrate as the dopant. Lactic acid with water was used as the acidic catalyst to control the hydrolysis reaction. Ammonia was added to vary the pH of the solution and the shape of the nanostructures changed with the change in pH of the solution. The films were deposited on ultrasonically cleaned glass substrates by dip coating technique. X-ray diffraction patterns indicated that the obtained nanostructures were polycrystalline in nature with (1 0 0), (0 0 2) and (1 0 1) reflections of hexagonal ZnO crystal structure. The ZnO films exhibited nanostructures with a rod/lathe like morphology on changing the yttrium concentration. The diameters of the structures varied from 100 nm to 250 nm and the aspect ratio was found to be in the range of 50–70.     

The effect of copper ions addition on structural and optical properties of zinc borate glasses

Glasses in the ternary system xCuO?(100 ? x)[55B₂O₃·45ZnO] (0 ≤ x ≤ 20 mol%) have been prepared by melting at 1200 °C and rapidly cooling at room temperature. The effect of copper ions addition in 55B₂O₃·45ZnO glass matrix together with the matrix effect on paramagentic behavior has been investigated using X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, differential thermal analysis (DTA), electron paramagnetic resonance (EPR), ultraviolet–visible (UV–VIS) spectroscopy and density measurements. The increase of the number of non-bridging oxygen (NBO) atoms as a function of CuO content in these glasses leads to the decrease of glass polymerization which reduces the stability of the glasses and favors the association of copper ions in clusters. This leads to the major changes of structural and optical properties of the studied glasses as can be seen from the data obtained by FTIR and EPR spectroscopies.     

Two routes of forming nanorods on the base of nanoparticles

With ZnS nanoparticles as raw materials, two kinds of nanorods were fabricated. When ZnS nanoparticles were dispersed in Zn(NO₃)₂ solution and were treated in a sealed autoclave at 150 °C for 24 h, ZnO nanorods formed. ZnS nanoparticles work as a source of monomers for the growth of ZnO nanorods. With increase of concentration of Zn(NO₃)₂ solution, the products present long nanorods, short nanorods, star structure and bulk particle sequentially. When ZnS nanoparticles were kept in a solution at room temperature, ZnS nanorods formed after 21 days. ZnS nanoparticles work as assembly parts. They fit together spontaneously and present ZnS nanorods with many parallel stripes along the lengthways surface. To check the generality of self-assembling, PdS and Y₂S₃ nanorods were also fabricated.     

The effect of cooling rate during hydrothermal synthesis of ZnO nanorods

The hydrothermal method was employed in order to obtain zinc oxide nanorods directly on Si/SiO₂/Ti/Zn substrates forming brush-like layers. In the final stages of synthesis, the reaction vessel was naturally cooled or submitted to a quenching process. X-ray diffraction results showed that all the nanostructures grew [0 0 0 1] oriented perpendicular to the substrate. The influence of the cooling process over the morphology and dimensions of the nanorods was studied by scanning electron microscopy. High-resolution transmission electron microscopy images of the quenched samples showed that the zinc oxide (ZnO) crystal surfaces exhibit a thin-layered coating surrounding the crystal with a high degree of defects, as confirmed by Raman spectroscopy results. Photodetectors made from these samples exhibited enhanced UV photoresponses when compared to the ones based on naturally cooled nanorods.     

Growth improvement and quality evaluation of ZnGeP2 single crystals using vertical Bridgman method

ZnGeP₂ single crystals were grown using two-temperature zone vertical Bridgman method. The effect of crucible material, crucible shape, and cooling program on the growth of the ZnGeP₂ crystal was investigated. The qualities of the crystals were evaluated by high resolution X-ray diffraction, X-ray fluorescence spectrometry, and IR transmittance spectra. The results show that the full width at half maximum of the rocking curves for (200), (004), and (220) faces are 45″, 37″, and 54″, respectively. The concentration of the P, Zn and Ge are almost homogeneous along the growth axis, but P and Zn are slightly deficient compared with Ge in the as-grown ZnGeP₂ crystals. The increase of annealing temperature from 600 °C to 700 °C has little effect on the reduction of the absorption losses in ZnGeP₂ powders, and has negative effect on the reduction of the absorption losses in ZnP₂ powders. Annealed in ZnP₂ powders at 600 °C for 300 h, the optical absorption loss at 2.05 μm reduce by 37%, compared with that of 27% reduction annealed in ZnGeP₂ powders.