The optical properties of CdxZn1−xS thin films on glass substrate prepared by spray pyrolysis method

A series of Cd_xZn_1−xS thin films have been deposited on glass substrates using spray pyrolysis technique. The crystallinity and microstructure of Cd_xZn_1−xS thin films have been investigated by X-ray diffraction (XRD). Based on the results of Hall measurements, the films obtained were an n-type semiconductor. The X-ray data analysis of Cd_xZn_1−xS thin films showed that the grain size of the Cd_xZn_1−xS increased with increase in Cd composition. It is observed that the band gap increases as the Cd composition decreases. The results also showed a blue shift of absorption edge of optical transmission spectra is increases as Zn ratio increases. The effects of Cd composition on the structural and optical properties of Cd_xZn_1−xS thin films were related to their grain size, stress and carrier concentration.     

Structural, optical and electrical properties of Zn1−xCdxO thin films prepared by PLD

Ternary polycrystalline Zn_1−xCd_xO semiconductor films with cadmium content x ranging from 0 to 0.23 were obtained on quartz substrate by pulse laser deposited (PLD) technique. X-ray diffraction measurement revealed that all the films were single phase of wurtzite structure grown on c-axis orientation with its c-axis lattice constant increasing as the Cd content x increasing. Atomic force microscopy observation revealed that the grain size of Zn_1−xCd_xO films decreases continuously as the Cd content x increases. Both photoluminescence and optical measurements showed that the band gap decreases from 3.27 to 2.78 eV with increasing the Cd content x. The increase in Cd content x also leads to the broadening of the emission peak. The resistivity of Zn_1−xCd_xO films decreases evidently for higher values of Cd content x. The shift of PL emission to visible light as well as the decrease of resistivity makes the Zn_1−xCd_xO films potential candidate for optoelectronic device.     

Oxygen flux influence on the morphological, structural and optical properties of Zn1−xMgxO thin films grown by plasma-assisted molecular beam epitaxy

The Zn_1−xMg_xO thin films were grown on Al₂O₃ substrate with various O₂ flow rates by plasma-assisted molecular beam epitaxy (P-MBE). The growth conditions were optimized by the characterizations of morphology, structural and optical properties. The Mg content of the Zn_1−xMg_xO thin film increases monotonously with decreasing the oxygen flux. X-ray diffractometer (XRD) measurements show that all the thin films are preferred (0 0 2) orientated. By transmittance and absorption measurements, it was found that the band gap of the film decreases gradually with increasing oxygen flow rate. The surface morphology dependent on the oxygen flow rate was also studied by field emission scanning electron microscopy (FE-SEM). The surface roughness became significant with increasing oxygen flow rate, and the nanostructures were formed at the larger flow rate. The relationship between the morphology and the oxygen flow rate of Zn_1−xMg_xO films was discussed.     

Effect of substrate temperature on the morphology, structural and optical properties of Zn1−xCoxO thin films

Zn_1−xCo_xO thin films with c-axis preferred orientation were deposited on sapphire (0 0 0 1) by pulsed laser deposition (PLD) technique at different substrate temperatures in an oxygen-deficient ambient. The effect of substrate temperature on the microstructure, morphology and the optical properties of the Zn_1−xCo_xO thin films was studied by means of X-ray diffraction (XRD), atomic force microscopy (AFM), UV-visible-NIR spectrophotometer, fluorescence spectrophotometer. The results showed that the crystallization of the films was promoted as substrate temperature rose. The structure of the samples was not distorted by the Co incorporating into ZnO lattice. The surface roughness of all samples decreased as substrate temperature increased. The Co concentration in the film was higher than in the target. Emission peak near band edge emission of ZnO from the PL spectra of the all samples was quenched because the dopant complexes acted as non-radiative centers. While three emission bands located at 409 nm (3.03 eV), 496 nm (2.5 eV) and 513 nm (2.4 eV) were, respectively, observed from the PL spectra of the four samples. The three emission bands were in relation to Zn interstitials, Zn vacancies and the complex of V_O and Zn_i (V_OZn_i). The quantity of the Zn interstitials maintained invariable basically, while the quantity of the V_OZn_i slightly decreased as substrate temperature increased.     

Characterization and properties of ZnO1−xSx alloy films fabricated by radio-frequency magnetron sputtering

A series of ZnO_1−xS_x alloy films (0 ≤ x ≤ 1) were grown on quartz substrates by radio-frequency (rf) magnetron sputtering of ZnS ceramic target, using oxygen and argon as working gas. X-ray diffraction measurement shows that the ZnO_1−xS_x films have wurtzite structure with (0 0 2) preferential orientation in O-rich side (0 ≤ x ≤ 0.23) and zinc blende structure with (1 1 1) preferential orientation in S-rich side (0.77 ≤ x ≤ 1). However, when the S content is in the range of 0.23 < x < 0.77, the ZnO_1−xS_x film consists of two phases of wurtzite and zinc blende or amorphous ZnO_1−xS_x phase. The band gap energy of the films shows non-linear dependence on the S content, with an optical bowing parameter of about 2.9 eV. The photoluminescence (PL) measurement reveals that the PL spectrum of the wurtzite ZnO_1−xS_x is dominated by visible band and its PL intensity and intensity ratio of UV to visible band decrease greatly compared with undoped ZnO. All as-grown ZnO_1−xS_x films behave insulating, but show n-type conductivity for w-ZnO_1−xS_x and maintain insulating properties for β-ZnO_1−xS_x after annealed. Mechanisms of effects of S on optical and electrical properties of the ZnO_1−xS_x alloy are discussed in the present work.     

Growth, structural and optical transport properties of nanocrystal Zn1−xCdS thin films deposited by solution growth technique (SGT) for photosensor applications

Solution Growth Technique (SGT) has been used for deposition of Zn_1−xCdS nanocrystalline thin films. Various parameters such as solution pH (10.4), deposition time, concentration of ions, composition and deposition and annealing temperatures have been optimized for the development of device grade thin film. In order to achieve uniformity and adhesiveness of thin film on glass substrate, 5 ml triethanolamine (TEA) have been added in deposition solution. The as-deposited films have been annealed in Rapid Thermal Annealing (RTA) system at various temperature ranges from 100 to 500 °C in air. The changes in structural formation and optical transport phenomena have been studied with annealing temperatures and composition value (x). As-deposited films have two phases of ZnS and CdS, which were confirmed by X-ray diffraction studies; further the X-ray analysis of annealed (380 °C) films indicates that the films have nanocrystalline size (150 nm) and crystal structure depends on the films stoichiometry and annealing temperatures. The Zn_0.4CdS films annealed at 380 °C in air for 5 min have hexagonal structure where as films annealed at 500 °C have represented the oxide phase with hexagonal structure. Optical properties of the films were studied in the wavelength range 350-1000 nm. The optical band gap (E_g=2.94-2.30 eV) decreases with the composition (x) value. The effect of air rapid annealing on the photoresponse has also been observed on Zn_1−xCdS nanocrystal thin films. The Zn_1−xCdS thin film has higher photosensitivity at higher annealing temperatures (380-500 °C), and films also have mixed Zn_1−xCdS/Zn_1−xCdSO phase with larger grain size than the as-deposited and films annealed up to 380 °C. The present results are well agreed with the results of other studies.     

BiFeO3/Zn1−xMnxO bilayered thin films

BiFeO₃/Zn_1−xMn_xO (x = 0-0.08) bilayered thin films were deposited on the SrRuO₃/Pt/TiO₂/SiO₂/Si(1 0 0) substrates by radio frequency sputtering. A highly (1 1 0) orientation was induced for BiFeO₃/Zn_1−xMn_xO. BiFeO₃/Zn_1−xMn_xO thin films demonstrate diode-like and resistive hysteresis behavior. A remanent polarization in the range of 2P_r ∼ 121.0-130.6 μC/cm² was measured for BiFeO₃/Zn_1−xMn_xO. BiFeO₃/Zn_1−xMn_xO (x = 0.04) bilayer exhibits a highest M_s value of ∼15.2 emu/cm³, owing to the presence of the magnetic Zn_0.96Mn_0.04O layer with an enhanced M_s value.     

Structural,electronic and optical properties of CdxZn1 − xS alloys from first-principles calculations

Structural, electronic and optical properties as well as structural phase transitions of ternary alloy Cd_xZn_1 − xS have been investigated using the first-principles calculations based on the density functional theory. We found that the crystal structure of Cd_xZn_1 − xS alloys transforms from wurtzite to zinc blende as Cd content of x=0.83$x=0.83$. Effect of Cd content on electronic structures of Cd_xZn_1 − xS alloys has been studied. The bandgaps of Cd_xZn_1 − xS alloys with wurtzite and zinc blende structures decrease with the increase of Cd content. Furthermore, dielectric constant and absorption coefficient also have been discussed in detail.     

Growth of cubic MgxZn1−xO alloy films by electron beam evaporation

We report the growth of cubic Mg_xZn_1−xO alloy thin films on quartz by electron beam evaporation. It can be found that all the samples have sharp absorption edges by the absorption measurements. X-ray diffraction measurements indicate the Mg_xZn_1−xO films are cubic phase with preferred orientation along the (1 1 1) direction. Energy dispersive spectrometry (EDS) demonstrates that the Mg concentration in Mg_xZn_1−xO films is much higher than the ceramic target used, and the composition can be tuned in a small scope by varying the substrate temperature and the beam electric current. The reasons of this phenomenon are also discussed.     

Properties of MgxZn1−xO thin films sputtered in different gases

Mg_xZn_1−xO alloy films were prepared on sapphire substrates using Ar and N₂ as the sputtering gases. The effect of the sputtering gas on the structural, optical and electrical properties of the Mg_xZn_1−xO films was studied. By using N₂ as the sputtering gas, the Mg_xZn_1−xO film shows p-type conductivity and the band gap is larger than that employing Ar as the sputtering gas. The reason for this phenomenon is thought to be related to the reaction between N-O or N-Zn, and the N-doping.     

Study on the structure and optical property of Zn1−xCuxO sol–gel thin films on quartz substrate

Zn_1−xCu_xO thin films (x=0, 1.0, 3.0, 5.0%) are prepared on quartz substrate by sol–gel method. The structure and morphology of the samples are investigated by X-ray diffraction (XRD) and atomic force microscopy (AFM). The results show that Cu ions were effectively penetrated into the ZnO crystal lattices with substitutional and interstitial impurities to form stable solid solutions without changing the polycrystalline wurtzite structure. Two peaks at 420 nm (2.95 eV, violet), 485 nm (2.56 eV, blue) have been observed from the photoluminescence (PL) spectra of the samples. It is concluded that the violet peak may correspond to the exciton emission; the blue emission corresponds to the electron transition from the bottom of the conduction band to the acceptor level of zinc vacancy. The optical test shows that the optical band gap E_g is decreased with the increase amount of Cu doping in ZnO. The band gap decrease from 3.40 eV to 3.25 eV gradually. It is also found that the transmission rate is increased rapidly with the increase of Cu ions concentration.     

Optical properties of MgxZn1−xO thin films deposited on silicon and sapphire substrate by rf magnetron sputtering

The index dispersion at UV–VIS range for polycrystalline Mg_xZn_1−xO films on silicon with different Mg concentration was obtained by spectroscopic ellipsometry (SE) method. It decreases with the increase of the Mg content. Above the relative peak wavelength, they are well fitted by the first-order Sellmeier relation. The band gap of films on sapphire of different Mg content was determined from transmission measurements. Photoluminescence (PL) illustrated that for Mg_xZn_1−xO films every PL peak corresponded to a special excitation wavelength. The wavelength of the PL peak was proportional to the special excitation wavelength. A strong peak was obtained in the blue band for the films due to the large amount of oxygen vacancies caused by excess Zn and Mg atoms, while weak peak at ultraviolet band.     

Structural,optical, FTIR and photoluminescence properties of Zn0.96−xCo0.04CuxO (x=0.03, 0.04 and 0.05) nanopowders

Un-hydrogenated and hydrogenated Cu, Co co-doped ZnO (Zn_0.96−xCo_0.04Cu_xO, x=0.03, 0.04 and 0.05) nanopowders have been synthesized by co-precipitation method. The synthesized samples have been characterized by powder X-ray diffraction, energy dispersive X-ray spectra, UV–Visible spectrophotometer and Fourier transform infrared spectroscopy. The calculated average crystalline size increases from 37.3 to 50.6 nm for un-hydrogenated samples from x=0.03 to 0.05 and it changes from 29.4 to 34.9 nm for hydrogenated samples. The change in lattice parameters, micro-strain, a small shift of X-ray diffraction peaks towards lower angles and reduction in energy gap reveal the substitution of Cu²⁺ ions into Zn–Co–O lattice. The hydrogenation effect reduces the particle size and induces the more uniform distribution of particles than the un-hydrogenated samples which is confirmed by SEM micrographs. Photoluminescence spectra of Zn_0.96−xCo_0.04Cu_xO system shows that red shift in near band edge ultraviolet emission from 393 to 403 nm with suppressing intensity and a blue shift in green band emission from 537 to 529 nm with enhancing intensity confirms the substitution of Cu into the Zn–Co–O lattice.     

High-throughput characterization of BixY3−xFe5O12 combinatorial thin films by magneto-optical imaging technique

Bi_xY_3−xFe₅O₁₂ thin films have been grown on GGG (Gd₃Ga₅O₁₂) (1 1 1) substrates by the combinatorial composition-spread techniques under substrate temperature (T_sub) ranging from 410 to 700 °C and O₂ pressure of 200 mTorr. In order to study the effect of substrates on the deposition of Bi_xY_3−xFe₅O₁₂ thin films, garnet substrates annealed at 1300 °C for 3 h were also used. Magneto-optical properties were characterized by our home-designed magneto-optical imaging system. From the maps of Faraday rotation angle θ_F, it was evident that the Faraday effect appears only when T_sub = 430-630 °C. θ_F reaches to the maximum value (∼6°/μm, λ = 632 nm) at 500 °C, and is proportional to the Bi contents. XRD and EPMA analyses showed that Bi ions are easier to substitute for Y sites and better crystallinity is obtained for annealed substrates than for commercial ones.     

Structural and electrical characterization of SxSe100−x thin films

Thin films of samples of the glassy S_xSe_100−x system with 0 ≤ x ≤ 7.28 have been prepared by thermal evaporation technique at room temperature (300 K). X-ray investigations show that the structure of pure selenium (Se) does change seriously by the addition of small amount of sulphur S ≤7.28%. The lattice parameters were determined as a function of sulphur content. Results of differential thermal analysis (DTA) of the glassy compositions of the system S_xSe_100−x were discussed. The characteristic temperatures (T_g, T_c and T_m) were evaluated. Dark electrical resistivities, ρ, of S_xSe_100−x thin films with different thicknesses from 100 to 500 nm, were measured in the temperature range from 300 to 423 K. Two distinct linear parts with different activation energies were observed. The variation of electrical resistivity of examined compositions has been discussed as a function of the film thickness, temperature and the sulphur content. The application of Mott model for the phonon assisted hopping of small polarons gave the same two activation energies obtained from the resistivity temperature calculations.     

Optical and electrical properties of plasma-oxidation derived HfO2 gate dielectric films

High-k gate dielectric HfO₂ thin films have been deposited on Si(1 0 0) by using plasma oxidation of sputtered metallic Hf thin films. The optical and electrical properties in relation to postdeposition annealing temperatures are investigated by spectroscopic ellipsometry (SE) and capacitance-voltage (C-V) characteristics in detail. X-ray diffraction (XRD) measurement shows that the as-deposited HfO₂ films are basically amorphous. Based on a parameterized Tauc-Lorentz dispersion mode, excellent agreement has been found between the experimental and the simulated spectra, and the optical constants of the as-deposited and annealed films related to the annealing temperature are systematically extracted. Increases in the refractive index n and extinction coefficient k, with increasing annealing temperature are observed due to the formation of more closely packed thin films and the enhancement of scattering effect in the targeted HfO₂ film. Change of the complex dielectric function and reduction of optical band gap with an increase in annealing temperature are discussed. The extracted direct band gap related to the structure varies from 5.77, 5.65, and 5.56 eV for the as-deposited and annealed thin films at 700 and 800 °C, respectively. It has been found from the C-V measurement the decrease of accumulation capacitance values upon annealing, which can be contributed to the growth of the interfacial layer with lower dielectric constant upon postannealing. The flat-band voltage shifts negatively due to positive charge generated during postannealing.     

Effects of oxygen partial pressure and substrate temperature on the structure and optical properties of MgxZn1−xO thin films prepared by magnetron sputtering

Deposited with different oxygen partial pressures and substrate temperatures, Mg_xZn_1−xO thin films were prepared using a Mg_0.6Zn_0.4O ceramic target by magnetron sputtering. The structural and optical properties of the prepared thin films were investigated. The X-ray diffraction spectra reveal that all the films on quartz substrate are grown along (2 0 0) orientation with cubic structure. The lattice constant decreases and the crystallite size increases with the increase of substrate temperature. Both energy dispersive X-ray spectroscopy and calculated results suggest the ratio of Mg/Zn increases with increasing substrate temperature. The thin film deposited with T_s = 500 °C has a minimal rms roughness of 7.37 nm. The transmittance of all the films is higher than 85% in the visual region. The optical band gap is not sensitive to the oxygen partial pressure, while it increases from 5.63 eV for T_s = 100 °C to 5.95 eV for T_s = 700 °C. In addition, the refractive indices calculated from transmission spectra are sensitive to the substrate temperature. The photoluminescence spectra of Mg_xZn_1−xO thin films excited by 330 nm ultraviolet light indicate that the peak intensity of the spectra is influenced by the oxygen partial pressure and substrate temperature.     

Structure and electrical properties of Bi5GexSe95−x thin films

Bi₅Ge_xSe_95−x (30, 35, 40 and 45 at.%) thin films of thickness 200 nm were prepared on glass substrates by the thermal evaporation technique. The influence of composition and annealing temperature, on the structural and electrical properties of Bi₅Ge_xSe_95−x films was investigated systematically using X-ray diffraction (XRD), energy dispersive X-ray analysis (EDX). The XRD patterns showed that the as-prepared films were amorphous in nature with few tiny crystalline peaks of relatively low intensity for 30 and 45 at.% and the Bi₅Ge₄₀Se₅₅ annealed film was polycrystalline. The chemical composition of the Bi₅Ge₃₀Se₆₅ film has been checked using energy dispersive X-ray spectroscopy (EDX). The electrical conductivity was measured in the temperature range 300-430 K for the studied compositions. The effect of composition on the activation energy (ΔE) and the density of localized states at the Fermi level N(E_F) were studied, moreover the electrical conductivity was found to increase with increasing the annealing temperature and the activation energy was found to decrease with increasing the annealing temperature. The results were discussed on the basis of amorphous-crystalline transformations.     

Characterization of chemically deposited ZnSe/SnO2/glass films: Influence of annealing in Ar atmosphere on physical properties

The Zinc Selenide (ZnSe) thin films have been deposited on SnO₂/glass substrates by a simple and inexpensive chemical bath deposition (CBD). The structural, optical and electrical properties of ZnSe films have been characterized by X-ray diffraction (XRD), Energy Dispersive X-ray Analysis (EDAX), optical absorption spectroscopy, and four point probe techniques, respectively. The films have been subjected to different annealing temperature in Argon (Ar) atmosphere. An increase in annealing temperature does not cause a complete phase transformation whereas it affects the crystallite size, dislocation density and strain. The optical band gap (E_g) of the as-deposited film is estimated to be 3.08 eV and decreases with increasing annealing temperature down to 2.43 eV at 773 K. The as-deposited and annealed films show typical semiconducting behaviour, dρ/dT > 0. Interestingly, the films annealed at 373 K, 473 K, and 573 K show two distinct temperature dependent regions of electrical resistivity; exponential region at high temperature, linear region at low temperature. The temperature at which the transition takes place from exponential to linear region strongly depends on the annealing temperature.     

Spray pyrolytic synthesis of large area NiOx thin films from aqueous nickel acetate solutions

Non-stoichiometric nickel oxide thin films were prepared by pyrolytic decomposition of aerosol droplets of aqueous nickel acetate solution. Conventional un-nebulized spray pyrolysis system was used for the synthesis of thin films. The fine droplets were atomized by employing compressed air as carrier gas and allowed to decompose onto pre-heated Sn doped In₂O₃ (ITO) coated glass. The preparative parameters such as substrate temperature, solution concentration, distance from spray-nozzle to substrate, pressure of carrier air, etc., were optimized to obtain large area, uniform, thin films. The appropriate substrate temperature was selected after thermo-gravimetric analysis of nickel acetate. The temperature range of 330-420 °C was investigated for pyrolysis. Structural studies using X-ray diffraction (XRD) show the formation of cubic NiO. Morphological aspects of the films as-prepared and air annealed films have been studied by employing scanning electron microscopy. The optical absorption studies give direct band gap equal to 3.61 eV. The compositional analysis was carried out from the elemental depth profiles employing Auger electron spectroscopy. These indicate the formation of non-stoichiometric nickel oxide thin films. By studying I-V characteristics in alkaline electrolyte, electrocatalytic activity is tested.