Influence of oxygen partial pressure on structural, electrical, and optical properties of Al-doped ZnO film prepared by the ion beam co-sputtering method

Aluminum doped zinc oxide (AZO) films were prepared at room temperature by ion beam co-sputtering system under various oxygen partial pressures. The structural, electrical, and optical properties of the films were studied by XRD, XPS, Hall measurement, and spectrometer. The AZO film with low resistivity, 7.8 × 10^?4 Ω cm, and high transparency, ~80 %, was obtained at the optimum oxygen partial pressure of 1.3 × 10^?4 Torr and the intense (002) diffraction peak was observed simultaneously. Different optical band gaps observed in the films prepared under various oxygen partial pressures are closely related to the carrier concentrations in the films. Three O_1s components were applied to fit the XPS O_1s spectra. They consist of adsorbed oxygen species, oxygen in O-Zn bonds surrounded by oxygen vacancies, and oxygen in the O-Zn bonds. Two components, Zn in Zn–O bonds and Zn with higher than +2 oxidation states, were used to fit Zn_2p3/2 spectra. It was found that the increase of film’s resistivity which may result from the drops in the oxygen vacancy, Zn interstitial, carrier concentration, and grain size. No apparent transmission change of the film in the visible light region as a function of oxygen partial pressure was detected.     

The Influence of Oxygen on the Structural and Optical Properties of MoO3 Thin Films Prepared Using the Laser-Assisted Evaporation Technique

In this study, MoO₃ thin films were prepared using the CO₂ laser-assisted evaporation technique. The effect on the structural and optical properties of the oxygen content in the sample was evaluated. The samples were grown at a substrate temperature of 230 °C, pressure base of 5.3×10^?3 Pa, and at various oxygen pressures. The material was characterized through X-ray diffraction and optical transmittance in the visible spectral range (250–900 nm). The analysis showed that both structural and optical properties are critically dependent on the oxygen content. The samples prepared without oxygen crystallized in the β-Mo₈O₂₃ phase, indicating the presence of non-stoichiometric MoO₃. With increasing oxygen content during the growth of the film, it becomes stoichiometric in the alpha phase of MoO₃. An energy gap of 3.7 eV was observed in samples prepared without oxygen; the value increased up to 3.98 eV for the final 7.5×10^?2 Pa oxygen pressure. An absorption center appeared around 780 nm in the transmittance spectra of samples prepared in vacuum, and the intensity of this center diminished as the oxygen content increased in the chamber. This indicates that the absorption center is associated with the oxygen vacancies.     

Growth of CZTS thin films by sulfurization of sputtered single-layered Cu–Zn–Sn metallic precursors from an alloy target

Cu₂ZnSnS₄ (CZTS) thin films were prepared by sulfurizing single-layered metallic Cu–Zn–Sn precursors which were deposited by DC magnetron sputtering using a Cu–Zn–Sn ternary alloy target. The composition, microstructure and properties of the CZTS thin films prepared under different sputtering pressure and DC power were investigated. The results showed that the sputtering rate of Cu atom increases as the sputtering pressure and DC power increased. The microstructure of CZTS thin films can be optimized by sputtering pressure and DC power. The CZTS thin film prepared under 1 Pa and 30 W showed a pure Kesterite phase and a dense micro-structure. The direct optical band gap of this CZTS thin film was calculated as 1.49 eV with a high optical absorption coefficient over 10⁴ cm^?1. The Hall measurement showed the film is a p-type semiconductor with a resistivity of 1.06 Ω cm, a carrier concentration of 7.904 × 10¹⁷ cm^?3 and a mobility of 7.47 cm² Vs^?1.     

Nanocrystalline CuO thin films: synthesis, microstructural and optoelectronic properties

Nanocrystalline copper oxide (CuO) thin films have been synthesized by a sol–gel method using cupric acetate Cu (CH₃COO) as a precursor. The as prepared powder was sintered at various temperatures in the range of (300–700?°C) and has been deposited onto a glass substrates using spin coating technique. The structural, compositional, morphological, electrical optical and gas sensing properties of CuO thin films have been studied by X-ray diffraction, Scanning Electron Microscopy (SEM), Four Probe Resistivity measurement and UV–visible spectrophotometer. The variation in annealing temperature affected the film morphology and optoelectronic properties. X-ray diffraction patterns of CuO films show that all the films are nanocrystallized in the monoclinic structure and present a random orientation. The crystallite size increases with increasing annealing temperature (40–45?nm).The room temperature dc electrical conductivity was increased from 10^?6 to 10^?5 (Ω?cm)^?1, after annealing due to the removal of H₂O vapor which may resist conduction between CuO grain. The thermopower measurement shows that CuO films were found of n-type, apparently suggesting the existence of oxygen vacancies in the structure. The electron carrier concentration (n) and mobility (μ) of CuO films annealed at 400–700?°C were estimated to be of the order of 4.6–7.2?×?10¹⁹?cm^?3 and 3.7–5.4?×?10^?5?cm²?V^?1?s^?1?respectively. It is observed that CuO thin film annealing at 700?°C after deposition provide a smooth and flat texture suited for optoelectronic applications. The optical band gap energy decreases (1.64–1.46?eV) with increasing annealing temperature. It was observed that the crystallite size increases with increasing annealing temperature. These modifications influence the morphology, electrical and optical properties.     

Property variations of direct-current reactive magnetron sputtered copper oxide thin films deposited at different oxygen partial pressures

Cuprous oxide (Cu₂O) and cupric oxide (CuO) thin films were deposited on glass substrates at different oxygen partial pressures by direct-current reactive magnetron sputtering of pure copper target in a mixture of argon and oxygen gases. Oxygen partial pressure was found to be a crucial parameter in controlling the phases and, thus, the physical properties of the deposited copper oxide thin films. Single-phase Cu₂O thin films with cubic structure were obtained at low oxygen partial pressure between 0.147 Pa and 0.200 Pa while higher oxygen partial pressure promoted the formation of CuO thin films with base-centered monoclinic structure. Polycrystalline Cu₂O thin films deposited with oxygen partial pressure at 0.147 Pa possessed the lowest p-type resistivity of 1.76 Ω cm as well as an optical band gap of 2.01 eV. On the other hand, polycrystalline CuO thin films deposited with oxygen partial pressure at 0.320 Pa were also single phase but showed a n-type resistivity of 0.19 Ω cm along with an optical band gap of 1.58 eV.     

Effect of CoCl<Subscript>2</Subscript>–BaCl<Subscript>2</Subscript> fillers on morphology,dielectric constant and conductivity of PVDF composite for pressure sensing application

This present study focuses on the effect of addition of CoCl₂–BaCl₂ fillers on the β phase formation and dielectric constant in the PVDF composite films. The pristine and filler based PVDF films were prepared using solution casting technique. XRD analysis were carried out to investigate the crystalline structure in the prepared composite films. The surface morphology of the films were observed using SEM indicating the formation of agglormated structures. The UV–Vis absorption spectrum was obtained to investigate the effect of filler concentration on the optical band gap. The decrease in optical band gap with increase in filler concentration was confirmed from Tauc plot. The incorporation of filler significantly improved the ac conductivity. The dielectric study reveals the increase in value of dielectric constant from 10.8 to 42.3 as the filler content increased from 0 to 12 wt%. A pressure measurement set up was developed and voltage output was measured from the PVDF thin film sensor for variation in applied pressure.     

Influence of substrate temperature on the growth and properties of reactively sputtered In-rich InAlN films

Indium-rich InAlN films were prepared on Si (111) substrates by using reactive co-sputtering in a mixed Ar-N₂ atmosphere. The substrate temperature was varied from room temperature to 300 °C to investigate the film’s growth and properties at different temperatures. Structural and optical properties of the films were evaluated through high resolution XRD and Raman spectroscopy respectively, surface morphology and roughness analysis was performed by using FE-SEM and AFM respectively, whereas the electrical characterizations were made through resistivity and current–voltage (I–V) measurements respectively. Highly c-axis oriented nanocrystalline InAlN films with wurtzite structure were obtained at a substrate temperature of 100 °C and above. Structural quality of the films was improved with increase of the substrate temperature. The Raman spectroscopy revealed A₁ (LO) modes which became more intense by the increasing the substrate temperature. The electrical studies indicated n-type nature of InAlN film having electron concentration in the range 3 × 10¹⁹–20 × 10¹⁹ cm^?3. The electrical resistivity exhibited a decreasing trend with increase of the deposition temperature. The I–V measurements showed a noticeable increase in the value of current by increasing the substrate temperature to 300 °C.     

Influence of Relevant Gas Pressure on the Properties of Ionplated Ta2O5 Films. Einfluss relevanter Gasdrücke auf die Eigenschaften ionenplattierter Ta2O5 Schichten

Ta₂O₅ films were deposited onto unheated fused silica substrates (Suprasil®) by reactive low voltage ion plating (RLVIP). From these films of about 200 nm thickness the optical properties (refractive index n and the absorption coefficient k) and also the mechanical properties (density ρ and intrinsic stress σ) were investigated in dependence of the working gas pressure (Ar) and the reactive gas pressure (O₂). The experiments show a reasonable correlation between refractive index, density and intrinsic stress of the films. With low total pressure high refractive indices (up to n₅₅₀=2.25), high compressive film stress and high relative film density were found. However the film density, the refractive index and also the intrinsic stress decreased with films prepared under raising total gas pressure. The optical absorption depends on the amount of oxygen in the gas phase during deposition. By adding more oxygen to the Ar/O₂ gas mixture primarily the absorption could clearly be decreased.     

Enhanced photocatalytic activity of Mg0.05Zn0.95O thin films prepared by sol–gel method through a cycle

Mg_0.05Zn_0.95O thin films were prepared on silicon substrates by a sol–gel dip-coating technique. Microstructure, surface topography and optical properties of the thin films were characterized by X-ray diffraction, atom force microscopy, Fourier transform infrared spectrophotometer and fluorescence spectrometer. The results show that the thin film annealed at 700 °C has the largest average grain size and exhibits the best c-axis preferred orientation. As annealing temperature increases to 800 °C, the grain along c-axis has been suppressed. Roughness factor and average particle size increase with the increase of annealing temperature. The IR absorption peak appearing at about 416 cm^?1 is assigned to hexagonal wurtzite ZnO. The thin film annealed at 700 °C has the maximum oxygen vacancy, which can be inferred from the green emission intensity. Photocatalytic results show that the thin film annealed at 700 °C exhibits remarkable photocatalytic activity, which may be attributed to the larger grain size, roughness factor and concentration of oxygen vacancy. Enhanced photocatalytic activity of Mg_0.05Zn_0.95O thin films after a cycle may be attributed to the increase of surface oxygen vacancy and photocorrosion of amorphous MgO on the surface of thin film under UV irradiation.     

Influence of pyrolytic temperature on the properties of ZnO films optimized for H2 sensing application

In this work, we report the influence of pyrolytic temperature on the properties of ZnO films deposited by a novel spray pyrolysis deposition route. XRD results revealed an improvement in crystal quality of the films with increase in growth temperature. The optical measurements of the films show a maximum transmittance of ~85 % and the band gap of ~3.5 eV. Photoluminescence spectra revealed that the UV emission peaks at 385 nm is improved with increase in growth temperature upto 300 °C, which corresponds to the increase of optical quality and decrease of Zn interstitial defect in the films. Gold ohmic contacts were evaporated on the optimized ZnO film prepared at the substrate temperature of 300 °C, and response of the film to different concentrations of hydrogen (150–500 ppm) at room temperature was investigated. The ZnO sensor showed significant sensitivity to hydrogen for concentration as low as 150 ppm at room temperature, and the sensor response was observed to increase with increase in hydrogen concentration. The increased sensitivity of the film was attributed to the large roughness of the film revealed from AFM analysis. The results ensure the application of our novel sensor, to detect H₂ at low concentration and at room temperature.     

The Effect of Substrate Temperature on the Optical Properties of MoO3 Nano-crystals Prepared Using Spray Pyrolysis

In this study, thin films of molybdenum oxide were prepared by spray pyrolysis technique on glass substrates. The influence of substrate temperature on their crystallographic structure, surface morphology, and optical properties was studied. The formation of a MoO₃ film on the substrate was confirmed through XRD analysis. Furthermore, the presence of the two phases α and β in each of the films was evident. The percentage of phase α varied from 55 % for the film deposited at 200 °C up to 97 % for the film deposited at 400 °C. According to SEM images, MoO₃ films have a sponge-type structure on the order of nanometers. Both the optical gap and the refraction index strongly depend on substrate temperature. The optical gap decreases from 3.63 eV for the film deposited at 150 °C up to 3.30 eV for the one prepared at 400 °C. On the contrary, the refraction index measured at 800 nm increases from 1.54 up to 1.61 for the films prepared at 150 °C and 400 °C, respectively.     

Study of Ar + O2 deposition pressures on properties of pulsed laser deposited CdTe thin films at high substrate temperature

Cadmium telluride (CdTe) thin films deposited by pulsed laser deposition (PLD) on fluorine–tin–oxide substrates under different pressures of argon (Ar) + oxygen (O₂) at high substrate temperature (T_s = 500 °C) was reported in this paper. In our work, the CdTe thin films were prepared successfully at high T_s by inputting Ar + O₂. As reported, PLD-CdTe thin films were almost prepared at low substrate temperatures (<300 °C) under vacuum conditions. The deposition of CdTe thin films at high T_s by PLD is rarely reported. The influence of the Ar + O₂ gas pressure on thickness, structural performance, surface morphology, optical property and band gap (E_g) had been investigated respectively by Ambios probe level meter, X-ray diffraction (XRD), scanning electron microscopy (SEM) and UV–Vis spectrometer. Strong dependence of properties on the deposition pressures was revealed. In the range of Ar + O₂ gas pressure from 5 to 12 Torr, the deposition rate and the E_g of CdTe films vary in the range of 41.9–57.66 nm/min then to 35.26 nm/min and 1.51–1.54 eV then to 1.47 eV, respectively. The XRD diagrams showed that the as-deposited films were polycrystalline, and the main phase was cubic phase. However, the preferred orientation peak disappeared when the deposition pressure was higher. SEM images indicated that the CdTe film deposited at a higher deposition pressure was more uniform and had a higher compactness and a lower pinhole density. Furthermore, based on this thorough study, FTO/PLD-CdS (100 nm)/PLD-CdTe (~1.5 μm)/HgTe:Cu/Ag solar cells with an efficiency of 6.68 % and an area of 0.64 mm² were prepared successfully.     

Effect of growth temperature on structural, electrical and optical properties of dual ion beam sputtered ZnO thin films

ZnO epitaxial thin films were grown on p-type Si(100) substrates by dual ion beam sputtering deposition system. The crystalline quality, surface morphology, optical and electrical properties of as-deposited ZnO thin films at different growth temperatures were studied. Substrate temperature was varied from 100 to 600 °C at constant oxygen percentage O₂/(O₂ + Ar) % of 66.67 % in a mixed gas of Ar and O₂ with constant chamber pressure of 2.75 × 10^?4 mBar. X-Ray diffraction analyses revealed that all the films had (002) preferred orientation. The minimum value of stress was reported to be ?0.32 × 10¹⁰ dyne/cm² from ZnO film grown at 200 °C. Photoluminescence measurements demonstrated sharp near-band-edge emission (NBE) was observed at ~375 nm along with deep level emission (DLE) in the visible spectral range at room temperature. The DLE Peak was found to have decrement as ZnO growth temperature was increased from 200 to 600 °C. The minimum FWHM of the NBE peak of 16.76 nm was achieved at 600 °C growth temperature. X-Ray photoelectron spectroscopy study revealed presence of oxygen interstitials and vacancies point defects in ZnO film grown at 400 °C. The ZnO thin film was found to be highly resistive when grown at 100 °C. The ZnO films were found to be n-type conducting with decreasing resistivity on increasing substrate temperature from 200 to 500 °C and again increased for film grown at 600 °C. Based on these studies a correlation between native point defects, optical and electrical properties has been established.     

Effect of substrate temperature on structural, morphological and optical properties of crystalline titanium dioxide films prepared by DC reactive magnetron sputtering

Titanium dioxide (TiO₂) thin films have been deposited with various substrate temperatures by dc reactive magnetron sputtering method onto glass substrate. The effects of substrate temperature on the crystallization behavior and optical properties of the films have been studied. Chemical composition of the films was investigated by X-ray photoelectron spectroscopy (XPS). X-ray diffraction (XRD) analysis of the films revealed that they have polycrystalline tetragonal structure with strong (101) texture. The surface morphological study revealed the crystalline nature of the films at higher substrate temperatures. The TiO₂ films show the main bands in the range 400–700 cm^?1, which are attributed to Ti–O stretching and Ti–O–Ti bridging. The transmittance spectra of the TiO₂ thin film measured with various substrate temperatures ranged from 75 to 90 % in the visible light region. The optical band gap values of the films are increasing from 3.44 to 4.0 eV at growth temperature from 100 to 400 °C. The structural and optical properties of the films improved with the increase in the deposition temperature.     

Influence of ion-beam sputtering deposition parameters on highly photosensitive and transparent CdZnO thin films

CdZnO thin films with a nominal thickness of ~200 nm were grown on c-plane sapphire substrates by dual ion-beam sputtering deposition technique. The effect of substrate temperature (300–600 °C) and gas ambience on structural, morphological, compositional and opto-electronic properties was studied. X-ray diffraction patterns confirmed that all the films were polycrystalline in nature and were preferentially oriented along the c-axis. It was revealed that the films grown at Ar/O₂ ratio of 4:1 were structurally more ordered and the film quality was found to be the best at 500 °C. The compositional studies specify that approximately 11.8 at.% of cadmium were present in the film deposited at 300 °C in Ar–O₂ mixture. Investigations on optical properties by photoluminescence and absorption studies indicate band gap shrinkage with the increase in argon partial pressure and substrate temperature. It was found that photosensitivity of the deposited films was highly dependent on growth conditions. The photosensitivity was found to be 5000-fold higher for CdZnO film grown at 600 °C in Ar–O₂ ambience compared to the best reported result, and this was promising to realize high-performance opto-electronic devices on such CdZnO films.     

A study of crystallographic phases in non-stoichiometric (oxygen deficiency) indium oxide thin films

Indium oxide is a well-known transparent conductive oxide (TCO) in its stoichiometric composition (In₂O₃). Its electrical and optical properties are strongly influenced by the chemical composition. This work focuses on an experimental investigation of the crystallographic phases in non-stoichiometric (oxygen deficiency) compositions of indium oxide thin films. The thin films were deposited at 300 °C by reactive sputtering of pure indium target at different oxygen gas flow rates on Si substrates. Two different phases are identified only in the non-stoichiometric compositions: metallic indium- and crystalline indium-rich oxide. The metallic indium phase appears as nano-crystals, a few nano-meters in diameter, evenly dispersed and occupies only 1 vol. % of the film. These metallic nano-particles have a negligible effect on the optical transparency and electrical conductivity of the films. The indium-rich oxide (In_xO_y) phase which occupies about 99 vol. % of the film has the bixbyite crystallographic structure and average grain size of about 50 nm. This phase has a pronounced effect on improving the TCO figure-of-merit (FM) relative to stoichiometric crystalline In₂O₃ films due to a higher increase of the electrical conductivity than the decrease of the optical transparency.     

Effect of annealing temperature on optical and electrical properties of ZrO2–SnO2 nanocomposite thin films

ZrO₂–SnO₂ nanocomposite thin films were deposited onto quartz substrate by sol–gel dip-coating technique. Films were annealed at 500, 800 and 1,200 °C respectively. X-ray diffraction pattern showed a mixture of three phases: tetragonal ZrO₂ and SnO₂ and orthorhombic ZrSnO₄. ZrSnO₄ phase and grain size increased with annealing temperature. Fourier transform infra-red spectroscopy spectra indicated the reduction of –OH groups and increase in ZrO₂–SnO₂, by increasing the treatment temperature. Scanning electron microscopy observations showed nucleation and particle growth on the films. The electrical conductivity decreased with increase in annealing temperature. An average transmittance greater than 80 % (in UV–visible region) was observed for all the films. The optical constants of the films were calculated. A decrease in optical band gap from 4.79 to 4.59 eV was observed with increase in annealing temperature. Photoluminescence (PL) spectra revealed an emission peak at 424 nm which indicates the presence of oxygen vacancy in ZrSnO₄. PL spectra of the films exhibited an increase in the emission intensity with increase in temperature which substantiates enhancement of ZrSnO₄ phase and reduction in the non-radiative defects in the films. The nanocomposite modifies the structure of the individual metal oxides, accompanied by the crystallite size change and makes it ideal for gas sensor and optical applications.     

Effect of pyrolytic temperature on the properties of nano-structured Cuo optimized for ethanol sensing applications

In the present work, copper oxide thin films have been deposited at different substrate temperatures from 250 to 400 °C by spray pyrolysis technique. The desired properties of phase pure CuO with good crystal quality and conductivity have been optimized with respect to pyrolytic temperature. X-ray diffraction studies and Hall effect measurements indicated that these two properties are achieved at an optimum temperature of 350 °C. The band gap of CuO films was found to decrease from 1.8 to 1.2 eV with increase in substrate temperature, based on the UV-absorption spectrum of the film. The microstructures revealed that the film optimized at 350 °C, showed uniform surface with trapezium shaped particles, which are well compacted. The dynamic sensing behavior of the optimized p-type CuO sensor, prepared at a substrate temperature of 350 °C, was used to sense ethanol for concentrations: 100 and 200 ppm. The response time and the recovery time were within the range of 15–20 s and 15–18 s, respectively. The results revealed good response even at room temperature, with characteristics dependent on the size of the grains and the concentration of ethanol.     

High performance humidity sensing properties of indium tin oxide (ITO) thin films by sol–gel spin coating method

The tin doped indium oxide (ITO) thin films prepared by sol–gel spin coating method with In(NO₃)3H₂O and SnCl₄·5H₂O as indium and tin sources respectively is presented. The as deposited samples were annealed at 500 °C for 2 h in order to improve the crystallinity. The structural, morphological and optical properties of the films were analysed by using X-ray diffraction, scanning electron microscope (SEM), UV–Vis transmission spectra and photoluminescence, spectra analysis. The SEM images ensure the uniform and smooth surface of the as prepared and annealed film. The optical transmittance of more than 85 % has been observed in the UV–Vis region with a band gap of 3.91 and 3.73 eV for the as prepared and annealed films of ITO respectively. The PL spectra reveal that the optical properties were significantly improved due to the annealing effect. The annealed film shows high sensitivity for humidity approximately two order changes in the resistance and the sensitivity increases for different relative humidity from 10 to 90 % due to the physisorption between the water molecules and the surface of the thin films.     

Europium incorporated barium titanate thin films for optical applications

BaTiO₃:Eu (BT:Eu) thin films were deposited onto quartz substrates by RF magnetron sputtering. The effect on structural, morphological, optical and photoluminescence (PL) properties in the films with different Eu concentrations (0–5 wt%) were investigated. The X-ray diffraction (XRD) pattern of the undoped BT thin film revealed a tetragonal (T) phase with orientations along (101) plane. From XRD pattern, the crystallinity of the films increased with increase in Eu concentration. The SEM images revealed that the films exhibited tetragonal shape, crack free and good adherence to the substrate. Atomic force microscopy studies showed an increase of grain growth with doping concentration. The rms roughness value increased with increase in Eu concentration and the film surface revealed positive skewness and high value of kurtosis which make them suitable for tribological applications. X-ray photoelectron spectroscopy revealed the presence of barium, titanium, europium and oxygen in BT:Eu film. An average transmittance of >80 % (in visible region) was observed for all the films. Optical band gap of Eu doped BT films decreased from 3.86 to 3.53 eV. Such films with optical properties such as high transparency, decrease in band gap and high refractive index are suitable for optoelectronic applications. PL properties showed a sharp line at 625 nm and a broad line at 552 nm due to europium (Eu³⁺) transitions. PL phenomena were observed, owing to the electronic structure of Eu³⁺ ions as well as BT nanocrystallites in the films. The sharp and intense red luminescence is useful for photoelectric devices and optical communications.