Structural and optical characterizations of spin coated cobalt-doped cadmium oxide nanostructured thin films

Cd_1−xCo_xO thin films (with molar ratios x=0.0–8.0%) were grown onto glass substrates via the sol–gel spin coating technique. XRD results indicate that a CdO single phase with a cubic polycrystalline structure is formed. The crystallinity of CdO thin films is gradually deteriorated with increasing the Co ratio. AFM images of the films confirm the decrease of the grain size of the CdO films with increasing Co content. The direct optical band gap is red shifted from 2.580 eV to 2.378 eV with the increase of Co content. The refractive index, the dispersion parameters, and the optical conductivity of CdO thin films showed an enhancement with increasing cobalt dopant ratio. The correlation between the structural modifications and the resultant optical properties are reported.     

Effect of processing parameter on structural,optical and electrical properties of photovoltaic chalcogenide nanostructured RF magnetron sputtered thin absorbing films

The aim of this work was to develop high quality of CuIn_1−xGa_xSe₂ thin absorbing films with x (Ga/In+Ga)<0.3 by sputtering without selenization process. CuIn_0.8Ga_0.2Se₂ (CIGS) thin absorbing films were deposited on soda lime glass substrate by RF magnetron sputtering using single quaternary chalcogenide (CIGS) target. The effect of substrate temperature, sputtering power & working pressure on structural, morphological, optical and electrical properties of deposited films were studied. CIGS thin films were characterised by X-ray diffraction (XRD), Field emission scanning electron microscope (FE-SEM), Energy dispersive X-ray spectroscopy (EDAX), Atomic force microscopy (AFM), UV–vis–NIR spectroscopy and four probe methods. It was observed that microstructure, surface morphology, elemental composition, transmittance as well as conductivity of thin films were strongly dependent on deposition parameters. The optimum parameters for CIGS thin films were obtained at a power 100 W, pressure 5 mT and substrate temperature 500 °C. XRD revealed that thin film deposited at above said parameters was polycrystalline in nature with larger crystallite size (32 nm) and low dislocation density (0.97×10¹⁵ lines m⁻²). The deposited film also showed preferred orientation along (112) plane. The morphology of the film depicted by FE-SEM was compact and uniform without any micro cracks and pits. The deposited film exhibited good stoichiometry (Ga/In+Ga=0.19 and In/In+Ga=0.8) with desired Cu/In+Ga ratio (0.92), which is essential for high efficiency solar cells. Transmittance of deposited film was found to be very low (1.09%). The absorption coefficient of film was ~10⁵ cm⁻¹ for high energy photon. The band gap of CIGS thin film evaluated from transmission data was found to be 1.13 eV which is optimum for solar cell application. The electrical conductivity (7.87 Ω⁻¹ cm⁻¹) of deposited CIGS thin film at optimum parameters was also high enough for practical purpose.     

Study of structural and optical properties of nanostructured V2O5 thin films doped with fluorine

In this study, vanadium oxide (V₂O₅) was doped with different percentages of fluorine (F) and deposited on glass substrates by using spray pyrolysis method. The substrate temperature during the film deposition was kept constant at 450 °C. The obtained nanostructured thin films were characterised by X-ray Diffraction (XRD), UV–visible spectroscopy, and Scanning Electron Microscopy (SEM). The XRD results showed that F doped films are polycrystalline with main phase of β-V₂O₅ and with preferred orientation along (200). Increasing dopant to 30% improved crystallinity, but for more doping, the structure of samples tended to be amorphous. VF₂ phase was also observed when doping of F was increased to more than 10%. The incorporation of fluorine in nano-layers led to a decrease in optical absorption by 1.3 a.u. and an increase in band gap of energy from 2.23 to 2.83 eV. SEM images showed that the shape of grains was spherical with 10% doping and changed to bacilliform with 70% F concentration. The cyclic voltammetry results obtained for different samples showed expanded anodic and cathodic peaks for the undoped sample. The samples prepared with 20% and 40% F-doping level had milder anodic and cathodic peaks. However, by increasing the dopant to 70%, the peaks were expanded. The thin film with 40% F-doping showed the least resistance, but the resistance increased dramatically with 70% F dopant concentrations.     

Synthesis and gas sensing behavior of nanostructured V2O5 thin films prepared by spray pyrolysis

Nanocrystalline vanadium pentoxide (V₂O₅) thin films have been deposited by a spray pyrolysis technique on preheated glass substrates. The substrate temperature was changed between 300 and 500 °C. The structural and morphological properties of the films were investigated by means of X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and atomic force microscopy (AFM). The influence of different substrate temperatures on ethanol response of V₂O₅ has also been investigated. XRD revealed that the films deposited at T_pyr=300 °C have low peak intensities, but the degree of crystallinity improved when the temperature was increased to 500 °C and films had orthorhombic structures with preferential orientations along the (0 0 1) direction. The fractal analysis showed a decreasing trend versus the pyrolysis temperature. Sensing properties of the samples were studied in the presence of ethanol vapor. The operating temperature of the sensor was optimized for the best gas response. The response increased linearly with different ethanol concentrations. It was found that films deposited at the lowest substrate temperature (300 °C) had the highest sensing response to ethanol.     

Effects of the Cd:Zn:S molar ratio and heat treatment on the optical and photoluminescence properties of nanocrystalline CdZnS thin films

Nanocrystalline cadmium zinc sulfide thin films with different molar ratios were prepared by sol–gel dip-coating in a polyethyleneglycol matrix. After heat treatment in air at 250, 350 and 450 °C, the thin films were characterized by studying their structural, morphological, compositional, optical (linear and nonlinear) and photoluminescence (PL) properties. According to X-ray diffraction (XRD) results, the samples are polycrystalline with a hexagonal crystal structure and an average grain size of 12–18 nm. The surface morphology of the films was examined by scanning electron microscopy (SEM). The results show that the films consist of nanocrystalline grains included in clusters with uniform coverage over the substrate surface. To determine their chemical composition, X-ray photoelectron spectra (XPS) of composite films were measured. The transmittance and bandgap of the films increased with the Zn concentration and decreased with increasing annealing temperature. The refractive index of the films was measured and the related dispersion is discussed in terms of the Wemple–DiDomenico single oscillator model. The third-order nonlinear polarizability of the films was estimated using a semi-empirical relation based on the single oscillator model. The results show that the films are suitable as optical switches. PL spectra were recorded for an excitation wavelength of 210 nm. The emission intensity for the films varied with the Zn ratio and the annealing temperature and the behavior of different peaks is discussed.     

Effect of Co doping on structural, optical, electrical and thermal properties of nanostructured ZnO thin films

Nanocrystalline Zn1-x CoxO(where x varies from 0 to 0.04 in steps of 0.01) thin films were deposited onto glass substrate by the spray pyrolysis technique at a substrate temperature of 350 ℃. The X-ray diffraction patterns confirm the formation of hexagonal wurtzite structure. The crystal grain size of these films was found to be in the range of 11–36 nm. The scanning electron micrographs show a highly crystalline nanostructure with different morphologies including rope-like morphology for undoped ZnO and nanowalls and semispherical morphology for Co-doped Zn O. The transmittance increases with increasing Co doping. The optical absorption edge is observed in the transmittance spectra from 530 to 692 nm, which is due to the Co2C absorption bands corresponding to intraionic d–d shifts. The direct and indirect optical band gap energies decrease from 3.05 to 2.75 eV and 3.18 to 3.00 eV, respectively for 4 mol% Co doping. The electrical conductivity increases with increasing both the Co doping and temperature, indicating the semiconducting nature of these films. The temperature dependence thermal electromotive force measurement indicates that both undoped and Co-doped ZnO thin films show p-type semiconducting behavior near room temperature. This behavior dies out beyond 313 K and they become n-type semiconductors.     

Effect of post-growth annealing on the structural,optical and electrical properties of V2O5 nanorods and its fabrication,characterization of V2O5/p-Si junction diode

We report the synthesis of V₂O₅ nanorods by utilizing simple wet chemical strategy with ammonia meta vanadate (NH₄VO₃) and polyethylene glycol (PEG) exploited as precursor and surfactant agent, respectively. The effect of post-annealing on structural, optical and electrical properties of V₂O₅ nanorods was characterized by XRD, HRSEM-EDX, TEM, FT-IR, UV (DRS), PL, TG–DTA and DC conductivity studies. The X-ray diffraction analysis revealed that the prepared sample annealed at 150 °C for 5 h which exhibited anorthic phase of V₅O₉ and annealed at 300–600 °C showed the anorthic phase change to orthorhombic phase of V₂O₅ due to the post-annealing effect. The surface morphology results indicated that increasing temperature caused a change from microrods to a nanorods shape in the morphology of V₂O₅. FT-IR spectrum confirmed that the presence of V₂O₅ functional groups and the formation of V–O bond. The optical band gap was found in the range 2.5–2.48 eV and observed to decreases with various annealed temperature. The DC electrical conductivity was studied as a function of temperature which indicated the semiconducting nature. Further, the potential of V₂O₅ nanostructures were grown on the p-Si substrate using the nebulizer spray technique. The junction properties of the V₂O₅/p-Si diode were evaluated by measuring current (I)–voltage (V) and AC characteristics.     

Effects of Sb,Zn doping on structural,electrical and optical properties of SnO2 thin films

Highly transparent, low resistive pure and Sb, Zn doped nanostructured SnO₂ thin films have been successfully prepared on glass substrates at 400° C by spray pyrolysis method. Structural, electrical and optical properties of pure and Sb, Zn doped SnO₂ thin films are studied in detail. Powder X-ray diffraction confirms the phase purity, increase in crystallinity, size of the grains (90–45 nm), polycrystalline nature and tetragonal rutile structure of thin films. The scanning electron microscopy reveals the continuous change in surface morphology of thin films and size of the grains decrease due to Sb, Zn doping in to SnO₂. The optical transmission spectra of SnO₂ films as a function of wavelength confirm that the optical transmission increases with Sb, Zn doping remarkably. The optical band gap of undoped film is found to be 4.27 eV and decreases with Sb, Zn doping to 4.19 eV, 4.07 eV respectively. The results of electrical measurements indicate that the sheet resistance of the deposited films improves with Sb, Zn doping. The Hall measurements confirm that the films are degenerate n-type semiconductors.     

Magnetic,optical, microscopic and electrical behavior of Ca2−xYxCo2O5 prepared by a molten flux method

In this present study, we have reported the preparation of yttrium doped polycrystalline Ca_2−xY_xCo₂O₅ (x=0.0–1.0) material by a molten flux method and its various properties like electrical, optical, dielectric and magnetic behaviors. Characterization techniques have been adopted to confirm its physical nature and properties. X-ray diffraction results confirmed the crystal structure of prepared Ca_2−xY_xCo₂O₅ as orthorhombic and the scanning electron microscope pictured the presence of platelet-shaped particles with the dimensions of 150–300 nm. It also reveals the state of higher concentration of yttrium (Y³⁺) controls the grain size of Ca_2−xY_xCo₂O₅ ceramics. Further, we find out that the higher concentration of yttrium (Y³⁺) increases the optical band gap due to the occurrence of metal–insulator transition and also the same in electrical resistivity from 0.2 mΩ cm to 0.5 mΩ cm, which is due to the replacement of holes by Y³⁺ ions. The result of dielectric studies proves that the conduction mechanism of yttrium doped calcium cobalt oxide is due to space charge polarization. The magnetic saturation behavior shows the decreasing area in the hysteresis curve while the Y³⁺ concentration is increased, which is due to the phase transition of ferromagnetic to paramagnetic.     

氧氩流量比对RF溅射ZnO:Mg薄膜结构及光学性能的影响

利用射频(RF)磁控溅射技术,采用单质Zn靶和 MgO陶瓷靶共溅射,在O₂和Ar气的混合气氛下制备了Mg掺杂ZnO(ZnO:Mg)薄膜,并通过改变O₂和Ar的流量比O ₂/Ar,研究了 对ZnO:Mg薄膜的物相结构、表面形貌及光学性能的影响。结果表明,室 温下O₂/Ar在1∶1～3∶1 范围内制备的薄膜均为单相的ZnO(002)薄膜,薄膜具有三维(3D)的结核生长模式;沉积的 ZnO:Mg薄膜在 N₂氛下200℃退火处理后,O₂/Ar为3∶1制备的薄膜在380～1200nm光谱范围内具有较高的透过率,可见光区平 均透过率约为85%、最大透过率达90%;薄膜的光学带隙 Eg为3.51eV,Mg掺杂对ZnO薄膜的光学带隙具有 较为明显的调制作用;采用极值包络线法计算表明,薄膜在589.3nm 处的折射率为1.963,膜厚约285nm。     

Effects of ammonia concentration on morphology, composition and optical properties of ZnO1-xSx thin films of Cu(In, Ga)Se2 solar cells

ZnO_1-xS_x films were prepared by chemical bath deposition(CBD) on glass substrate. The effects of ammonia concentration on the structure characteristics of ZnO_1-xS_x films were studied. The results of scanning electron microscope(SEM) show that the film has good density when the concentration of ammonia is 0.4 M. Because more S2-ions are involved in the reaction and less precipitates are generated, the film is relatively dense. The distribution of the fi...     

Correlation between the structural, morphological, optical, and electrical properties of In2O3 thin films obtained by an ultrasonic spray CVD process

Indium oxide (In₂O₃) thin films are successfully deposited on glass substrate at different deposition times by an ultrasonic spray technique using Indium chloride as the precursor solution; the physical properties of these films are characterized by XRD, SEM, and UV-visible. XRD analysis showed that the films are polycrystalline in nature having a cubic crystal structure and symmetry space group Ia3 with a preferred grain orientation along the (222) plane when the deposition time changes from 4 to 10 min, but when the deposition time equals 13 min we found that the majority of grains preferred the (400) plane. The surface morphology of the In₂O₃ thin films revealed that the shape of grains changes with the change of the preferential growth orientation. The transmittance improvement of In₂O₃ films was closely related to the good crystalline quality of the films. The optical gap energy is found to increase from 3.46 to 3.79 eV with the increasing of deposition time from 4 to 13 min. The film thickness was varied between 395 and 725 nm. The film grown at 13 min is found to exhibit low resistivity (10^-2 Ω·cm), and relatively high transmittance (~ 93%).     

Effect of substrate temperature on structural,morphological, optical and electrical properties of MnIn2S4 thin films prepared by nebulizer spray pyrolysis technique

Manganese indium sulphide (MnIn₂S₄) thin films were deposited using an aqueous solution of MnCl₂, InCl₃ and (NH₂)₂CS in the molar ratio 1:2:4 by simple chemical spray pyrolysis technique. The thin film substrates were annealed in the temperature range between 250 and 350 °C to study their various physical properties. The structural properties as studied by X-ray diffraction showed that MnIn₂S₄ thin films have cubic spinel structure. The formation of cube and needle shaped grains was clearly observed from FE-SEM analysis. The energy dispersive spectrum (EDS) predicts the presence of Mn, In and S in the synthesized thin film. From the optical studies, it is analyzed that the maximum absorption co-efficient is in the order between 10⁴ and 10⁵ cm⁻¹ and the maximum transmittance (75%) was noted in the visible and infrared regions. It is noted that, the band gap energy decreases (from 3.20 to 2.77 eV) with an increase of substrate temperature (from 250 to 350 °C). The observations from photoluminescence studies confirm the emission of blue, green, yellow and red bands which corresponds to the wavelength range 370–680 nm. Moreover, from the electrical studies, it is observed that, as the substrate temperature increases the conductivity also increases in the range 0.29–0.41×10⁻⁴ Ω⁻¹ m⁻¹. This confirms the highly semiconducting nature of the film. The thickness of the films was also measured and the values ranged between 537 nm (250 °C) to 483 nm (350 °C). This indicates that, as the substrate temperature increases, the thickness of the film decreases. From the present study, it is reported that the MnIn₂S₄ thin films are polycrystalline in nature and can be used as a suitable ternary semiconductor material for photovoltaic applications.     

Antimony sulfide (Sb2S3) thin films by pulse electrodeposition: Effect of thermal treatment on structural,optical and electrical properties

Antimony sulfide films have been deposited by pulse electrodeposition on Fluorine doped SnO₂ coated glass substrates from aqueous solutions containing SbCl₃ and Na₂S₂O₃. The crystalline structure of the films was characterized by X-ray diffraction, Raman spectroscopy and TEM analysis. The deposited films were amorphous and upon annealing in nitrogen/sulfur atmosphere at 250 °C for 30 min, the films started to become crystalline with X-ray diffraction pattern matching that of stibnite, Sb₂S₃, (JCPDS 6-0474). AFM images revealed that Sb₂S₃ films have uniformly distributed grains on the surface and the grain agglomeration occurs with annealing. The optical band gap calculated from the transmittance and the reflectance studies were 2.2 and 1.65 eV for as deposited and 300 °C annealed films, respectively. The annealed films were photosensitive and exhibited photo-to-dark current ratio of two orders of magnitude at 1 kW/m² tungsten halogen radiation.     

Optical and electrical properties of epitaxial (Mg,Cd)xZn1−xO, ZnO, and ZnO:(Ga,Al) thin films on c-plane sapphire grown by pulsed laser deposition

A consistent set of epitaxial, n-type conducting ZnO thin films, nominally undoped, doped with Ga or Al, or alloyed with Mg or Cd, was grown by pulsed laser deposition (PLD) on single-crystalline c-plane sapphire (0 0 0 1) substrates, and characterized by Hall measurement, and UV/VIS optical transmission spectroscopy.The optical band gap of undoped ZnO films at nearly 3.28 eV was shifted by alloying with Mg up to 4.5 eV and by alloying with Cd down to 3.18 eV, dependent on the alloy composition. In addition, highly doped ZnO:Al films show a blue-shifted optical absorption edge due to filling of electronic states in the conduction band.The Hall transport data of the PLD (Mg,Zn,Cd)O:(Ga,Al) thin films span a carrier concentration range of six orders of magnitude from 3 × 10¹⁴ to 3 × 10²⁰ cm⁻³, which corresponds to a resistivity from 5 × 10⁻⁴ to 3 × 10³ Ω cm. Structurally optimized, nominally undoped ZnO films grown with ZnO nucleation and top layer reached an electron mobility of 155 cm²/V s (300 K), which is among the largest values reported for heteroepitaxial ZnO thin films so far.Finally, we succeeded in combining the low resistivity of ZnO:Ga and the band gap shift of MgZnO in MgZnO:Ga thin films. This results demonstrate the unique tunability of the optical and electrical properties of the ZnO-based wide-band gap material for future electronic devices.     

Annealing effect on physical and electrical characteristics of thin HfO2, HfSixOy and HfOyNz films on Si

We report the effect of annealing on electrical and physical characteristics of HfO₂, HfSi_xO_y and HfO_yN_z gate oxide films on Si. Having the largest thickness change of 0.3 nm after post deposition annealing (PDA), HfO_yN_z shows the lowest leakage current. It was found for both as-grown and annealed structures that Poole-Frenkel conduction is dominant at low field while Fowler-Nordheim tunneling in high field. Spectroscopic ellipsometry measurement revealed that the PDA process decreases the bandgap of the dielectric layers. We found that a decreasing of peak intensity in the middle HfO_yN_z layer as measured by Tof-SIMS may suggest the movement of N toward the interface region between the HfO_yN_z layer and the Si substrate during the annealing process.     

Sn掺杂对(In0.95-xSnxFe0.05)2O3薄膜的结构、电学及磁特性的影响

我们利用脉冲激光沉积的方法制备了一系列(In0.95-xSnxFe0.05)2O3 (x=0~0.09)薄膜,并在其中发现了室温铁磁性。X射线衍射结果表明锡与铁离子已掺入氧化铟晶格。随着锡的掺入,样品内的载流子浓度得到了很大的提高,但相应的铁磁性却几乎没有变化。我们认为氧空位相关的束缚磁极化子模型能够跟好的解释我们的铁掺杂氧化铟薄膜中的铁磁耦合的机制,而载流子传导的RKKY相互作用则不适用于这一系统。