Optoelectronics and formaldehyde sensing properties of tin-doped ZnO thin films

Sn-doped ZnO thin films were deposited on clean glass substrates using the chemical spray pyrolysis technique. XRD analyses confirm stable ZnO hexagonal wurtzite structure of the films with crystallite size in the range of 20–28 nm. The surface roughness of the films increases on Sn doping, which favors to higher adsorption of oxygen species on the film surface, resulting in higher gas response. Optical studies reveal that the band gap decreases on Sn doping. All the films show near band edge emission, and on Sn doping the luminescence peak intensity has been found to increase. Photocurrent in the 1.5 at.% doped film enhances about three times to that observed in the undoped ZnO film. Among all the films examined, the 1.5 at.% Sn-doped film exhibits the maximum response (～94.5 %) at the operating temperature of 275?°C for 100 ppm concentration of formaldehyde, which is much higher than the response (～35 %) in the undoped film. The gas response of the film is attributed to the chemisorption of oxygen on the film surface and the subsequent reaction between the adsorbed oxygen species and the formaldehyde molecules.     

Co,Sn共掺ZnO薄膜结构与光致发光的研究

采用溶胶-凝胶旋涂法在玻璃衬底上制备了Co,Sn掺杂ZnO系列薄膜.通过金相显微镜和X射线衍射(XRD)研究了Co与Sn掺杂对薄膜的表面形貌和微结构的影响.XRD结果表明,所有ZnO薄膜样品都存在(002)择优取向,特别Sn单掺ZnO薄膜的c轴择优取向最为显著,而且晶粒尺寸最大.XPS测试表明样品中Co和Sn的价态分别为2+和4+,证实Co²⁺,Sn⁴⁺进入了ZnO的晶格.室温光致发光谱(PL)显示在所有的样品中都有较强的蓝光双峰发射和较弱的绿光发 关键词： ZnO薄膜 溶胶-凝胶 掺杂 光致发光     

Thickness effect on the structural and optical constants of stibnite thin films prepared by sulfidation annealing of antimony films

This paper deals with some physical properties of antimony sulphide Sb₂S₃ thin films obtained by an annealing process in sulphur vapors at 300 °C of Sb thermal evaporated thin films deposited on glass substrate. The crystal structure and surface morphology were investigated by both XRD and AFM techniques. This structural study shows that Sb₂S₃ thin films were well crystallized in orthorhombic structure and some parameters such as the lattice parameter, crystallite size, microstrain and degree of preferred orientation have been reported and correlated with the effect of crystallite size. On the other hand, the refractive index and the extinction coefficient were discussed in terms of the Forouhi–Bloomer model. The optical band gap was found to range from 1.75 to 2.23 eV. Finally, the analysis of the optical parameters extracted from the Urbach–Martienssen and Forouhi–Bloomer models lead to some explanations of the correlations between the structural properties in terms of the crystallite size and optical ones.     

Structural,electrical and optical studies on spray-deposited aluminium-doped ZnO thin films

Thin films of zinc oxide (ZnO) were deposited on cleaned glass substrates by chemical spray pyrolysis technique using Zn(CH₃COO)₂ as precursor solution. Also, aluminium-doped thin films of ZnO were prepared by using AlCl₃ as doping solution for aluminium. The dopant concentration [Al/Zn atomic percentage (at%)] was varied from 0 to 1.5 at% in thin films of ZnO prepared in different depositions. Structural characterization of the deposited films was performed with X-ray diffraction (XRD) studies. It confirmed that all the films were of zinc oxide having polycrystalline nature and possessing typical hexagonal wurtzite structure with crystallite size varying between 100.7 and 268.6 nm. The films exhibited changes in relative intensities and crystallite size with changes in the doping concentration of Al. The electrical studies established that 1 at% of Al-doping was the optimum for enhancing electrical conduction in ZnO thin films and beyond that the distortion caused in the lattice lowered the conductivity. The films also exhibited distinct changes in their optical properties at different doping concentrations, including a blue shift and slight widening of bandgap with increasing Al dopant concentration.     

Effect of dopants on the structural,optical and electrical properties of sol–gel derived ZnO semiconductor thin films

Undoped, Ga-, In-, Zr-, and Sn-doped ZnO transparent semiconductor thin films were deposited on alkali-free glasses by sol–gel method. 2-methoxyethanol (2-ME) and diethanolamine (DEA) were chosen as a solvent and a stabilizer, respectively. The doping concentration was maintained at 2 at.% in the impurity doping precursor solutions. The effects of different dopants on the structural, optical, and electrical properties of ZnO thin films were investigated. XRD results show that all annealed ZnO-based thin films had a hexagonal (wurtzite) structure. ZnO thin films doped with impurity elements obviously improved the surface flatness and enhanced the optical transmittance. All impurity doped ZnO thin films showed high transparency in the visible range (>91%). The Ga- and In- doped ZnO thin films exhibited higher Hall mobility and lower resistivity than did the undoped ZnO thin film.     

Effects of metal doping on the physical properties of ZnTe thin films

Zinc telluride (ZnTe) thin films were sublimated on a glass substrate using closed space sublimation (CSS) technique. ZnTe thin films of same thickness were tailored with copper (Cu) & silver (Ag) doping, considered for comparative study. X-ray diffraction (XRD) patterns of as-deposited ZnTe thin film and doped ZnTe samples exhibited polycrystalline behavior. The preferred orientation of (111) having cubic phase was observed. XRD patterns indicated that the crystallite size had increased after silver and copper immersion in as-deposited ZnTe thin films. Scanning electron microscopy (SEM) was used to observe the change of as-deposited and doped sample's grains sizes. EDX confirmed the presence of Cu and Ag in the ZnTe thin films after doping respectively. The optical studies showed the decreasing trend in energy band gap after Cu and Ag-doping. Transmission also decreased after doping. Resistivity of as-deposited ZnTe thin film was about 10⁶ Ω cm. The resistivity was reduced to 68.97 Ω cm after Cu immersion, and 10⁴ Ω cm after Ag immersion. Raman spectra were used to check the crystallinity of as-deposited, Cu and Ag-doped ZnTe thin film samples.     

Sn掺杂ZnO薄膜的室温气敏性能及其气敏机理

采用化学气相沉积方法在预制好电极的玻璃基底上制备出Sn掺杂ZnO薄膜和纯ZnO薄膜. 两种样品典型的形貌为四足状ZnO晶须, 其直径约为150-400 nm, 呈疏松状结构. 气敏测试结果显示Sn掺杂ZnO薄膜具有优良的室温气敏性, 并对乙醇具有良好的气敏选择性, 而纯ZnO薄膜在室温条件下对乙醇和丙酮均没有气敏响应. X射线衍射结果表明两种样品均为六方纤锌矿结构. Sn掺杂ZnO样品中没有出现Sn及其氧化物的衍射峰, 其衍射结果与纯ZnO样品对比, 衍射峰向小角度偏移. 光致发光结果表明, Sn掺杂ZnO薄膜与纯ZnO薄膜均出现紫外发光峰和缺陷发光峰, 但是Sn的掺杂使得ZnO的缺陷发光峰明显增强. 将Sn掺杂ZnO样品在空气中退火后, 其室温气敏性消失, 说明Sn掺杂ZnO样品的室温气敏性可能与其缺陷含量高有关. 采用自由电子散射模型解释了Sn掺杂ZnO薄膜的室温气敏机理.     

Influence of substrate temperature and Cobalt concentration on structural and optical properties of ZnO thin films prepared by Ultrasonic spray technique

Pure and Cobalt doped zinc oxide were deposited on glass substrate by Ultrasonic spray method. Zinc acetate dehydrate, Cobalt chloride, 4-methoxyethanol and monoethanolamine were used as a starting materials, dopant source, solvent and stabilizer, respectively. The ZnO samples and ZnO:Co with Cobalt concentration of 2 wt.% were deposited at 300, 350 and 400 °C. The effects of substrate temperature and presence of Co as doping element on the structural, electrical and optical properties were examined. Both pure and Co doped ZnO samples are (0 0 2) preferentially oriented. The X-ray diffraction results indicate that the samples have polycrystalline nature and hexagonal wurtzite structure with the maximum average crystallite size of ZnO and ZnO:Co were 33.28 and 55.46 nm. An increase in the substrate temperature and presence doping the crystallinity of the thin films increased. The optical transmittance spectra showed transmittance higher than 80% within the visible wavelength region. The band gap energy of the thin films increased after doping from 3.25 to 3.36 eV at 350 °C.     

Sn doping effects on the electro-optical properties of sol gel derived transparent ZnO films

Undoped and tin (Sn) doped ZnO films have been deposited by sol gel spin coating method. The Sn/Zn nominal volume ratio was 1, 3 and 5% in the solution. The effect of Sn incorporation on structural and electro-optical properties of ZnO films was investigated. All the films have polycrystalline structure, with a preferential growth along the ZnO (002) plane. The crystallite size was calculated using a well-known Scherrer's formula and found to be in the range of 26-16 nm. X-ray diffraction patterns of the films showed that Sn incorporation leads to substantial changes in the structural characteristics of ZnO films. The SEM measurements showed that the surface morphology of the films was affected from the Sn incorporation. The highest average optical transmittance value in the visible region was belonging to the undoped ZnO film. The optical band gap and Urbach energy values of these films were determined. The absorption edge shifted to the lower energy depending on the Sn dopant. The shift of absorption edge is associated with shrinkage effect. The electrical conductivity of the ZnO film enhanced with the Sn dopant. From the temperature dependence of conductivity measurements, the activation energy of ZnO film increased with Sn incorporation.     

Optical and structural properties of CdS thin films grown by chemical bath deposition doped with Ag by ion exchange

In this work thin CdS films using glycine as a complexing agent were fabricated by chemical bath deposition and then doped with silver (Ag), by an ion exchange process with different concentrations of AgNO₃ solutions. The CdS films were immersed in silver solutions using different concentrations during 1 min for doping and after that the films were annealed at 200 °C during 20 min for dopant diffusion after the immersion on the AgNO₃ solutions. The aim of this research was to know the effects of different concentrations of Ag on the optical and structural properties of CdS thin films. The optical band gap of the doped films was determined by transmittance measurements, with the results of transmittance varying between 35% and 70% up to 450 nm in the electromagnetic spectra and the band gap varying between 2.31 and 2.51 eV depending of the silver content. X-ray photoelectron spectroscopy was used to study the influence of silver on the CdS:Ag films, as a function of the AgNO₃ solution concentration. The crystal structure of the thin CdS:Ag films was studied by the X-ray diffraction method and the film surface morphology was studied by atomic force microscopy. Using the ion exchange process, the CdS films’ structural, optical and electric characteristics were modified according to silver nitrate concentration used.     

Tin-mono-sulfide (SnS) thin films prepared by chemical spray pyrolysis with different [S]/[Sn] ratios

SnS thin films were deposited by chemical spray pyrolysis using cost-effective and low-toxicity sources materials like tin (II) chloride dihydrate and thiourea as sources of tin and sulphur, respectively. We have studied the properties of sprayed SnS thin films with [S]/[Sn] ratios were varied from 1 to 4 in order to optimize these parameters. X-ray diffraction was used for analyzing the films structure, Raman Spectroscopy for assessing the films quality and structure, scanning electron microscope (SEM) for surface morphology and energy dispersive energy (EDS) for compositional element in samples, atomic force microscopy (AFM) for the topography of surfaces and optical spectroscopy for measuring transmittances and then deducing the band gap energies. All films obtained are polycrystalline with (111) as preferential direction for films with [S]/[Sn] ratio equals to one while for [S]/[Sn] ratios from 2 to 4 the main peak becomes (101) and the (111) peak decreases in intensity. Raman spectroscopy confirms the presence of only one SnS phase without any additional parasite secondary phases. SEM images revealed that films are well adhered onto glass surface with rounded grain. AFM confirms this result being films with [S]/[Sn] = 1 the roughest and also with the largest grain size. EDS results show an improvement of stoichiometry with the increase of the [S]/[Sn] ratio. From optical analysis, it is inferred that the band gap energy decreases from 1.83 to 1.77 eV when the [S]/[Sn] ratio changes from 2 to 4.     

Thermal phase change and activation energy of crystallization of Ge-Sb-Te-Sn thin films

To improve the optical storage performance, Sn was doped into Ge2Sb2Te5 phase change thin films. The optical and thermal properties of Sn-doped Ge2Sb2Te5 film were investigated. The crystal structures of the as-sputtered and the annealed films were identified by the X-ray diffraction (XRD) method. The differential scanning calorimeter (DSC) method is used to get the crystallization temperature and crystallization energy (Ea). It was found that proper Sn-doping could highly improve storage performance of the Ge2Sb2Te5 media.     

Structural,optical,and electrical properties of Cu-doped ZrO_2 films prepared by magnetron co-sputtering

Copper(Cu)-doped ZrO_2(CZO) films with different Cu content(0 at.%～ 8.07 at.%) are successfully deposited on Si(100) substrates by direct current(DC) and radio frequency(RF) magnetron co-sputtering. The influences of Cu content on structural, morphological, optical and electrical properties of CZO films are discussed in detail. The CZO films exhibit ZrO_2 monocline(ˉ111) preferred orientation, which indicates that Cu atoms are doped in ZrO_2 host lattice. The crystallite size estimated form x-ray diffraction(XRD) increases by Cu doping, which accords with the result observed from the scanning electron microscope(SEM). The electrical resistivity decreases from 2.63 ?.cm to 1.48 ?·cm with Cu doping content increasing, which indicates that the conductivity of CZO film is improved. However, the visible light transmittances decrease slightly by Cu doping and the optical band gap values decrease from 4.64 eV to 4.48 eV for CZO films.     

Effect of 60Co γ-irradiation on structural and optical properties of thin films of Ga10Se80Hg10

Thin films of Ga₁₀Se₈₀Hg₁₀ have been deposited onto a chemically cleaned Al₂O₃ substrates by thermal evaporation technique under vacuum. The investigated thin films are irradiated by ⁶⁰Co γ-rays in the dose range of 50–150 kGy. X-ray diffraction patterns of the investigated thin films confirm the preferred crystallite growth occurs in the tetragonal phase structure. It also shows, the average crystallite size increases after γ-exposure, which indicates the crystallinity of the material increases after γ-irradiation. These results were further supported by surface morphological analysis carried out by scanning electron microscope and atomic force microscope which also shows the crystallinity of the material increases with increasing the γ-irradiation dose. The optical transmission spectra of the thin films at normal incidence were investigated in the spectral range from 190 to 1100 nm. Using the transmission spectra, the optical constants like refractive index (n) and extinction coefficient (k) were calculated based on Swanepoel’s method. The optical band gap (E_g) was also estimated using Tauc’s extrapolation procedure. The optical analysis shows: the value of optical band gap of investigated thin films decreases and the corresponding absorption coefficient increases continuously with increasing dose of γ-irradiation.     

Effect of Si doping on optical and thermal properties of MOVPE GaN thin layers

Photothermal deflection spectroscopy is used to investigate thermal and optical properties of MOVPE grown GaN thin layers deposited on sapphire substrate. The effects of Si doping on absorption spectrum and gap energy are revealed. Also, doping-induced free carrier absorption is extracted from absorption in the sub-gap region. Moreover, the variations of photothermal signal versus modulation frequency are used to determine thermal properties of these films. The measured thermal conductivity is clearly decreased by Si doping, the main reason should be the phonon scattering on point defects.     

A comparative study of the microstructures and optical properties of Cu- and Ag-doped ZnO thin films

Cu- and Ag-doped ZnO films were deposited by direct current co-reactive magnetron sputtering technique. The microstructure, the chemical states of the oxygen, zinc, copper and silver and the optical properties in doped ZnO films were investigated by X-ray diffraction spectroscopy (XRD), X-ray photoelectron spectroscopy (XPS) and UV-Visible spectroscopy. XRD analysis revealed that both of Cu- and Ag-doped ZnO films consist of single phase ZnO with zincite structure while the doping elements had an evident effect on the (0 0 2) preferential orientation. The XPS spectra showed that the chemical states of oxygen were different in Cu- and Ag-doped ZnO thin films, which may lead to the shift of the band gap as can be observed in the transmittance and absorption spectra. Meanwhile, the widths of band tails of ZnO films became larger after Cu and Ag doping.     

Influences of the iron ion (Fe)-doping on structural and optical properties of nanocrystalline TiO2 thin films prepared by sol-gel spin coating

Titanium dioxide (TiO₂) thin films doping of various iron ion (Fe³⁺) concentrations were deposited on silicon (Si) (100) and quartz substrates by sol-gel Spin Coating technique followed by a thermal treatment at 600 °C. The structure, surface morphology and optical properties, as a function of the doping, have been studied by X-ray diffractometer (XRD), Raman, ultraviolet-visible (UV-vis) and Spectroscopic Ellipsometry (SE). XRD and Raman analyzes of our thin films show that the crystalline phase of TiO₂ thin films comprised only the anatase TiO₂, but the crystallinity decreased when the Fe³⁺ content increased from 0% to 20%. During the Fe³⁺ addition to 20%, the phase of TiO₂ thin film still maintained the amorphous state. The grain size calculated from XRD patterns varies from 29.3 to 22.6 nm. The complex index and the optical band gap (E_g) of the films were determined by the spectroscopic ellipsometry analysis. We have found that the optical band gap decreased with an increasing Fe³⁺ content.     

Influence of Concentration of Vanadium in Zinc Oxide on Structural and Optical Properties with Lower Concentration

ZnO films doped with different vanadium concentrations are deposited onto glass substrates by dc reactive magnetron sputtering using a zinc target doped with vanadium. The vanadium concentrations are examined by energy dispersive spectroscopy （EDS） and the charge state of vanadium in ZnO thin films is characterized by x-ray photoelectron spectroscopy. The results of x-ray diffraction （XRD） show that all the films have a wurtzite structure and grow mainly in the c-axis orientation. The grain size and residual stress in the deposited films are estimated by fitting the XRD results. The optical properties of the films are studied by measuring the transmittance. The optical constants （refractive index and extinction coefficient） and the film thickness are obtained by fitting the transmittance. All the results are discussed in relation with the doping of the vanadium.     

Electrochemical,structural, compositional and optical properties of Cuprous Selenide thin films

This work focussed the electrochemical growth, structural, compositional and optical properties of Cuprous Selenide thin films. An electrochemical route has been used to prepare Cuprous Selenide thin films on different non transparent and transparent conducting substrates. Cyclic voltammetry has been carried out to find out the range of potential of the deposited films. X-ray diffraction shown that the deposited films possess polycrystalline nature. Structural parameters such as crystallite size, strain, dislocation density and stacking fault probability has been determined by the method of Williamson Hall plot analysis. Scanning electron microscopy with Energy dispersive X-ray analysis shown that the deposited films exhibited smooth surface with well defined stoichiometry. Ultraviolet Visible spectroscopic measurements showed that the band gap value around 2.84 eV for the deposited films.     

Laser radiation effects on optical and structural properties of nanostructure CdSe thin film

Cadmium selenide (CdSe) thin films were deposited on a glass substrate using the thermal evaporation method at room temperature. The changes in the optical properties (optical band gap and absorption coefficient) after irradiation by TEA N₂ laser at different energies were measured in the wavelength range 190–800 nm using a spectrophotometer. It was found that the optical band gap is decreased after irradiating the thin films. The samples were characterized using X-ray diffraction (XRD), and the grain size of the CdSe thin film was calculated from XRD data, which was found to be 41.47 nm as-deposited. It was also found that grain size increases with laser exposure. The samples were characterized using a scanning electron microscope and it was found that big clusters were formed after irradiation by TEA N₂ laser.