Microstructural parameters and optical constants of ZnTe thin films with various thicknesses

Different thickness of polycrystalline ZnTe films have been deposited onto glass substrates at room temperature by vacuum evaporation technique. The structural characteristics studied by X-ray diffraction (XRD) showed that the films are polycrystalline and have a zinc blende (cubic) structure. The calculated microstructure parameters revealed that the crystallite size increases and microstrain decreases with increasing film thickness. The transmittance and reflectance have been measured at normal and near normal incidence, respectively, in the spectral range 400-2500 nm. For ZnTe films of different thicknesses, the dependence of absorption coefficient, α on the photon energy showed the occurrence of a direct transition with band gap energy (For ZnTe films of different thicknesses) confirming the independency of deduced energy gap on film thickness. The refractive indices have been evaluated in terms of envelope method, which has been suggested by Swanepoul in the transparent region. The refractive index could be extrapolated by Cauchy dispersion relationship over the whole spectra range, which extended from 400 to 2500 nm. It was observed that the refractive index, n increased upon increasing the film thickness up to 508 nm, lying within the experimental error for further increases in film thickness.     

Preparation and characterization of ZnTe thin films by SILAR method

Nanocrystalline zinc telluride (ZnTe) thin films were prepared by using successive ionic layer adsorption and reaction (SILAR) method from aqueous solutions of zinc sulfate and sodium telluride. The films were characterized by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray analysis and optical absorption measurement techniques. The synthesized ZnTe thin films were nanocrystalline with densely aggregated particles in nanometer scale and were free from the voids or cracks. The optical band gap energy of the film was found to be thickness dependent. The elemental chemical compositional stoichiometric analysis revealed good Zn:Te elemental ratio of 53:47.     

Study on the electrical and optical properties of Ag/Al-doped ZnO coatings deposited by electron beam evaporation

A layer of silver was deposited onto the surface of glass substrates, coated with AZO (Al-doped ZnO), to form Ag/AZO film structures, using e-beam evaporation techniques. The electrical and optical properties of AZO, Ag and Ag/AZO film structures were studied. The deposition of Ag layer on the surface of AZO films resulted in lowering the effective electrical resistivity with a slight reduction of their optical transmittance. Ag (11 nm)/AZO (25 nm) film structure, with an accuracy of ±0.5 nm for the thickness shows a sheet resistance as low as 5.6 ± 0.5 Ω/sq and a transmittance of about 66 ± 2%. A coating consisting of AZO (25 nm)/Ag (11 nm)/AZO (25 nm) trilayer structure, exhibits a resistance of 7.7 ± 0.5 Ω/sq and a high transmittance of 85 ± 2%. The coatings have satisfactory properties of low resistance, high transmittance and highest figure of merit for application in optoelectronics devices including flat displays, thin films transistors and solar cells as transparent conductive electrodes.     

Optical inhomogeneity of ZnS films deposited by thermal evaporation

Zinc sulfide (ZnS) films with optical thickness (reference wavelength is 620 nm) ranging from 310 to 1240 nm were deposited on quartz substrates at room temperature by a thermal evaporation system. The structure and morphology of the films were investigated by X-ray diffraction, atomic force microscopy, respectively. The optical properties of the films were determined by in situ transmittance measurements and wideband spectra photometric measurements, respectively. The experimental results show that the films exhibit cubic structure, and the intensity of the (2 2 0) diffraction peak enhances with the increase of optical thickness. Surface grain size and surface roughness increase monotonously with increasing film thickness. Refractive indices and extinction coefficients calculated by in situ transmittance measurements are well consistent with those calculated by wideband spectra photometric measurements. Both the refractive index and packing density of the film increase as the increase of film thickness, which confirms the film is positive inhomogeneous and has an expanding columnar structure. Extinction coefficients of the films increase with increasing film thickness, which results from the increase of surface roughness.     

Effect of some preparative parameters on optical properties of spray deposited iridium oxide thin films

Optical properties of iridium oxide films fabricated by the spray pyrolysis technique (SPT) have been investigated. The transmission and reflection spectra of the sprayed films were measured by using a double-beam spectrophotometer in the wavelength range from 200 to 2500 nm. Influences of the preparative parameters; namely, substrate temperature (350-500 °C) and solution molarity (0.005-0.03 M), on the optical characteristics were examined. The solution molarity of the iridium chloride solution was varied so as to prepare iridium oxide thin films with thicknesses ranging from 160 to 325 nm. Some important characteristics of optical absorption, such as optical dispersion energies, the dielectric constant, the ratio of the number of charge carriers to the effective mass, the single oscillator wavelength, and the average value of the oscillator strength, were evaluated. The value of the refractive index was found to depend on the chemical composition as well as the degree of stoichiometry of IrO₂. The values obtained for the high frequency dielectric constant through two procedures are in the range of 2.8-3.9 and 3.3-4.6 over the relevant ranges of the substrate temperature and solution molarity, respectively. Analysis of the energy dispersion curve of the absorption coefficient indicated a direct optical transition with the bandgap energy ranging between 2.61 and 2.51 eV when the substrate temperature increases from 350 to 500 °C.     

PED沉积La-Sr-Cu-O薄膜表面的有序纳米结构

采用脉冲电子束沉积(PED)技术在Si(100)衬底上生长La_Sr_Cu_O薄膜，在750℃生长温度下获得具有有序纳米结构的表面形貌.采用聚集离子束(FIB)技术对获得的纳米结构进行表征，结果表明，这种有序的纳米结构是由于Si衬底和La_Sr_Cu_O薄膜之间的热膨胀系数和晶格的 失配引起的纳米裂纹.在这些纳米裂纹处，La_Sr_Cu_O成核生长获得独立的纳米线.通过控制 这种有序的纳米结构的生长，这种有序的纳米结构可以用来构造弱连接形成的器件. 关键词： 脉冲电子束沉积 La_Sr_Cu_O薄膜 纳米结构     

Physical properties of ZnO thin films deposited by spray pyrolysis technique

Thin films of ZnO have been prepared on glass substrates at different thicknesses by spray pyrolysis technique using 0.2 M aqueous solution of zinc acetate. X-ray diffraction reveals that the films are polycrystalline in nature having hexagonal wurtzite type crystal structure. The resistivity at room temperature is of the order 10⁻² Ω cm and decreased as the temperature increased. Films are highly transparent in the visible region. The dependence of the refractive index, n, and extinction coefficient, k, on the wavelength for a sprayed film is also reported. Optical bandgap, E_g, has been reported for the films. A shift from E_g = 3.21 eV to 3.31 eV has been observed for deposited films.     

Influence of substrate temperature on the electrical behaviour of zinc stannate thin films deposited by electron beam evaporation technique

Summary  A series of zinc stannate (Zn₂ SnO₄) thin films were prepared at four different substrate temperatures; namely, room-temperature (25°C), 50°C, 100°C and 200°C. Direct-current resistivity measurements were performed on these samples in the temperature range from room temperature (∼290 K) up to about 500 K. A phase transition (of positive temperature coefficient (PTC) of resistance) was observed in the thin film grown at room temperature at about 385 K. Other investigated samples showed a semiconducting behaviour of three distinct conduction mechanisms extending from intrinsic to thermal freeze-out conduction. The width of the band gapE _g was found to depend on the substrate temperature and was discussed in terms of a formation of a band tailing. Thermal freeze-out was dominant at the lower temperature region. On leave from Department of Physics, Faculty of Science, Alexandria University, Alexandria, Egypt.     

Structural and Magnetic properties of Cr-diffused CdTe nanocrystalline thin films deposited by electron beam evaporation

Cr-diffused cadmium telluride (CdTe) thin films with different Cr content were prepared using electron beam evaporation method at a substrate temperature of 373 K followed by annealing at 573 K. The structures, composition, chemical and magnetic properties of the prepared films were studied using appropriate techniques. The X-ray diffraction spectra showed a predominant (1 1 1) reflection corresponding to the zinc blende structure of CdTe. Increase of lattice parameter with increase in Cr content has been observed. The cross-sectional HRSEM images displayed a columnar grain growth in the films. EDAX data exposed the presence of Cr, Cd and Te with near stoichiometry. The Raman spectra revealed emission peaks corresponding to A1, TO and LO modes of CdTe showing gradual shift in peak position and decreased intensity confirming the incorporation of Cr into CdTe host lattice. M–H plots displayed a clear well-defined room temperature ferromagnetic hysteresis loop with increase in Cr content.     

Structure and optical properties of chemically synthesized titanium oxide deposited by evaporation technique

Titanium oxide inorganic ion exchange material was synthesized by hydrolysis with water and ammonia solution. Structural feature of the synthesized titanium oxide was analyzed using X-ray diffraction, X-ray fluorescence and infrared spectrometer technique. Tentative formula of titanium oxide was determined and written as TiO₂·0.58H₂O. Titanium oxide films were deposited on glass substrates by means of an electron beam evaporation technique at room temperature from bulk sample. The films were annealed at 250, 350, 450, and 550 °C temperatures. Transmittance, reflectance, optical energy gap, refractive index and extinction coefficient were investigated. The transmittance values of 85% in the visible region and 88% in the near infrared region have been obtained for titanium oxide film annealed at 550 °C. Kubelka-Munk function was used to evaluate the absorption coefficient which was used to determine the optical band gap. It was found that the optical band gap increases with increasing annealing temperature whereas the refractive index and extinction coefficient decreases.     

Preparation and characterization of transparent NiO thin films deposited by spray pyrolysis technique

Nickel oxide thin films were successfully fabricated with various deposition time (t_d = 5, 10, and 15 min) on glass substrates using spray pyrolysis technique. The deposited films undergo thermal treatment at 350 °C for various annealing time (t_a = 0, 15, 30 and 60 min). In this study, the effect of t_d and t_a on film thickness was observed and their influence on structural, morphological and optical properties were investigated. The films deposited with t_d = 5 min showed amorphous structure while the films grown at higher deposition time became partially crystallized with preferred growth along (1 1 1) direction. Heat treatment carried out in air allowed us to tune the polycrystalline structure and the diffraction intensity at preferred peak increases with the increase in t_a which is a consequence of better crystallinity. This was reflected in the AFM micrographs of the films which suggested that the thermal annealing (or increasing t_a) facilitates the process of grain-growth, and improves the crystalline microstructure. The optical transmission of the films was found to vary with t_d and t_a and thus film thickness. The thinner films show higher transparency in the UV–vis spectral region. The optical band gap was blue-shifted from 3.35 eV to 3.51 eV depending on t_a. The effect of t_a on the various optical constants of the NiO films has also been discussed.     

Characterisation of porous doped ZnO thin films deposited by spray pyrolysis technique

Al or Sn doped ZnO films were deposited by spray pyrolysis using aqueous solutions. The films were deposited on either indium tin oxide coated or bare glass substrates. ZnCl₂, AlCl₃ and SnCl₂ were used as precursors. The effect of ZnCl₂ molar concentration (0.1-0.3 M) and doping percentage (2-4% AlCl₃ or SnCl₂) have been investigated. The main goal of this work being to grow porous ZnO thin films, small temperature substrates (200-300 °C) have been used during the spray pyrolysis deposition. It is shown that, if the X-ray diffraction patterns correspond to ZnO, the films deposited onto bare glass substrate are only partly crystallized while those deposited onto ITO coated glass substrate exhibit better crystallization. The homogeneity of the films decreases when the molar concentration of the precursor increases, while the grain size and the porosity decrease when the Al doping increases. The optical study shows that band tails are present in the absorption spectrum of the films deposited onto bare glass substrate, which is typical of disordered materials. Even after annealing 4 h at 400 °C, the longitudinal resistivity of the films is quite high. This result is attributed to the grain boundary effect and the porosity of the films. Effectively, the presence of an important reflection in the IR region in samples annealed testifies of a high free-carriers density in the ZnO crystallites. Finally it is shown that when deposited in the same electrochemical conditions, the transmission of a polymer film onto the rough sprayed ZnO is smaller than that onto smooth sputtered ZnO.     

Annealing temperature dependent on structural,optical and electrical properties of indium oxide thin films deposited by electron beam evaporation method

In the present work the influence of annealing temperature on the structural and optical properties of the In₂O₃ films deposited by electron beam evaporation technique in the presence of oxygen was studied. The deposited films were annealed from 350 to 550 °C in air. The chemical compositions of In₂O₃ films were carried out by X-ray photoelectron spectroscopy (XPS). The film structure and surface morphologies were investigated as a function of annealing temperature by X-ray diffraction (XRD) and atomic force microscopy (AFM). The structural studies by XRD reveal that films exhibit preferential orientation along (2 2 2) plane. The refractive index (n), packing density and porosity (%) of films were arrived from transmittance spectral data obtained in the range 250–1000 nm by UV–vis-spectrometer. The optical band gap of In₂O₃ film was observed and found to be varying from 3.67 to 3.85 eV with the annealing temperature.     

Effects of depositing temperatures on structure and optical properties of TiO2 film deposited by ion beam assisted electron beam evaporation

TiO₂, which is high in refractive index and dielectric constant, plays an important role in the fields of optics and electronics. In this work, TiO₂ films were prepared on glass substrates by the technique of ion beam assisted electron beam evaporation. The films were deposited at 50, 150 and 300 °C, respectively. Then the as-deposited TiO₂ films were annealed at 450 °C for 1 h in vacuum atmosphere. Structures and optical properties of TiO₂ films were characterized by XRD, SEM, ellipsometry and spectrophotometer. As a result, the structure and the refractive index of films were improved by both the annealing and the increasing of the deposition temperature. The UV-vis transmittance spectra also confirmed that the deposition temperature has a significant effect on the transparency of the thin films. The highest transparency over the visible wavelength region of spectra was obtained at the deposition temperature of 300 °C. The allowed direct band gap at the deposition temperature ranging from 50 to 300 °C was estimated to be in the range from 3.81 to 3.92 eV.     

电子束蒸发氧化锆薄膜的粗糙度和光散射特性

利用电子束蒸发工艺，以Ag层为衬底，沉积了中心波长为632.8nm的氧化锆(ZrO₂)薄膜，膜层厚度在80—480nm范围内变化.研究了不同厚度样品的粗糙度变化规律和表面散射特性.结果发现，随着膜层厚度的逐渐增加，其表面均方根(RMS)粗糙度和总积分散射(TIS)均呈现出先减小后增大的趋势.利用非相关表面粗糙度的散射模型对样品的TIS特性进行了理论计算，所得结果与测量结果相一致. 关键词： 氧化锆 表面粗糙度 标量散射 电子束蒸发     

Cu-In-O composite thin films deposited by reactive DC magnetron sputtering

Cu-In-O composite thin films were deposited by reactive DC magnetron sputtering at room temperature. The samples were characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), UV/vis spectrophotometer, four-probe measurement and Seebeck effect measurement, etc. The samples contain Cu, In and O. The ratios of Cu to In and O to In increase with increase in O₂ flow rates. The ratio of Cu to In is over 1 and this suggests that Cu is in excess. The obtained Cu-In-O thin films are very possibly made of rhombohedral In₂O₃ and monoclinic CuO. Transmittance of the films decreases with increase in O₂ flow rate. The decrease in transmittance results from increase in Cu content in the films. The optical band gap of all the samples is estimated to be 4.1-4.4 eV, which is larger than those of In₂O₃ and CuO. The sheet resistance of the films decreases with increase in O₂ flow rate. Conductivity of the films is a little low, due to the addition of Cu and the poor crystalline quality of the film. The conduction behavior of the films is similar to that of In₂O₃ and the conduction mechanism of Cu-In-O thin films is through O vacancy.     

Oxygen incorporation in ZnTe thin films grown by plasma-assisted pulsed laser deposition

We studied oxygen incorporation into ZnTe thin films with nitrogen and oxygen plasma during a plasma-assisted pulsed laser deposition (PA-PLD). It was shown that ZnTe:O layer formed with oxygen plasma exhibits an enhancement of optical transparency in visible spectral region due to the formation of amorphous TeO_x. Especially, the ZnTe:NO deposited by PA-PLD under nitrogen and oxygen partial pressures with N₂:O₂ of 10:3 sccm showed p-type semiconducting characteristics and the formation of intermediate band at about 0.5–0.8 eV below the ZnTe band edge. These results for oxygen incorporation in ZnTe thin film such as the enhancement of optical transparency in visible spectral region and the intermediate band formation will be useful for optoelectronic devices or intermediate band solar cells.     

Synthesis of P-type transparent conducting silver:indium oxide (AIO) thin films by reactive electron beam evaporation technique

Present paper reports the synthesis, electrical and optical properties of p-type conducting and transparent silver indium oxide (AIO) thin films prepared on glass substrates by reactive electron beam evaporation technique at three substrate temperatures (50, 200 and 250 °C) and at five evaporation rates (0.05 to 16.0 nm/s). The source material is pure powders of Ag₂O:In₂O₃=50:50 mol%. The AIO films are amorphous. The films, though not corresponding to Delafossite crystal structure, exhibit p-type conductivity, when prepared at an evaporation rate of 0.05 nm/s at all the three substrate temperatures. With increasing filament current, it is observed that (i) the electrical resistivity decreases and (ii) the refractive index of the films (at 632.8 nm, and is in the range: 1.219-1.211) decreases. The work function (effective Fermi level) has been measured on these samples by Kelvin Probe method. The results are explained on the basis of partial ionic charge and localization of covalent bonds in the AIO thin films.     

Electrical and optical properties of Jäger-nickel (II)-based molecular-material thin films prepared by the vacuum thermal evaporation technique

Semiconductor molecular-material thin films of [6,13-Ac₂-5,14-Me₂-[14]-4,6,11,13-tetraenato-1,4,8,11-N₄] and the bidentate amines 1,4-diaminebutane, 1,12-diaminedodecane and 2,6-diamineanthraquinone have been prepared by vacuum thermal evaporation on corning glass substrates and crystalline silicon wafers. The films thus obtained were characterized by infrared (FTIR), ultraviolet-visible (UV-VIS) and photoluminescence (PL) spectroscopies. The surface morphology, thickness and structure of these films were analyzed by atomic force microscopy (AFM), ellipsometry and X-ray diffraction (XRD), respectively. IR spectroscopy showed that the molecular-material thin films exhibit the same intra-molecular bonds as the original compounds, which suggests that the thermal evaporation process does not significantly alter their bonds. The effect of temperature on conductivity was also measured in these samples; it was found that the temperature-dependent electric current is always higher for the voluminous amines with large molecular weights and suggests a semiconductor behavior with conductivities in the order of 10⁻⁶-10⁻¹ Ω⁻¹ cm⁻¹. Finally, the optical band gap (E_g) and cubic χ⁽³⁾ non-linear optical (NLO) properties of these amorphous molecular complexes were also evaluated from optical absorption and optical third harmonic generation (THG) measurements, respectively.     

退火温度对电子束蒸发沉积Cu_2O薄膜性能的影响

近年来,钙钛矿太阳电池(PSCs)得到了迅猛发展,而无机空穴传输材料(IHTMs)的使用可进一步降低电池的成本,提高电池的稳定性.本文通过电子束蒸发制备了Cu_2O薄膜,研究了空气中退火温度及时间对薄膜组成、结构及光电性能的影响,并构筑了p-i-n反型平面异质结钙钛矿太阳电池.研究发现:由于热解作用,直接通过电子束蒸发制备的薄膜为Cu_2O和Cu的混合物;而在空气中经过退火后,由于氧化作用,随着退火温度的升高,薄膜的组分由混合物转变为纯的Cu_2O,再转变成纯的CuO.通过控制退火温度制备的Cu_2O薄膜的光学带隙约为2.5 eV,载流子迁移率约为30 cm~2·V~(-1)·s~(-1).应用于PSCs,薄膜的最佳厚度为40 nm,但电池性能低于PEDOT:PSS基的PSCs.这主要是由于钙钛矿前驱液在Cu_2O薄膜的润湿性较差,吸收层中有大量微孔洞存在,致使漏电流增强,电池的性能降低.然而,当采用Cu_2O/PEDOT:PSS双HTMs设计时,由于PEDOT:PSS对Cu_2O具有较强的腐蚀作用,使电池性能恶化.