化学水浴法制备ZnS薄膜及其光学性能

以酒石酸与柠檬酸钠为络合剂,采用化学水浴法(CBD)沉积ZnS薄膜.利用X射线衍射仪(XRD)、X射线能谱仪(EDAX)、扫描电镜(SEM)、紫外-可见分光光度计(UV-Vis)研究ZnS薄膜的结构、组成、形貌及光学性能,利用透射光谱计算ZnS薄膜的光学禁带宽度(Eg).结果表明:ZnS薄膜呈立方相晶体结构,经过300℃熟处理1h的ZnS薄膜原子比为Zn:S=1:0.85,表面均一致密,在可见光区的平均透射率达到80%,光学禁带宽度为3.74ev,适合作为太阳能电池过渡层.     

Structural and optical characterizations of chemically deposited cadmium selenide thin films

Synthesis of cadmium selenide thin films by CBD method has been presented. The deposited film samples were subjected to XRD, SEM, UV-vis-NIR and TEP characterization. X-ray diffraction analysis showed that CdSe film sample crystallized in zinc blende or cubic phase structure. SEM studies reveal that the grains are spherical in shape and uniformly distributed all over the surface of the substrates. The optical band gap energy of as deposited film sample was found to be in the order of 1.8 eV. The electrical conductivity of the film sample was found to be 10⁻⁶ (Ω cm)⁻¹ with n-type of conduction mechanism.     

ZnS薄膜的制备及性能研究

用射频溅射法在Si基片和石英基片上分别制备了490nm厚的ZnS薄膜,并在不同温度下进行退火处理.微结构分析表明:退火后的ZnS薄膜均呈多晶状态,晶体结构为立方闪锌矿结构的β-ZnS;随着退火温度的升高,薄膜的平均晶粒尺寸逐渐增大,由20℃的10.91nm增大到500℃的15.59nm,晶格常数在不同退火温度下均比标准值0.5414nm稍小.应力分析表明:退火后的ZnS薄膜应力减小,400℃时分布较均匀,平均应力为1.481×108Pa,应力差为1.939×108Pa.且400℃前为张应力,400℃以后转变为压应力.光学分析表明,随着退火温度的升高,ZnS薄膜的透过率增强,吸光度减弱.     

Substrate temperature influence on ZnS thin films prepared by ultrasonic spray

ZnS thin films were deposited by ultrasonic spray technique. The starting solution is a mixture of 0.1 M zinc chloride as source of Zn and 0.05 M thiourea as source of S. The glass substrate temperature was varied in the range of 250 °C-400 °C to investigate the influence of substrate temperature on the structure, chemical composition and optical properties of ZnS films. The DRX analyses indicated that ZnS films have nanocrystalline hexagonal structure with (002) preferential orientation and grain size varied from 20 to 50 nm, increasing with substrate temperature. The optical films characterization was carried out by the UV-visible transmission. The optical gap and films disorder were deduced from the absorption spectra and the refractive indices of the films were determined by ellipsometric measurements. It is shown that the obtained films are generally composed of ZnO and ZnS phases with varied proportion, while at deposition temperature of 400 °C, they are near stoichiometric ZnS.     

ZnS薄膜的水浴法制备及其光学性能

以酒石酸和柠檬酸钠为络合剂,采用水浴法(CBD)制备ZnS薄膜.利用X射线衍射(XRD)、X射线能谱仪(EDAX)、扫描电镜(SEM)、紫外-可见分光光度计(UV-vis)研究ZnS薄膜的结构、成分、形貌及光学性能.利用透射光谱计算了ZnS薄膜的光学禁带宽度.结果表明:ZnS薄膜呈立方相晶体结构,水浴沉积时间为3h的ZnS薄膜原子比Zn∶S为1∶0.85,薄膜表面均一致密,在可见光区有着好的透射性能,在300～800 nm的光谱范围内平均透射率达到80.8%,光学禁带宽度为3.78eV,适合作为太阳能电池过渡层.     

Investigation of the effect of temperature on growth mechanism of nanocrystalline ZnS thin films

In this paper the temperature effect on the growth mechanism of ZnS thin films prepared in a chemical bath containing zinc acetate, ethylenediamine, and thioacetamide aqueous solutions has been studied in the temperature range between 25 and 75 °C. These ZnS thin films possess a nanocrystalline structure, exhibit quantum size effects due to the small crystal size and produce a blue shift in the optical spectra. This blue shift was attributed to a decrease in crystal size by using X-ray diffraction and scanning electron microscopy. The growth mechanism of the thin films is suggested to proceed by two fundamental steps: in the first step, the ZnS nanocrystallites coalesce into small grains through homogeneous nucleation in the solution phase. In the second step, eventually, these small grains or large-sized clusters diffuse and stick to the surface of the substrate to form the ZnS thin film, in a way called a cluster-by-cluster manner, resulting in particulate thin film.     

Preparation and characterization of chemically deposited PbSnS3 thin films

High-quality and well-reproducible PbSnS₃ thin films have been prepared by a simple and inexpensive chemical-bath deposition method from an aqueous medium, using thioacetamide as a sulphide ion source. X-ray diffraction analysis of the deposited films revealed that the as-deposited films were amorphous, however, an amorphous-to-crystalline phase transition was observed as the result of thermal annealing at 425 K for 1 h. The X-ray structure analysis of the collected powder from the bath annealed at 425 K for 1.5 h revealed an orthorhombic phase.

Analysis of the optical absorption data of crystalline PbSnS₃ films revealed that both direct and indirect optical transitions exist in the photon energy range 1.24–2.48 eV with optical band gaps of 1.68 and 1.42 eV, respectively. However, a forbidden direct optical transition with a band gap value of 1.038 eV dominates at low energy (<1.24 eV). The refractive index changes from 3.38 to 2.16 in the range 500–1300 nm. The high frequency dielectric constant and the carrier concentration to the effective mass ratio calculated from the refractive index analysis were found to be 4.79 and 2.3×10²⁰ cm⁻³, respectively. The temperature dependence of the electrical resistivity of the deposited films follows the semiconductor behaviour with extrinsic and intrinsic conduction. The determined activation energies range are 0.35–0.42 and 0.76–85 eV, respectively.     

Effect of annealing on the structural and optical properties of InSe bilayer thin films

InSe bilayer thin films with different thickness were prepared on to a glass substrate by sequential thermal evaporation. Preparation and post deposition treatment conditions were optimized in order to achieve effective bilayer mixing. The influence of bilayer film thickness and annealing temperature on the structural and optical properties was investigated. The prepared films were characterized by X-ray diffraction analysis, scanning electron microscopy, energy dispersive X-ray analysis, UV-Visible spectroscopy, photoconduction and resistivity measurement. Structural studies show that the material undergoes phase transition with thickness, due to co-existence of many phases. Morphological analysis revealed that Se content plays an important role in determining the surface morphology of the film. It has been observed that grain growth and grain splitting phenomena depend on film thickness and annealing temperature. From the photoconduction measurements, the photocurrent increases rapidly when the sample is illuminated using 135 K Lux of white light. Absorption coefficient is in the order of 10⁴ cm⁻¹, makes the InSe thin film useful for the preparation of absorber layer in hybrid solar cell.     

The effect of annealing on structural, electrical and optical properties of nanostructured ZnS/Ag/ZnS films

In this paper a ZnS/Ag/ZnS (ZAZ) nano-multilayer structure is designed theoretically and optimum thicknesses of ZnS and Ag layers are calculated at 35 and 17 nm, respectively. Several conductive transparent ZAZ nano-multilayer films are deposited on a glass substrate at room temperature by thermal evaporation method. Changes in the electrical, structural, and optical properties of samples are investigated with respect to annealing in air at different temperatures. High-quality nano-multilayer films with the sheet resistance of 8 Ω/sq and the optical transmittance of 83% at 200 °C annealing temperature are obtained. The figure of merit is applied on the ZAZ films and their performance as transparent conductive electrodes are determined.     

Studies on chemically deposited CuInSe2 thin films

Nanocrystalline thin films of CuInSe₂ have been prepared by chemical bath deposition technique at temperatures below 60 °C. X-ray diffraction of the films confirmed the identity of CuInSe₂ and with largely broadened peaks indicated the nanocrystalline nature of the films. Images from scanning electron microscope represented spherical nanoparticles.     

Effect of cadmium oxide incorporation on the microstructural and optical properties of pulsed laser deposited nanostructured zinc oxide thin films

CdO doped (doping concentration 0, 1, 3 and 16 wt%) ZnO nanostructured thin films are grown on quartz substrate by pulsed laser deposition and the films are annealed at temperature 500 °C. The structural, morphological and optical properties of the annealed films are systematically studied using grazing incidence X-ray diffraction (GIXRD), energy dispersive X-ray analysis (EDX), scanning electron microscopy (SEM), atomic force microscopy (AFM), Micro-Raman spectra, UV–vis spectroscopy, photoluminescence spectra and open aperture z-scan. 1 wt% CdO doped ZnO films are annealed at different temperatures viz., 300, 400, 500, 600, 700 and 800 °C and the structural and optical properties of these films are also investigated. The XRD patterns suggest a hexagonal wurtzite structure for the films. The crystallite size, lattice constants, stress and lattice strain in the films are calculated. The presence of high-frequency E₂ mode and the longitudinal optical A₁ (LO) modes in the Raman spectra confirms the hexagonal wurtzite structure for the films. The presence of CdO in the doped films is confirmed from the EDX spectrum. SEM and AFM micrographs show that the films are uniform and the crystallites are in the nano-dimension. AFM picture suggests a porous network structure for 3% CdO doped film. The porosity and refractive indices of the films are calculated from the transmittance and reflectance spectra. Optical band gap energy is found to decrease in the CdO doped films as the CdO doping concentration increases. The PL spectra show emissions corresponding to the near band edge (NBE) ultra violet emission and deep level emission in the visible region. The 16CdZnO film shows an intense deep green PL emission. Non-linear optical measurements using the z-scan technique indicate that the saturable absorption (SA) behavior exhibited by undoped ZnO under green light excitation (532 nm) can be changed to reverse saturable absorption (RSA) with CdO doping. From numerical simulations the saturation intensity (I_s) and the effective two-photon absorption coefficient (β) are calculated for the undoped and CdO doped ZnO films.     

Sulfidation growth and characterization of nanocrystalline ZnS thin films

Nanocrystalline ZnS thin films are prepared on glass and quartz substrates by sulfurizing ZnO thin films in the H₂S-containing mixture at 500 °C. These films are investigated by X-ray diffraction, scanning electron morphology, optical transmittance and photoluminescence spectra. The results show that the ZnS thin films have the hexagonal structure with a c-axis preferred orientation. Also, these nanostructure ZnS thin films with the grain size of ∼50 nm along the c-axis, exhibit the optical transparency as high as ∼80% in the visible region. It is found that sulfur replacement of oxygen sites in crystal lattices and recrystallization can take place during sulfidation, resulting in an evident increase of the grain size for the sulfurized films. Under the optimum sulfidation time of 2 h, the resultant ZnS thin films have a high crystallinity, low defect concentration and good optical properties with the band gap of 3.66 eV.     

Growth and properties of ZnS thin films by sulfidation of sputter deposited Zn

ZnS thin films with the hexagonal structure have been produced by sulfurizing sputter deposited Zn in sulfur vapor for 1 h. These films have been analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), synchrotron radiation photoelectron spectroscopy (SR-PES), Auger electron spectroscopy (AES) and UV-VIS transmission spectra. It is found that at the sulfidation temperature (T_S) of 400 °C a little and partial Zn can be transformed to ZnS. At T_S = 500 °C, the total conversion of Zn in sulfur vapor can take place and form ZnS with a c-axis preferred orientation. The Zn-to-ZnS conversion is kinetically a reactive diffusion process. Also the ZnS thin film has much greater size of grains than the as-deposited Zn film, due to ZnS recrystallization and growth in sulfur vapor. Residual sulfur existing on the surface of ZnS grains leads to the poor optical transparency and great broadening of absorbing edge in the optical transmittance. However, ZnS thin film prepared by gradient sulfidation exhibits the improved optical transmittance, with a band-gap energy of 3.64 eV.     

Antimony sulfide thin films in chemically deposited thin film photovoltaic cells

Antimony sulfide thin films of thickness ≈ 500 nm have been deposited on glass slides from chemical baths constituted with SbCl₃ and sodium thiosulfate. Smooth specularly reflective thin films are obtained at deposition temperatures from − 3 to 10 °C. The differences in the film thickness and improvement in the crystallinity and photoconductivity upon annealing the film in nitrogen are presented. These films can be partially converted into a solid solution of the type Sb₂S_xSe_3 − x, detected in X-ray diffraction, through heating them in contact with a chemically deposited selenium thin film. This would decrease the optical band gap of the film from ≈ 1.7 eV (Sb₂S₃) to ≈ 1.3 eV for the films heated at 300 °C. Similarly, heating at 300 °C of sequentially deposited thin film layers of Sb₂S₃-Ag₂Se, the latter also from a chemical bath at 10 °C results in the formation of AgSb(S/Se)₂ with an optical gap of ≈ 1.2 eV. All these thin films have been integrated into photovoltaic structures using a CdS window layer deposited on 3 mm glass sheets with a SnO₂:F coating (TEC-15, Pilkington). Characteristics obtained in these cells under an illumination of 850 W/m² (tungsten halogen) are as follows: SnO₂:F-CdS-Sb₂S₃-Ag(paint) with open circuit voltage (V_oc) 470 mV and short circuit current density (J_sc) 0.02 mA/cm²; SnO₂:F-CdS-Sb₂S₃-CuS-Ag(paint), V_oc ≈ 460 mV and J_sc ≈ 0.4 mA/cm²; SnO₂:F-CdS-Sb₂S_xSe_3 − x-Ag(paint), V_oc ≈ 670 mV and J_sc ≈ 0.05 mA/cm²; SnO₂:F-CdS-Sb₂S₃-AgSb(S/Se)₂-Ag(paint), V_oc ≈ 450 mV and J_sc ≈ 1.4 mA/cm². We consider that the materials and the deposition techniques reported here are promising toward developing ‘all-chemically deposited solar cell technologies.’     

Thin films containing Mn-doped ZnS nanocrystals synthesised by chemical method and study of some of their optical properties

In this article, we present the optical properties of thin films containing Mn-doped ZnS nanocrystals synthesised by the chemical method. The ZnS nanoparticles within the polymer matrix (polyvinyl alcohol) were investigated by SEM and TEM images and analysed by X-ray diffraction. The effect of polymer concentration on the direct band gap of Mn-doped ZnS thin films was calculated from the data for absorption measurements. The values of the band gap are in the range of 3.73–3.90?eV. In addition, we discuss the photoluminescence of these films.     

Combined theoretical studies of the optical characteristics of II-IV-V2 semiconductor thin films

The optical absorbance of four ternary thin films, i.e. MgSiP₂, MgGeP₂, MgSiAs₂, MgGeAs₂ have been theoretically examined over a wide range of wavelength from 300 nm to 800 nm. The combination of first-principle electronic structure calculations and the optical matrix approach for modeling the multilayer assembly have been employed for theoretical studies. The analysis of the calculated absorbance spectra at room temperature with unpolarized light and normal incidence, revealed that MgGeAs₂ with a direct energy band gap of 1.6 eV exhibit a considerable high optical absorption, where a thickness of 3.2 μm of this thin film is sufficient to absorb 90% of the incident light and generates a maximum photocurrent of ∼23 mA/cm².     

Physical characteristics of thermally evaporated Bismuth thin films

Thin films of bismuth with different thicknesses were produced by thermal evaporation from a molybdenum boat source onto cleaned glass substrates at room temperature. The material has been characterized using X-ray diffraction, electrical and optical measurements. A polycrystalline transition phase was observed. The resistivity was calculated for different film thicknesses and found to vary with thickness and temperature. An anomalous dependence of resistivity on temperature was observed during heating. The optical constants were determined from the transmission and reflection data of these thin films for normal incidence. The absorption coefficient revealed the existence of an allowed direct transition with energy gap (E_g) values ranging from 3.45 to 3.6 eV.     

双靶溅射法制备M-SmS光学薄膜的研究

为了制备难以直接获得的金属相SmS,以Sm和Sm2S3为靶材,采用双靶子溅射系统,于单晶Si基板上直接获得了常温常压下稳定存在的M-SmS微晶薄膜,并采用XRD分析、内应力和RBS成分测试等手段对M-SmS的形成机理进行了研究.结果表明:M-SmS薄膜的形成是由于薄膜中存在压应力,压应力的形成与薄膜基板温度、薄膜沉积速率、薄膜中Sm元素过量以及基板之间膨胀系数的差异有关.     

Size dependent structural, optical and morphological properties of ZnS:Cu thin films

ZnS:Cu thin films have been deposited on glass substrate by a simple neutral pH solution synthesis route and chemical bath deposition technique. The copper concentration was varied between 0 and 0.1 M%. The X-ray diffraction and scanning electron microscope studies show the average size of the nanoparticles are below 4 nm (Bohr diameter). The effect of film thickness on the optical and structural properties has been studied. The optical absorption studies show the band gap energy of ZnS:Cu films decreases from 3.68 to 3.43 eV as thickness varied from 318.3 to 334.1 nm. The structural estimation shows the variation in particle size from 2.67 to 3.14 nm with thickness. The insignificant change in band gap may be due to the increase in particle size and quantum size effect.     

Absorption and photocurrent properties of thin ZnS films formed by pulsed-laser deposition on quartz

The absorption and photocurrent properties of thin film ZnS on quartz glass formed by pulsed-laser deposition have been studied experimentally and theoretically at room temperature. Using the Lorentzian function to describe the exciton density of states, we show that the absorption is strongly influenced by excitonic formation. The theory for the absorption, however, does not describe the PC spectra of the film since the exciton remains electrically neutral up to fields of 1 kV/cm due to the high binding energy of 36 meV. Therefore, the fundamental absorption according to density of states and Urbach rule determines the shape of the photocurrent spectrum.