Intrinsic optical and structural properties of SrS thin films

SrS thin films were deposited by electron beam evaporation on heated silica substrates. The optical properties of the layers – complex refractive index and optical band gap –were derived from optical transmission spectra, measured by means of UV-VIS-NIR spectrophotometry. The influence of post-deposition annealing by rapid thermal processing (RTP) was studied. X-ray powder diffraction (XRD) was used to study the film crystal structure and preferential orientation.     

Effect of alumina doping on structural, electrical, and optical properties of sputtered ZnO thin films

A systematic study of the influence of alumina (Al₂O₃) doping on the optical, electrical, and structural characteristics of sputtered ZnO thin films is reported in this study. The ZnO thin films were prepared on 1737F Corning glass substrates by R.F. magnetron sputtering from a ZnO target mixed with Al₂O₃ of 0-4 wt.%. X-ray diffraction (XRD) analysis demonstrates that the ZnO thin films with Al₂O₃ of 0-4 wt.% have a highly (002) preferred orientation with only one intense diffraction peak with a full width at half maximum (FWHM) less than 0.5°. The electrical properties of the Al₂O₃-doped ZnO thin films appear to be strongly dependent on the Al₂O₃ concentration. The resistivity of the films decreases from 74 Ω·cm to 2.2 × 10^− 3 Ω·cm as the Al₂O₃ content increases from 0 to 4 wt.%. The optical transmittance of the Al₂O₃-doped ZnO thin films is studied as a function of wavelength in the range 200-800 nm. It exhibits high transparency in the visible-NIR wavelength region with some interference fringes and sharp ultraviolet absorption edges. The optical bandgap of the Al₂O₃-doped ZnO thin films show a short-wavelength shift with increasing of Al₂O₃ content.     

Effects of laser irradiation on the structure and optical properties of ZnO thin films

The effects of laser irradiation on the surface microstructure and optical properties of ZnO films deposited on glass substrates were investigated experimentally and compared with those of thermal annealing. X-ray diffraction (XRD) and atomic force microscopy (AFM) measurements showed that the irradiation treatment with an Ar⁺ laser of 514 nm for 5 min improves the crystalline quality of ZnO thin films through increasing the grain size and enhancing the c-axis orientation, with the effects similar to those of the thermal annealing at 500 °C for 1 h. Laser irradiation was found to be more effective both for the relaxation of the residual compressive stress in the as-grown films and for the modification of the surface morphology. A significant increase in the UV absorption and a widening in the optical band-gap of the films were also observed after laser irradiation.     

Influence of dopant concentration on the optical properties of ZnO: In films by sol-gel method

Undoped and In doped ZnO films have been deposited by sol-gel spin coating method. The effect of indium incorporation on structural and optical properties of ZnO films has been investigated. X-ray diffraction patterns of the films showed the hexagonal wurtzite type polycrystalline structure and that indium incorporation leads to substantial changes in the structural characteristics of ZnO films. The SEM and AFM measurements showed that the surface morphology of the films was affected from the indium incorporation. Optical reflectance and transmittance were recorded with a double beam spectrophotometer with an integrating sphere. The optical band gap of these films was determined. The absorption edge shifted to the lower energy depending on the dopant materials. The optical constants of these films were determined using transmittance and reflectance spectra.     

Effect of substrate temperature on the structure and optical properties of ZnO thin films deposited by reactive rf magnetron sputtering

Zinc Oxide films were deposited on quartz substrates by reactive rf magnetron sputtering of zinc target. The effect of substrate temperature on the crystallinity and band edge luminescence has been studied. The films deposited at 300 °C exhibited the strongest c-axis orientation. AFM and Raman studies indicated that the films deposited at 600 °C possess better overall crystallinity with reduction of optically active defects, leading to strong and narrow PL emission.     

Effect of annealing treatment on structural, electrical, and optical properties of Ga-doped ZnO thin films deposited by RF magnetron sputtering

The effect of annealing on structural, electrical, and optical properties of Ga-doped ZnO (GZO) films prepared by RF magnetron sputtering was investigated in air and nitrogen. GZO films are polycrystalline with a preferred 002 orientation. The resistivities of annealed films are larger than the as-deposited. The transmittance in the near IR region increases greatly and the optical band gap decreases after annealing. The photoluminescence spectra is composed of a near band edge emission and several deep level emissions (DLE) which are dominated by a blue emission. After annealing, these DLEs are enhanced evidently.     

Electrical and optical properties of ZnO:Mn thin films grown by MOCVD

Diluted magnetic semiconductor epitaxial thin films of Zn_1 − xMn_xO have been grown on c-sapphire by the MOCVD technique. Variations of a and c lattice parameters follow Vegard's law and attest to the incorporation of substitutional Mn²⁺ ions. Carrier concentration (n-type) and electron mobility were studied versus temperature for different concentrations of manganese. Incorporation of manganese leads to the opening of the band gap, observed as a blue shift in energy regarding pure ZnO.     

Effect of oxygen pressure on the structural and optical properties of ZnO thin films on Si (111) by PLD

ZnO thin films were grown on Si (111) substrates by pulsed laser deposition (PLD) at various oxygen pressures in order to investigate the structural and optical properties of the films. The optical properties of the films were studied by photoluminescence spectra using a 325 nm He-Cd laser. The structural and morphological properties of the films were investigated by XRD and AFM measurements, respectively. The results suggest that films grown at 20 Pa and 50 Pa have excellent UV emission and high-quality crystallinity. The research of PL spectra indicates that UV emission is due to excitonic combination, the green band is due to the replacing of Zn in the crystal lattice for O and the blue band is due to the O vacancies.     

Structure and optical properties of ZnO:V thin films with different doping concentrations

A series of ZnO thin films doped with various vanadium concentrations were prepared on glass substrates by direct current reactive magnetron sputtering. The results of the X-ray diffraction (XRD) show that the films with doping concentration less than 10 at.% have a wurtzite structure and grow mainly along the c-axis orientation. The residual stress, estimated by fitting the XRD diffraction peaks, increases with the doping concentration and the grain size also has been calculated from the XRD results, decreases with increasing the doping concentration. The surface morphology of the ZnO:V thin films was examined by SEM. The optical constants (refractive index and extinction coefficient) and the film thickness have been obtained by fitting the transmittance. The optical band gap changed from 3.12 eV to 3.60 eV as doping concentration increased from 1.8 at.% to 13 at.% mol. All the results have been discussed in relation with doping concentration.     

Effect of Al dopants on the structural,optical and gas sensing properties of spray-deposited ZnO thin films

Undoped and Al-doped ZnO thin films were deposited on glass substrates by the spray pyrolysis method. The structural, morphological and optical properties of these films were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), UV–Vis spectroscopy, photoluminescence (PL) and photoconductivity (PC) measurements, respectively. XRD analyses confirm that the films are polycrystalline zinc oxide with the hexagonal wurtzite structure, and the crystallite size has been found to be in the range 20–40 nm. SEM and AFM analyses reveal that the films have continuous surface without visible holes or faulty zones, and the surface roughness decreases on Al doping. The Al-doped films have been found to be highly transparent (>85%) and show normal dispersion behavior in the wavelength range 450–700 nm. The doped films show only ultraviolet emission and are found to be highly photosensitive. Among all the films examined, at 300 °C the 1.0 at% Al-doped film shows the selective high response (98.2%) to 100 ppm acetone concentration over to methanol, ethanol, propan-2-ol, formaldehyde and hydrogen.     

Microstructure and optical properties of plasmapolymer thin films with embedded silver nanoparticles

Plasmapolymer thin films with embedded silver nanoparticles were deposited by simultaneous plasma polymerization and metal evaporation. The particle size and shape were determined by transmission electron microscopy (TEM) and analysed by optical image processing. The optical properties in the UV/ VIS/NIR spectral region were determined by the plasma resonance absorption of the silver particles. Transmittance spectra were calculated with the Bergman effective medium theory and compared with experimental spectra.     

Effect of the oxygen partial pressure on the microstructure and optical properties of ZnO:Cu films

Cu-doped zinc oxide (ZnO:Cu) films were deposited on Si substrates using radio frequency reactive magnetron sputtering at different oxygen partial pressures. The effect of oxygen partial pressure on the microstructures and optical properties of ZnO:Cu thin films were systematically investigated by X-ray diffraction (XRD), atomic force microscopy (AFM) and fluorescence spectrophotometer. The results indicated that the grain orientation of the films was promoted by appropriate oxygen partial pressures. And with increasing oxygen partial pressure, the compressive stress of the films increased first and then decreased. The photoluminescence (PL) of the samples were measured at room temperature. A violet peak, two blue peaks and a green peak were observed from the PL spectra of the four samples. The origin of these emissions was discussed and the mechanism of violet emission of ZnO:Cu thin films were suggested.     

ZnO thin films prepared by pulsed laser deposition

Zinc oxide (ZnO) thin films were deposited on soda lime glass substrates by pulsed laser deposition (PLD) in an oxygen-reactive atmosphere. The structural, optical, and electrical properties of the as-prepared thin films were studied in dependence of substrate temperature and oxygen pressure. High quality polycrystalline ZnO films with hexagonal wurtzite structure were deposited at substrate temperatures of 100 and 300 °C. The RMS roughness of the deposited oxide films was found to be in the range 2-9 nm and was only slightly dependent on substrate temperature and oxygen pressure. Electrical measurements indicated a decrease of film resistivity with the increase of substrate temperature and the decrease of oxygen pressure. The ZnO films exhibited high transmittance of 90% and their energy band gap and thickness were in the range 3.26-3.30 eV and 256-627 nm, respectively.     

Effect of sputtering power on the electrical and optical properties of Ca-doped ZnO thin films sputtered from nanopowders compacted target

In the present work, we have deposited calcium doped zinc oxide thin films by magnetron sputtering technique using nanocrystalline particles elaborated by sol–gel method as a target material. In the first step, the nanoparticles were synthesized by sol–gel method using supercritical drying in ethyl alcohol. The structural properties studied by X-ray diffractometry indicates that Ca doped ZnO has a polycrystalline hexagonal wurzite structure with a grain size of about 30 nm. Transmission electron microscopy (TEM) measurements have shown that the synthesized CZO is a nanosized powder. Then, thin films were deposited onto glass substrates by rf-magnetron sputtering at ambient temperature. The influence of RF sputtering power on structural, morphological, electrical, and optical properties were investigated. It has been found that all the films deposited were polycrystalline with a hexagonal wurtzite structure and preferentially oriented in the (0 0 2) crystallographic direction. They have a typical columnar structure and a very smooth surface. The as-deposited films show a high transmittance in the visible range over 85% and low electrical resistivity at room temperature.     

Annealing effect on properties of transparent and conducting ZnO thin films

This work presents the effect of postdeposition annealing on the structural, electrical and optical properties of undoped ZnO (zinc oxide) thin films, prepared by radio-frequency sputtering method. Two samples, 0.17 and 0.32 µm-thick, were annealed in vacuum from room temperature to 350 °C while another 0.32 µm-thick sample was annealed in air at 300 °C for 1 h. X-ray diffraction analysis revealed that all the films had a c-axis orientation of the wurtzite structure normal to the substrate. Electrical measurements showed that the resistivity of samples annealed in vacuum decreased gradually with the increase of annealing temperature. For the 0.32 µm-thick sample, the gradual decrease of the resistivity was essentially due to a gradual increase in the mobility. On the other hand, the resistivity of the sample annealed in air increased strongly. The average transmission within the visible wavelength region for all films was higher than 80%. The band gap of samples annealed in vacuum increased whereas the band gap of the one annealed in air decreased. The main changes observed in all samples of this study were explained in terms of the effect of oxygen chemisorption and microstructural properties.     

Effect of thermal annealing treatment on structural, electrical and optical properties of transparent sol-gel ZnO thin films

Effect of thermal annealing in different ambients on the structural, electrical and optical properties of the sol-gel derived ZnO thin films are studied. XRD results show that the annealed ZnO films with wurtzite structure are randomly oriented. Crystallite size, carrier concentration, resistivity and mobility are found to be dependent on the annealing temperature. The change in carrier concentration is discussed with respect to the removal of adsorbed oxygen from the grain boundaries. The highest carrier concentration and lowest resistivity are 8 × 10¹⁸ cm⁻³ and 2.25 × 10⁻¹ Ω cm, respectively, for the film annealed at 500 °C in vacuum. The annealed films are highly transparent with average transmission exceeding 80% in the wavelength region of 400-800 nm. In all three ambients, the optical band gap value does not change much below 500 °C temperature while above this temperature band gap value decreases for nitrogen and air and increases for vacuum.     

Effect of heat treatment on microstructural and optical properties of CBD grown Al-doped ZnO thin films

Investigations on the effect of annealing temperature on the structural, optical properties and morphology of Al-doped ZnO thin films deposited on glass substrate by chemical bath deposition have been carried out. X-ray diffraction studies revealed that deposited films are in polycrystalline nature with hexagonal structure along the (0 0 2) crystallographic plane. Microstructural properties of films such as crystallite size, texture coefficient, stacking fault probability and microstrain were calculated from predominant (0 0 2) diffraction lines. The UV-Vis-NIR spectroscopy studies revealed that all the films have high optical transmittance (>60%) in the visible range. The optical band gap values are found to be in the range of 3.25-3.31 eV. Optical constants have been estimated and the values of n and k are found to increase with increase of heat treatment. The films have increased transmittance with increase of heat treatment. Al-doped ZnO thin films fabricated by this simple and economic chemical bath deposition technique without using any carrier gas are found to be good in structural and optical properties which are desirable for photovoltaic applications. Scanning electron microscopic images revealed that the hexagonal shaped grains that occupy the entire surface of the film with its near stoichiometric composition.     

Phase transition and optical properties of Ge doped ZnO films synthesised by sputtering

Ge doped ZnO films were deposited on Si substrates by sputtering technique. With the increasing annealing temperature, the crystal quality of samples becomes gradually better and the phase transition can be observed at annealing temperature of 600°C. X-ray photoelectron spectroscopy results show the incorporation of Ge into the ZnO films with 14·81 at-%Ge content. Fourier transform infrared spectroscopy absorption spectra of samples annealed at above 600°C display vibration mode of ν (ZnO₄) and ν (GeO₄) in Zn₂GeO₄. The enhancement of ultraviolet emission intensity should be attributed to the yielded mass holes caused by Ge doping and the rising crystal quality. The sample annealed at 800°C displays the strongest blue emission due to the native defects in Zn₂GeO₄ films or/and surface defects.     

Effect of thickness on the structural, electrical and optical properties of ZnO films

A series of ZnO films of different thickness have been deposited on glass substrates using sol-gel technique by varying the number of spin coatings and the effect of film thickness on the structural, electrical and optical properties have been investigated. The XRD results indicate that the full width at half maximum (FWHM) of the (0 0 2) diffraction peak and the strain along c-axis are decreased as the film is grown up to a thickness of 300 nm. Above 300 nm, the strain again becomes appreciable. The surface morphology shows that the grains become more uniform and bigger in size as the film thickness increases. Electrical result shows that although ZnO film with thickness of around 260 nm has the highest resistivity but is better for current conduction. The excitonic nature in the absorption spectrum becomes prominent for a film with thickness of around 260 nm. The band gap increases and then decreases as the film grows thicker.     

溶剂体系对c轴择优取向ZnO薄膜结构和光学性质的影响

以无水乙醇、乙二醇甲醚、乙二醇甲醚/乙醇混合溶液(1∶1)为溶剂体系,采用溶胶-凝胶法制备了ZnO透明薄膜,并利用场发射扫描电镜、X射线衍射和反射光谱仪等研究了溶剂体系对薄膜组成、结构和光学性能的影响。结果表明,3种溶剂所制备的ZnO薄膜均为六方纤锌矿型结构,具有c轴择优取向;以乙二醇单甲醚/乙醇混合溶液(1∶1)为溶剂制备的ZnO薄膜平整、致密,在可见光区域透光率达到90%左右,禁带宽度为3.25eV,具备制作薄膜太阳能电池透明导电电极材料的应用价值。