Structural and optical properties of ZnS thin films deposited by RF magnetron sputtering

Zinc sulfide [ZnS] thin films were deposited on glass substrates using radio frequency magnetron sputtering. The substrate temperature was varied in the range of 100°C to 400°C. The structural and optical properties of ZnS thin films were characterized with X-ray diffraction [XRD], field emission scanning electron microscopy [FESEM], energy dispersive analysis of X-rays and UV-visible transmission spectra. The XRD analyses indicate that ZnS films have zinc blende structures with (111) preferential orientation, whereas the diffraction patterns sharpen with the increase in substrate temperatures. The FESEM data also reveal that the films have nano-size grains with a grain size of approximately 69 nm. The films grown at 350°C exhibit a relatively high transmittance of 80% in the visible region, with an energy band gap of 3.79 eV. These results show that ZnS films are suitable for use as the buffer layer of the Cu(In, Ga)Se₂ solar cells.     

The evolution behavior of microstructures and optical properties of ZnO films using a Ti buffer layer

ZnO thin films without and with Ti buffer layer were prepared on Si and glass substrates by radio frequency (RF) magnetron sputtering. The effects of Ti buffer layer with different sputtering time on the microstructure and optical properties of ZnO thin films had been investigated by means of X-ray diffraction (XRD), energy dispersive spectrometer, X-fluorescence spectrophotometer and ultraviolet–visible spectrophotometer. The XRD results showed that the full-width at half-maximum (FWHM) for the ZnO (002) diffraction peak gradually decreased with the increase of sputtering time of Ti buffer layer, indicating that the crystalline quality of ZnO thin films was improved. The UV peak located at 390 nm, two blue peaks located at about 435 and 487 nm, two green peaks located at about 525 and 560 nm were observed from PL spectra. The PL spectra showed that the strongest blue light emission of ZnO films was obtained from Ti buffer layer with the sputtering time of 10 min. Meanwhile, the origins of the emission peaks were discussed through the Gaussian deconvolution. We also studied the optical band gaps.     

Microstructural and optical properties of Ta-doped ZnO films prepared by radio frequency magnetron sputtering

Ta-doped ZnO films with different doping levels (0–5.02 at%) were prepared by radio frequency magnetron sputtering. The effects of the doping amount on the microstructure and the optical properties of the films were investigated. The grain size and surface roughness first significantly decrease and then slowly increase with the increase of Ta doping concentration. Both the grain size and the root mean square (RMS) roughness reach their minimum values at the doping content of 3.32 at%. X-ray Diffraction (XRD) patterns confirmed that the prepared Ta-doped ZnO films are polycrystalline with hexagonal wurtzite structure and a preferred orientation along the (002) plane. X-ray photoelectron spectroscopy (XPS) analysis reveals that Ta exists in the ZnO film in the Ta⁵⁺ and Ta⁴⁺ states. The average optical transmission values of the Ta-doped ZnO films are higher than those of the un-doped ZnO film in the visible region. The band gap energy extracted from the absorption edge of transmission spectra becomes large and the near band edge (NBE) emission energy obtained from PL spectra blueshifts to high energy when the Ta doping content grows from 0 at% to 5.02 at%, which can be explained by the Burstein–Moss shift.     

Effect of Fe-doping on the structural,optical and magnetic properties of ZnO thin films prepared by RF magnetron sputtering

In this paper, we report the fabrication and systematic characterization of Fe Doped ZnO thin Films. Fe_xZn_1−x O (x=0<0.05) films were prepared by RF magnetron sputtering on Si (400) substrate. Influence of Fe doping on structural, optical and magnetic properties has been studied. The X-ray diffraction (XRD) analysis shows that Fe doping has affected the crystalline structure, grain size and strain in the thin films. The best crystalline structure is obtained for 3% Fe Doping as observed from Atomic Force Microscopy (AFM) and X-ray diffraction (XRD). The magnetic properties studied using Vibrating Sample Magnetometer reveals the room temperature ferromagnetic nature of the thin films. However, changing the Fe concentration degrades the magnetic property in turn. The mechanism behind the above results has been discussed minutely in this paper.     

Improvement of optical transmittance and electrical properties for the Si quantum dot-embedded ZnO thin film

A Si quantum dot (QD)-embedded ZnO thin film is successfully fabricated on a p-type Si substrate using a ZnO/Si multilayer structure. Its optical transmittance is largely improved when increasing the annealing temperature, owing to the phase transformation from amorphous to nanocrystalline Si QDs embedded in the ZnO matrix. The sample annealed at 700°C exhibits not only high optical transmittance in the long-wavelength range but also better electrical properties including low resistivity, small turn-on voltage, and high rectification ratio. By using ZnO as the QDs’ matrix, the carrier transport is dominated by the multistep tunneling mechanism, the same as in a n-ZnO/p-Si heterojunction diode, which clearly differs from that using the traditional matrix materials. Hence, the carriers transport mainly in the ZnO matrix, not through the Si QDs. The unusual transport mechanism using ZnO as matrix promises the great potential for optoelectronic devices integrating Si QDs.     

Effect of oxygen flow rate on the ultraviolet sensing properties of zinc oxide nanocolumn arrays grown by radio frequency magnetron sputtering

Highly transparent metal–semiconductor–metal ultraviolet (UV) photoconductive sensors were fabricated using thin (less than 100 nm in thickness), dense, small-diameter ZnO nanocolumn arrays prepared via low-power, catalyst-free radio frequency (RF) magnetron sputtering at different oxygen flow rates ranging from 0 to 25 sccm. The FESEM images revealed the average nanocolumn diameter decreased with increasing oxygen flow rate. The transmittance spectra show that with the introduction of oxygen, the transmittance of the nanocolumn arrays in the visible region improves relative to that of a film prepared in the absence of oxygen with values greater than 95%. The UV responsivity and sensitivity were significantly improved for sputtered ZnO nanocolumn arrays prepared at oxygen flow rates up to 10 sccm, with the highest values of 9.70 mA/W and 2.20×10⁴. Furthermore, the responsivity and sensitivity decreased at oxygen flow rates greater than 10 sccm, which can be attributed to the increased electrical resistance of the nanocolumn arrays. Our findings indicate that a high-performance UV photoconductive sensor can be realised using very thin sputtered ZnO nanocolumn arrays and that such a sensor would exhibit high sensitivity.     

Dip coated nanostructured ZnO thin film: Synthesis and application

The preparation and characterization of highly selective room temperature ammonia sensorusing nanostructured dip coated ZnO thin films were discused. A highly viscous precursor solution was prepared using Zinc Nitrate hexahydrate as a starting material and Sodium Carboxymethyl Cellulose as a thickening agent. Morphology and structure of the annealed films were analyzed by field emission scanning electron microscopy and X-ray Diffractometer characterization techniques. The presence of zinc and oxygen in the sample was confirmed with Fourier Transform Infrared spectroscopy The gas sensing behavior of ZnO thin films was studied at room temperature. It exhibited very high selectivity and excellent sensing towards ammonia gas. Further, sensing behavior towards other gases like ethanol and formaldehyde and the various concentrations of NH₃ were studied.     

Fabrication and characterization of silicon wire solar cells having ZnO nanorod antireflection coating on Al-doped ZnO seed layer

In this study, we have fabricated and characterized the silicon [Si] wire solar cells with conformal ZnO nanorod antireflection coating [ARC] grown on a Al-doped ZnO [AZO] seed layer. Vertically aligned Si wire arrays were fabricated by electrochemical etching and, the p-n junction was prepared by spin-on dopant diffusion method. Hydrothermal growth of the ZnO nanorods was followed by AZO film deposition on high aspect ratio Si microwire arrays by atomic layer deposition [ALD]. The introduction of an ALD-deposited AZO film on Si wire arrays not only helps to create the ZnO nanorod arrays, but also has a strong impact on the reduction of surface recombination. The reflectance spectra show that ZnO nanorods were used as an efficient ARC to enhance light absorption by multiple scattering. Also, from the current-voltage results, we found that the combination of the AZO film and ZnO nanorods on Si wire solar cells leads to an increased power conversion efficiency by more than 27% compared to the cells without it.     

Influence of ZnO buffer layer on AZO film properties by radio frequency magnetron sputtering

Transparent conductive films of Al-doped zinc oxide (AZO) were deposited on glass substrates under various ZnO buffer layer deposition conditions (radio frequency (r.f.) power, sputtering pressure, thickness, and annealing) using r.f. magnetron sputtering at room temperature. This work investigates the influence of ZnO buffer layer on structural, electrical, and optical properties of AZO films. The use of grey-based Taguchi method to determine the ZnO buffer layer deposition processing parameters by considering multiple performance characteristics has been reported. Findings show that the ZnO buffer layer improves the optoelectronic performances of AZO films. The AZO films deposited on the 150-nm thick ZnO buffer layer exhibit a very smooth surface with excellent optical properties. Highly c-axis-orientated AZO/ZnO/glass films were grown. Under the optimized ZnO buffer layer deposition conditions, the AZO films show lowest electrical resistivity of 6.75 × 10⁻⁴ Ω cm, about 85% optical transmittance in the visible region, and the best surface roughness of R_a = 0.933 nm.     

Optical and electrical properties of Al doped ZnO thin film with preferred orientation in situ grown at room temperature

To optimize the process and obtain highly conducting and transparent Aluminum-doped zinc oxide (AZO) thin films, AZO films were deposited on glass substrates at room temperature by Radio-frequency (RF) magnetron sputtering with various Argon flow rates. The influences of Argon flow rate on structure, morphology, optical, electrical and photoluminescence properties of AZO films were investigated by varying the Argon flow rate from 36 to 68 sccm. The best quality AZO film with resistivity 1.39 × 10⁻³ Ω cm, sheet resistance 8.2 Ω/sq and 84.2% average visible transmittance was prepared at 44 sccm for 30 min. Also, the self-heating effect of target was investigated by preparing AZO films for 10 min and 20 min at 44 sccm, 180 W and 1.0 Pa. The influence of increasing structural quality actually affected by Argon flow rate was more prominent on carrier concentration than mobility. The schematic illustration of microstructural evolution was proposed. The average growth rate of around 60 nm/min demonstrated the self-heating effect of target was weak and could be ignored.     

Growth and optical properties of ZnO nanorod arrays on Al-doped ZnO transparent conductive film

ZnO nanorod arrays (NRAs) on transparent conductive oxide (TCO) films have been grown by a solution-free, catalyst-free, vapor-phase synthesis method at 600°C. TCO films, Al-doped ZnO films, were deposited on quartz substrates by magnetron sputtering. In order to study the effect of the growth duration on the morphological and optical properties of NRAs, the growth duration was changed from 3 to 12 min. The results show that the electrical performance of the TCO films does not degrade after the growth of NRAs and the nanorods are highly crystalline. As the growth duration increases from 3 to 8 min, the diffuse transmittance of the samples decreases, while the total transmittance and UV emission enhance. Two possible nanorod self-attraction models were proposed to interpret the phenomena in the sample with 9-min growth duration. The sample with 8-min growth duration has the highest total transmittance of 87.0%, proper density about 75 μm⁻², diameter about 26 nm, and length about 500 nm, indicating that it can be used in hybrid solar cells.     

CIGS absorbing layers prepared by RF magnetron sputtering from a single quaternary target

Cu(In_1−xGa_x)Se₂ (CIGS) thin films were prepared by RF magnetron sputtering from a single quaternary target at multiple processing parameters. The structural, compositional, and electrical properties of the as-deposited films were systematically investigated by XRD, Raman, SEM, and Hall effects analysis. The results demonstrate that by adjusting the processing parameters, the CIGS thin films with a preferential orientation along the (112) direction which exhibited single chalcopyrite phase were obtained. The films deposited at relatively higher substrate temperature, sputtering power, and Ar pressure exhibited favorable stoichiometric ratio (Cu/(In+Ga):0.8–0.9 and Ga/(In+Ga):0.25–0.36) with grain size of about 1–1.5 µm, and desirable electrical properties with p-type carrier concentration of 10¹⁶−10¹⁷ cm⁻³ and carrier mobility of 10–60 cm²/Vs. The CIGS layers are expected to fabricate high efficiency thin film solar cells.     

UV photodetection properties of pulsed laser deposited Cu-doped ZnO thin film

Nanocrystalline undoped and 2 at% copper (Cu) doped zinc oxide (ZnO) thin films were successfully grown onto SiO₂/n-Si substrates at 600 °C by using pulsed laser deposition (PLD) technique. The influence of Cu incorporation on structural, surface morphological, elemental composition and UV detection properties of ZnO film was investigated. X-ray diffraction studies of thin films show that they are polycrystalline and have a hexagonal wurtzite structure; however, Cu doping improves the preferential orientation along c-axis. The chemical state of constituent elements was analysed by X-ray photoelectron spectroscopy (XPS). It indicates the presence of Cu ions in the doped film that exist in a mixed univalent and bivalent state. FE-SEM observations support the crystallographic results. The effective incorporation of Cu ions into the lattice of the ZnO nanostructure without changing its wurtzite structure was confirmed by an energy dispersive X-ray spectroscopic analysis (EDX). The UV photodetection characteristics of both films were further studied in metal-semiconductor-metal (MSM) planar configurations at room temperature and are found to be greatly influenced by Cu doping. The incorporation of Cu into ZnO lattice increases the resistivity of thin film; which leads to lower dark current. As a result, the Cu-doped ZnO film based UV PD demonstrates improved UV sensitivity of about 66.92 upon 2 mW/cm² UV illumination at 365 nm peak wavelengths and 5 V applied bias. The reproducible UV detection performance of MSM devices was also ensured by periodically switching UV light on and off at fixed time intervals.     

Investigation into the effect of substrate material on microstructure and optical properties of thin films deposited via magnetron sputtering technique

This study aims at investigating the effect of the substrate material on growth mechanism and also microstructure of Ta₂O₅ thin films. For this purpose, atomic force microscopy, scanning electron microscopy, and interferometry analyses were implemented to reveal the influence of silicon wafer and amorphous BK7 glass substrates on the nucleation and growth mechanisms of Ta₂O₅ thin films deposited via the radio frequency magnetron sputtering technique. Results indicated that those films with finer morphologies had relatively higher nucleation densities. Compared with BK7 glass substrate, crystals formed on the silicon wafer were shown to be finer and had lower mean areas in more nucleation sites. Moreover, optical properties and morphological characteristics of the films on the silicon substrates had much more endurance after the annealing treatment. It was observed that shift in the transmission spectra of the deposited films after the treatment was insignificant, implying high packing density of the films. However, a 6-nm shift in the transmission spectra indicated low density and high porosity of the films. Finally, atomic force microscopy analysis along with the light scattering measurements confirmed the formation of a low-roughness film on the silicon wafer substrates.     

Structural and optical properties of ZnO nanorods by electrochemical growth using multi-walled carbon nanotube-composed seed layers

We reported the enhancement of the structural and optical properties of electrochemically synthesized zinc oxide [ZnO] nanorod arrays [NRAs] using the multi-walled carbon nanotube [MWCNT]-composed seed layers, which were formed by spin-coating the aqueous seed solution containing MWCNTs on the indium tin oxide-coated glass substrate. The MWCNT-composed seed layer served as the efficient nucleation surface as well as the film with better electrical conductivity, thus leading to a more uniform high-density ZnO NRAs with an improved crystal quality during the electrochemical deposition process. For ZnO NRAs grown on the seed layer containing MWCNTs (2 wt.%), the photoluminescence peak intensity of the near-band-edge emission at a wavelength of approximately 375 nm was enhanced by 2.8 times compared with that of the ZnO nanorods grown without the seed layer due to the high crystallinity of ZnO NRAs and the surface plasmon-meditated emission enhancement by MWCNTs. The effect of the MWCNT-composed seed layer on the surface wettability was also investigated.     

Fabrication and characterization of superhard tungsten boride layers deposited by radio frequency magnetron sputtering

The most promising areas of research of new super-hard materials are transition metal borides. These materials are one of the candidates for future superhard layers that will be competitive to DLC and c-BN layers. In this paper MoB-type tungsten boride (WB) layers were examined. WB layers have been deposited by radio frequency magnetron sputtering on Silicon (100), 304 stainless steel (SS 304) and Inconel 601 substrates. Measured thickness of herein prepared layers was about 1 µm, and all studied samples were dense, uniform and smooth. Surface investigation was performed by using an optical profilometer, atomic force microscopy, and scanning electron microscopy. The structure analysis was examined by using X-ray diffractometer (XRD) and transmission electron microscopy (TEM) techniques. Results from the XRD and TEM analysis showed that WB layers were dominated by (101) reflection and indicated a fine grain structure with a grain size of 20–40 nm. The effect of target sputtering power and ambient gas pressure was investigated. The hardness of WB layers deposited on silicon substrate was compared under the load from 1 mN to 5 mN. The hardness of WB layers deposited on SS 304 and Inconel was measured up to 50 mN. All layers of WB revealed excellent hardness exceeding 40 GPa.     

射频磁控溅射法制备FC/ZnO杂化材料及其基本性质

采用射频磁控溅射法,首先以聚四氟乙烯（PTFE）为靶,氩气为载气,在聚对苯二甲酸乙二醇酯（PET）基底上沉积氟碳（FC）膜;然后以金属锌为靶,氩气为载气,氧气为反应气体,在FC膜上再沉积一层ZnO膜而形成FC/ZnO有机-无机纳米杂化材料。用AFM、XPS、UV以及静态接触角测定仪对杂化材料的基本性质进行了研究。结果表明,该法制得的杂化材料是由纳米粒子组成的岛状结构,岛的表面起伏不平。其生长模式是一种依附于有机核的沉积-扩张生长。杂化材料具有较好的紫外吸收特性,这是由于其分子结构中含有π-π共轭双键、表面的不平整性以及纳米氧化锌粒子对紫外光的吸收共同作用的结果。静态水接触角均大于90°,呈现出良好的疏水性。     

Li-ion diffusion kinetics in LiFePO4 thin film prepared by radio frequency magnetron sputtering

LiFePO₄ thin films were prepared by radio frequency (RF) magnetron sputtering and were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and atomic force microscope (AFM). Li-ion chemical diffusion coefficients, , were measured by potentiostatic intermittent titration technique (PITT), electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV). The effects of Ag content, film thickness, and film orientation on the electrochemical performance and Li-ion chemical diffusion coefficients of the LiFePO₄ thin films were investigated. values were measured using the liquid electrolyte and the solid electrolyte, and the obtained values were discussed. The values by PITT and EIS were in the range of 10⁻¹⁴ to 10⁻¹² and 10⁻¹⁵ to 10⁻¹² cm² s⁻¹, respectively and that by CV was in the order of 10⁻¹⁴ cm² s⁻¹.     

The optical and electrical properties of ZnO:Al thin films deposited at low temperatures by RF magnetron sputtering

Several ZnO:Al thin films have been successfully deposited on glass substrates at different substrate temperatures by RF (radio frequency) magnetron sputtering method. Effects of the substrate temperatures on the optical and electrical properties of these ZnO:Al thin films were investigated. The UV–VIS–NIR spectra of the ZnO:Al thin films revealed that the average optical transmittances in the visible range are very high, up to 88%. X-ray diffraction results showed that crystallization of these films was improved at higher substrate temperature. The band gaps of ZnO:Al thin films deposited at 25 ℃, 150 ℃, 200 ℃, and 250 ℃ are 3.59 eV, 3.55 eV, 3.53 eV, and 3.48 eV, respectively. The Hall-effect measurement demonstrated that the electrical resistivity of the films decreased with the increase of the substrate temperature and the electrical resistivity reached 1.990×10^?3 Ω cm at 250 ℃.