Influence of the doping and annealing atmosphere on zinc oxide thin films deposited by spray pyrolysis

Undoped and doped (indium and aluminium) zinc oxide (ZnO) thin films have been prepared by spray pyrolysis, and the effect of the doping and annealing atmosphere on the electrical, optical and structural properties of the produced films has been investigated. The deposited films have a high resistivity. Annealing the films in an argon atmosphere or under vacuum leads to a substantial reduction of the electrical resistivity of the films and to an increase on the degree of cristallinity of the deposited material. The most pronounced changes were observed in the films annealed in Argon. The results also indicate that doping highly influences the electrical and structural properties of the films, which is more pronounced in the films doped with Indium.     

Synthesis,characterization and photoresponse study of undoped and transition metal (Co,Ni, Mn) doped ZnO thin films

The synthesis, characterization and photoresponse studies of undoped and transition metal doped zinc oxide thin films are carried out in this work, in prospect of visible light photo detection and sensor applications. The undoped and transition metal ions such as, Co, Ni and Mn doped ZnO films in this study were synthesized by chemical solution deposition, involving spin-coating. We have characterized the deposited films using X-ray diffraction, scanning electron microscopy, photoluminescence and UV–vis spectroscopy studies. The devices of the films for photoresponse study were fabricated by top Ag contacts on the film surface in metal–semiconductor–metal configuration. The current–voltage characteristics and switching measurements of these devices were studied under the illumination of an incandescent lamp. We found a high ON/OFF ratio of 8 and highest photocurrent density of 0.7 mA/cm² for Ni doped ZnO film.     

Effect of doping concentration on UV accelerated chemically deposited ZnS:Mn thin films

Pure and Mn alloyed ZnS thin films have been prepared by UV accelerated chemical deposition technique which is simple, economic and easy to monitor. Influence of doping concentration on ZnS thin films was investigated through the structural, compositional, morphological, optical and luminescent studies. The XRD studies confirmed the formation of crystalline films with hexagonal structure. In doped samples the intensities of the prominent peaks increased up to 0.5 wt% Mn and then decreased. The optimum concentration means the amount required to get most suitable characteristics for photovoltaic application. The thickness of the films and the sizes of the crystallites varied in consistent with the structural results. Crystallites became larger in size on doping and appeared to be denser than undoped film. Various structural parameters like stress and micro strain were calculated. The observed strain is compressive in nature which rapidly increased with doping and then remained almost same with doping concentration. The SEM studies revealed the formation of films with almost similar morphology of spherical architectures. All the films exhibited uniform transmission in the high visible region, with a maximum of 80 % for the sample with optimum Mn concentration. Both direct and indirect band gap decreased due to the incorporation of Mn, but showed a blue shift in the fundamental absorption edge with doping concentration up to the optimum dopant content. Undoped and doped films exhibit five distinct luminescence peaks located around 391, 451, 458, 482 and 492 nm. The observed variation in the intensity of the luminescence in doped films clearly indicated the influence of thickness of the films which varied on doping.     

Structural,luminescence and magnetic properties of Mn doped ZnO thin films using spin coating technique

Manganese doped zinc oxide (ZnO) thin films were synthesized for various wt% doping of Mn using sol–gel spin coating technique. The effects of Mn doping on the structural, morphological, compositional, photoluminescence (PL) and magnetic behaviour of ZnO thin films were investigated. Although, Mn doping did not change the lattice constants of the films, the texture coefficient is found to be improved for the films having higher percentage of Mn doping. PL studies reveal that as doping concentration of Mn increases, the intensity of emission peaks corresponding to violet and blue colour increases and the peak position shifts slightly. The saturated magnetic moments are found to decrease with the increase in Mn doping and the reason for such behavior is discussed.     

Optoelectronic,magnetic and antibacterial properties of CdO thin films doubly doped with Mn (cationic) and F (anionic) ions

This paper outlines the effect of (Mn?+?F) double doping on the structural, morphological, optoelectronic, magnetic and antibacterial properties of CdO thin films. Undoped CdO, Mn-doped CdO and (Mn?+?F) doubly doped CdO films exhibit face-centered cubic structure with a strong (1 1 1) preferential growth. Crystallite size value of the undoped film estimated using the Scherrer formula decreases with Mn doping and with double doping it increases. Cauliflower shaped nanostructures are evinced from the SEM images. Increased optical transparency is observed for the doubly doped films. The optical band gap value of the Mn-doped CdO film is found to be red shifted and for the (Mn?+?F) doubly doped films it is blue shifted which may be attributed to the Moss-Burstein effect. Ferromagnetic ordering is observed for the doped films. The doped films show increased antibacterial efficiency against K. pneumonia a gram ?ve bacteria. The obtained results infer that the CdO films doubly doped with Mn (cationic) and F (anionic) ions exhibited better optical, electrical, magnetic and antibacterial properties.     

Development of thickness measurement program for transparent conducting oxide thin films

The gallium doped zinc oxide has been one of the candidates for the transparent conducting oxide thin film electrode. It is not suitable to use a conventional light interference method to measure the thickness of the gallium doped zinc oxide thin film because the refractive index and extinction coefficient of the thin film is unknown during the optimization of the deposition conditions. In this paper, we report on the details of the film thickness program which uses the measured optical and electric properties and relationship between the plasma frequency and the optical constant of the film. The obtained film thickness of the prepared gallium doped zinc oxide thin film using the program was comparable with thicknesses measured by a cross-sectional analysis of the atomic force microscopy and the surface profiler. Moreover, the optical constant of refractive index and extinction coefficient of the film could also be estimated.     

Advances in piezoelectric thin films for acoustic biosensors,acoustofluidics and lab-on-chip applications

Recently, piezoelectric thin films including zinc oxide (ZnO) and aluminium nitride (AlN) have found a broad range of lab-on-chip applications such as biosensing, particle/cell concentrating, sorting/patterning, pumping, mixing, nebulisation and jetting. Integrated acoustic wave sensing/microfluidic devices have been fabricated by depositing these piezoelectric films onto a number of substrates such as silicon, ceramics, diamond, quartz, glass, and more recently also polymer, metallic foils and bendable glass/silicon for making flexible devices. Such thin film acoustic wave devices have great potential for implementing integrated, disposable, or bendable/flexible lab-on-a-chip devices into various sensing and actuating applications. This paper discusses the recent development in engineering high performance piezoelectric thin films, and highlights the critical issues such as film deposition, MEMS processing techniques, control of deposition/processing parametres, film texture, doping, dispersion effects, film stress, multilayer design, electrode materials/designs and substrate selections. Finally, advances in using thin film devices for lab-on-chip applications are summarised and future development trends are identified.     

Influence of incorporation of Al3+ ions on the structural, optical and AC impedance characteristics of spin coated ZnO thin films

Aluminium doped zinc oxide thin films were deposited onto glass substrate using spin coating technique. The effects of Al doping on structural, optical and electrical properties of these films were investigated. X-ray diffraction analysis showed that all the thin films were of polycrystalline hexagonal wurtzite structure with (002) as preferential orientation except 2 at.% of Al doped ZnO films. The optical band gap was found to be 3.25 eV for pure ZnO film. It increases up to 1.5 at.% of Al doping (3.47 eV) and then decreased slightly for the doping level of 2 at.% (3.42 eV). The reason for this widening of the optical band gap up to 1.5 at.% is well described by Burstein–Moss effect. The photoluminescence spectra of the films showed that the blue shift and red shift of violet emission were due to the change in the radiative centre between zinc vacancy and zinc interstitial. Variation in ZnO grain boundary resistance against the doping concentration was observed through AC impedance study.     

Thin composite films consisting of polypyrrole and polyparaphenylene

This study demonstrates that the combined method for the formation of thin composite films, consisting of polypyrrole (PPy) as a film forming agent and polyparaphenylene (PPP) with controlled electrical properties and high stability, enables one to avoid the low processability of PPP and to extend the possibilities for the development of electronic devices. The high temperature (250-600 °C) doping method was used for PPP preparation. The crystallinity and grindability of PPP was found to be increasing with the thermochemical modification. Thin composite films were prepared onto the light transparent substrates using the simple electropolymerization technique. The properties of films were characterized by the optical transmittance and temperature-dependent conductivity measurements. The morphology and thickness of the prepared films were determined using the scanning electron microscopy. The composite films showed a better adhesion to an inorganic substrate. It was found to be connected mostly with the improved properties of the high temperature doped PPP. The current-voltage characteristics of indium tin oxide/film/Au hybrid organic-inorganic structures showed the influence of the doping conditions of PPP inclusions in the obtained films.     

Formation of sulphide 'patches' on inclusions in C – Mn steel weld metal

Abstract

Following earlier observations indicating that sulphide coatings can form on inclusion surfaces in a C – Mn steel weld metal when cooled from high temperature, experiments have been carried out to examine the effects of cooling rate on the nature of sulphide precipitation on inclusions when cooled through the austenite range. It is found that fast cooling rates give thin films whereas slow rates produce thick films or 'patches'. The increase in film thickness is assessed in terms of the S/Mn ratio as measured by EDX.     

Synthesis and structural-optical properties of Ga-doped ZnO nanowires by hot-walled pulsed laser deposition method

Well-aligned single-crystalline zinc oxide (ZnO) and Ga doped ZnO (GZO) NWs (NWs) were successfully fabricated on Au film catalyzed sapphire substrate using vapor-liquid-solid (VLS) method in hot-walled pulsed laser deposition (HW-PLD). The structural and optical properties of Ga doped ZnO NWs have been investigated depending on various concentration of Ga dopants in ZnO NWs. As increasing Ga concentration, stacking faults were observed by using FE-SEM and an exciton bound to a neutral donor (D(0)X) peak was clearly observed by using PL spectra. From the structural and optical properties, the ZnO NWs by doping could be application to electronic and optoelectronic devices, such as nano-FETs, nano-inverters, nano-logic circuits and nano-sensors.     

Durability of doped zinc oxide/silver/doped zinc oxide low emissivity coatings in humid environment

The relationship between internal stress of doped zinc oxide films and durability of doped zinc oxide/silver/doped zinc oxide low emissivity (low-e) coatings in humid environment was investigated. Aluminum, titanium, tin, chromium, silicon, gallium, magnesium, boron, barium, and calcium were chosen as a doping element in sputtering targets. Ratios of dopant/zinc in the oxide targets were 4/96-5/95 at.%. Films were formed by radio frequency sputtering. Doping of barium and calcium to the zinc oxide film led to a large increase in the internal stress. Doping of the other elements resulted in decreasing the internal stress. It was concluded that durability of the low-e coatings in humid environment closely correlated with the internal stress of the oxide layers.     

Influence of Zn doping on electrical and optical properties of multilayered tin oxide thin films

In this study, the electrical and optical properties of Zn doped tin oxide films prepared using sol-gel spin coating process have been investigated. The SnO² : Zn multi-coating films were deposited at optimum deposition conditions using a hydroalcoholic solution consisting of stannous chloride and zinc chloride. Films with Zn doping levels from 0–10 wt% in solution are developed. The results of electrical measurements indicate that the sheet resistance of the deposited films increases with increasing Zn doping concentration and several superimposed coatings are necessary to reach expected low sheet resistance. Films with three coatings show minimum sheet resistance of 1–479 kΩ/ in the case of undoped SnO₂ and 77 kΩ/ for 5 wt% Zn doped SnO₂ when coated on glass substrate. In the case of single layer SnO₂ film, absorption edge is 3.57 eV and when doped with Zn absorption edge shifts towards lower energies (longer wavelengths). The absorption edge lies in the range of 3.489-3.557 eV depending upon the Zn doping concentration. The direct and indirect transitions and their dependence on dopant concentration and number of coatings are presented.     

Surface textured molybdenum zinc oxide for light diffusion enhancement

Surface textures have been fabricated on a molybdenum doped zinc oxide (MZO) film using a shadow mask in a co-sputter process. The surface textures yielded 5.3% and 10.1% of light diffusion in the visible light region for MZO films with a thickness of 100 nm and 200 nm, respectively. Light diffusion in the near infra-red region was slightly less with 4.5% for the 100 nm MZO film and 8.9% for the 200 nm MZO film. The enhanced light diffusion will be beneficial to the light trapping efficiency of a-Si/µ-Si based thin film solar cells.     

Fabrication of high quality zinc-oxide layers through electrohydrodynamic atomization

Zinc oxide (ZnO) is a useful material in the fabrication of many electronic devices because of its wide band-gap, excellent transparency and high electron mobility. Thin films of ZnO have been fabricated where an alcosol solution containing 7 wt.% ZnO nano-particles was synthesized and subjected to controlled flow through a metal capillary exposed to an electric field at the ambient temperature to generate an electrohydrodynamic jet, which subsequently disintegrated into droplets thereby depositing a uniform thin film of zinc oxide on the glass substrates with an average thickness of 115 nm at a constant substrate speed of 0.25 mm/s. Pure and perfectly uniform transparent films with an average transmittance of 88% have been deposited with wurtzite crystal structure and an electrical resistivity of approximately 64 Ω.cm.     

Enhanced dielectric properties of Mn doped Ba0.6Sr0.4TiO3 thin films fabricated by pulsed laser deposition

Pure and 2 mol% Mn doped Ba_0.6Sr_0.4TiO₃ (BST) thin films have been deposited on La_0.67Sr_0.33MnO₃ (LSMO) coated single-crystal (001) oriented LaAlO₃ substrates using pulsed-laser deposition technique. The bilayer films of BST and LSMO were epitaxially grown in pure single-oriented perovskite phases for both samples, and an enhanced crystallization effect in the BST film was obtained by the addition of Mn, which were confirmed by X-ray diffraction (XRD) and in situ reflective high energy electron diffraction (RHEED) analyses. The dielectric properties of the BST thin films were measured at 100 kHz and 300 K with a parallel-plate capacitor configuration. The results have revealed that an appropriate concentration acceptor doping is very effective to increase dielectric tunability, and to reduce loss tangent and leakage current of BST thin films. The figure-of-merit (FOM) factor value increases from 11 (undoped) to 40 (Mn doped) under an applied electric field of 200 kV/cm. The leakage current density of the BST thin films at a negative bias field of 200 kV/cm decreases from 2.5 × 10^− 4 A/cm² to 1.1 × 10^− 6 A/cm² by Mn doping. Furthermore, a scanning-tip microwave near-field microscope has been employed to study the local microwave dielectric properties of the BST thin films at 2.48 GHz. The Mn doped BST film is more homogeneous, demonstrating its more potential applications in tunable microwave devices.     

Polycrystalline ZnO: B grown by LPCVD as TCO for thin film silicon solar cells

Conductive zinc oxide (ZnO) grown by low pressure chemical vapor deposition (LPCVD) technique possesses a rough surface that induces an efficient light scattering in thin film silicon (TF Si) solar cells, which makes this TCO an ideal candidate for contacting such devices. IMT-EPFL has developed an in-house LPCVD process for the deposition of nanotextured boron doped ZnO films used as rough TCO for TF Si solar cells. This paper is a general review and synthesis of the study of the electrical, optical and structural properties of the ZnO:B that has been performed at IMT-EPFL.The influence of the free carrier absorption and the grain size on the electrical and optical properties of LPCVD ZnO:B is discussed. Transport mechanisms at grain boundaries are studied. It is seen that high doping of the ZnO grains facilitates the tunnelling of the electrons through potential barriers that are located at the grain boundaries. Therefore, even if these potential barriers increase after an exposition of the film to a humid atmosphere, the heavily doped LPCVD ZnO:B layers show a remarkable stable conductivity. However, the introduction of diborane in the CVD reaction induces also a degradation of the intra-grain mobility and increases over-proportionally the optical absorption of the ZnO:B films. Hence, the necessity to finely tune the doping level of LPCVD ZnO:B films is highlighted. Finally, the next challenges to push further the optimization of LPCVD ZnO:B films for thin film silicon solar cells are discussed, as well as some remarkable record cell results achieved with LPCVD ZnO:B as front electrode.     

Synthesis and studies on effect of indium doping on physical properties of electrodeposited CdSe thin films

Semiconducting CdSe and indium doped CdSe (In: CdSe) thin films have been synthesized on stainless steel and fluorine doped tin oxide coated glass substrates in an aqueous medium using a potentiostatic mode of electrodeposition. The doping concentration of indium has been optimized to 0.15 vol% using the reliable photoelectrochemical technique. To study the effect of indium doping these films are characterized using X-ray diffraction, X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy, energy dispersive X-ray spectroscopy, elemental mapping, Raman spectroscopy, contact angle measurement and UV–visible spectrophotometry techniques. CdSe and In: CdSe thin films are low crystalline with a cubic crystal structure. The valence states of CdSe and In: CdSe thin films are analyzed by means of XPS. Undoped CdSe thin film shows fiberlike morphology, which transforms into a beautiful web of nanofibers upon doping. The Elemental composition of both films analyzed by means of energy dispersive X-ray spectroscopy. Raman studies show transverse optical and longitudinal optical modes of phonon. Indium doping improves the hydrophilic nature of CdSe photoanode. The optical band gap (direct) found to be decreased from 2.02 to 1.67 eV upon indium doping. Both films are photoactive in nature.     

Growth and characterization of transparent conducting nanostructured zinc indium oxide thin films

Transparent conductive oxide (TCO) films have been widely used in various applications, such as for transparent electrodes in flat-panel displays, and in solar cells, optoelectronic devices, touch panels and IR reflectors. Among these, tin doped zinc oxide (ZTO) and indium doped zinc oxide (ZIO) have attracted considerable attention. Particularly, IZO thin film is the best candidate for high-quality transparent conducting electrodes in OLEDs and flexible displays. In this work zinc indium oxide (ZIO) thin films were deposited on glass substrate with varying concentration (ZnO:In₂O₃ — 100:0, 90:10, 70:30 and 50:50 wt.%) at room temperature by flash evaporation technique. These deposited ZIO films were annealed in vacuum to study the thermal stability and to see the effects on the physical properties. The XRF spectra revealed the presence of zinc and indium with varying concentration in ZIO thin films, while the surface composition and oxidation state were analyzed by X-ray photoelectron spectroscopy. The core level spectra were deconvoluted to see the effect of chemical changes, while the valance band spectra manifest the electronic transitions. The surface morphology studies of the films using atomic force microscopy (AFM) revealed the formation of nanostructured ZIO thin films. The optical band gap was also found to be decreased for both types of films with increasing concentration of In₂O₃.     

Preparation of manganese-doped ZnO thin films and their characterization

In this study, pure and manganese-doped zinc oxide (Mn:ZnO) thin films were deposited on quartz substrate following successive ion layer adsorption and reaction (SILAR) technique. The film growth rate was found to increase linearly with number of dipping cycle. Characterization techniques of XRD, SEM with EDX and UV–visible spectra measurement were done to investigate the effect of Mn doping on the structural and optical properties of Mn:ZnO thin films. Structural characterization by X-ray diffraction reveals that polycrystalline nature of the films increases with increasing manganese incorporation. Particle size evaluated using X-ray line broadening analysis shows decreasing trend with increasing manganese impurification. The average particle size for pure ZnO is 29·71 nm and it reduces to 23·76 nm for 5% Mn-doped ZnO. The strong preferred c-axis orientation is lost due to manganese (Mn) doping. The degree of polycrystallinity increases and the average microstrain in the films decreases with increasing Mn incorporation. Incorporation of Mn was confirmed from elemental analysis using EDX. As the Mn doping concentration increases the optical bandgap of the films decreases for the range of Mn doping reported here. The value of fundamental absorption edge is 3·22 eV for pure ZnO and it decreases to 3·06 eV for 5% Mn:ZnO.