Studies on the structural and electrical properties of spray deposited SnO2:Sb thin films as a function of substrate temperature

Thin films of antimony doped tin oxide (SnO₂:Sb) were prepared by spray pyrolysis technique using SnCl₂ as precursor with the various antimony doping levels ranging from 1 to 4 wt%. The XRD analysis showed that the undoped SnO₂ films grow in (211) preferred orientation whereas the Sb doped films grow in (200) plane. Scanning electron microscopy studies indicated that the surface of the films prepared with lower doping level (1 wt%) consists of larger grains whereas those prepared with higher doping levels (>1 wt%) consist of smaller grains. The sheet resistance has been found to be reduced considerably (2.17 Ω/□) for Sb doped films. To the best of our knowledge this is the lowest sheet resistance obtained for Sb doped SnO₂ thin films.     

Highly conducting and crystalline doubly doped tin oxide films fabricated using a low-cost and simplified spray technique

Doubly doped (simultaneous doping of antimony and fluorine) tin oxide films (SnO₂:Sb:F) have been fabricated by employing an inexpensive and simplified spray technique using perfume atomizer from aqueous solution of SnCl₂ precursor. The structural studies revealed that the films are highly crystalline in nature with preferential orientation along the (2 0 0) plane. It is found that the size of the crystallites of the doubly doped tin oxide films is larger (69 nm) than that (27 nm) of their undoped counterparts. The dislocation density of the doubly doped film is lesser (2.08×10¹⁴ lines/m²) when compared with that of the undoped film (13.2×10¹⁴ lines/m²), indicating the higher degree of crystallinity of the doubly doped films. The SEM images depict that the films are homogeneous and uniform. The optical transmittance in the visible range and the optical band gap of the doubly doped films are 71% and 3.56 eV respectively. The sheet resistance (4.13 Ω/□) attained for the doubly doped film in this study is lower than the values reported for spray deposited fluorine or antimony doped tin oxide films prepared from aqueous solution of SnCl₂ precursor (without using methanol or ethanol).     

Properties of highly oriented spray-deposited fluorine-doped tin oxide thin films on glass substrates of different thickness

Transparent conducting thin films of fluorine-doped tin oxide (FTO) have been deposited onto the preheated glass substrates of different thickness by spray pyrolysis process using SnCl₄·5H₂O and NH₄F precursors. Substrate thickness is varied from 1 to 6 mm. The films are grown using mixed solvent with propane-2-ol as organic solvent and distilled water at optimized substrate temperature of 475 °C. Films of thickness up to 1525 nm are grown by a fine spray of the source solution using compressed air as a carrier gas. The films have been characterized by the techniques such as X-ray diffraction, optical absorption, van der Pauw technique, and Hall effect. The as-deposited films are preferentially oriented along the (2 0 0) plane and are of polycrystalline SnO₂ with a tetragonal crystal structure having the texture coefficient of 6.19 for the films deposited on 4 mm thick substrate. The lattice parameter values remain unchanged with the substrate thickness. The grain size varies between 38 and 48 nm. The films exhibit moderate optical transmission up to 70% at 550 nm. The figure of merit (φ) varies from 1.36×10⁻⁴ to 1.93×10⁻³ Ω⁻¹. The films are heavily doped, therefore degenerate and exhibit n-type electrical conductivity. The lowest sheet resistance (R_s) of 7.5 Ω is obtained for a typical sample deposited on 4 mm thick substrate. The resistivity (ρ) and carrier concentration (n_D) vary over 8.38×10⁻⁴ to 2.95×10⁻³ Ω cm and 4.03×10²⁰ to 2.69×10²¹ cm⁻³, respectively.     

Studies on the structural and electrical properties of F-doped SnO2 film prepared by APCVD

Fluorine-doped tin oxide films (SnO₂:F, FTO) were deposited by atmosphere pressure chemical vapor deposition (APCVD) on Na-Ca-Si glass coated with a diffusion barrier layer of SiO_xC_y. The effects of post-heating time at 700 °C on the structural and electrical properties of SnO₂:F films were investigated. The results showed that SnO₂:F films were polycrystalline with tetragonal SnO₂ structure, SnO phase was present in SnO₂ film, and abnormal grain growth was observed. The element distribution in the film depth was measured with X-ray photoelectron spectroscopy (XPS) and revealed that when the heating time increased from 202 s to 262 s, the oxygen content in the surface increased from 78.63% to 83.38%. The resistivity increased from 3.13 × 10⁻⁴ for as-deposited films to 4.73 × 10⁻⁴ Ω cm when post-heated for 262 s. Hall mobility is limited by the ionized impurity scattering rather than the grain boundary scattering.     

W doped SnO2 growth via sol–gel routes and characterization: Nanocubes

The effects of W doping on the characteristical properties of SnO₂ thin films prepared by sol–gel spin coating method were investigated. The SnO₂ thin films were deposited at various W doping ratios and characterized by various measurements. XRD studies indicated that the undoped and W doped SnO₂ films had cubic and tetragonal phases. The SEM images of WTO thin films showed cubic shaped nanocubes corresponding to cubic phase and the smaller particles corresponding to tetragonal phase were formed on the film surfaces, and their distributions and sizes were dependent on the W doping ratio. EDX spectroscopy analyses showed that the calculated and participated atomic ratios of W/(W + Sn) (at.%) in the starting solution and in the WTO thin films were almost close. It was found that the sheet resistance depended on W doping ratio and 2.0 at.% W doped SnO₂ (WTO) exhibited lowest value of sheet resistance (7.11 × 10³ Ω/cm²).     

Sensitisation of erbium emission by silicon nanocrystals-doped SnO2

SnO₂ thin films undoped and doped with antimony (Sb), erbium (Er) and Si nanocrystals (Si-nc) have been grown on silicon (Si) substrate using sol-gel method. Room-temperature photoluminescence (PL) measurement of undoped SnO₂, under excitation at 280 nm, shows only one broad emission at 395 nm, which is related to oxygen vacancies. The PL of Er³⁺ ions was found to be enhanced after doping SnO₂ with Sb and Si-nc. The excitation process of Er is studied and discussed. The calculation of cross-section suggests a sensitisation of Er PL by Si-nc.     

High-resolution transmission electron microscopy investigation of the nanostructure of undoped and Pt-doped nanocrystalline pulsed laser deposited SnO2 thin films

Pulsed laser deposition (PLD) was used to grow nanocrystalline SnO₂ thin films onto alumina substrates. The reactive PLD process was carried out at different substrate deposition temperatures (T_d) between 20 and 600 °C under an oxygen background pressure of 150 mtorr. The same PLD technique was used to produce SnO₂ films in situ-doped with Pt (at the level of ∼2 at. %) through the concomitant ablation of both SnO₂ target and Pt strips. Conventional and high-resolution transmission electron microscopy (HRTEM) observations have revealed that the microstructure of the PLD SnO₂ films is highly sensitive to their deposition temperature. Indeed, its changes from a porous granular structure with extremely fine equiaxed grains (∼4 nm diameter), at T_d=20 °C to a very compact and textured columnar structure characterized by SnO₂ columns (∼25 nm diameter) composed of grains of ∼12 nm of diameter, at T_d=600 °C. In addition, the PLD SnO₂ films were found to exhibit the highest nanoporosity at T_d=300 °C which also coincides with the granular-to-columnar microstructural transition. On the other hand, the microstructure of the Pt-doped SnO₂ films, deposited at 300 °C, was found to contain a high density of defects, such as twin boundaries and edge dislocations. By combining HRTEM and EDS microanalysis, we were able to show that the Pt-dopant self-organizes into spherical nanoparticles (1-2 nm diameter) randomly distributed at the SnO₂ grain boundaries. Finally, doping the films with such platinum nanoclusters is found to affect the SnO₂ nanostructure by particularly reducing the SnO₂ mean grain size (from ∼10 nm when undoped to ∼6 nm for the doped films).     

Microstructural, optical and photocatalytic properties of CdS doped TiO2 thin films

CdS doped TiO₂ thin films (with CdS content=0, 3, 6, 9 and 12 at%) were grown on glass substrates. The X-ray diffraction analysis revealed that the films are polycrystalline of monoclinic TiO₂ structure. The microstructure parameters of the films such as crystallite size (D_ν) and microstrain (e) are calculated. Both the crystallites size and the microstrain are decreased with increasing CdS content. The optical constants have been determined in terms of Murmann's exact equations. The refractive index and extinction coefficient are increased with increasing CdS content. The optical band gap is calculated in the strong absorption region. The possible optical transition in these films is found to be an allowed direct transition. The values of E_g^opt are found to decrease as the CdS content increased. The films with 3 at% CdS content have better decomposition efficiency than undoped TiO₂. The films with 6 at% and 9 at% CdS content have decomposition efficiency comparable to that of undoped TiO₂, although they have lower band gap. The CdS doped TiO₂ could have a better impact on the decomposing of organic wastes.     

Optical and electrochemical properties of Cu-doped NiO films prepared by electrochemical deposition

Cu-doped nickel oxide (NiO) thin films were prepared by electrochemial deposition (cathodic deposition) technique onto the fluorine doped tin oxide (F: SnO₂; FTO) coated glass substrates from organic solutions. Effects of Cu content on the morphology, structure, optical and electrochromic properties of NiO films were investigated by means of scanning electron microscope (SEM), X-ray diffraction (XRD), ultraviolet-visible spectrophotometer (UV-vis) and cyclic voltammetry (CV), respectively. SEM images indicated the formation of nanorods after Cu was added. The films were formed with amorphous or short-range ordered NiO grains and a trace of face-centered cubic Ni_xCu_1−xO confirmed by XRD. The transmittances of both bleached state and colored state were significantly lowered when Cu was added. The NiO films doped with Cu (the molar ratio was 1/8) exhibited the optimum electrochromic behavior with a variation of transmittance (ΔT) up to ∼80% at the wavelength range of 350-600 nm. Cu doping reduces the response time for both the coloring and bleaching states, and the reversibility of the redox reaction was increased as well.     

Structural, electrical and optical properties of TiO2 doped WO3 thin films

TiO₂ doped WO₃ thin films were deposited onto glass substrates and fluorine doped tin oxide (FTO) coated conducting glass substrates, maintained at 500 °C by pyrolytic decomposition of adequate precursor solution. Equimolar ammonium tungstate ((NH₄)₂WO₄) and titanyl acetyl acetonate (TiAcAc) solutions were mixed together at pH 9 in volume proportions and used as a precursor solution for the deposition of TiO₂ doped WO₃ thin films. Doping concentrations were varied between 4 and 38%. The effect of TiO₂ doping concentration on structural, electrical and optical properties of TiO₂ doped WO₃ thin films were studied. Values of room temperature electrical resistivity, thermoelectric power and band gap energy (E_g) were estimated. The films with 38% TiO₂ doping in WO₃ exhibited lowest resistivity, n-type electrical conductivity and improved electrochromic performance among all the samples. The values of thermoelectric power (TEP) were in the range of 23-56 μV/K and the direct band gap energy varied between 2.72 and 2.86 eV.     

Preparation and properties of spray-deposited ZnIn2Se4 nanocrystalline thin films

Zinc indium selenide (ZnIn₂Se₄) thin films have been deposited onto amorphous and fluorine doped tin oxide (FTO)-coated glass substrates using a spray pyrolysis technique. Aqueous solution containing precursors of Zn, In, and Se has been used to obtain good quality deposits at different substrate temperatures. The preparative parameters such as substrate temperature and concentration of precursors solution have been optimized by photoelectrochemical technique and are found to be 325 °C and 0.025 M, respectively. The X-ray diffraction patterns show that the films are nanocrystalline with rhombohedral crystal structure having lattice parameter a=4.05 Å. The scanning electron microscopy (SEM) studies reveal the compact morphology with large number of single crystals on the surface. From optical absorption data the indirect band gap energy of ZnIn₂Se₄ thin film is found to be 1.41 eV.     

Optical and electrical properties of SnO2:Sb thin films deposited by oblique angle deposition

The antimony doped tin oxide (SnO₂:Sb) (ATO) thin films were prepared by oblique angle electron beam evaporation technique. X-ray diffraction, field emission scanning electron microscopy, UV-vis-NIR spectrophotometer and four-point probe resistor were employed to characterize the structure, morphology, optical and electrical properties. The results show that oblique angle deposition ATO thin films with tilted columns structure are anisotropic. The in-plane birefringence of optical anisotropy is up to 0.035 at α = 70°, which means that it is suitable as wave plate and polarizer. The electrical anisotropy of sheet resistance shows that the sheet resistance parallel to the deposition plane is larger than that perpendicular to the deposition plane and it can be changed from 900 Ω/□ to 3500 Ω/□ for deposition angle from 40° to 85°, which means that the sheet resistance can be effectively tuned by changing the deposition angle. Additionally, the sandwich structure of SiO₂ buffer layer plus normal ATO films and oblique angle deposition ATO films can reduce the resistance, which can balance the optical and electrical anisotropy. It is suggested that oblique angle deposition ATO thin films can be used as transparent conductive thin films in solar cell, anti-foggy windows and multifunctional carrier in liquid crystal display.     

Effects of O2/Ar flow ratio on the alcohol sensitivity of tin oxide film

The aim of this study is to find the effects of oxygen flow rate during manufacturing on the sensitivity of SnO₂ (tin oxide) thin films to ethanol (C₂H₅OH). In this study, an RF sputtering process was employed to fabricate the SnO₂ thin films. The SnO₂ was deposited on gold electrode silicon microchips. A target composed of SnO₂ doped with 1 at.% Li was used with a working pressure of 3 mTorr. The RF power was fixed at 150 W. The reaction gas was a mixture of argon and oxygen. The total flow rate was constant at 50 sccm with the O₂/Ar ratio varying from 0.2 to 0.8. An annealing heat treatment was employed at 400 °C for 1 h to stabilize the properties of the films. The sensitivity of the film to ethanol was tested by placing the micro-reactor device on a hot plate, heated to 300 °C, and measuring the variation of electrical resistivity of the film with and without the presence of ethanol. The results show that an O₂/Ar flow ratio of 0.2 produces films with the highest ethanol sensitivity. Before heat treating, the ethanol sensitivity was 126. After heat treating at 400 °C for 1 h, the sensitivity decreased to 104.     

Structural and electrical properties of fluorine doped tin oxide films prepared by spray-pyrolysis technique

Fluorine doped SnO₂ films have been successfully prepared at optimized substrate temperature of 723 K by spray pyrolysis technique. The XRD analysis confirmed that films deposited with F/Sn ratio of 0.05 showed a partial amorphous nature whereas films deposited with F/Sn = 0.10 exhibited tetragonal structure (2 0 0) as the preferred orientation and polycrystalline structure. The lattice constants were found to be a = 0.4750 and c = 0.3197 nm. The theoretically constructed XRD pattern for SnO₂ was used to compare with experimental pattern, the difference between them is discussed. By using SEM analysis, the surface morphology of the films was observed as an effect of the variation of F/Sn ratio. At low temperature, the mobility due to lattice, polar, impurity, grain boundary and neutral scattering was estimated for SnO₂ and the possible scattering mechanisms were assigned to SnO₂:F films using experimentally obtained electrical data. The Mott parameters were determined by applying variable range hopping (VRH) conduction mechanism for SnO₂:F films (F/Sn = 0.05) where band conduction mechanism shifted to VRH conduction at below about 250 K.     

Effect of indium doping in CdO thin films prepared by spray pyrolysis technique

Preparation of transparent and conducting indium doped CdO thin films by spray pyrolysis on glass substrate is reported for various concentration of indium (2-8 wt%) in the spray solution. The electrical, optical and structural properties of indium doped CdO films were investigated using different techniques such as Hall measurement, optical transmission, X-ray diffraction and scanning electron microscope. X-ray analysis shows that the undoped CdO films are preferentially orientated along (2 0 0) crystallographic direction. Increase of indium doping concentration increases the films packing density and reorient the crystallites along (1 1 1) plane. A minimum resistivity of 4.843×10⁻⁴ Ω cm and carrier concentration of 3.73×10²⁰ cm⁻³ with high transmittance in the range 300-1100 nm were achieved for 6 wt% indium doping. The band gap value increases with doping concentration and reaches a maximum of 2.72 eV for 6 wt% indium doping from 2.36 eV of that of undoped film. The minimum resistivity achieved in the present study is found to be the lowest among the reported values for In-doped CdO films prepared by spray pyrolysis method.     

Effects of thermal oxidation temperature on vacuum evaporated tin dioxide film

In order to investigate the effect of thermal oxidation temperature on tin dioxide (SnO₂), tin dioxide films were obtained on quartz substrates by vacuum evaporation of tin metal. The films were characterized by X-ray diffraction (XRD) analyses, scanning electron microscopy (SEM), temperature dependent electrical resistivity measurement and optical absorption spectroscopy. The SEM images showed that the films are dense, continuous and are composed of nanoparticles and particle sizes are increased after thermal oxidation. From the X-ray measurement results, the films indicated two strong reflection peaks of tetragonal structure in the orientations of (1 0 1) and (2 0 0) at 2θ = 33.89° and 37.95°, respectively. Intensity of the peaks increased with increasing thermal oxidation temperature. We found resistivity values of about 10⁻⁴ Ω-cm. Optical absorption spectra of the films in the UV–Vis spectral range revealed that optical band gap (E_g) value of the films increases with increasing thermal oxidation temperature.     

Highly thermal stable transparent conducting SnO2:Sb epitaxial films prepared on α-Al2O3 (0 0 0 1) by MOCVD

Antimony-doped tin oxide (SnO₂:Sb) single crystalline films have been prepared on α-Al₂O₃ (0 0 0 1) substrates by metal organic chemical vapor deposition (MOCVD). The antimony doping was varied from 2% to 7% (atomic ratio). Post-deposition annealing of the SnO₂:Sb films was carried out at 700-1100 °C for 30 min in atmosphere ambient. The effect of annealing on the structural, electrical and optical properties of the films was investigated in detail. All the SnO₂:Sb films had good thermal stability under 900 °C, and the 5% Sb-doped SnO₂ film exhibited the best opto-electrical properties. Annealed above 900 °C, the 7% Sb-doped SnO₂ film still kept high thermal stability and showed good electrical and optical properties even at 1100 °C.     

Electrosynthesis and characterization of Fe doped CdSe thin films from ethylene glycol bath

The CdSe and Fe doped CdSe (Fe:CdSe) thin films have been electrodeposited potentiostatically onto the stainless steel and fluorine doped tin oxide (FTO) glass substrates, from ethylene glycol bath containing (CH₃COO)₂·Cd·2H₂O, SeO₂, and FeCl₃ at room temperature. The doping concentration of Fe is optimized by using (photo) electrochemical (PEC) characterization technique. The deposition mechanism and Fe incorporation are studied by cyclic voltammetry. The structural, surface morphological and optical properties of the deposited CdSe and Fe:CdSe thin films have been studied by X-ray diffraction, scanning electron microscopy (SEM) and optical absorption techniques respectively. The PEC study shows that Fe:CdSe thin films are more photosensitive than that of undoped CdSe thin films. The X-ray diffraction analysis shows that the films are polycrystalline with hexagonal crystal structure. SEM studies reveal that the films with uniformly distributed grains over the entire surface of the substrate. The complete surface morphology has been changed after doping. Optical absorption study shows the presence of direct transition and a considerable decrease in bandgap, E_g from 1.95 to 1.65 eV.     

Enhanced field emission from Si doped nanocrystalline AlN thin films

Si doped and undoped nanocrystalline aluminum nitride thin films were deposited on various substrates by direct current sputtering technique. X-ray diffraction analysis confirmed the formation of phase pure hexagonal aluminum nitride with a single peak corresponding to (1 0 0) reflection of AlN with lattice constants, a = 0.3114 nm and c = 0.4986 nm. Energy dispersive analysis of X-rays confirmed the presence of Si in the doped AlN films. Atomic force microscopic studies showed that the average particle size of the film prepared at substrate temperature 200 °C was 9.5 nm, but when 5 at.% Si was incorporated the average particle size increased to ∼21 nm. Field emission study indicated that, with increasing Si doping concentration, the emission characteristics have been improved. The turn-on field (E_to) was 15.0 (±0.7) V/μm, 8.0 (±0.4) V/μm and 7.8 (±0.5) V/μm for undoped, 3 at.% and 5 at.% Si doped AlN films respectively and the maximum current density of 0.27 μA/cm² has been observed for 5 at.% Si doped nanocrystalline AlN film. It was also found that the dielectric properties were highly dependent on Si doping.     

Properties of a-Si:H films deposited by RF magnetron sputtering at 95 °C

In this work we have investigated the dependence of optical and electrical properties of RF sputtered undoped a-Si:H films and B or P doped a-Si:H films on hydrogen flow rate (F_H). Low deposition temperature of 95 °C was used, a process compatible with low-cost plastic substrates. FTIR spectroscopy and ESR measurements were used for the investigation of Si-H_x bonding configurations, and concentrations of hydrogen and dangling bonds. We found that there is a strong correlation between the total hydrogen concentration, the dangling bonds density and the optoelectronic properties of the films. The best photosensitivity value was found to be 1.4 × 10⁴ for the undoped films. The dark conductivity (σ_D) of the doped layers varied from 5.9 × 10⁻⁸ to 6.5 × 10⁻⁶ (Ω cm)⁻¹ for different ratios F_Ar/F_H. These variations are attributed to both the different B and P concentrations in the films (according to SIMS measurements) and the enhanced disorder of the films introduced by the large number of inactive impurities. The B doping efficiency is lower compared to the P one. A small photovoltaic effect is also observed in n-i-p solar cells fabricated on polyimide (PI) substrates having ITO as antireflective coating, with an efficiency of 1.54%.