Nanocrystalline CuO thin films: synthesis, microstructural and optoelectronic properties

Nanocrystalline copper oxide (CuO) thin films have been synthesized by a sol–gel method using cupric acetate Cu (CH₃COO) as a precursor. The as prepared powder was sintered at various temperatures in the range of (300–700?°C) and has been deposited onto a glass substrates using spin coating technique. The structural, compositional, morphological, electrical optical and gas sensing properties of CuO thin films have been studied by X-ray diffraction, Scanning Electron Microscopy (SEM), Four Probe Resistivity measurement and UV–visible spectrophotometer. The variation in annealing temperature affected the film morphology and optoelectronic properties. X-ray diffraction patterns of CuO films show that all the films are nanocrystallized in the monoclinic structure and present a random orientation. The crystallite size increases with increasing annealing temperature (40–45?nm).The room temperature dc electrical conductivity was increased from 10^?6 to 10^?5 (Ω?cm)^?1, after annealing due to the removal of H₂O vapor which may resist conduction between CuO grain. The thermopower measurement shows that CuO films were found of n-type, apparently suggesting the existence of oxygen vacancies in the structure. The electron carrier concentration (n) and mobility (μ) of CuO films annealed at 400–700?°C were estimated to be of the order of 4.6–7.2?×?10¹⁹?cm^?3 and 3.7–5.4?×?10^?5?cm²?V^?1?s^?1?respectively. It is observed that CuO thin film annealing at 700?°C after deposition provide a smooth and flat texture suited for optoelectronic applications. The optical band gap energy decreases (1.64–1.46?eV) with increasing annealing temperature. It was observed that the crystallite size increases with increasing annealing temperature. These modifications influence the morphology, electrical and optical properties.     

Optimization of PbS thin films using different metal ion sources for photovoltaic applications

An extensive study on the influence of metal ion sources on the properties of chemical bath deposited lead sulphide thin films is reported in this paper. Four different lead sources namely lead nitrate, lead acetate, lead chloride and lead sulphate in alkaline medium have been used for the synthesis along with thiourea as sulphur source. The influence of lead sources on structural, surface morphological optical and electrical properties is investigated for photovoltaic applications. According to X-ray diffraction studies, all the films are poly crystalline with face centered cubic structure. The average crystallite sizes are found to be in the range 13–24 nm. The SEM photographs showed diverse morphology. The optical band gap is found to be very sensitive to the metal sources used. The direct band gap energy values obtained are in the range of 1.862–2.609 eV. The electrical conductivity varies in the range 33.6 ?7.62 × 10^?9 (Ω cm)^?1. Photosensitivity is closely linked to surface morphology. In this work, we established that the cationic precursor sources have significant role in physical properties of as-deposited PbS thin films. Samples prepared using nitrate as metal source are found to be most suitable to be used as solar control coating and the samples with lead acetate can be used as absorber layers for solar cell fabrication.     

Structural,optical and electrical properties of PbS and PbSe quantum dot thin films

PbS and PbSe were prepared by hot injection method. The powders were used for preparing the corresponding films by using thermal evaporation technique. The structural, optical and electrical properties of PbS and PbSe thin films were investigated. The structural properties of PbS and PbSe were investigated by X-ray diffraction, transmission electron microscopy and energy dispersive X-ray techniques (EDX). PbS and PbSe films were found to have cubic rock salt structure. The particles size ranged from 1.32 to 2.26 nm for PbS and 1.28–2.48 nm for PbSe. EDX results showed that PbS films have rich sulphur content, while PbSe films have rich lead content. The optical constants (absorption coefficient and the refractive index) of the films were determined in the wavelength range 200–2500 nm. The optical energy band gap of PbS and PbSe films was determined as 3.25 and 2.20 eV, respectively. The refractive index, the optical dielectric constant and the ratio of charge carriers concentration to its effective mass were determined. The electrical resistivity, charge carriers concentration and carriers mobility of PbS at room temperature were determined as 0.55 Ω cm, 1.7 × 10¹⁶ cm^?3 and 656 cm² V^?1 s^?1, respectively, and for PbSe films they were determined as 0.4 Ω cm, 9 × 10¹⁵ cm^?3 and 1735 cm² V^?1 s^?1, respectively. These electrical parameters were investigated as a function of temperature.     

Surface morphology and optoelectronic studies of sol–gel derived nanostructured CdO thin films: heat treatment effect

Morphological dependence of the optoelectronic properties of sol–gel derived CdO thin films annealed at different temperatures in air has been studied. After preparing, the films were investigated by studying their structural, morphological, d.c. electrical and optical properties. X-ray diffraction results suggest that the samples are polycrystalline and the crystallinity of them enhanced with annealing temperature. The average grain size is in the range of 12–34?nm. The root mean square roughness of the films was increased from 3.09 to 6.43?nm with annealing temperature. It was observed that the electro-optical characteristics of the films were strongly affected by surface roughness. As morphology and structure changed due to heat treatment, the carrier concentration was varied from 1.13?×?10¹⁹ to 3.10?×?10^19?cm^?3 with annealing temperature and the mobility increased from less than 7 to 44.8?cm² V^?1 s^?1. It was found that the transmittance and the band gap decreased as annealing temperature increased. The optical constants of the film were studied and the dispersion of the refractive index was discussed in terms of the Wemple–DiDomenico single oscillator model. The real and imaginary parts of the dielectric constant of the films were also determined. The volume energy loss increases more than the surface energy loss at their particular peaks.     

Effect of different solvents on the key structural,optical and electronic properties of sol–gel dip coated AZO nanostructured thin films for optoelectronic applications

Transparent conducting aluminum (i.e. 2 at.%) doped zinc oxide (AZO) thin films were prepared on glass substrates by sol–gel dip coating technique using different solvents. This inexpensive dip coating method involves dipping of substrate consecutively in zinc solution and tube furnace for required cycles. Prepared films were investigated by XRD, SEM, PL, Raman spectroscopy optical and electrical studies. From the XRD studies, it confirmed the incorporation of aluminum in ZnO lattice. The prepared samples are polycrystalline nature, and these films reveal hexagonal wurtzite arrangement with (002) direction. The structural parameters such as crystallite size, dislocation density, micro strain, texture coefficient and lattice constant were investigated. SEM study showed well defined smooth and uniformed ganglia shaped grains are regularly distributed on to the entire glass substrate without any pinholes and cracks, and the average grain size is 75 nm. From the optical studies, the observed highest transmittance is 93% in the visible range and the band gap (E_g) is 3.26 eV. Room temperature PL spectra exhibited strong UV emission peak located at 386 nm for all the films. The electrical properties of the AZO thin films were studied by Hall-Effect measurements and found as n-type conductivity with high carrier concentrations (n), 2.76?×?10¹⁹ cm^??3 and low resistivity (ρ), 7.56?×?10^??3 Ω cm for the film deposed using methanol as solvent.     

Nitrogen ion implantation effects on the structural,optical and electrical properties of CdSe thin film

In the present study, thin films of cadmium selenide (CdSe) are deposited on ITO substrate by electrodeposition method using aqueous solution of 3CdSO₄·8H₂O and SeO₂. These films are implanted with 40 keV N⁺ ions with different fluencies i.e. 1?×?10¹⁵, 5?×?10¹⁵, 1?×?10¹⁶ and 5?×?10¹⁶ ions/cm² using a beam current of 0.9 µA. The structural, morphological, optical and electrical properties of pristine and nitrogen ion-implanted CdSe thin films are analyzed using XRD, SEM, AFM, UV-PL Spectrophotometer and I–V four probes setup. XRD analysis revealed the effects of nitrogen ions on the structural parameters such as grain size, FWHM, micro strain and dislocation density etc. Crystallanity of the material increased with increase in implantation dose. SEM and AFM analysis show decrease in the surface roughness with implantation. From the optical studies, band gap value decreased from 2.50 to 2.29 eV with increase in N⁺ implantation doses. Noticeable changes in the electrical properties are also reported. The effect of N⁺ ion implantation on the properties of CdSe thin films are discussed on the basis of lattice disorder.     

Evaluation of the physical,optical, and electrical properties of SnO<Subscript>2</Subscript>: F thin films prepared by nebulized spray pyrolysis for optoelectronics

Fluorine-doped tin oxide (SnO₂:F, FTO) thin films were prepared by the nebulized spray pyrolysis technique on glass substrates using tin(IV) chloride pentahydrate (SnCl₂·5H₂O) and ammonium fluoride (NH₄F) as source materials. Different volumes of solvent were used to prepare the spray solution, and their effects on structural, optical, morphological, and electrical properties were investigated. X-ray diffraction patterns revealed the polycrystalline tetragonal structure of FTO films. FESEM images demonstrated well-aligned trigonal-shaped nano-grains. Optical band gap values were estimated to be in the range of 3.71–3.66 eV by Tauc’s plot. The effects of solvent volume on the resistivity, conductivity, carrier concentration, mobility, and figure of merit of FTO films were examined. The lowest electrical resistivity and sheet resistance values were 1.90?×?10^?4 Ω cm and 4.96 Ω/cm, respectively.     

A study of the structural,optical, and electrical properties of SnS<Subscript>2</Subscript>:Cu optical semiconductor thin films deposited by the spray pyrolysis technique

Cu-doped tin-sulfide thin films were deposited onto glass substrates at T = 400 °C through spray pyrolysis. The effects of Cu doping on the structural, optical, and electrical properties of the thin films were investigated. The precursor solution was prepared by dissolving tin chloride (SnCl₄·5H₂O) and thiourea (CS(NH₃)₂) in deionized water and then adding copper chloride (Cl₂Cu₂H₂O). SnS₂:Cu thin films were prepared with \(\frac{{\left[ {Cu} \right]}}{{\left[ {Sn} \right]}}\% = 0, 1, 2, 3, 4 \,{\text{at}}.\%\). X-ray diffraction analysis showed that the thin films had a preferred (001) orientation of the SnS₂ phase and that the intensity of the (001) peak decreased with increased doping concentration from 1–4 at.%. Scanning electron microscopy studies indicated that the thin films had spherical grains. Characterization results of thin films showed that single-crystal grains, average grain size, optical band gap, carrier concentration, Hall mobility, and electrical resistance varied within 5–14 nm, 46–104 nm, 2.81–2.99 eV, 2.42 × 10¹⁶–26.73 × 10¹⁶ cm^?3, 2.41 × 10^?3–20.04 × 10^?3 cm²/v.s, and 9.05–12.89 Ω cm, respectively. Hall effect studies further revealed that the films exhibited n-type conductivity.     

Effect of annealing on microstructural and optoelectronic properties of nanocrystalline TiO2 thin films

In this study, semi-transparent nanostructured titanium oxide (TiO₂) thin films have been prepared by sol–gel technique. The titanium isopropoxide was used as a source of TiO₂ and methanol as a solvent and heat treated at 60°C. The as prepared powder was sintered at various temperatures in the range of 400–700°C and has been deposited onto a glass substrate using spin coating technique. The effect of annealing temperature on structural, morphological, electrical and optical properties was studied by using X-ray diffraction (XRD), high resolution transmittance electron microscopy (HRTEM), atomic force microscopy (AFM), scanning electron microscopy (SEM), dc resistivity measurement and optical absorption studies. The XRD measurements confirmed that the films grown by this technique have good crystalline nature with tetragonal-mixed anatase and rutile phases and a homogeneous surface. The HRTEM image of TiO₂ thin film (annealed at 700°C) showed grains of about 50–60?nm in size with aggregation of 10–15?nm crystallites. Electron diffraction pattern shows that the TiO₂ films exhibited a tetragonal structure. SEM images showed that the nanoparticles are fine and varies with annealing temperature. The optical band gap energy decreases with increasing annealing temperature. This means that the optical quality of TiO₂ films is improved by annealing. The dc electrical conductivity lies in the range of 10^?6 to 10^?5?Ω?cm^?1 and it decreases by the order of 10 with increase in annealing temperature from 400°C to 700°C. It is observed that the sample Ti700°C has a smooth and flat texture suitable for different optoelectronic applications.     

Structural,optical, and electrical properties of ZnTe:Cu thin films by PLD

In this work, ZnTe and ZnTe:Cu films were obtained by pulsed laser deposition using the co-deposition method. ZnTe and Cu₂Te were used as targets and the shots ratio were varied to obtain 0.61, 1.47, 1.72, and 3.46% Cu concentration. Doping of ZnTe films with Cu was performed with the purpose of increasing the p-type carrier concentration and establishing the effect of concentration of Cu on structural, optical, and electrical properties of ZnTe thin films to consider their potential application in electronic devices. According to X-ray diffraction, X-ray photoelectron spectroscopy, UV–visible spectroscopy, and Hall effect results, ZnTe and ZnTe:Cu films correspond to polycrystalline zinc–blende phase with preferential orientation in (111) plane. Optical characterization results indicate that as-deposited films (band gap?=?2.16 eV) exhibit a band gap decrease as function of the increase of Cu concentration (2.09–1.64 eV), while, annealed films exhibit a decrease from 1.75 to 1.46 eV, as the Cu concentration increases. Lastly, Hall effect results show that ZnTe films correspond to a p-type semiconductor with a carrier concentration of 3?×?10¹³ cm^?3 and a resistivity of 1.64?×?10⁵ Ω?cm. ZnTe:Cu films remain like a p-type material and present an increasing carrier concentration (from 3.8?×?10¹⁵ to 1.26?×?10¹⁹ cm^?3) as function of Cu concentration and a decreasing resistivity (from 7.01?×?103 to 2.6?×?10^?1 Ω cm). ZnTe and ZnTe:Cu thin films, with the aforementioned characteristics, can find potential application in electronic devices, such as, solar cells and photodetectors.     

A novel route for synthesis, characterization of molybdenum diselenide thin films and their photovoltaic applications

Molybdenum diselenide thin films were deposited by chemical method. The precursor solution contains ammonium molybdate, sodium selenosulphite with hydrazine hydrate as a reducing agent. Various preparative conditions were optimized for the formation of thin films. The X-ray diffraction pattern shows that thin films have a layer-hexagonal phase. EDAX analysis shows that the films are nearly stoichiometric of Mo: Se: 1:2. Optical properties show a direct band gap nature with band gap energy 1.43 eV and having specific electrical conductivity in the order of 10^?5 (Ωcm)^?1. The configuration of fabricated cell is n-MoSe₂ | NaI (2 M) + I₂ (1 M) | C (graphite). The photoelectrochemical characterization of the films is carried out by studying current–voltage characterization, capacitance–voltage and power output characteristics. The fill factor and efficiency of the cell were found to be 34.22 and 1.01 % respectively.     

Preparation of Sb:SnO2 thin films and its effect on opto-electrical properties

The present study focuses on pure and antimony (Sb)-doped tin oxide thin film and its influence on their structural, optical, and electrical properties. Both undoped and Sb-doped SnO₂ thin films have been grown by using simple, inexpensive pyrolysis spray technique. The deposition temperature was optimized to 450 °C. X-ray diffractions pattern have revealed that the films are polycrystalline and have tetragonal rutile-type crystal structure. Undoped SnO₂ films grow along (110) preferred orientation, while the Sb-doped SnO₂ films grow along (200) direction. The size of Sb-doped tin oxide crystals changes from 26.3 to 58.0 nm when dopant concentration is changed from 5 to 25 wt%. The transmission spectra revealed that all the samples are transparent in the visible region, and the optical bandgap varies between 3.92 and 3.98 eV. SEM analysis shows that the surface morphology and grain size are affected by the doping rate. All the films exhibit a high transmittance in the visible region and show a sharp fundamental absorption edge at about 0.38–0.40 nm. The maximum electrical conductivity of 362.5 S/cm was obtained for the film doped with 5 wt% Sb. However, the carrier concentration is increased from 0.708?×?10¹⁸ to 4.058?×?10²⁰ cm³. The electrical study reveals that the films have n-type electrical conductivity and depend on Sb concentration. We observed a decrease in sheet resistance and resistivity with the increase in Sb dopant concentration. For the dopant concentration of 5 wt% of Sb in SnO₂, the Rs and ρ were found minimum with the values of 88.55 (Ω cm^?2) and 2.75 (Ω cm), respectively. We observed an increase in carrier concentration and a decrease in mobility with the addition of Sb up to 25 wt%. The highest figure of merit values 2.5?×?10^–3 Ω^?1 is obtained for the 5wt% Sb, which may be considered potential materials for solar cells' transparent windows.

     

Nanocrystalline copper selenide thin films by chemical spray pyrolysis

Thin films of copper selenide were deposited onto amorphous glass substrates at various substrate temperatures by computerized spray pyrolysis technique. The as deposited copper selenide thin films were used to study a wide range of characteristics including structural, surface morphological, optical and electrical, Hall Effect and thermo-electrical properties. X-ray diffraction study reveals that the films are polycrystalline in nature with hexagonal (mineral klockmannite) crystal structure irrespective of the substrate temperature. The crystalline size is found to be in the range of 23–28 nm. The SEM study reveals that the grains are uniform with uneven spherically shaped and spread over the entire surface of the substrates. EDAX analysis confirmed the nearly stoichiometric deposition of the film at 350 °C. The direct band gap values are found to be in the range 2.29–2.36 eV depending on the substrate temperature. The Hall Effect study reveals that the films exhibit p-type conductivity. The values of carrier concentration and mobility for the film are found to be 5.02 × 10¹⁷ cm^?3 and 5.19 × 10^?3 cm² V^?1 s^?1; respectively for film deposited at 350 °C.     

Effect of very low to high Sb-doping on the structural,electrical, photo-conductive and thermoelectric properties of fluorine-doped SnO<Subscript>2</Subscript> (FTO) thin films prepared by spray pyrolysis technique

Transparent conducting fluorine and Sb-doped [SnO₂: (F, Sb)] thin films have been deposited onto preheated glass substrates using the spray pyrolysis technique by the various dopant quantity of spray solution. The effect of antimony impurities on the structural, morphological, electrical, Thermo-electrical, optical and photoconductive properties of films has been investigated. The [F/Sn] atomic concentration ratio (x) in the spray solution is kept at value of 0.7 and the [Sb/Sn] atomic ratio (y) varied at values of 0, 0.0005, 0.001, 0.002, 0.01, 0.03, 0.05, 0.07 and 0.10. It is found that the films are polycrystalline in nature with a tetragonal crystal structure corresponding to SnO₂ phase having orientation along the (110) and (200) planes. SEM images indicated that nanostructure of the films has a particle type growth. The average grain size increases with increasing spraying quantity of Sb-dopant. The compositional analysis of SnO₂: (F, Sb) thin films were studied using EDAX. SEM and AFM study reveals the surface of SnO₂: (F, Sb) to be made of nanocrystalline particles. The Hall Effect measurements have shown n-type conductivity in all deposited films. The lowest sheet resistance and highest the carrier concentration about 7.7 Ω/□ and 6.6 × 10²², respectively, were obtained for the film deposited with y = [Sb/Sn] = 0.001 and x = [F/Sn] = 0.7. The maximum of the Seebeck coefficient equal to 12.8 μV K^?1 was obtained at 400 K for the film deposited with y = [Sb/Sn] = 0.10. The average transmittance of films varied over the range 10–80 % with change of Sb-concentration. The band gap values of samples were obtained in the range of 3.19–3.8 eV. From the photoconductive studies, the Sb-doped films exhibited sensitivity to incident light especially in y = 0.001. The electrical resistivity and carrier concentration vary in range 5.44 × 10^?4 to 1.02 × 10^?2Ω cm and 2.6 × 10²²–6.6 × 10²² cm^?3, respectively.     

Effect of acetic acid and water content in the spray solution on structural,morphological, optical and electrical properties of Al and In co-doped zinc oxide thin films

Aluminium and indium co-doped zinc oxide (AIZO) thin films were deposited using ultrasonic spray pyrolysis. Depositions were performed by varying the acetic acid and water content in the spraying solution which resulted in the formation of different nanostructures like hexagons, flowers, chisels, curved nanostructures, hexagonal pyramids, super grown hexagons, and inter-connected nanostructures. Further, the physical properties such as structural, optical, electrical, and surface texture parameters were examined. The structural studies showed that films were of crystalline nature, with different crystallite sizes and grown with a preferential orientation along (002) plane. The optical transmittance assessments proved that films were highly transparent (>?80%) in the visible region. The electrical sheet resistance was found to be in the range 29–1K Ω/□. Surface parameters like average roughness, root mean square roughness, and peak-valley height values helped to understand the homogeneity of the thin films. Finally, the suitability of AIZO films for transparent conductive oxide applications were tested by estimating the figure of merit (FOM). Among the different solution conditions, films fabricated using a starting solution containing 25 ml of acetic acid and 25 ml of water exhibited the lowest resistivity (2.47?±?0.03?×?10^?3 Ω-cm) along with the highest FOM (5.83?±?0.42?×?10^?3/Ω).     

Brush plated copper indium sulphide films and their properties

Copper indium sulphide films were deposited for the first time by the brush plating technique at different electrolyte temperatures in the range of 30–80 °C and at a constant deposition current density of 5.0 mA cm^?2. The Films exhibited single phase copper indium sulphide. The grain size increased with increase of electrolyte temperature. Optical band gap of the films varied in the range of 1.30–1.42 eV. Atomic force microscopy studies indicated that the grain size vary from 600 to 1,000 nm, with increase of substrate temperature. Solar cells fabricated with the films exhibited V_oc of 650 mV, J_sc of 19.5 mA cm^?2, ff of 0.73 and efficiency of 9.50 %.     

Band gap engineering in PbSe thin films from near-infrared to visible region by photochemical deposition method

Lead selenide (PbSe) thin films have been synthesized by the established photochemical deposition technique using lead nitrate and lead acetate as sources for the metal ions and sodium seleno sulphate as the selenium source along with triethanolamine, ammonia and hydrazine hydrate as complexing agents. A comprehensive study of the effect of substrate materials on physical properties of as deposited PbSe thin films is reported in this work. Two substrates were used in this investigation, namely soda lime glass slides and gold coin corning glass slides. The solution is irradiated with UV light and the photochemical reactions in the aqueous solution resulted in highly adherent metallic thin films. X-ray diffraction (XRD), scanning electron microscopy, optical and electrical measurement techniques were used for film characterization. The XRD analysis confirmed that all films were cubic, regardless of the cationic precursors and substrates used. The scanning electron microscope micrographs showed variations in morphology. The optical studies revealed that the films have good absorption in the visible region. The remarkable success of our effort was that we have been able to modify optical band gap of PbSe thin films over a wide spectral range by a cost effective route. The band gaps estimated from the transmission spectra were in the range 1.32–1.40 eV for films deposited on soda lime glass substrates and 1.46–1.55 eV for corning glass substrates. The room temperature conductivity of the PbSe films were in the range of 3.71 × 10^?7–513 × 10^?7 (Ω cm)^?1. The as deposited PbSe thin films with low transmittance in the visible region coupled with an appreciable reflectance in infrared region were found to satisfy the basic requirements for solar control coatings for window glazing applications in warm climates. Through this work we established that irrespective of metal salts, soda lime glass substrate was superior to corning glass substrate.     

Influence of Al doping on the structural,morphological and opto-electrical properties of spray deposited lead sulfide thin films

This paper reports the synthesis of Al-doped PbS (PbS:Al) thin films by spray pyrolysis technique on glass substrates. Al doping concentration is varied as 0, 2, 4, 6 and 8 at.% in undoped PbS. Undoped and doped films exhibit cubic crystal structure with a (2 0 0) preferential orientation. The 2θ value of the doped films shifts towards higher Bragg angles confirming a contraction in their unit cell volume. The crystallite size values determined using the Scherrer formula decreased from 27.88 to 25.79 nm with increase in Al doping concentration. EDX spectra confirmed the presence of Al in the doped films. Increased transparency and blue shift in the optical band gap is observed with Al doping. The resistivity range of all the films were found to be in the order of 10² Ω-cm. Increased transparency, widened band gap and decreased resistivity observed make PbS:Al films suitable for tandem solar cells which uses multilayered pn junctions.     

Facile chemical synthesis of nano-silver powders for printable electronics applications

In this article, a simple and reproducible technique for the synthesis of silver nanoparticles in organic phase without using external reducing agents is reported. The organic phase contains silver acetate as precursor, oleic acid and oleyl amine as capping molecules and diphenyl ether as solvent. Monodispersed silver nanoparticles with an average size of 5?nm could be easily synthesised at large scale and it was possible to isolate the particles suitable for electronics applications. The formation of silver nanoparticles has been characterised in terms of optical absorption, transmission electron microscopy images and small-angle X-ray scattering. Recovered silver nanoparticles reveal X-ray diffraction of a well grown-up fcc-Ag lattice. Chemical and thermal characterisations of silver nanopowders were carried out using X-ray photoelectron spectroscopy and thermogravimetric analysis, respectively. For the latter purpose, concentrated dispersions of silver nanoparticles were prepared and used for depositing uniform thin layers. Thin films were sintered at low temperature to obtain conductive films and the films were characterised using scanning electron microscope. Electrical conductivity of the conductive films was in the range 2–3?×?10⁴?S?cm^?1.     

Influence of RF power on structural,morphology, electrical,composition and optical properties of Al-doped ZnO films deposited by RF magnetron sputtering

In this study, influence of RF power on the structural, morphology, electrical, composition and optical properties of Al-doped ZnO (ZnO:Al) films deposited by RF magnetron sputtering have been investigated. Films were systematically and carefully investigated by using variety of characterization techniques such as low angle X-ray diffraction, UV–visible spectroscopy, Raman spectroscopy, Hall measurement, X-ray photoelectron spectroscopy, field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy etc. Low angle X-ray diffraction analysis showed that the films are polycrystalline with hexagonal wurtzite structure and which was further confirmed by Raman spectroscopy analysis. Its preferred orientation shifts from (102) to (002) with increase in RF power. The average grain size was found in the range of 15–21 nm over the entire range of RF power studied. The FE-SEM analysis showed that grain size and surface roughness of ZnO:Al films increase in with increase in RF power. The UV–visible spectroscopy analysis revealed that all films exhibit transmittance >85 % in the visible region. The optical band gap increases from 3.37 to 3.85 eV when RF power increased from 75 to 225 W. Hall measurements showed that the minimum resistivity has been achieved for the film deposited at 200 W. The improvement in the electrical properties may attribute to increase in the carrier concentration and Hall mobility. Based on the experimental results, the RF power of 200 W appears to be an optimum sputtering power for the growth of ZnO:Al films. At this optimum sputtering power ZnO:Al films having minimum resistivity (8.61 × 10^?4 Ω-cm), highly optically transparent (~87 %) were obtained at low substrate temperature (60 °C) at moderately high deposition rate (22.5 nm/min). These films can be suitable for the application in the flexible electronic devices such as TCO layer on LEDs, solar cells, TFT-LCDs and touch panels.