Nonlinear optical investigations on Al doping ratio in ZnO thin film under pulsed Nd:YAG laser irradiation

In the present study, it has been reported on the effect of Al doping on linear and nonlinear optical properties of ZnO thin films synthesized by spray pyrolysis method. The structural properties of ZnO thin films with different Al doping levels (0–4 wt%) were analyzed using X-ray diffraction (XRD). The results obtained from XRD analysis indicated that the grain size decreased as the Al doping value increased. The UV–Vis diffused refraction spectroscopy was used for calculation of band gap. The optical band gap of Al-doped ZnO (AZO) thin films is increased from 3.26 to 3.31 eV with increasing the Al content from 0 to 4 wt%. The measurements of nonlinear optical properties of AZO thin films have been performed using a nanosecond Nd:YAG pulse laser at 532 nm by the Z-scan technique. The undoped ZnO thin film exhibits reverse saturation absorption (RSA) whereas the AZO thin films exhibit saturation absorption (SA) that shows RSA to SA process with adding Al to ZnO structure under laser irradiation. On the other hand, all the films showed a self-defocusing phenomenon because the photons of laser stay on below the absorption edge of the ZnO and AZO films. The third-order nonlinear optical susceptibility, χ⁽³⁾, of AZO thin films, was varied from of the order of 10^?5–10^?4 esu. The results suggest that AZO thin films may be promising candidates for nonlinear optical applications.     

Single and multiple doping effects of silicon–boron and fluorine on ZnO thin films deposited with sol–gel spin coating technique

Undoped, Si and B single doped, Si–B co-doped and Si–B–F triple doped ZnO thin films were grown by sol–gel spin coating method. Effects of these doping elements on microstructural, morphological and optical properties were investigated. X-ray diffraction studies showed that all films had hexagonal wurtzite structure. Although Si doping increased crystallinity of ZnO, single boron doping, Si–B co-doping and Si–B–F triple doping gave rise to a decreasing in crystallinity. Scanning electron microscope micrographs indicated that the grain size and morphological characters of ZnO depended on doping element type and their concentrations. The micrographs also demonstrated that Si doping deteriorated grain size and their distribution on film surface of ZnO structure. Although single B, doubly Si–B and triple Si–B–F doping at low contents improved grain distribution and film morphology, when their content increased, film morphology started to deteriorate. Optical band gap value of undoped film increased with Si doping irrespective of Si doping content. Although single B, doubly Si–B and triple Si–B–F doping at low contents caused an increase in optical band gap of undoped ZnO, more doping content brought about a decrease in optical band gap. From the optical parameters such as absorption coefficient, the Urbach energy values of the films were calculated by using ln α vs. photon energy graphs. In generally, Urbach energies of the films changed reversely with the band gap energies of the films.     

Dependence of structural, optical and electrical properties on substrate temperature for hexagonal MgxZn1−xO films

Single hexagonal-phase Mg_xZn_1?xO films were deposited on glass substrates by pulsed laser deposition from a ZnO target mixed with MgO. The effect of substrate temperature on the structural, electrical and optical properties was investigated by X-ray diffraction and the transmittance measurements. It was observed that Mg incorporation lead to a clear shift of the (002) peak position to lower angle with reference to pure ZnO films due to the residual stress change with deposition temperature. It was also found that Mg doping increased the resistivity by 2 orders of magnitude and the maximum resistivity was 0.072 Ω·cm at 550 °C with the carrier concentration of 1.1 × 10¹⁹ cm^?3. The visible transmittance of above 80 % was obtain in the alloy films, which optical band gap was observed to increase with the substrate temperature, attaining 3.85 eV at 600 °C. The possible mechanism was discussed.     

Optical and photoconductivity properties of ZnO thin films grown by pulsed filtered cathodic vacuum arc deposition

High quality transparent conductive ZnO thin films with various thicknesses were prepared by pulsed filtered cathodic vacuum arc deposition (PFCVAD) system on glass substrates at room temperature.The high quality of the ZnO thin films was verified by X-ray diffraction and optical measurements. XRD analysis revealed that all films had a strong ZnO (200) peak, indicating c-axis orientation. The ZnO thin films are very transparent (92%) in the near vis regions. For the ZnO thin films deposited at a pressure of 0.086 Pa (6.5 × 10⁻⁴ Torr) optical energy band gap decreased from 3.21 eV to 3.19 eV with increasing the thickness. Urbach tail energy also decreased as the film thickness increased.Spectral dependence of the photoconductivity was obtained from measurements of the samples deposited at various thicknesses. Photoconductivities were observed at energies lower than energy gap which indicates the existence of energy states in the forbidden gap. Photoconductivities of ZnO thin films increase with energy of the light and reach its maximum value at around 2.32 eV. Above this value surface recombination becomes dominant process and reduces the photocurrent. The photoconductivity increases with decreasing the film thickness.     

Pulsed laser deposited ZnO:In as transparent conducting oxide

Zinc oxide (ZnO) and indium doped ZnO (IZO) thin films with different indium compositions were grown by pulsed laser deposition technique on corning glass substrate. The effect of indium concentration on the structural, morphological, optical and electrical properties of the film was studied. The films were oriented along c-direction with wurtzite structure and highly transparent with an average transmittance of more than 80% in the visible wavelength region. The energy band gap was found to decrease with increasing indium concentration. High transparency makes the films useful as optical windows while the high band gap values support the idea that the film could be a good candidate for optoelectronic devices. The value of resistivity observed to decrease initially with doping concentration and subsequently increases. IZO with 1% of indium showed the lowest resistivity of 2.41 × 10⁻² Ω cm and large transmittance in the visible wavelength region. Especially 1% IZO thin film was observed to be a suitable transparent conducting oxide material to potentially replace indium tin oxide.     

Transparent conductive ZnO:B films deposited by magnetron sputtering

This paper focuses on the preparation of boron doped ZnO (ZnO:B) films prepared by nonreactive mid-frequency magnetron sputtering from ceramic target with 2 wt.% doping source. Adjusting power density, ZnO:B film with low resistivity (1.54 × 10^− 3 Ω cm) and high transparency (average transparency from 400 to 1100 nm over 85%) was obtained. Different deposition conditions were introduced as substrate fixed in the target center and hydrogen mediation. Hall mobility increased from 11 to above 26 cm²/V·s, while carrier concentration maintained almost the same, leading to low resistivity of 6.45 × 10^− 4 Ω cm. Transmission spectra of ZnO:B films grown at various growth conditions were determined using a UV-visible-NIR spectrophotometer. An obvious blue-shift of absorption edge was obtained while transmittances between 600 nm and 1100 nm remained almost the same. Optical band baps extracted from transmission spectra showed irregular enhancement due to the Burstein-Moss effect and band gap renormalization. Photoluminescence spectra also showed a gradual increase at UV emission peak due to free exciton transition near band gap. We contributed this enhancement in both optical band gap and UV photoluminescence emission to the lattice structure quality melioration.     

Structural and optoelectronic characterization of prepared and Sb doped ZnO nanoparticles

This paper briefly reports the structural and optoelectronics properties of prepared pure and Sb doped ZnO nanoparticles. Doping with suitable elements offers an efficient method to control and enhance the optical properties of ZnO nanoparticles, which is essential for various optoelectronics applications. Sb doped ZnO nanoparticles have significant concern due to their unique and unusual electrical and optical properties. In the present work, we report the synthesis of Sb doped ZnO successfully with average particle size range from 26 to 29 nm via direct precipitation method. The phase purity and crystallite size of synthesized ZnO and Sb doped nano-sized particles were characterized and examined via X-ray diffraction (XRD) and scanning electron microscopy (SEM). The elemental analyses of undoped and doped ZnO nanoparticles were examined by using energy-dispersive X-ray spectroscopy (EDAX).We investigated and measured the optoelectronics properties of synthesized ZnO and Sb doped ZnO nanoparticles by employing photoluminescence and UV–Visible spectroscopy. The influence of Sb doping on photoluminescence (PL) spectra of ZnO nanoparticles, which consists of UV emission and broad visible emission band, is found to be strongly dependent upon the Sb concentration for all the Sb doped ZnO nanoparticles samples under investigation. The UV–Visible absorption study shows an increase in band gap energy as Sb is incorporated on the ZnO nanoparticles.     

Investigation of the substrate effect for Zr doped ZnO thin film deposition by thermionic vacuum arc technique

ZnO is a fundamental wide band gap semiconductor. Especially, doped elements change the optical properties of the ZnO thin film, drastically. Doped ZnO semiconductor is a promising materials for the transparent conductive oxide layer. Especially, Zr doped ZnO is a potential material for the high performance TCO. In this paper, ZnO semiconductors were doped with Zr element and microstructural, surface and optical properties of the Zr doped ZnO thin films were investigated. Zr doped ZnO thin films were deposited thermionic vacuum arc (TVA) technique. TVA is a rapid and high vacuum deposition method. A glass, polyethylene terephthalate and Si wafer (111) were used as a substrate material. Zr doped ZnO thin films deposited by TVA technique and their substrate effect investigated. As a results, deposited thin films has a high transparency. The crystal orientation of the films are in polycrystal formation. Especially, substrate crystal orientation strongly change the crystal formation of the films. Substrate crystal structure can change the optical band gap, microstructural properties and deposited layer formation. According to the atomic force microscopy and field emission scanning electron microscopy measurements, all deposited layer shows homogeneous, compact and low roughness. The band values of the deposited thin film were approximately found as to be 3.1–3.4 eV. According to the results, Zr elements created more optical defect and shifted to the band gap value towards to blue region.     

Low-temperature synthesis of ZnO nanoparticles for inverted polymer solar cell application

Zinc oxide (ZnO) nanoparticles were synthesized by a simple wet chemical method at low temperature. Morphologies, crystalline structure, and optical transmission of ZnO nanoparticles were investigated. The results showed that the average diameter of as-synthesized ZnO nanoparticles was about 4.9 nm, the nanoparticles were wurtzite-structured (hexagonal) ZnO and had optical band gap of 3.28 eV. Very high optical transmission (>80 %) in visible light region of ZnO nanoparticulate thin films was achieved. Furthermore, an inverted polymer solar cell consisted of ZnO nanoparticles and polymer were fabricated. The device exhibited an open circuit voltage (V_oc) of 0.50 V, a short circuit current density (J_sc) of 1.76 mA/cm², a fill-factor of 38 %, and a power conversion efficiency of 0.42 %.     

Characterization of mesoporous ZnO:SiO2 films obtained by the sol-gel method

ZnO:SiO₂ films are intensively investigated for optical and electronic applications. Additionally, porous ZnO:SiO₂ films are of great interest as catalyst and gas-sensing materials. The sol-gel method is an efficient and low-cost process for the deposition of meso- and microporous silica-based films. The present paper studies the effect of the withdrawal speed on the microstructure and optical properties of mesoporous ZnO:SiO₂ films obtained by the sol-gel method. The morphology of the films was investigated by atomic force microscopy and the overall structure was studied by X-ray diffraction. The structure and size of the zinc oxide nanoparticles embedded in the silica matrix were investigated in more detail by transmission electron microscopy. These techniques showed ZnO:SiO₂ films with crack-free mesoporous morphology and highly efficient embedding of ZnO nanoparticles with (100) preferred orientation. Furthermore, the optical transmittance (in the visible and near infrared regions) and the optical band gap value were observed to vary with withdrawal speed. It is shown that ZnO:SiO₂ nanocomposites films which possess ZnO particles exhibiting a (100) orientation, with possible special applications in non-linear optics, could be prepared by the low-temperature crystallization sol-gel method.     

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.     

Structural and optical characterization of Al-doped ZnO films prepared by thermal oxidation of evaporated Zn/Al multilayered films

Aluminum-doped zinc oxide (ZnO:Al) thin films (t = 68–138 nm) were prepared by thermal oxidation in air flow, at 720 K, of the multilayered metallic Zn/Al thin stacks deposited in vacuum onto glass substrates by physical vapor deposition. The effect of Al content (3.7–8.2 at.%) on the structural (crystallinity, texture, stress, surface morphology) and optical (transmittance, absorbance, energy band gap) characteristics of doped ZnO thin films was investigated. The X-ray diffraction spectra revealed that the Al-doped ZnO films have a hexagonal (wurtzite) structure with preferential orientation with c-axis perpendicular to the substrate surface. A tensile residual stress increasing with Al content was observed. The films showed a high transmittance (about 90%) in the visible and NIR regions. The optical band gap value was found to decrease with Al content from 3.22 eV to 3.18 eV. The results are discussed in correlation with structural characteristics and Al content in the films.     

Effects of Al content on the properties of ZnO:Al films prepared by Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and ZnO co-sputtering

Aluminum doped zinc oxide (AZO) films were deposited on quartz substrates by radio-frequency magnetron co-sputtering method with ZnO and Al₂O₃ ceramic targets. The structural, optical and electrical properties of these films as a function of the Al content were investigated. XRD results reveal that the AZO films are wurtzite structure with (002) preferred orientation. The average transmittance of all the films is higher than 80% in a wide wavelength range from 400 to 1,500 nm. The band gap energy, calculated from their optical absorption spectra, is in the range of 3.50–3.66 eV depending on the Al content. Doping of Al³⁺ in the ZnO makes the film surface roughness decrease. The dopant Al³⁺ acts as electron donor by which the electrical conductivity and carrier concentration of the films are obviously increased until the Al³⁺ reaches its saturation content of about 4.50 at.%.     

Influence of Al concentration on structural and optical properties of Al-doped ZnO thin films

Undoped ZnO and Al-doped zinc oxide (ZnO:Al) thin films with different Al concentrations were prepared onto Si (100) substrate by pulsed filtered cathodic vacuum arc deposition system at room temperature. The influence of doping on the structural and optical properties of thin films was investigated. The preferential (002) orientation was weakened by high aluminum doping in films. Raman measurement was performed for the doping effects in the ZnO. Atomic force microscopy images revealed that the surface of undoped ZnO film grown at RT was smoother than that of the Al-doped ZnO (ZnO:Al) films. The reflectance of all films was studied as a function of wavelength using UV–Vis–NIR spectrophotometer. Average total reflectance values of about 35 % in the wavelength range of 400–800 nm were obtained. Optical band gap of the films was determined using the reflectance spectra by means of Kubelka–Munk formula. From optical properties, the band gap energy was estimated for all films.     

Optical and structural characteristics of ZnO thin films grown by rf magnetron sputtering

Nanostructured ZnO thin films on Pyrex glass substrates were deposited by rf magnetron sputtering at different substrate temperatures. Structural features and surface morphology were studied by X-ray diffraction and atomic force microscopy analyses. Films were found to be transparent in the visible range above 400 nm, having transparency above 90%. Sharp ultraviolet absorption edges around 370 nm were used to extract the optical band gap for samples of different particle sizes. Optical band gap energy for the films varied from 3.24 to 3.32 eV and the electronic transition was of the direct in nature. A correlation of the band gap of nanocrystalline ZnO films with particle size and strain was discussed. Photoluminescence emission in UV range, which is due to near band edge emission is more intense in comparison with the green band emission (due to defect state) was observed in all samples, indicating a good optical quality of the deposited films.     

Effect of Ga Doping Concentration on Electrical and Optical Properties of Nano-ZnO:Ga Transparent Conductive Films

Transparent conductive nano ZnO thin films with different Ga doping concentrations (1, 3, 5, 7 at.%) were prepared on glass substrate by RF magnetron sputtering. The influence of Ga doping concentration on the structural, electrical and optical properties of ZnO:Ga films was investigated by XRD, SEM, Hall measurement and optical-transmission spectroscopy. It shows that the nano ZnO:Ga films are dense and flat, and have polycrystalline structure with preferential (002) and weak (101) orientation. The grain sizes, carrier concentration and Hall mobility changes non-linearly with the increase of Ga-content. The lowest resistivity of 1.44×10⁻³ Ωcm appears at 3 at.% Ga doping concentration. The average transmittance of the films is about 80∼90% in the visible range. The optical band gap obtained for these films is larger than for pure ZnO (∼3.37 eV).     

Effects of the annealing treatment on electrical and optical properties of ZnO transparent conduction films by ultrasonic spraying pyrolysis

Effects of the annealing treatment on properties of ZnO thin films prepared on silica glass substrates by the ultrasonic spraying pyrolysis process were studied. Zinc acetate dihydrate and methanol were used as a starting material and a solvent, respectively. For ZnO thin films untreated with annealing, the preferred grain growth along the (0 0 2) plane was observed. The electrical resistivity and the direct band gap values of these films decreased with increasing the deposit temperature. By applying the annealing treatment in a reducing atmosphere, while the degree of the preferred (0 0 2) orientation of films decreased, the electrical conductivity of films was improved. When compared with the resistivity values of films without the annealing treatment, the values of films annealed in the reducing atmosphere were decreased by about two orders of magnitude. The lowest resistivity value was 1.62×10⁻¹ Ω cm, which was obtained in the film annealed at 500 °C in nitrogen with 5% hydrogen. The optical transmittances of the films were higher than 80% regardless of the application of the annealing treatment in a reducing atmosphere. The direct band gap values of films annealed in a reducing atmosphere were approximately 3.27 eV.     

Effect of deposition time on sputtered ZnO thin films and their gas sensing application

Nowadays, advanced industrialization and population growth have led to increasing the environmental related issues. This paper reports the effect of deposition time on ZnO films deposited on to the glass substrate by using rf magnetron sputtering technique and their further use for gas sensing applications. Herein, deposition time is considered to be changed from 300 s, 800 s (S1, S2). The thickness of deposited films lies in the range of 130–180 nm. The synthesized films were characterized by various techniques in terms of structural, morphological, optical and gas sensing properties. The typical crystal size of ZnO films was found to be in the range of 15–27 nm. FESEM analysis revealed the growth of nanospheres was lies in the range of 80–120 nm. Fourier transform infrared spectroscopy confirmed the ZnO bonding located at a wavelength of 430 cm^?1. The average optical transmittance of the film was about 90–95% in the visible range. The optical band gap of ZnO films was decreased from 3.31 to 3.29 eV. The detailed characterization study showed 800 s is an optimum deposition time for good optoelectronic properties. For gas sensing application, highest sensitivity was obtained at operating temperature of 205 °C. Prepared films have a quick response and fast recovery time in the range of 128 s and 163 s respectively. These response and recovery time characteristics were explained by valence ion mechanism.     

Effect of post-annealing on the optoelectronic properties of ZnO:Ga films prepared by pulsed direct current magnetron sputtering

In this study, highly conductive films of ZnO:Ga (GZO) were deposited by pulsed direct current magnetron sputtering to explore the effect of post-annealing on the structural, electrical and optical properties of the films. XRD patterns showed that after annealing, the intensity of c-axis preferentially oriented GZO (002) peak was apparently improved. GZO film annealing at 300 °C for 0.5 h exhibits lowest resistivity of 1.36 × 10^− 4 Ω cm. In addition, the film shows good optical transmittance of 88% with optical band gap, 3.82 eV. Carrier concentration and optical band gap both decreases with the annealing temperature. Besides, the near-infrared transmittance at 1400 nm is below 5%, while the reflectivity at 2400 nm is as high as 70%.     

Enhancement in the electrical and antibacterial properties of sprayed ZnO films by simultaneous doping of Mg and F

Undoped and Doubly (Magnesium + Fluorine) doped zinc oxide (ZnO:Mg:F) thin films with different Mg doping levels (4, 8, 12 and 16 at.%) and constant F doping level (20 at.%) were fabricated by employing a simplified spray pyrolysis technique. The antibacterial and certain physical properties of the films were studied as a function of Mg doping level. All the films exhibited hexagonal wurtzite structure with preferential orientation along the (002) plane. A lesser electrical resistivity was achieved in the present study than earlier reports of ZnO:Mg films thanks to the simultaneous doping of F with Mg in ZnO films. From the optical studies, it was observed that, all the films showed good transparency (≈85 %) with significant enhancement in the optical band gap with Mg doping level. The obtained PL spectra were well corroborated with the structural and optical studies. Further, it was also found that the antibacterial activity of doubly doped ZnO films was enhanced remarkably by the increasing incorporation of Mg concentration.