A noticeable effect of Pr doping on key optoelectrical properties of CdS thin films prepared using spray pyrolysis technique for high-performance photodetector applications

High-quality thin film-based photodetectors containing praseodymium doped cadmium sulfide (Pr:CdS) were fabricated through spray pyrolysis and studied for various opto-electrical applications. Field emission electron microscopy (FE-SEM) revealed that the prepared films were highly compacted with an extremely fine nanostructure without any pinhole or crack. X-ray diffraction and FT-Raman spectroscopy studies confirmed the single hexagonal phase of all the films. The crystallite size was found to lie between 19 and 32 nm. Optical spectroscopy revealed that the fabricated films have low absorbance and high transmittance (in range of 70–80%). The energy gap was found to lie in the range of 2.40–2.44 eV. The PL spectra contained an intense green emission band at ~531 ± 5 nm (2.33 eV), and its intensity was enhanced by increasing the Pr doping content in CdS. The dark and photo currents of CdS increased by approximately 950 and 42 times, respectively with the addition of 5.0 wt% Pr. The responsivity (R) and specific detectivity (D*) were remarkably enhanced to 2.71 AW^-1 and 6.9 × 10¹¹ Jones, respectively, for the 5.0 wt% Pr:CdS film. The external quantum efficiency (EQE) of 5 wt% Pr:CdS films was 43 times that of pure CdS films, and the on/off ratio was 3.95 × 10² for 5.0 wt% Pr:CdS film. Its high R, D*, and EQE values, and photo-switching behavior make Pr:CdS a good contender for high quality photodetector applications.     

Tuning PL emission energy and bandgap with Ni dopant of MgO thin films

In this study, for the first time, the effect of Nickel (Ni) additive on Magnesium oxide (MgO) thin films produced by using successive ionic layer adsorption and reaction technique (SILAR) was investigated. Absorption, photoluminescence (PL), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscope (SEM) measurements were executed to examine how the optical, structural and morphological properties of the samples were affected by the addition of Ni. In the absorption analysis, it was noted that the band gaps of the MgO samples decreased from 4 eV to 3.5 eV with the increase of Ni dopant concentrations. Also, the transmittance values of MgO nanostructures decreases with the increase of Ni contribution, and in the same way, the reflection measurements show that the reflection of MgO decreases with the increase of Ni doping. PL measurements revealed that the fabricated structures radiate around 410 nm and 730 nm. According to XRD measurements, besides the cubic structure of the samples, NiO formations were detected inside the MgO thin film samples due to the increase in Ni dopant. XPS measurements have proven the presence of Ni doping in MgO. SEM measurements showed that all samples exhibited nanowall structure. All these results demonstrate that Ni doping on MgO thin films can be achieved by using SILAR deposition technique.     

Effect of pH on the structural,optical and nanomechanical properties of CdS thin films grown by chemical bath deposition

CdS nano-structured thin films were prepared on glass substrates with chemical bath deposition technique for different pH values. The effects of pH and annealing on the structural, optical and nanomechanical properties of CdS films were studied using X-ray diffraction (XRD), scanning electron microscopy (SEM), UV–vis spectrophotometer and nanoindentation techniques. The results of XRD analysis and SEM investigation reveal that both different pH values of the bath solution and annealing affect the crystal structure and the surface morphology of the films markedly. Also, the results of the optical absorption show that the E_g values of the films decrease with increasing pH values. In this kind of study the mechanical properties of the CdS thin films determined using nanoindentation tests are being reported here for the first time. Nanoindentation experimental results show that nanohardness and elastic modulus values exhibit a peak load dependence. Our results reveal that, the annealing of CdS films at 300 °C results in slow and normal grain coarsening. The slow grain growth also influences the lattice strain (microstrain) which effects nanohardness and elastic modulus. The results also indicate that there is a direct dependence of the physical and optical properties of the CdS films on pH and annealing process.     

A comprehensive study on the effects of alternative sulphur precursor on the material properties of chemical bath deposited CdS thin films

Chemical bath deposition (CBD) method was used to deposit CdS thin films on soda-lime glass substrates by using n-methylthiourea (NTU) as an alternative sulphur source and were compared to typical thiourea (TU) precursor. The sulphur source concentration was varied from 0.01 M to 0.1 M and the impact on the microstructural, surface morphology, optical and electrical properties of the grown films were studied. Increasing n-methylthiourea concentration in the precursor yielded thinner films that are less than 100 nm thickness, surface morphology with average surface roughness of 6.4 nm, larger granular structure, wider band gap at 2.3 eV–2.6 eV range. Raman spectroscopy revealed Raman peak at 303 cm-1. In contrast, an increase in thiourea concentration resulted in thinner amorphous films, less distinct granular structure, narrower energy band gap from 2.3 eV to 2.4 eV and a resonance Raman peak at 302 cm-1. CdS thin film deposited from n-methylthiourea precursor at higher precursor concentration of 0.1 M showed better electrical properties such as lower resistivity and higher carrier mobility compared to the thin film deposited from typical thiourea precursor.     

Effect of nickel doping on structural,optical, electrical and ethanol sensing properties of spray deposited nanostructured ZnO thin films

Undoped and nickel (Ni)-doped ZnO thin films were spray deposited on glass substrates at 523 K using 0.1 M of zinc acetate dihydrate and 0.002–0.01 M of nickel acetate tetrahydrate precursor solutions and subsequently annealed at 723 K. The effect of Ni doping in the structural, morphological, optical and electrical properties of nanostructured ZnO thin film was investigated using X-ray Diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM), UV–vis Spectrophotometer and an Electrometer respectively. XRD patterns confirmed the polycrystalline nature of ZnO thin film with hexagonal wurtzite crystal structure and highly oriented along (002) plane. The crystallite size was found to be increased in the range of 15–31 nm as dopant concentration increased. The SEM image revealed the uniformly distributed compact spherical grains and denser in the case of doped ZnO thin films. All the films were highly transparent with average transmittance of 76%. The measured optical band gap was found to be varied from 3.21 to 3.09 eV. The influence of Ni doping in the room temperature ethanol sensing characteristics has also been reported.     

Novel method of fabrication of polyaniline–CdS nanocomposites: Structural,morphological and optoelectronic properties

Polyaniline–CdS nanocomposites have been synthesized by spin coating technique. The nanocrystalline CdS powder of particle size 40–50 nm was synthesized by sol–gel technique and the polyaniline was synthesized by chemical oxidative polymerization of aniline. The composite films were characterized by X-ray diffraction (XRD), field effect scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FTIR), UV–Vis spectroscopy and Four probe method. The results were compared with corresponding data on pure polyaniline films. The intensity of diffraction peaks for PANi–CdS composites is lower than that for CdS. The conductivity measurement shows that molecular chain constitution of polyaniline is the most important carrier in polyaniline–CdS nano composite. The optical studies showed that variation in band gap of polyaniline (3.40 eV) to 2.54 eV CdS which is attributed to the interaction of CdS nanoparticles with PANi molecular chains.     

Characterization of Pure and Al Doped ZnO Thin Films Prepared by Sol Gel Method for Solar Cell Applications

Pure and Al-doped Zin Oxide ZnO (AZO) thin films with different aluminum (Al) concentrations (0.5, 1, 2, and 3 at.%) were prepared on glass substrates by a dip-coating technique using different Zn and Al precursors. The structural, morphological, optical and electrical properties of these films were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), Atomic force electron microscopy, ultraviolet–visible spectrophotometry, photoluminescence (PL) spectroscopy and four-point probe technique. XRD results showed that the obtained AZO thin films were polycrystalline with a highly c-axis preferred (002) orientation, and the average crystallites size decreased from 29 to 25 nm with the increase in Al doping concentration. EDS microanalysis confirmed the presence of Zn, O and Al elements in the prepared films as expected. The optical study demonstrated that the ZnO thin film had a good transparency in the visible range with a maximum transmittance of 90% and the band gaps varied from 3.16 to 3.26 eV by Al doping. SEM micrographs showed a wrinkles-like morphology of the thin films that changed in density with the increase of Al concentrations. The PL emission spectra indicated that except the thin film doped with 1 at.%, other films exhibited high emission intensities under an excitation of 325 nm which allows to apply them as downconversion layers for solar cell applications.

     

Effect of gamma irradiation on structural,morphological and optical properties of thermal spray pyrolysis deposited CuO thin film

This study reports the influences of gamma irradiation (GI) in the range of 20–100 kGy on CuO thin films via thermal spray pyrolysis technique on the glass substrates. The results demonstrate significant influences of GI on the crystallographic, microstructural and optical characteristics of CuO thin films. The obtained XRD results showed that the crystallinity of the films deteriorates by gradually decreasing crystallite size (from 59.13 to 46 nm) as applied gamma doses increases. However, the basic monoclinic crystal structure remains same. The dislocation density and lattice strain increased with the rise of GI absorbed dose due to the creation of defects. The values of number of crystallites per unit surface area increased as dose increased indicating the abundance of crystallization of nano CuO thin films. A UV–Vis–NIR spectrophotometer was utilized to determine the optical properties and obtained results indicated that the optical energy band gap (OBG) energies reduced from 2.00 to 1.72 eV as the doses increased from 0 to 100 kGy. No distinctions of the monoclinic phase of virgin CuO thin film have been perceived under applied absorbed doses, notwithstanding the slight deterioration of the crystallinity and narrowing the OBG.     

Conjugated polythiophene/Ni doped ZnO hetero bilayer nanocomposite thin films: Its structural,optical and photoluminescence properties

In this study, synthesis and characterization of plasma polymerized Thiophene/ Nickel doped Zinc Oxide (PTNZO) bilayer nanocomposite films were carried out. Nickel doped zinc oxide (NZO) thin films were obtained by magnetron sputtering technique on glass substrates at 40 W Radio Frequency (RF) power. Plasma polymerized Thiophene (PT) thin films were deposited on the NZO thin films obtained on the glass substrate by Radio Frequency (RF) plasma polymerisation technique. X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), FTIR and Photoluminescence (PL) analyzes were performed for the characterization of PTNZO hetero bilayer nanocomposite films. In the XRD spectra of PTNZO bilayer nanocomposite thin films, (002) planes were determined as the most basic peak, and it was determined that the intensity of this peak, changed depending on the RF power of polymer thin films. Optical properties of nanocomposite thin films such as transmittance, absorbance and optical band gap were determined by UV–Vis spectroscopy. Optical band gap for PTNZO nanocomposites were 2.72?eV, 2.34?eV, and 2.45?eV, respectively, with increasing RF power. For NZO thin films, this value is 3.12?eV. The optical band gaps calculated from the absorption and transmittance spectra obtained using UV–visible spectroscopy had a good compatibility with those of the optical band spectra calculated from the PL spectra. The tetragonal wurtzite structure of the NZO thin films was examined by SEM analysis. The grain size of NZO nanostructure was found to be approximately 59?nm.     

Synthesis and characterization of ZnO:Ni thin films grown by spray-deposition

In the present study, nickel-doped zinc oxide thin films (ZnO:Ni) at different percentages (0–10%) were deposited on glass substrates by using a chemical spray technique. The effect of Ni concentration on the structural and optical properties of the ZnO:Ni thin films was investigated. The effect of Ni contents on the crystalline structure and optical properties of the films was systematically investigated by X-ray diffraction (XRD), scanning electronic microscopy (SEM), UV–vis, Photoluminescence spectra PL, and Raman spectrometry. The XRD analysis showed that both the undoped and Ni-doped ZnO films were crystallized in the hexagonal structure with a preferred orientation of the crystallites along the [002] direction perpendicular to the substrate. The XRD analysis also showed that the films were well crystallized in würtzite phase with the crystallites preferentially oriented towards (002) direction parallel to the c-axis. SEM study reveals the surface of NiZnO to be made of nanocrystalline particles. The SEM images showed a relatively dense surface structure composed of crystallites in the spherical form whose average size decreases when the [Ni]/[Zn] ratio increases. The optical study showed that all the films were highly transparent. The band gap decreased up to the 7 at% Ni doping level, but the band gap increased after 10 at% Ni doping level. All thin films exhibited approximately 80% and above transmittance in the visible region. PL spectra of undoped and Ni-doped ZnO thin films showed some marked peaks at 376, 389, 494, and 515 nm. The obtained results revealed that the structures and optical properties of the films were greatly affected by doping levels. These films are useful as conducting layers in electro chromic and photovoltaic devices. Finally, all results were discussed in terms of the nickel doping concentration.     

Micro-Raman,SEM, XPS,and electron field emission characterizations of nitrogen-induced shallow defects on nanodiamond films fabricated with different growth parameters

Nitrogen-induced shallow defects on nanodiamond films have been systematically characterized as a function of growth parameters using micro-Raman, SEM, XPS, and field emission measurements. Distinct peaks indicating diamond and graphite phases were observed in the micro-Raman spectroscopy. The increased in peak intensity and peak shifts due to growth parameters including pressure, power, and nitrogen flow-rate were observed and explained. The electronic behavior is further supplemented with SEM and XPS studies. Finally, electron field emission measurement is used to verify the deduced findings. The result of this study indicates that depending on the growth conditions nitrogen can act as a shallow donor in nanodiamond due to the formation of shallow defects with effective work functions ranging between 0.023 eV and 0.045 eV, as deduced from field emission characteristics. The correlation of film morphologies, spectroscopic analysis and field emission measurements to the growth conditions provide a better understanding of the nitrogen-induced shallow defects on the electronic properties of nanodiamond films.     

Structural,optical and electrical properties of low temperature grown undoped and (Al,Ga) co-doped ZnO thin films by spray pyrolysis

Aluminum and gallium co-doped ZnO (AGZO) thin films were grown by simple, flexible and cost-effective spray pyrolysis method on glass substrates at a temperature of 230 °C. Effects of equal co-doping with aluminum (Al) and gallium (Ga) on structural, optical and electrical properties were investigated by X-ray diffraction (XRD), UV–vis–NIR spectrophotometry and Current–Voltage (I–V) measurements, respectively. XRD patterns showed a successful growth with high quality polycrystalline films on glass substrates. The predominant orientation of the films is (002) at dopant concentrations ≤2 at% and (101) at higher dopant concentrations. Incorporation of Al and Ga to the ZnO crystal structure decreased the crystallite size and increased residual stress of the thin films. All films were highly transparent in the visible region with average transmittance of 80%. Increasing doping concentrations increased the optical band gap, from 3.12 to 3.30 eV. A blue shift of the optical band gap was observed from 400 nm to 380 nm with increase in equal co-doping. Co-doping improved the electrical conductivity of ZnO thin films. It has been found from the electrical measurements that films with dopant concentration of 2 at% have lowest resistivity of 1.621×10⁻⁴ Ω cm.     

Low-cost preparation of La4Co3O9 perovskite thin films with distinct absorbance ability and ferromagnetic behaviour

La₄Co₃O₉ perovskite thin film was grown on a glass substrate using spray pyrolysis technique at 460 °C. X-ray diffraction (XRD) pattern indicates a high orthorhombic structure in Ruddlesden-Popper phase along (040) orientation. A nanometric scale size varying between 10 and 20 nm of the La₄Co₃O₉ films were proved via Transmission Electron Microscopy (TEM). The High-Resolution Transmission Electron Microscopy (HRTEM) specifically displayed the lattice fringe among the (040) and (1 10 0) planes. A direct transition band was revealed in the synthesized La₄Co₃O₉ films through transmittance and reflectance spectra, with a band gap of 1.42 eV. Urbach effect as well as a relatively high absorptivity were evidenced. The prepared thin films exhibit a ferromagnetic behaviour. The saturated magnetization (M_S) and coercive field (H_C) were equal to M_S = 4.69810^?4 emu/g and an H_C = 45.56 Oe, respectively, at room temperature. The revealed ferromagnetic behaviour was due to the non-stoichiometry of La₄Co₃O₉ constituents. The present work emphasizes the specificity and suitability of La₄Co₃O₉ thin film perovskite for magneto-optical applications.     

Improved optical and structural properties of cadmium sulfide nanostructures for optoelectronic applications

In this study, the effect of ZnO seed layer on the growth of uniform CdS nanostructures was investigated using chemical bath deposition technique. Besides, the influence of molar concentration of reagents on the surface morphology, structural and optoelectrical properties of the deposited CdS thin films were examined. The CdS nanostructures were grown on bare glass and ZnO/glass substrates with different reagent molar concentrations. The results indicated an improvement in the homogeneity and uniformity of the grown CdS nanostructures on ZnO seed layer which can be due to the low lattice mismatch between ZnO and CdS structures. The CdS/ZnO samples were optimized by changing the molar concentration of reagents. A three–dimensional intersecting vertical nanosheet morphology with hexagonal structure was obtained when modified chemical concentration of 0.5 M was applied. The XRD pattern of CdS nanosheets indicated the hexagonal phase of CdS which were strongly orientated along (002) plane. The elevated intensity of dominant peak related to this sample confirmed the improved crystal quality of this CdS nanostructure comparing to the other samples. The UV–Vis spectrum demonstrated a high absorption coefficient for CdS intersecting nanosheets which might be due to the high specific surface area and light trapping behavior of this sample. The photoluminescence study also showed an improvement in optical properties of optimized CdS nanostructures. In order to study the optoelectrical properties of CdS nanostructures, metal–semiconductor–metal photodetectors were fabricated with different CdS samples and their current–voltage characteristics were analyzed. The results indicated an enhancement in photosensitivity, responsivity, and speed of photodetectors based on optimized CdS nanostructures.     

Spray-deposited kesterite Cu2ZnSnS4 (CZTS): Optical,structural, and electrical investigations for solar cell applications

Kesterite Cu₂ZnSnS₄ (CZTS)-based solar devices have become a popular alternative to copper indium gallium selenide (CIGS) due to its outstanding properties such as high efficiency, non-toxicity, cost-effectiveness, suitable optoelectrical properties, and earth-abundancy. In this study, we directly fabricated CZTS films via a single-step spray pyrolysis technique, in contrast to conventional techniques where post sulfurization is required. The spray deposited CZTS films are investigated for their optical, structural, and electrical properties. The X-ray diffraction (XRD) and Raman analysis study revealed the synthesis of the phase-pure kesterite CZTS films without impurity phases. Large crystallites of CZTS are obtained at a deposition temperature of 400 °C, exhibiting a porous granular morphology with different grain sizes upon temperature variation. The size-dependent optical properties revealed that the CZTS films exhibited admirable visible light absorption of 10⁵ cm^?1 and an electronic bandgap ranging between 1.42 and 1.58 eV. The minimum dielectric loss obtained for optimized CZTS due to fewer intrinsic defects confirmed the materials’ applicability. Thus, the study provides a simple, viable route to fabricate CZTS without post-treatment to build affordable solar cells.     

Enhancing the ultraviolet photosensing properties of nickel oxide thin films by Zn–La co-doping

In this work, co-doping effects of transition (Zn) and rare-earth (La) elements on the crystalline structure, surface morphology, photoluminescence, optical and photosensing properties of NiO thin films are studied. NiO, NiO:Zn(1%), NiO:La(1%), and NiO:Zn(1%):La(1%) thin films are fabricated using the nebulizer spray pyrolysis (NSP) method. X-ray diffraction study revealed the cubic NiO structure of all the films. Photoluminescence (PL) spectra of thin films exhibit various emission peaks centered at the wavelengths of 387, 414, 437, 451, 477, and 521 nm. The optical bandgap energy (E_g) values are found to be 3.46, 3.43, 3.39 and 3.33 eV for NiO, NiO:Zn(1%), NiO:La(1%) and NiO:Zn(1%):La(1%) thin films, respectively. The fabricated (Zn, La) co-doped NiO i.e., NiO:Zn(1%):La(1%) photo-detector exhibits highest responsivity (R), external quantum efficiency (EQE) and detectivity (D*) values of 0.50AW^-1, 169% and 14.5 × 10⁹ Jones, respectively as compared to NiO, NiO:Zn(1%) and NiO:La(1%) photo-detectors. The present study revealed that the transition and rare-earth elements co-doping can be an effective approach for tuning the various physical properties of semiconducting oxide films.     

Dithizone,carminic acid and pyrocatechol violet dyes sensitized metal (Ho,Ba& Cd) doped TiO2/CdS nanocomposite as a photoanode in hybrid heterojunction solar cell

Considering the great importance of nanocomposite based photo-active nanomaterials for a variety of electronics, photonics and photovoltaics application, it is always worth considering to synthesize new hetreostructure. This paper describes the sol-gel and hydrothermal synthesis of metal (holmium, barium, and cadmium) doped TiO₂/CdS nanocomposites for photoanode applications. Various characterization techniques, including XRD, FTIR, UV–VIS, EDX, and SEM were used to examine the synthesized heterostructures. The band gap of pure TiO₂ NPs is 3.10 eV, which was effectively decreased to 2.16 eV by doping and coupling with CdS. The nanomaterial's crystallinity, crystallite size, morphology and elemental composition were determined by XRD, SEM and EDX, respectively. As sensitizers, the organic dyes dithizone, carminic acid, and pyrocatechol violet were used. FTIR was used to analyze the effective dye grafting on the surface of nanomaterials. In the presence of hole conducting P3HT polymer as solid state electrolyte, the sensitized materials were evaluated for solid state dye-sensitized solar cells. Compared to the reference device, Cd–TiO₂/CdS photosensitized using Pyrocatechol violet dye demonstrated the highest efficiency of 2.68% (0.82%). Other parameters of this device, including open circuit voltage (Voc) and short circuit current (Jsc), were determined to be 16.97 mA cm² and 0.41V, respectively.     

Physical properties of copper-treated cadmium telluride thin films by vacuum evaporation technique

Cadmium telluride thin films were prepared on microscopic glass substrates by vacuum evaporation technique. The morphology of the thin films as a function of substrate temperature and postdeposition heat treatment was investigated by atomic force microscopy. The grain size increases with the increase of substrate temperature and postdeposition annealing. Calculated amount of copper was evaporated to deposit on the top of the already deposited CdTe thin films. The whole assembly was then annealed at 450°C for about 4–6 min. These samples were characterized structurally, optically, and electrically by using XRD, spectrophotometer, and Hall Effect measurements, respectively. Doping with Cu has significantly changed the electrical properties of the CdTe films. The measurements have shown band gap of 1.475 eV and resistivity ranging from 0.132 to 0.002 Ω cm, depending on the copper concentration. Increase in the weight percentage of copper showed decreasing trends in resistivity up to 3 wt%. Mobility showed the opposite behavior than those of the resistivity. The carrier concentration showed a systematic increase.     

The study of BiCrxFe1−xO3 thin films synthesized by sol–gel technique

Cr-doped bismuth ferrite (BiCr_xFe_1?xO₃, BCFO) thin films were prepared by a sol–gel method with the value of x varying from 0 mol% to 10 mol%. The structures of the BCFO thin films were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis was employed to represent the surface and cross-sectional morphologies of the thin films. Dielectric, electrical, ferroelectric and magnetic properties were measured by HP4294A, Keithley 4200, RT6000 and 6700 Magnet Controller at room temperature, respectively. The dielectric behaviour and insulation are improved in 3% Cr-doped BFO thin film which may be due to the reduced concentration of oxygen vacancies by 3% Cr doping.     

Influence of annealing on the structural,optical and photoluminescence properties of ZnO thin films for enhanced H2 sensing application

Nanostructured zinc oxide (ZnO) thin film sensors were prepared by spray pyrolysis, and their structural, optical, photoluminescence and morphological properties were investigated by X-ray diffractometer, UV–vis spectrometer, photoluminescence spectrometer, and scanning electron microscope (SEM), respectively. The post-annealing of ZnO film in air at 400 °C was found to be effective for the distribution of grains and their sizes, which favors the c-axis orientation of the film. This enhancement is accompanied by an increase in the optical band gap from 3.4 eV to 3.53 eV, which confirms the uniformity of ZnO film prepared by using a specially designed spray nozzle. SEM micrograph after heat treatment revealed uniform distribution of particles with well grown grains of ZnO. Hydrogen sensing measurement indicated the annealed ZnO film to show much higher response than the as deposited film. To understand the enhancement of the sensing performance of the annealed ZnO film, the gas sensing mechanism of the film was proposed and discussed. The magnitudes of the sensor response as well as its dependence on annealing differ significantly depending on the crystallite size of the film.