CdSe thin films: morphological, optoelectronic and photoelectrochemical studies

Polycrystalline cadmium selenide (CdSe) thin films have been synthesized at room temperature by using chemical bath deposition method. The synthesized films were characterized by using X-ray diffraction (XRD), optical absorbance, electrical conductivity, scanning electron microscope, energy dispersive X-ray analysis, photoluminescence and photoelectrochemical (PEC) techniques. The film of 0.84 μm thickness, deposited on glass substrate showed uniform spherical morphology with an optical band gap of 1.99 eV. The XRD analysis confirmed presence of cubic structure. Scanning electron micrograph shows a typical spherical ball like morphology with large surface area, which is useful for absorption of large solar radiation. The conductivity measurements showed n type semiconducting nature of the film. A PEC cell device fabricated using ‘as deposited’ CdSe film as anode showed a stable conversion efficiency of 0.7 %.     

Effect of post annealing on structural and optical properties of ZnO thin films deposited by vacuum coating technique

We report the effect of annealing temperature on structural, electrical and optical properties of polycrystalline zinc oxide thin films grown on p-type silicon (100) and glass substrates by vacuum coating technique. The XRD and AFM measurements confirmed that the thin films grown by this technique have good crystalline hexagonal wurtzite structures and homogenous surfaces. The study also reveals that the rms value of thin film roughness increases from 6 to 16 nm, the optical band gap increases from 3.05 to 3.26 eV and resistivity from 0.3 to 5 Ωcm when the post-deposition annealing temperature is changed from 400 to 600 °C. It is observed that ZnO thin film annealed at 600 °C after deposition provide a smooth and flat texture suited for optoelectronic applications.     

Deposition of ZnS thin films by photochemical deposition technique

ZnS thin films have been deposited on a glass substrate by photochemical deposition (PCD) technique from an aqueous solution. The effect of pH and stirring speed of the solution on deposition has been studied. The optical transmission spectra of the solutions have been recorded before and after deposition and also for the deposited film. The as-deposited and annealed films were characterized by X-ray diffraction (XRD) and it is observed that the crystallinity of the deposited films is improved by annealing at various temperature from 100 to 500 °C. The surface coverage of the film has been studied using optical microscope.     

Influence of Fe dopant concentration and annealing temperature on the structural and optical properties of ZnO thin films deposited by sol–gel method

Nanostructured Fe doped ZnO thin films were deposited onto glass substrates by sol–gel spin coating method. Influence of Fe doping concentration and annealing temperature on the structural, compositional, morphological and optical properties were investigated using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), UV–Vis spectroscopy and photoluminescence (PL) measurements. XRD analysis showed that all the films prepared in this work possessed a hexagonal wurtzite structure and were preferentially oriented along the c-axis. Pure ZnO thin films possessed extensive strain, whereas Fe doped films possessed compressive strain. In the doped films, least value of stress and strain was observed in the 0.5 at.% Fe doped thin film, annealed at 873 K. Average crystallite size was not significantly affected by Fe doping, but it increased from 15.57 to 17.79 nm with increase in annealing temperature from 673 to 873 K. Fe ions are present in +3 oxidation state as revealed by XPS analysis of the 0.5 at.% Fe doped film. Surface morphology is greatly affected by changes in Fe doping concentration and annealing temperature which is evident in the SEM images. The increase in optical band gap from 3.21 to 3.25 eV, with increase in dopant concentration was attributed to Moss–Burstein shift. But increase in annealing temperature from 673 to 873 K caused a decrease in band gap from 3.22 to 3.20 eV. PL spectra showed emissions due to excitonic combinations in the UV region and defect related emissions in the visible region in all the investigated films.     

Photoelectrochemical (PEC) studies on CdSe thin films electrodeposited from non-aqueous bath on different substrates

Thin films of CdSe were deposited by potentiostatic mode on different substrates such as stainless steel, titanium and fluorine tin-oxide (FTO) coated glass using non-aqueous bath. The preparative parameters were optimized to get good quality CdSe thin films. These films were characterized by X-ray diffraction (XRD), optical absorption and photoelectrochemical (PEC) techniques. XRD study revealed that the films were polycrystalline in nature with hexagonal phase. Optical absorption study showed that CdSe films were of direct band gap type semiconductor with a band gap energy of 1·8 eV. PEC study revealed that CdSe film deposited on FTO coated glass exhibited maximum values of fill factor (FF) and efficiency (η) as compared to the films deposited on stainless steel and titanium substrate.     

Synthesis and characterization of 10% Sb doped CdTe thin films by stacked elemental layer (SEL) method

Antimony doped CdTe thin films have been prepared by stacked elemental layer (SEL) method. The X-ray diffraction spectra have demonstrated that the structure of the annealed films are polycrystalline in nature and mixed CdTe and Sb₂Te₃ phases have been observed at high annealing temperature (500 °C). The increased texture coefficient has been observed for planes (311) and (220) rather than (111) plane of CdTe in annealed stack (Te/Cd/Sb). Transmission spectra have been recorded and the calculated band gap lies between 1.45 and 1.68 eV. A pronounced PL spectrum has been noticed at 532 nm and depicted the presence of nano size particles in annealed thin films.     

Effects of annealing on the structural properties of indium rich InGaN films

Indium rich (In-rich) InGaN films were grown on Ge (111) substrate by plasma assisted molecular beam epitaxy with thin GaN as a buffer layer. The effects of annealing temperature and annealing time on the structural properties of In-rich InGaN films were investigated by X-ray diffraction (XRD). XRD results indicate that the as-grown InGaN films annealed at different temperatures for 1 min and 1 h respectively did not improve the film crystalline quality. But with the annealing at 750 °C and 800 °C for 1 min respectively the metallic indium was desorbed from the InGaN structure. The InGaN films annealed at higher than 660 °C for 1 h also showed the indium desorption. The InGaN film has the best film quality after annealed at 660 °C for 6 h with the full-width at half-maximum of InGaN (002) peak to be 879 arcsec. The InGaN crystalline quality started to degrade after annealed at the temperatures higher than 660 °C for 6 h.     

Structural and optical characterization of CdS and CdHgTe thin films for the fabrication of CdHgTe/CdS structure

This article presents the deposition and characterization of CdS and CdHgTe thin films for the fabrication of CdHgTe/CdS structure. The growth of CdS and CdHgTe thin films on FTO-coated conducting glass substrates have been performed by chemical bath deposition (CBD) and electrodeposition methods, respectively. The deposition conditions have been optimized for getting better quality layers of CdS and CdHgTe. The grown layers of both CdS and CdHgTe have been characterized by photoelectrochemical cell (PEC) measurement, X-ray diffraction (XRD), scanning electron microscopy (SEM) and UV–vis spectrophotometer. Annealing effect of the deposited films has also been investigated. Finally the fabrication of CdHgTe/CdS structure has been performed and investigated by I–V characteristics. PEC, XRD, SEM and UV–vis spectrophotometer studies reveal that chemically deposited CdS layers are n-type with band gap values vary from 2.29 to 2.41 eV and cubic with (111) preferential orientation, and have spherical grain distributed over the surface. However, electrodeposited CdHgTe layers are p-type with band gap values varying from 1.50 to 1.53 eV and cubic with highly oriented CdHgTe crystallites with the (111) planes parallel to the substrate, and have uniform distribution of granular grains over the surface. The fabricated CdHgTe/CdS structure gave an open-circuit photovoltage and a short-circuit photocurrent of 510 mV and 13 mA/cm² respectively, under AM 1.5 illumination.     

Effects of annealing temperature on the structural,morphology, optical properties and resistivity of sputtered CCTO thin film

CaCu₃Ti₄O₁₂ (CCTO) thin films with a thickness of 200 nm were deposited on ITO substrates by RF magnetron sputtering using a pure CCTO target. After the deposition, thin films were annealed at 400, 450, 500 and 550?°C, respectively, for 1 h. The effects of annealing temperature on the structural, surface morphology, optical properties and resistivity of (CCTO) thin films were investigated. The X-ray diffractometer results show that the thin films are polycrystalline in nature and are assigned to body-centered cubic perovskite configuration with a space group of Im-3. The intensity of the peaks and crystallinity gradually increased with the increase in annealing temperature. Microstructural investigation through FESEM showed that the grain size increased with increase in annealing temperature from 32 to 85 nm. The root mean square and roughness (Ra) were also enhanced with higher annealing temperatures, from 3.8 to 6.2 nm and from 4.7 to 7.7 nm, respectively, as confirmed by AFM. Increase in annealing temperature also affected the optical transmittance values which decreased to almost 60% at the visible range (550–850), as well as the optical energy band gap which decreased from 3.86 to 3.39 eV. The relevance between resistance behaviors and film microstructure is discussed. Therefore, it can be concluded that the desirable crystallinity, surface roughness, energy band gap and resistivity for 200 nm thick CCTO thin films deposited by RF magnetron sputtering can be achieved through the annealing process.     

Effect of pyrolytic temperature on the properties of nano-structured Cuo optimized for ethanol sensing applications

In the present work, copper oxide thin films have been deposited at different substrate temperatures from 250 to 400 °C by spray pyrolysis technique. The desired properties of phase pure CuO with good crystal quality and conductivity have been optimized with respect to pyrolytic temperature. X-ray diffraction studies and Hall effect measurements indicated that these two properties are achieved at an optimum temperature of 350 °C. The band gap of CuO films was found to decrease from 1.8 to 1.2 eV with increase in substrate temperature, based on the UV-absorption spectrum of the film. The microstructures revealed that the film optimized at 350 °C, showed uniform surface with trapezium shaped particles, which are well compacted. The dynamic sensing behavior of the optimized p-type CuO sensor, prepared at a substrate temperature of 350 °C, was used to sense ethanol for concentrations: 100 and 200 ppm. The response time and the recovery time were within the range of 15–20 s and 15–18 s, respectively. The results revealed good response even at room temperature, with characteristics dependent on the size of the grains and the concentration of ethanol.     

Studies on electrosynthesized zinc mercury selenide alloys

Zn_1-x Hg _x Se ternary alloy thin films with x ranging from 0.14 to 0.5 have been deposited on conducting glass substrates by electrodeposition from aqueous bath containing ZnSO₄, HgCl₂ and SeO₂ at bath temperatures from 30 °C to 80 °C. The influence of deposition parameters on the crystallinity, composition, band gap and lattice constants of the film is studied. The films deposited at the potentials between −0.4 V and −1.0 V vs SCE at 70 ° C were characterized by X-ray diffraction (XRD), Energy dispersive X-ray (EDX), scanning electron microscope and optical absorption technique. Photoelectrochemical (PEC) solar cells based on Hg _x Zn_1-x Se thin film electrodes were constructed and the effects of annealing and photo etching on solar cell parameters were studied.     

Structural, photoluminescence and optical properties of chemically deposited (Cd1−xBix)S thin films as a function of dopant concentration

In this study, (Cd_1?xBi_x)S thin films were successfully deposited on suitably cleaned glass substrate at 60 °C temperature, using the chemical bath deposition technique. After deposition, the films were also annealed at 400 °C for 2 min in air. The structural properties of the deposited films were characterized using X-ray diffraction and AFM. Formation of cubic structure with preferential orientation along the (111) plane was confirmed together with BiS second phase from structural analysis. The interplanar spacing, lattice constant, and crystallite size of (Cd_1?xBi_x)S thin films were calculated by the XRD. The crystallite size of the un-doped CdS thin films was found to be 7.84 nm, which increased to 11.1 nm with increasing Bi content from 0 to 10 %. The surface roughness of the films was measured by AFM studies. The photoluminescence spectra were observed at red shifted band edge peak with increasing doping concentration of Bi from 0 to 5 % in the un-doped CdS thin films. The optical properties of the films are estimated using optical absorption and transmission spectra in the range of 400–800 nm using UV–VIS spectrophotometer. The optical band gap energy of the films was found to be decreased from 2.44 to 2.23 eV with the Bi content being from 0 to 5 %. After annealing, the band gap of these films further decreased.     

Influence of pH on electrochemically deposited CdSe thin films

Polycrystalline CdSe thin films have been electrodeposited at room temperature on stainless steel (ss) and fluorine doped tin oxide (FTO) coated glass substrate from aqueous electrolytes containing salts of cadmium acetate and selenium dioxide. The pH of the bath is varied from 1.75, at the interval of 0.25, to 3. The effect of pH on the photoelectrochemical (PEC), structural and optical properties of the deposited film is studied. The pH of the bath is optimized by the PEC technique and is observed to be 2.75. The analysis of the XRD patterns show that the deposited CdSe material is polycrystalline with a hexagonal crystal structure. SEM study shows that the total substrate surface is well covered by uniformly distributed spherical shaped grains. The optical absorption studies reveal that the pH of the electrolytic solution has a significant effect on the band gap of the CdSe thin film. The transition involved is direct with band gap energy E_g of 1.72 eV.     

Annealing effects on the structural and optical properties of growth ZnO thin films fabricated by pulsed laser deposition (PLD)

Annealed ZnO thin film at 300, 350, 400, 450 and 500 °C in air were deposited on glass substrate by using pulsed laser deposition. The effects of annealing temperature on the structural and optical properties of annealed ZnO thin films by grazing incident X-ray diffraction (GIXRD), transmittance spectra, and photoluminescence (PL) were investigated. The GIXRD reveal the presence of hexagonal wurtzite structure of ZnO with preferred orientation (002). The particle size is calculated using Debye–Scherrer equation and the average grain size were found to be in the range 5.22–10.61 ± 0.01 nm. The transmittance spectra demonstrate highly transparent nature of the films in visible region (>70 %). The calculation of optical band gap energy is found to be in the range 2.95–3.32 ± 0.01 eV. The PL spectra shows that the amorphous film gives a UV emission only and the annealed films produce UV, violet, blue and green emissions this indicates that the point defects increased as the amorphous film was annealed.     

Synthesis and characterization of zinc stannate thin films prepared by spray pyrolysis technique

The zinc stannate thin films were synthesized by simple and inexpensive spray pyrolysis technique on the glass and fluorine doped tin oxide coated conducting glass substrates. The as deposited films were further annealed at 500 °C temperature for 12 h. The structural optical and morphological characterization of as prepared and annealed films was carried out by XRD, UV–Vis spectroscopy, SEM and AFM techniques respectively. The structural analysis shows that films are polycrystalline and crystallized in cubic inverse spinel crystal structure. SEM studies show that grain size increases after annealing and exhibits spherical morphology. AFM study shows that roughness is higher for the post annealed film. Further the samples were tested for testing their applicability for dye sensitized solar cells. The as prepared, annealed and CNT doped samples exhibits photoconversion efficiencies 2.7, 2.8 and 3.1 % respectively.     

The Effect of Substrate Temperature on the Optical Properties of MoO3 Nano-crystals Prepared Using Spray Pyrolysis

In this study, thin films of molybdenum oxide were prepared by spray pyrolysis technique on glass substrates. The influence of substrate temperature on their crystallographic structure, surface morphology, and optical properties was studied. The formation of a MoO₃ film on the substrate was confirmed through XRD analysis. Furthermore, the presence of the two phases α and β in each of the films was evident. The percentage of phase α varied from 55 % for the film deposited at 200 °C up to 97 % for the film deposited at 400 °C. According to SEM images, MoO₃ films have a sponge-type structure on the order of nanometers. Both the optical gap and the refraction index strongly depend on substrate temperature. The optical gap decreases from 3.63 eV for the film deposited at 150 °C up to 3.30 eV for the one prepared at 400 °C. On the contrary, the refraction index measured at 800 nm increases from 1.54 up to 1.61 for the films prepared at 150 °C and 400 °C, respectively.     

Optical characterization of ZnO thin films deposited by Sol-gel method

In this paper, ZnO thin film is deposited on Pt/TiO₂/SiO₂/Si substrate using the sol-gel method and the effect of annealing temperature on the structural morphology and optical properties of ZnO thin films is investigated. The ZnO thin films are crystallized by the heat treatment at over 400°C. The ZnO thin film annealed at 600°C exhibits the greatest c-axis orientation and the Full-Width-Half-Maximum (FWHM) of X-ray peak is 0.4360°. A dense ZnO thin film is deposited by the growth of uniform grains with the increase of annealing temperature but when the annealing temperature increases to 700°C, the surface morphology of ZnO thin film becomes worse by the aggregation of ZnO particles. In the results of surface morphology of ZnO thin film using atomic force microscope (AFM), the surface roughness of ZnO thin film annealed at 600°C is smallest, that is, approximately 1.048 nm. For the PL characteristics of ZnO thin film, it is observed that ZnO thin film annealed at 600°C exhibits the greatest UV (ultraviolet) exciton emission at approximately 378 nm, and the smallest visible emission at approximately 510 nm among ZnO thin films annealed at various temperatures. It is deduced that ZnO thin film annealed at 600°C is formed most stoichiometrically, since the visible emission at approximately 510 nm comes from either oxygen vacancies or impurities.     

Study of Ar + O2 deposition pressures on properties of pulsed laser deposited CdTe thin films at high substrate temperature

Cadmium telluride (CdTe) thin films deposited by pulsed laser deposition (PLD) on fluorine–tin–oxide substrates under different pressures of argon (Ar) + oxygen (O₂) at high substrate temperature (T_s = 500 °C) was reported in this paper. In our work, the CdTe thin films were prepared successfully at high T_s by inputting Ar + O₂. As reported, PLD-CdTe thin films were almost prepared at low substrate temperatures (<300 °C) under vacuum conditions. The deposition of CdTe thin films at high T_s by PLD is rarely reported. The influence of the Ar + O₂ gas pressure on thickness, structural performance, surface morphology, optical property and band gap (E_g) had been investigated respectively by Ambios probe level meter, X-ray diffraction (XRD), scanning electron microscopy (SEM) and UV–Vis spectrometer. Strong dependence of properties on the deposition pressures was revealed. In the range of Ar + O₂ gas pressure from 5 to 12 Torr, the deposition rate and the E_g of CdTe films vary in the range of 41.9–57.66 nm/min then to 35.26 nm/min and 1.51–1.54 eV then to 1.47 eV, respectively. The XRD diagrams showed that the as-deposited films were polycrystalline, and the main phase was cubic phase. However, the preferred orientation peak disappeared when the deposition pressure was higher. SEM images indicated that the CdTe film deposited at a higher deposition pressure was more uniform and had a higher compactness and a lower pinhole density. Furthermore, based on this thorough study, FTO/PLD-CdS (100 nm)/PLD-CdTe (~1.5 μm)/HgTe:Cu/Ag solar cells with an efficiency of 6.68 % and an area of 0.64 mm² were prepared successfully.     

Effect of annealing temperature on electrical and nano-structural properties of sol–gel derived ZnO thin films

Zinc oxide (ZnO) thin films have been prepared on silicon substrates by sol–gel spin coating technique with spinning speed of 3,000 rpm. The films were annealed at different temperatures from 200 to 500 °C and found that ZnO films exhibit different nanostructures at different annealing temperatures. The X-ray diffraction (XRD) results showed that the ZnO films convert from amorphous to polycrystalline phase after annealing at 400 °C. The metal oxide semiconductor (MOS) capacitors were fabricated using ZnO films deposited on pre-cleaned silicon (100) substrates and electrical properties such as current versus voltage (I–V) and capacitance versus voltage (C–V) characteristics were studied. The electrical resistivity decreased with increasing annealing temperature. The oxide capacitance was measured at different annealing temperatures and different signal frequencies. The dielectric constant and the loss factor (tanδ) were increased with increase of annealing temperature.     

In situ and ex situ investigation on the annealing performance of the ZnO film grown by ion beam deposition

The effects of the post-annealing treatment on the properties of the ZnO thin films deposited by ion beam sputtering have been investigated. By using in situ X-ray diffraction technique, an overview of the crystallization behavior of the ZnO film during the annealing process was obtained. It was found that the whole process can be divided into three regions. The improvement of the film’s crystallinity performance mainly occurs within the annealing temperature ranging from 300 to 600 °C. Both in situ and ex situ XRD results show the shift of the ZnO (002) peak towards high angle with the increasing annealing temperature, which is attributed to the variation of the stress in the film. The stress is mainly caused by the intrinsic stress which is affected by the oxygen deficiency in the film. The oxygen deficiency is sensitive to the annealing ambient. The film annealed in the O₂ ambient has less oxygen deficiency and higher resistivity. All the ZnO films deposited on the glass substrates have an optical transmittance over 85% in the visible region. Our results show that the ZnO films deposited using ion beam sputtering exhibit good thermal stability and high performance after annealing.