Increase In Band Gap Energy Research Articles

Investigation of physico-chemical properties of conductive Ga-doped ZnO thin films deposited on glass and silicon wafers by RF magnetron sputtering

We report on the physico-chemical properties of Undoped and Ga-doped ZnO films fabricated on glass and p-Silicon wafers at room temperature by RF magnetron sputtering using a ZnO and Ga2O3 mixture raw powder target without sintering procedure. X-ray diffraction (XRD) and energy dispersion spectroscopy (EDS), scanning electronic microscopy, Raman scattering, ultraviolet–visible spectroscopy, photoluminescence (PL), Hall effect and impedance spectroscopy technique have been applied for the comparative study of ZnO and ZnO:Ga thin films. XRD and Raman studies have shown that the deposited films have a preferred orientation growth with Ga atoms both in substitutional and interstitial positions. EDS analyses have allowed to show that the metallic Ga atoms have been incorporated in the ZnO films. Doping by gallium resulted in a slight increase in the optical band gap energy of the films while the optical transmittance remains about 80 %. The PL analysis at room temperature revealed violet, blue, green and red emissions. Room temperature Hall measurements show that the lowest resistivity was 3.40 × 10−4 Ω cm with an electron mobility of 18.56 cm2/V.s for an optimum Ga concentration of 4 wt%. Impedance spectroscopy study showed that σac obeys the relation \(\sigma_{ac} = A\omega^{s}\). The exponent ‘‘s’’ was found to decrease with increasing the temperature. It is found that, the AC conductivity of all samples follow the correlated barrier hopping model. The Nyquist plots showed a single semicircle, indicating an equivalent circuit with a single parallel resistor R and capacitance C network. The values of the activation energy E a deduced from both DC conductivity and relaxation frequency for all the studied samples ranged from 0.51 to 0.73 eV and the results are explained on the basis of the induced defects due to the addition of Ga into the ZnO films.

Crystal growth of antimony substituted cobalt ferrites thin films deposited by electron beam

A series of antimony substituted cobalt ferrites (CoSb0.3Fe1.7O4) thin films have been deposited employing Electron Beam Deposition technique. The as deposited thin films have been post annealed at different temperature such as 200, 300, 400 and 500°C. The structural, surface, magnetic and optical properties of as-deposited and post annealed thin films have been studied using X-ray diffractometer, Raman spectroscopy, and Atomic Force Microscope, Vibrating Sample Magnetometer, spectroscopy ellipsometry and UV–vis techniques respectively. The X-ray diffraction and Raman spectroscopy analysis have confirmed the growth of single phase cubic spinel structure in thin films after post annealing. It is observed that the roughness of the thin films decreases and magnetization increases as the annealing temperature increases but not exceeded to as-deposited film. As the post annealing temperature increases the band gap energy increases which shows that the density of defects decreases and structure turn towards crystalline state from amorphous.

Close spaced vapor transport deposition of Cu2ZnSnS4 thin films: Effect of iodine pressure

High quality Cu2ZnSnS4 (CZTS) ingots obtained by cooling a molten stoichiometric mixture have been deposited as thin films on soda-lime glass by Close Spaced Vapor Transport (CSVT). Iodine pressure is one of the important parameters for the CSVT process. The effect of iodine pressure on compositional, morphological, structural, electrical and optical properties of CZTS thin films has been investigated. X-ray diffraction and Raman spectroscopy results revealed the formation of polycrystalline CZTS with a (112) preferred orientation plane and Raman shift of 338 cm−1 respectively. Iodine pressure does not have a significant effect on the composition nor on the electrical properties as measured by Hall effect measurements. However, scanning electron microscopy (SEM) and UV–Vis–NIR spectrophotometer data revealed an increase of crystallite size and band gap energy (1.47–1.56 eV) with iodine pressure. The photoluminescence (PL) measurements at 77 K exhibit emission peaks around 1.30 eV. The origin of this luminescence is attributed to band-to-impurity (BI) recombination.

Post deposition annealing: a route to bandgap tailoring of ZnSe thin films

The ZnSe semiconductor thin films thermally evaporated on a glass substrate and an ITO substrate are studied and compared for their optical properties. Surprisingly, two different values of band gaps 2.49 and 2.91 eV in ZnSe thin films are observed, respectively deposited on glass substrate and ITO substrate. Similarly, the ZnSe films on ITO substrate has shown a hexagonal crystal structure with higher crystallinity as compared to that of ZnSe on glass. The ZnSe thin films deposited on glass substrate are also annealed at 350, 400, 450 and 500 °C under vacuum conditions, which has been resulted in improvement in crystallinity and increase in band gap energy from 2.45 to 2.54 eV. The ZnSe thin film deposited on ITO coated glass were annealed in vacuum and air at 450 °C. The air annealing has been resulted in a large increase in energy bandgap from 2.9 to 3.21 eV. It is also observed from these studies that the electrical conductivity of the films annealed in vacuum is higher than those of the annealed in air.

Effect of Heat Treatment Under Nitrogen Atmosphere on Sprayed Fluorine Doped In2O3 Thin Films

Fluorine-doped indium oxide thin films (In2O3:F) were prepared at 500°C for different fluorine concentrations (0 at.%, 2 at.%, 6 at.% and 10 at.%) using the chemical spray pyrolysis technique. Structure and surface morphology of these films were characterized by x-ray diffraction (XRD) and atomic force microscopy (AFM). XRD analysis revealed that fluorine doped In2O3 thin films exhibit a centered cubic structure with the (400) preferential orientation. The change of the preferential reflection plane from (222) to (400) was found after doping. The doping optimum concentration of thin film crystal structure is obtained witha fluorine ratio equal to 2 at.%. The crystallinity improvement of In2O3:F (2 at.%) film is detected after annealing at 200°C, 300°C, and 400°C in nitrogen gas for 45 min. Transmission and reflection spectra measurements were performed over the wavelength range of 250–2500 nm. The band gap energy increase from 3.10 eV to 3.45 eV was detected after treatment at 400°C. In parallel, the electrical resistivity, deduced from Hall effect measurements, decreases from 428.90 × 10−4 Ω cm to 6.58 × 10−4 Ω cm.

Optical Properties of Nano-Crystalline Zirconia Thin Films Prepared at Different Post-Oxidation Annealing Times

The zirconia (ZrO2) is one of the transition-metal oxides with most excellent optical properties which thus attracts great attention in optical engineering. A variety of methods were used for deposition of ZrO2 thin films on different substrates. In the present work, homogenous, transparent nanocrystalline zirconia thin films were grown by thermal oxidation of zirconium (Zr) thin films deposited on quartz substrate using DC magnetron sputtering technique. The objective of this study is to reveal the effect of thermal oxidation time on structural and optical properties of deposited films. The XRD results revealed the formation of single phase ZrO2 with tetragonal structure in the films at different thermal oxidation times. The optical constant of ZrO2 thin films was calculated from the UV-visible transmission spectra. It was found that the increase of thermal oxidation time leads to the increase of transmittance and optical band gap energy of the films. The AFM results showed that thermal oxidation time influences the surface morphology of the films.

Structural, Morphological, Optical and Magnetic Properties of Al-Doped CoFe2 O 4 Nanoparticles Prepared by Sol–Gel Auto-Combustion Method

CoFe2−xAlxO4 (x = 0.0,0.5,1.0, and 1.5) ferrite nanoparticles have been synthesized by the sol–gel auto-combustion method. The effect of non-magnetic Al content on their structural, morphological, optical, and magnetic properties was also investigated. X-ray diffraction (XRD) diffraction analysis was applied and indicated that the synthesized nanopowders of samples with x<1.5 and calcined at 800 ∘C have single-phase spinel structure. It has shown also by increasing Al content, the particle size, lattice parameter, unit cell volume, coercivity, anisotropy constant, and magnetization decrease, while the energy band gap increases. The size of particles was measured by TEM being in the range of 65–75 nm (for x = 0.0) and 9–10 nm (for x = 1.0). For sample with x = 1.5, the minimum calcination temperature for obtaining a single-phase spinel structure was 1000 ∘C. By increasing the calcination temperature from 1000 to 1100 ∘C, the mean crystallite size and crystallinity increase, while the lattice parameter, coercivity, anisotropy constant, and magnetization decrease. The average grain size evaluated by SEM analysis was found to be \(\tilde 91\) and 166 nm for samples calcined at 1000 and 1100 ∘C, respectively.

Modulation of Physical Properties of Sprayed ZnO Thin Films by Substrate Temperature for Optical Applications

We investigated the structural, electrical and optical properties of zinc oxide thin films as the n-type semiconductor. In the present paper, the effect of substrate temperature on the synthesis of ZnO thin films was carried out from 250[Formula: see text]C to 500[Formula: see text]C. ZnO thin films were deposited on glass substrates via ultrasonic spray technique with 0.2[Formula: see text]mol/L of zinc acetate dehydrate. The crystal quality of the thin films was analyzed by X-ray diffraction which results in modified substrate temperature. The optical transmittance and electrical conductivity measurements were carried out by Ultraviolet-visible spectrophotometer and four-point methods, respectively. Polycrystalline films with a hexagonal wurtzite structure with (100) and (002) preferential orientation corresponding to ZnO films were observed at high temperature. The optimal values of the average crystallite size of the ZnO films under consideration are observed beginning with 350[Formula: see text]C of substrate temperature. All films exhibit an average optical transparency of about 85% in the visible region. The shift of optical transmittance toward higher wavelength can be shown by the increase of bandgap energy from 3.245[Formula: see text]eV to 3.281[Formula: see text]eV with increasing substrate temperature of 250–500[Formula: see text]C. The observed Urbach energy of ZnO thin films decreases from 0.11311[Formula: see text]eV to 0.04974[Formula: see text]eV. At a high temperature, the electrical conductivity of ZnO films was increased from [Formula: see text] to 41.58 ([Formula: see text].cm)[Formula: see text] with the increasing substrate temperature from 350[Formula: see text]C to 500[Formula: see text]C.

Superhalogens as building blocks of two-dimensional organic-inorganic hybrid perovskites for optoelectronics applications.

Organic-inorganic hybrid perovskites, well known for their potential as the next generation solar cells, have found another niche application in optoelectronics. This was demonstrated in a recent experiment (L. Dou, et al., Science, 2015, 349, 1518) on atomically thin (C4H9NH3)2PbBr4, where, due to quantum confinement, the bandgap and the exciton binding energy are enhanced over their corresponding values in the three-dimensional bulk phase. Using density functional theory we show that when halogen atoms (e.g. I) are sequentially replaced with superhalogen molecules (e.g. BH4) the bandgap and exciton binding energy increase monotonically with the superhalogen content with the exciton binding energy of (C4H9NH3)2Pb(BH4)4 approaching the value in monolayer black phosphorus. Lead-free admixtures (C4H9NH3)2MI4-x(BH4)x (M = Sn and Ge; x = 0-4) also show a similar trend. Thus, a combination of quantum confinement and compositional change can be used as an effective strategy to tailor the bandgap and the exciton binding energy of two-dimensional hybrid perovskites, making them promising candidates for optoelectronic applications.

Effect of BaO on physical, optical and structural characteristics of ZnO– Al2O3–B2O3 glasses

Zinc barium borate glasses with composition (65-x) B2O3-10Na2O-10Al2O3-10ZnO-5Li2O-xBaO with (0 ≤ x ≤40 % mol)have been prepared using melt quenching technique.The density, molar volume and the optical absorption studies revealed that the optical band gap energy (Eopt) and Urbachenergy increase with the increase of BaOcontent.This is mainly due to the increased polarization of theBa2+ ions and theenhanced formation of non-bridging oxygen (NBO). The IR studies indicate that these glasses are made up of [AlO6],[BO3],[BO4], and [AlO4] basic structural units.

700 keV Ni+2 ions induced modification in structural, surface, magneto-optic and optical properties of ZnO thin films

We investigate the effect of 700keV Ni+2 ions irradiation at different ion fluences (1×1013, 1×1014, 2×1014, 5×1014ions/cm2) on the structural, surface, magneto-optic and optical properties of ZnO thin films. The X-ray diffraction (XRD) results show improved crystallinity when ion fluence is increased to 2×1014ions/cm2, while deterioration is observed at the highest ion fluence of 5×1014ions/cm2. Scanning electron micrographs (SEM) show the formation of small grains at ion fluence 1×1013ions/cm2, micro-rods at fluences 1×1014 and 2×1014ions/cm2 and ultimate fracturing of thin film surface at ion fluence 5×1014ions/cm2. Faraday rotation measurements are also performed and show a decrease in Verdet constant from 53 to 31rad/(T-m) when irradiated at 1×1013ions/cm2, increasing up to 45rad/(T-m) at 2×1014ions/cm2, and then decreasing again to 36rad/(T-m) at 5×1014ions/cm2. The optical band gap energy of the films is determined using spectroscopic ellipsometry, which shows an increase in optical band gap energy (Eg) from 3.04eV to 3.19eV when the fluence increases to 2×1014ions/cm2 and a decrease to 3eV at fluence 5×1014ions/cm2. We argue that these properties can be explained using ion heating effect of thin films.

Room temperature ferromagnetism in undoped and Mn doped t-ZrO2 nanostructures originated due to oxygen vacancy and effect of Mn doping on its optical properties

In the present report, we have synthesized undoped and Mn doped (1, 5, and 10 at.%) t-ZrO2 nanostructures by sol–gel method and their magnetic and optical properties have been investigated. UV–VIS. spectroscopy revealed the increase in band gap energy with Mn doping in ZrO2 matrix. The increase of optical band gap is attributed to Moss–Burstein effect. Photoluminescence (PL) spectroscopy revealed the presence of oxygen vacancies in undoped and Mn doped ZrO2 nanostructures. The shifting of peak position of the emission band to higher wavelength region for Mn doped ZrO2 nanostructures is attributed to the quantum size effects. The possible PL mechanism in undoped and Mn doped ZrO2 nanostructures is also discussed. In the present report, we have observed room temperature ferromagnetism (RTFM) for undoped and Mn doped t-ZrO2 nanostructures. The value of saturation magnetization (Ms) is decreased with the increase of Mn content into t-ZrO2 matrix. Oxygen vacancies are found responsible for RTFM in undoped ZrO2. The paramagnetic nature of Mn doped (10 at.%) t-ZrO2 nanostructures is explained in terms of anti-ferromagnetic coupling of Mn–Mn at high doping concentration.

Structural, morphological, optical and electrical properties of CdS thin films simultaneously doped with magnesium and chlorine

CdS thin films simultaneously doped with Mg and Cl at different doping concentrations (0, 2, 4, 6 and 8 at%) were prepared on glass substrates by spray pyrolysis technique using perfume atomizer at 400 °C. The effect of Mg and Cl doping concentration on the structural, morphological, optical and electrical properties of the deposited films were investigated using X-ray diffraction (XRD), scanning electron microscopy, UV–Vis spectroscopy and dc electrical measurements, respectively. XRD analysis showed that the undoped and doped CdS films exhibit hexagonal structure with a preferential orientation along the (0 0 2) plane. The 2θ angle position of the (0 0 2) peak of the doped films was shifted towards a higher angle with increasing Mg and Cl concentration. The UV–Vis–NIR absorption spectra of Mg and Cl doped thin films are measured and classical Tauc approach was employed to estimate their band gap energies. The increase in band gap energy from 2.46 to 2.73 eV with the reduction in crystallite size supports quantum size effect. Raman spectra implied that more defects existed in the doped samples. Electrical studies showed that all the films have resistivity in the order of 101 Ω-cm and the CdS film with 6 at% Mg and Cl concentration has a minimum resistivity of 1.332 × 101 Ω-cm.

Effect of Al doping concentration on the electrical and optical properties of sol–gel derived Zn0.87Mg0.13O thin film

Zn0.87Mg0.13O thin film was developed by the sol–gel process. The effect of the Al doping concentration on the electrical and optical properties of Zn0.87Mg0.13O thin film was investigated. The lowest resistivity of 7.96 × 10−3 Ω·cm with an optical bandgap energy of 3.64 eV was achieved at a doping concentration of 0.8 mol % in solution (0.6 at. % in film). Al doping contributes to the decrease of resistivity and the increase of optical bandgap energy, whereas heavy doping of greater than 0.8 mol % shows detrimental effects on the resistivity and film crystallinity. The mobility is dominated by grain boundary scattering.

Defect-induced optical and electrical property modification in amorphous InGaZnO4 films

We report the physical characteristics of InGaZnO4 films deposited at various temperatures. The films were deposited on Al2O3(0001) substrates using pulsed laser deposition technique. Based on X-ray diffraction and field emission scanning electron microscopy measurements, the crystal structure changed from amorphous to polycrystalline as deposition temperature increased to 550°C. Furthermore, UV–vis measurements revealed a decrease in tail state i.e. improvement of local ordering, resulting in an increase of optical band-gap energy as deposition temperature increased. The core-level X-ray photoelectron spectra also showed an increase (decrease) in metal-oxide (oxygen deficiency) bond as the deposition temperature increased. The carrier concentration, Hall mobility and conductivity variation with deposition temperature are related to the competition between oxygen deficiency and grain boundary formation.

Enhancing photoresponse of ionic liquid–ZnO composite: Molecular docking study

Influence of the size of nanocrystalline ZnO on the emission of white light from ionic liquid, 1-butyl-2,3-dimethylimidazolium tetrafluoroborate (cationic IL) has been studied. Increase of crystalline size of ZnO decrease the shift of absorption edge due to semiconductor–ionic liquid interaction. The wavelength of green as well as blue emissions are increased on increasing the size of the nanocrystal. This is likely to be because of the increase of band gap energy of the semiconductor on decrease of the crystal size. In order to understand the binding interaction with DNA docking study has been carried out.

Thermal and optical properties of BaO–CaF2–P2O5 glasses

Thermal and optical properties of ternary phosphate glasses prepared by conventional melt-quenching technique, belonging to the series (50−X)BaO–XCaF2–50P2O5 (X=0 to 10mol%) were investigated with increase in CaF2 content. Thermal stability and glass forming ability studied using differential thermal analysis (DTA) were found to increase with the increase in CaF2 content. Powder X-ray diffraction (XRD) analysis of heat treated samples also revealed that CaF2 addition improves the thermal stability against crystallization. Increase in both glass transition temperature and onset crystallization temperature with the increase in CaF2 content can be attributed to the partial substitution of Ba2+ ion with Ca2+ ion, which is having larger field strength. The observed decrease in the melting temperature of glass batch with the increase in CaF2 content indicates that CaF2 acts as a flux and reduces the viscosity of the glass melt. The decrease in refractive index of the glasses with the increase in CaF2 content can be attributed to replacement of lower field strength Ba2+ by Ca2+ or the partial substitution of more polarizable oxygen ion by fluorine. Optical band gap energy slightly increased and Urbach energy marginally reduced with the increase in CaF2 content. Increase in optical band gap energy was further confirmed by calculating theoretical optical basicity of glasses. Average anion polarizability (αO/F) of (50−X)BaO–XCaF2–50P2O5 glasses calculated from refractivity data using Lorentz–Lorentz relation was correlated with its theoretical optical basicity (λth) using the previously established correlation for oxyfluoro phosphate glasses.

Chemical synthesis of porous web-structured CdS thin films for photosensor applications

The photo-activity of chemically deposited cadmium sulphide (CdS) thin film has been studied. The simple chemical route nucleates the CdS films with size up to the mean free path of the electron. Growth Kinematics of crystalline hexagonal CdS phase in the thin film form was monitored using X-ray diffraction. The time limitation set for the formation of the amorphous/nano-crystalline material is 40 and 60 min. Thereafter enhancement of the crystalline orientation along the desired plane was identified. Web-like porous structured surface morphology of CdS thin film over the entire area is observed. With decrease in synthesis time, increase of band gap energy i.e., a blue spectral shift was seen. The activation energy of CdS thin film at low and high temperature region was examined. It is considered that this activation energy corresponds to the donor levels associated with shallow traps or surface states of CdS thin film. The photo-electrochemical performance of CdS thin films in polysulphide electrolyte showed diode-like characteristics. Exposure of light on the CdS electrode increases the photocurrent. This suggests the possibility of production of free carriers via excited ions and also the light harvesting mechanism due to porous web-structured morphology. These studies hint that the obtained CdS films can work as a photosensor.

The post-growth effect on the properties of Cu2ZnSnS4 thin films

Cu2ZnSnS4 (CZTS) thin film was deposited on glass substrate by spray pyrolysis technique using a methanolic solution. This film was annealed under nitrogen atmosphere for an hour at different annealing temperatures. The effect of the annealing temperature on composition, structure, morphology, electrical, and optical properties of CZTS films was investigated. Energy dispersive x-ray analysis showed that after the annealing process, the atomic ratio values tend to their stoichiometric values. Moreover, the X-ray diffraction (XRD) and Raman spectroscopy revealed a kesterite structure with (112) preferential orientation for both as-deposited and annealed CZTS films. Moreover, they exhibited an improvement in crystallinity after annealing which was confirmed by SEM analysis. The conductivity of the heated CZTS films showed also an important increase in crystallinity. The absorption edge shifted toward lower wavelengths leading to an increase in band gap energy for the annealed CZTS films.

Effects of the growth temperature on the properties of spray deposited CuInS2 thin films for photovoltaic applications

CuInS2 absorber thin films were prepared by spray pyrolysis deposition at different substrate temperatures (250°C, 300°C and 350°C) using an aqueous solution of CuCl2, InCl3 and SC(NH2)2 at a precursor molar ratio of Cu:In:S=1:1.25:4.5. The effect of the substrate׳s temperature on the structural, morphological, optical and electrical properties of CuInS2 thin films was investigated. The X-ray diffraction patterns showed that CuInS2 has a tetragonal structure. The results show that the films deposited at 300°C have improved electrical conduction and photocurrent values. When increasing the substrate׳s temperature the absorbance decreases while the band gap energy increases, as a combined effect of crystallinity, morphology and deviation from stoichiometry.