Structural and the optical dispersion parameters of nano-CdTe thin film/flexible substrate

CdTe thin films of different thicknesses were deposited on polymer substrates for flexible optical devices applications. X-ray diffractogram of different thicknesses for CdTe films are measured and their patterns exhibit polycrystalline nature with a preferential orientation along the (111) plane. The optical constants of CdTe films were calculated based on the measured transmittance spectral data using Swanepoel's method in the wavelength range 400–2500 nm. The refractive index n and absorption index k were calculated and the refractive index exhibits a normal dispersion. The refractive index dispersion data followed the Wemple–DiDomenico model based on single oscillator. The oscillator dispersion parameters and the refractive index no. at zero photon energy were determined. The possible optical transition in these films is found to be allowed direct transition with energy gap increase from 1.46 to 1.60 eV with the increase in the film thickness. CdTe/flexible substrates are good candidates in optoelectronic devices     

Structural,opto-thermal and electrical properties of ZnO:Mo sprayed thin films

Zinc oxide (ZnO) thin films doped with molybdenum (Mo) have been prepared by the spray pyrolysis technique. X-ray analysis shows that ZnO:Mo thin films crystallize in hexagonal structure with a preferred orientation of the crystallites along (002) direction. The surface topography of these films was performed by the atomic force microscopy. The dispersion of the refractive index was discussed in terms of the single oscillator model proposed by Wemple and DiDomenico. The single oscillator energy (E₀) as well as the dispersion energy (E_d) were therefore calculated. Finally, the electric conductivity was investigated depending on the effect of temperature. The activation energy (E_a) was found to range from 0.63 to 0.94 eV; the electrical behavior can be correlated with Mo-doping.     

Physical investigations on Sb2S3 sprayed thin film for optoelectronic applications

Sb₂S₃ thin films have been obtained at 250 °C on glass substrates using the spray pyrolysis techniques. The structural study by means of XRD analysis shows that Sb₂S₃ thin film crystallized in the orthorhombic phase. The discussion of some structural constants has been made by means of both XRD and AFM investigations. Moreover, the optical analysis via the transmittance and the reflectance measurements reveals that Sb₂S₃ sprayed thin film has a direct transition with the band gap energy E_g equal to 1.72 eV. The analysis in 300–2500 nm domain of the refractive index data through Wemple–DiDomenico model leads to the single oscillator energy (E₀=2.32 eV), and the dispersion energy (E_d=10.03 eV). The electrical study leads to the dc activation energy is of the order of 0.72 eV and the maximum barrier high is W_M=0.87 eV. From the power exponent variation in terms of the heated temperature, it is found that the mechanism of conduction matches well the correlated barrier hopping CBH model.     

Structural,optical dispersion and dielectric properties of novel chromium nickel organic crystalline semiconductors

A novel organic crystalline semiconductor, [Cr(DPPP)(DPPM)(Ni-ap)(CO)₂] (Cr–Ni OSC) (6a), (DPPP=diphenylphosphino-propanone, DPPM=diphenylphosphino-methane and Ni-ap=nickel apyrazole ring) (6a) was synthesized. Structural characteristics of the Cr–Ni OSC complex have been investigated by IR, ¹HNMR, ³¹P NMR, thermal analysis (TG/DTA), and XRD. Thermal analysis of Cr–Ni OSC implies that, the complex was thermally stable up to 218 °C, and the melting point of it was 193 °C. Two discrete regions of (44.46%, 128–421 °C) and (41.15%, 600–823 °C) by TG analysis of Cr–Ni OSC complex was determined. XRD crystal data of Cr–Ni OSC showed the formation of monoclinic (P2₁/n). Transmittance and reflectance have been used to determine the optical dispersion and dielectric properties of the Cr–Ni OSC complex in the range of 200–800 nm. The transparency of the complex is 75–80% in the visible range. The optical and transport energy gaps were estimated as 1.87 eV and 2.01 eV respectively. Optical dispersion parameters have been calculated by using single term Sellmeier dispersion relation and Wemple–DiDomenico single oscillator model. Several dispersion parameters were determined by analysis of refractive index dispersion. The optical conductivity, surface and volume energy loss functions, and the electric modulus were also estimated from the optical dielectric constant analysis.     

Effects of the Cd:Zn:S molar ratio and heat treatment on the optical and photoluminescence properties of nanocrystalline CdZnS thin films

Nanocrystalline cadmium zinc sulfide thin films with different molar ratios were prepared by sol–gel dip-coating in a polyethyleneglycol matrix. After heat treatment in air at 250, 350 and 450 °C, the thin films were characterized by studying their structural, morphological, compositional, optical (linear and nonlinear) and photoluminescence (PL) properties. According to X-ray diffraction (XRD) results, the samples are polycrystalline with a hexagonal crystal structure and an average grain size of 12–18 nm. The surface morphology of the films was examined by scanning electron microscopy (SEM). The results show that the films consist of nanocrystalline grains included in clusters with uniform coverage over the substrate surface. To determine their chemical composition, X-ray photoelectron spectra (XPS) of composite films were measured. The transmittance and bandgap of the films increased with the Zn concentration and decreased with increasing annealing temperature. The refractive index of the films was measured and the related dispersion is discussed in terms of the Wemple–DiDomenico single oscillator model. The third-order nonlinear polarizability of the films was estimated using a semi-empirical relation based on the single oscillator model. The results show that the films are suitable as optical switches. PL spectra were recorded for an excitation wavelength of 210 nm. The emission intensity for the films varied with the Zn ratio and the annealing temperature and the behavior of different peaks is discussed.     

Structural and optoelectronic properties of nanostructured TiO2 thin films with annealing

About 480 nm thick titanium oxide (TiO₂) thin films have been deposited by electron beam evaporation followed by annealing in air at 300–600 °C with a step of 100 °C for a period of 2 h. Optical, electrical and structural properties are studied as a function of annealing temperature. All the films are crystalline (having tetragonal anatase structure) with small amount of amorphous phase. Crystallinity of the films improves with annealing at elevated temperatures. XRD and FESEM results suggest that the films are composed of nanoparticles of 25–35 nm. Raman analysis and optical measurements suggest quantum confinement effects since Raman peaks of the as-deposited films are blue-shifted as compared to those for bulk TiO₂ Optical band gap energy of the as-deposited TiO₂ film is 3.24 eV, which decreases to about 3.09 eV after annealing at 600 °C. Refractive index of the as-deposited TiO₂ film is 2.26, which increases to about 2.32 after annealing at 600 °C. However the films annealed at 500 °C present peculiar behavior as their band gap increases to the highest value of 3.27 eV whereas refractive index, RMS roughness and dc-resistance illustrate a drop as compared to all other films. Illumination to sunlight decreases the dc-resistance of the as-deposited and annealed films as compared to dark measurements possibly due to charge carrier enhancement by photon absorption.     

Synthesis and characterization of nanostructure CdO:Zn thin films deposited by spray pyrolysis technique: Molarity and heat treatment effects

Preparation of transparent conducting cadmium oxide doped with various concentration of Zinc (3%, 6%, 10%) in the spray solution, on glass substrate by spray pyrolysis is reported. we have tried to improve some physical properties of CdO films by Zn doping, hence the electrical, optical and structural properties of Zn doped CdO films were investigated using X-ray diffraction, Scanning electron microscopy, Hall Effect and UV–Visible spectrophotometry. Optical band gap, refractive index and extinction coefficient are also determined for different concentration. results show 6% doping is appropriate between other doping concentration, thereupon we selected this value and increased substrate temperature to acquire optimal condition. Observations like as mobility increment up to 46.9 (cm²/V s), transmittance up to 82% and increase of band gap up to 2.62 (eV) state the sample with 400 °C substrate temperature is good candidate for transparent and conducting oxide application.     

Determination of structural and optical properties of gold phthalocyanine thin films using density functional theory

We determined some optical and electrical properties of thin gold phthalocyanine films. Calculations were performed in the framework of density functional theory using the full potential linear augmented plane wave method. Studies on the density of states and band structure yielded a bandgap energy (E_g) of approximately 2 eV. Two trap energy levels were observed at 0.9 and 1.3 eV. Analysis of the dielectric function and electric loss function revealed a plasmon oscillation at 1.8 eV. In addition, we determined static refractive index values in the x, y and z directions of n_0xx = 2.16, n_0yy = 1.66 and n_0zz = 2.07. The optical bandgap of gold phthalocyanine was estimated to be 0.97 eV. Calculations revealed strong absorption at 400–700 nm, which compares favorably with experimental results.     

Gamma irradiation induced effects on optical properties and single oscillator parameters of Fe-doped CdS diluted magnetic semiconductors thin films

Gamma radiation (100–500 kGy) induced effects on optical properties and single oscillator parameters of nanocrystalline diluted magnetic semiconductor thin films Cd_1−xFe_xS (x=0.1, 0.15 and 0.2) with different compositions prepared by electron evaporation techniques have been studied. The optical characterization of the films has been carried out from spectral transmittance and reflectance obtained by double beam spectrophotometer in the wavelength range from 190 to 2500 nm. It is clearly shown that the direct optical band gap decreases with the increase in gamma radiation dose. This is attributed to the defect number growth. The refractive index and extinction coefficient have shown clear changes with irradiation and found to increase with the increase of the doses of γ radiation. This post-irradiation increase of the refractive index was interpreted in terms of the film density increase due to ionization and/or atomic displacements. Furthermore, the dispersion of the refractive index is discussed in terms of the Wemple–DiDomenico single oscillator model. The oscillator parameters, the single oscillator energy E_o, the dispersion energy E_d, the static refractive index n₀, average interband oscillator wavelength λ_o, and the average oscillator strength S_o, were estimated and revealed pronounced changes with irradiation. The observed changes in optical properties and single oscillator parameters clearly indicate the possibility of using Fe doped CdS thin films as a material for gamma radiation dosimeters     

Structural,optical and dielectric properties of HfSiO films prepared by co-evaporation method

HfSiO dielectric films were prepared on Si substrate by the co-evaporation method. The chemical composition, crystalline temperature, optical and electrical properties of the compound film were investigated. X-ray photoelectron spectroscopy analysis illustrated that the atom ratio of Hf to Si was about 4:1 and Hf–Si–O bonds appeared in the film. The X-ray diffraction analysis revealed that the crystalline temperature of the film was higher than 850 °C. Optical measurements showed that the refractive index was 1.82 at 550 nm wavelengths and the optical band gap was about 5.88 eV. Electrical measurements demonstrated that the dielectric constant and a fixed charge density were 18.1 and 1.95×10¹² cm⁻² respectively. In addition, an improved leakage current of 7.81 μA/cm² at the gate bias of −3 V was achieved for the annealed HfSiO film.     

Structural and optical characterizations of spin coated cobalt-doped cadmium oxide nanostructured thin films

Cd_1−xCo_xO thin films (with molar ratios x=0.0–8.0%) were grown onto glass substrates via the sol–gel spin coating technique. XRD results indicate that a CdO single phase with a cubic polycrystalline structure is formed. The crystallinity of CdO thin films is gradually deteriorated with increasing the Co ratio. AFM images of the films confirm the decrease of the grain size of the CdO films with increasing Co content. The direct optical band gap is red shifted from 2.580 eV to 2.378 eV with the increase of Co content. The refractive index, the dispersion parameters, and the optical conductivity of CdO thin films showed an enhancement with increasing cobalt dopant ratio. The correlation between the structural modifications and the resultant optical properties are reported.     

Nanocrystalline Bi2S3 thin films grown by thio-glycolic acid mediated successive ionic layer adsorption and reaction (SILAR) technique

Bismuth sulfide (Bi₂S₃) nanocrystalline thin films were deposited on glass substrate by a simple and low-cost thioglycolic-assisted successive ionic layer adsorption and reaction method, using bismuth acetate and thioacetamide as cationic and anionic precursors respectively. Influence of cationic concentration on the structural, optical and electrical properties of Bi₂S₃ thin films were investigated. X-ray diffraction pattern revealed that the prepared Bi₂S₃ thin films are polycrystalline with orthorhombic structure. The surface morphology of Bi₂S₃ thin films examined by atomic force microscopy showed cluster like morphology, and having small hillocks of fairly uniform distribution. Optical studies showed a direct band-to-band transition, and the estimated optical band gap decreases from 1.81 eV to 1.25 eV with the increase in cationic concentration from 0.01 M to 0.03 M. Electrical resistivity measurements by four probe technique revealed negative temperature coefficient of resistance, which confirms the semiconducting nature of Bi₂S₃ thin films. The activation energy of Bi₂S₃ thin films was found to decrease from 0.059 eV to 0.022 eV with the increase in cationic concentration from 0.01 M to 0.03 M, which is attributed to improved grain size and reduction in the defect levels.     

Effect of substrate temperature on the properties of ZnO thin films prepared by spray pyrolysis

Sprayed ZnO films were grown on glass at different substrate temperatures from 200 °C to 500 °C and their structural, optical and electrical properties were investigated. All films are polycrystalline with hexagonal wurtzite structure. ZnO films at substrate temperatures above 400 °C appear to be better crystalized with (002) plane as preferential orientation. Optical transmission spectrum shows that ZnO films have high transmission (above 80%) in visible region for substrate temperatures above 400 °C. Photoluminescence spectra at room temperature show an ultraviolet emission and two visible emissions at 2.82 eV and 2.37 eV. The resistivity of ZnO films increases with increasing substrate temperatures (above 400 °C). The ZnO film deposited at 400 °C shows highest figure of merit.     

Substrate temperature effect on structural,optical and electrical properties of vacuum evaporated SnO2 thin films

Tin oxide (SnO₂) thin films were deposited on glass substrates by thermal evaporation at different substrate temperatures. Increasing substrate temperature (T_s) from 250 to 450 °C reduced resistivity of SnO₂ thin films from 18×10⁻⁴ to 4×10⁻⁴▒ Ω ▒cm. Further increase of temperature up to 550 °C had no effect on the resistivity. For films prepared at 450 °C, high transparency (91.5%) over the visible wavelength region of spectrum was obtained. Refractive index and porosity of the layers were also calculated. A direct band gap at different substrate temperatures is in the range of 3.55−3.77 eV. X-ray diffraction (XRD) results suggested that all films were amorphous in structure at lower substrate temperatures, while crystalline SnO₂ films were obtained at higher temperatures. Scanning electron microscopy images showed that the grain size and crystallinity of films depend on the substrate temperature. SnO₂ films prepared at 550 °C have a very smooth surface with an RMS roughness of 0.38 nm.     

Flash evaporated cadmium sulfide films

Cadmium sulfide (CdS) thin films were deposited by the flash evaporation technique onto glass substrates kept at temperatures in the range 30–300 °C. The source material was CdS powder synthesized in the laboratory. The films exhibited hexagonal structure with dislocation density and the stress decreased as the substrate temperature increased. An optical band gap of 2.39 eV was obtained for the films deposited at 300 °C. Raman spectra exhibited peaks corresponding to Longitudinal Optical phonons of CdS with the full width at half maximum decreasing with increase of substrate temperature. Room temperature resistivity values are lower than earlier reports on chemically deposited CdS films.     

Deposition and characterization of pure and Cd doped SnO2 thin films by the nebulizer spray pyrolysis (NSP) technique

Pure and cadmium doped tin oxide thin films were deposited on glass substrates from aqueous solution of cadmium acetate, tin (IV) chloride and sodium hydroxide by the nebulizer spray pyrolysis (NSP) technique. X-ray diffraction reveals that all films have tetragonal crystalline structure with preferential orientation along (200) plane. On application of the Scherrer formula, it is found that the maximum size of grains is 67 nm. Scanning electron microscopy shows that the grains are of rod and spherical in shape. Energy dispersive X-ray analysis reveals the average ratio of the atomic percentage of pure and Cd doped SnO₂ films. The electrical resistivity is found to be 10² Ω cm at higher temperature (170 °C) and 10³ Ω cm at lower temperature (30 °C). Optical band gap energy was determined from transmittance and absorbance data obtained from UV–vis spectra. Optical studies reveal that the band gap energy decreases from 3.90 eV to 3.52 eV due to the addition of Cd as dopant with different concentrations.     

Investigation of structural and optoelectronic properties of annealed nickel phthalocyanine thin films

Thin films of nickel phthalocyanine (NiPc) were prepared by thermal evaporation and the effects of annealing temperature on the structural and optical properties of the samples were studied using different analytical methods. Structural analysis showed that the grain size and crystallinity of NiPc films improved as annealing temperature increased from 25 to 150 °C. Also, maximum grain size (71.3 nm) was obtained at 150 °C annealing temperature. In addition, NiPc films annealed at 150 °C had a very smooth surface with an RMS roughness of 0.41 nm. Optical analysis indicated that band gap energy of films at different annealing temperatures varied in the range of 3.22–3.28 eV. Schottky diode solar cells with a structure of ITO/PEDOT:PSS/NiPc/Al were fabricated. Measurement of the dark current density–voltage (J–V) characteristics of diodes showed that the current density of films annealed at 150 °C for a given bias was greater than that of other films. Furthermore, the films revealed the highest rectification ratio (23.1) and lowest barrier height (0.84 eV) demonstrating, respectively, 23% and 11% increase compared with those of the deposited NiPc films. Meanwhile, photoconversion behavior of films annealed at 150 °C under illumination showed the highest short circuit current density (0.070 mA/cm²) and open circuit voltage of (0.55 V).     

Effect of annealing temperature on structural,electrical and optical properties of spray pyrolytic nanocrystalline CdO thin films

Nanocrystalline CdO thin films were prepared onto a glass substrate at substrate temperature of 300 °C by a spray pyrolysis technique. Grown films were annealed at 250, 350, 450 and 550 °C for 2.5 h and studied by the X-ray diffraction, Hall voltage measurement, UV-spectroscopy, and scanning electron microscope. The X-ray diffraction study confirms the cubic structure of as-deposited and annealed films. The grain size increases whereas the dislocation density decreases with increasing annealing temperature. The Hall measurement confirms that CdO is an n-type semiconductor. The carrier density and mobility increase with increasing annealing temperature up to 450 °C. The temperature dependent dc resistivity of as-deposited film shows metallic behavior from room temperature to 370 K after which it is semiconducting in nature. The metallic behavior completely washed out by annealing the samples at different temperatures. Optical transmittance and band gap energy of the films are found to decrease with increasing annealing temperature and the highest transmittance is found in near infrared region. The refractive index and optical conductivity of the CdO thin films enhanced by annealing. Scanning electron microscopy confirms formation of nano-structured CdO thin films with clear grain boundary.     

Pulse electrodeposited copper indium sulfide films

Copper indium sulfide (CISu) films were deposited by the pulse galvanostatic deposition technique at different duty cycles. The films are polycrystalline with peaks corresponding to the chalcopyrite phase of CISu. The grain size and surface roughness increased from 10 to 25 nm and 0.85 to 2.50 nm respectively with increase of duty cycle. Optical band gap in the range of 1.30–1.51 eV was observed for the films deposited at different duty cycles. Room temperature resistivity of the films is in the range of 0.1–3.67 Ω cm. Photoconductivity measurements were made at room temperature. Photocurrent spectra exhibited maximum corresponding to the band gap of copper indium sulphide. CdS/CuInS₂ fabricated with CISu films deposited at 50% duty cycle have exhibited a V_oc of 0.62 V, J_sc of 16.30 mA cm^?2, FF of 0.71 and efficiency of 7.16%.     

Effect of doping concentration on the properties of bismuth doped tin sulfide thin films prepared by spray pyrolysis

Bismuth doped tin sulfide (SnS:Bi) thin films were deposited onto glass substrates by the spray pyrolysis technique at the substrate temperature of 350 °C. The effect of doping concentration [Bi/Sn] on their structural, optical and electrical properties was investigated as a function of bismuth doping between 0 and 8 at%. The XRD results showed that the films were polycrystalline SnS with orthorhombic structure and the crystallites in the films were oriented along (111) direction. Atomic force microscopy revealed that the particle size and surface roughness of the films increased due to Bi-doping. Optical analysis exhibited the band gap value of 1.40 eV for SnS:Bi (6 at%) which was lower than the band gap value for 0 at% of Bi (1.60 eV). The film has low resistivity of 4.788×10⁻¹ Ω-cm and higher carrier concentration of 3.625×10¹⁸ cm⁻³ was obtained at a doping ratio of 6 at%.