Optoelectronics properties of TiO<Subscript>2</Subscript>:Cu thin films obtained by sol gel method

In this research, Cu-doped TiO₂ thin films have been successfully deposited onto a glass substrate by Sol–gel technique using dip coating method. The films were annealed at different annealing temperatures (400–500 °C) for 1 h. The structural, optical and electrical properties of the films were investigated and compared using X-ray Diffraction, UV–visible spectrophotometer and 4-point probe method. Optical analysis by mean transmittance T(λ) and absorption A(λ) measurements in the wavelength range between 300 to 800 nm allow us to determine the indirect band gap energy. DRX analysis of our thin films of TiO₂:Cu shows that the intensities of the line characteristic of anatase phase increasing in function of the temperature.     

On the response of semitransparent nanoparticulated films of LuPO<Subscript>4</Subscript>:Eu in poly-energetic X-ray imaging applications

In the present work, we demonstrate the fabrication technique of highly translucent layers of nanoparticulated (~50 nm) LuPO₄:Eu phosphor, present their basic luminescent properties and give results of their performance in a planar imaging system coupled to a CMOS photodetector. For comparison, the imaging performance of an opaque Gd₂O₂S:Eu phosphor screen prepared by sedimentation is also shown. The X-ray detection parameters as well as the luminescence efficiency of the investigated films were discussed. Results show that the in-line transmittance at ~600–700 nm, in the range of the phosphor luminescence, varies with respect to the thickness of the films from 40 to 50 % for a film of 67 μm thick to 4–12 % when the thickness increases to 460 μm. Yet, X-ray detection parameters get enhanced as the thickness of the films increases. Those results affect the luminescence efficiency curves of the films under poly-energetic X-ray radiation of various tube energies. The normalized noise power spectrum values were found similar for LuPO₄:Eu films and a phosphor screen made using commercial Gd₂O₂S:Eu powder. The detective quantum efficiency of our films is clearly lower compared to the Gd₂O₂S:Eu screen from 2 to 10 cycles mm^?1 frequency range while the modulation transfer function is lower from 0 to 5.5 cycles mm^?1 frequency range. The acquired data allow to predict that high-temperature sintering of our films under pressure may help to improve their imaging quality, since such a processing should increase the luminescence efficiency without significant growth of the grains and thus without sacrificing their translucent character.     

Influence of annealing temperature on optical properties of zinc oxide thin films analyzed by spectroscopic ellipsometry method

Zinc oxide (ZnO) thin films were sol–gel spin coated on glass substrates, annealed at various temperatures 300 °C, 400 °C and 500 °C and characterized by spectroscopic ellipsometry method. The optical properties of the films such as transmittance, refractive index, extinction coefficient, dielectric constant and optical band gap energy were determined from ellipsometric data recorded over the spectral range of 300–800 nm. The effect of annealing temperature in air on optical properties of the sol–gel derived ZnO thin films was studied. The transmission values of the annealed films were about 65% within the visible range. The optical band gap of the ZnO thin films were measured between 3.25 eV and 3.45 eV. Also the dispersion parameters such as single oscillator energy and dispersive energy were determined from the transmittance graph using the Wemple and DiDomenico model.     

Room temperature deposition of ZnO and Al:ZnO ultrathin films on glass and PET substrates by DC sputtering technique

In the present work, ultrathin films of Zinc oxide (ZnO) and Aluminum doped zinc oxide (AZO) with 20 nm thick were fabricated at 300 K on glass and Polyethylene terephthalate (PET) substrates by means of direct-current sputtering method. The structural morphology of the films were analyzed by (XRD) diffractometry. The average transmittance of films deposited on different substrates showed high transparency (over 80%) in the visible spectrum. The objective of the present work is to investigate the thicknesses and optical constants of ZnO and AZO ultrathin films prepared by DC sputtering onto (glass and PET) substrates using two methods (UV–Vis–NIR spectrophotometer and ellipsometer (SE) by new amorphous dispersion formula) with comparison to check and confirm the results that obtained from UV with those obtained from SE measurements. The optical constants of films were extracted and compared using UV and SE techniques in the range of (200–2200 nm) with increment of 1 nm in order to confirm the accuracy of the UV and shown an excellent agreement.     

Thin films of molecular materials synthesized from C32H20N10M (M = Co, Pb, Fe): Film formation, electrical and optical properties

In this work, the synthesis of molecular materials formed from metallic phthalocyanines and 1,4-phenylenediamine is reported. The powder and thin film (∼80-115 nm thickness) samples of the synthesized materials, deposited by vacuum thermal evaporation, show the same intra-molecular bonds in the IR spectroscopy studies, which suggests that the thermal evaporation process does not alter these bonds. The morphology of the deposited films was studied using scanning electron microscopy (SEM) and atomic force microscopy (AFM) and their optical and electrical properties were studied as well. The optical parameters have been investigated using spectrophotometric measurements of transmittance in the wavelength range 200-1200 nm. The absorption spectra recorded in the UV-vis region for the deposited samples showed two bands, namely the Q and Soret bands. The optical activation energy was calculated and found to be 3.41 eV for the material with cobalt, 3.34 eV for the material including lead and 3.5 eV for the material with iron. The effect of temperature on conductivity was measured for the thin films and the corresponding conduction processes are discussed in this work.     

Electrical and optical properties of indium tin oxide thin films grown by pulsed laser deposition

Indium tin oxide (ITO) thin films (200-400 nm in thickness) have been grown by pulsed laser deposition (PLD) on glass substrates without a post-deposition anneal. The electrical and optical properties of these films have been investigated as a function of substrate temperature and oxygen partial pressure during deposition. Films were deposited at substrate temperatures ranging from room temperature to 300 °C in O₂ partial pressures ranging from 0.1 to 100 mTorr. For 300 nm thick ITO films grown at room temperature in oxygen pressure of 10 mTorr, the electrical conductivity was 2.6᎒^-3 Q^-1cm^-1 and the average optical transmittance was 83% in the visible range (400-700 nm). For 300 nm thick ITO films deposited at 300 °C in 10 mTorr of oxygen, the conductivity was 5.2᎒^-3 Q^-1cm^-1 and the average transmittance in the visible range was 87%. Atomic force microscopy (AFM) measurements showed that the RMS surface roughness for the ITO films grown at room temperature was ~7 Å, which is the lowest reported value for the ITO films grown by any film growth technique at room temperature.     

Effect of annealing on structural and optical properties of diamond-like nanocomposite thin films

The annealing effect on structural and optical properties of the Diamond-like Nanocomposite (DLN) thin film deposited on glass substrate by Plasma Assisted Chemical Vapor Deposition (PACVD) method has been investigated. The films were annealed at temperature ranging from 300 to 600 °C, with 100 °C interval for 9 minutes by rapid thermal process (RTP) under vacuum. The structural changes of the annealed films have been studied using Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, Scanning Electron Microscope (SEM), and optical parameters have been determined using transmittance and reflectance spectra in UV-UIS-NIR range. The result shows that the refractive index increases gradually from 1.79 to 2.84 with annealing temperature due to out-diffusion of H by breaking Si–H and C–H bond leads to Si–C bond, i.e. more cross linking structure. In higher temperature range, graphitization also enhanced the refractive index. However, the optical band gap at up to 400 °C initially increases from 3.05 to 3.20 eV and then decreases due to graphitization. The film has a great potential to be used as anti-reflection coating (ARC) on silicon-based solar cell.     

Comparable structural and optical properties of 4H-pyrano [3, 2-c] quinoline derivatives thin films

The structural and optical properties of 2-Amino-6-ethyl-5-oxo-4-(3-phenoxyphenyl) - 5, 6- dihydro - 4H-pyrano [3,2-c] quinoline-3- carbonitrile (Ph-HPQ) and 2-Amino-4-(2-chlorophenyl)-6-ethyl-5-oxo-5,6-dihydro-4H-pyrano [3,2-c] quinoline-3-carbonitrile (Ch-HPQ) thin films are studied. The compounds are polycrystalline in as- synthesised powder form; they became nanocrystallites dispersed in amorphous matrix upon thermal deposition to form thin films. FTIR spectral measurements showed no change in chemical bonds of the compounds after being deposited to form thin films. The optical properties have been determined based on spectrophotometer measurements of transmittance and reflectance at nearly normal incidence of light in the spectral range of 200–2500 nm. The absorption parameters, molar extinction coefficient, oscillator strength and electric dipole strength, are reported. The type of electron transition is determined from analysis of absorption coefficient spectra near the onset and optical absorption edges. The onset and optical energy gaps for Ph-HPQ and Ch-HPQ thin films are determined. The single oscillator model is applied to calculate the dispersion parameters of the investigated thin films. In addition, oscillator and dispersion energies, the high-frequency dielectric constant, lattice dielectric constant and ratio of free charge carriers concentrations to their effective masses are evaluated for the compounds under investigation.     

Properties of Eu-doped zinc oxide thin films grown on glass substrates by radio-frequency magnetron sputtering

Eu-doped ZnO (EZO) thin films were prepared on glass substrates at various growth temperatures by radio-frequency magnetron sputtering. The properties of deposited thin films showed a significant dependence on the growth temperature. The preferential growth orientation of all the thin films was occurred along the ZnO (002) plane. The maximum crystallite size and the minimum average transmittance in the wavelength range of 450–1100 nm were observed for the EZO thin film deposited at 25 °C. A red shift of the optical band gap was observed in the growth temperature range of 25–300 °C. The highest figure of merit, an index for evaluating the performance of transparent conducting thin films, was obtained at 200 °C of growth temperature. These results indicated that the high-quality EZO film was obtained at a growth temperature of 200 °C.     

The modification of the characteristics of nanocrystalline ZnO thin films by variation of Ta doping content

Thin films of Ta-doped ZnO were synthesised via sol–gel spin coating route. The structural and optical properties of the films were evaluated to find out the effect of Ta dopant content. X-ray diffraction results indicated that all samples have hexagonal wurtzite crystal structure with polycrystalline nature. (0 0 2) peak is the most intense peak observed in all samples as well as the highest textured coefficient. Standard deviation results have shown that the kind of nucleation varies from heterogeneous to homogenous with Ta doping content. Additionally, Ta-incorporated ZnO films revealed not only a decreased surface roughness, but also an increased optical transmittance. Direct optical band gap values increased from 3.14 to 3.28 eV, and Urbach energy values decreased from 217 to 147 meV with increasing Ta doping. Refractive index and dielectric constant values were determined by means of two different functions and a significant consistency was found among them. Moreover, the correlation between the optical and structural properties showed that there is a relationship between refractive index and lattice constants of Ta-doped ZnO films.     

Effect of Al doping on structural,optical and electrical properties of SnO2 thin films synthesized by pulsed laser deposition

Aluminium-doped (Al = 0–5?wt.%) SnO₂ thin films with low-electrical resistivity and high optical transparency have been successfully synthesized by pulsed laser deposition technique at 500 °C. Structural, optical and electrical properties of the as-deposited and post-annealed thin films were investigated. X-ray diffraction patterns suggest that the films transform from crystalline to amorphous state with increasing aluminium content. The root mean square (R_q) surface roughness parameter, determined by atomic force microscopy decreases upon annealing of the as-deposited film. While resistivity of the film is the lowest (9.49 × 10^?4 Ω-cm) at a critical doping level of 1?wt.% Al, optical transparency is the highest (nearly 90%) in the as-deposited condition. Temperature dependence of the electrical resistivity suggests that the Mott’s variable range hopping process is the dominant carrier transport mechanism in the lower temperature range (40–135 K) for all the films whereas, thermally activated band conduction mechanism seems to account for conduction in the higher temperature region (200–300 K).     

Thin films of asymmetrically substituted “ABAB-Type” indium phthalocyanine chloride: Preparation, structural characterization and optical properties

A synthetic route to the asymmetric octasubstituted metal-free phthalocyanines H₂Pcs (3-8) has been developed. They contain a combination of 2(3),16(17)-Tetra(2-ethyl-1-hexyl) and 9(10),23(24)-tetra(n-hexyl) as substituent groups in the peripheral positions. Thin films of the target asymmetric substituted “ABAB-Type” indium phthalocyanine chloride complex InPcCl 9, have been also fabricated for the first time, with different thickness (105-350 nm) using thermal evaporation technique. The structural and optical properties of the films have been investigated. The material in powder form showed a polycrystalline nature with triclinic structure. Miller indices, hkl, values for each diffraction line in X-ray diffraction (XRD) spectrum were calculated. The as-deposited films exhibited also a crystalline nature with a preferred orientation of growth. The scanning electron microscope showed the nano-structure property of the deposited films. The optical properties of the films are studied by the spectrophotometric measurements of the transmittance, T and the reflectance, R determined at the normal incident of the light in the spectral range 200-2500 nm. The refractive and absorption indices of the films are calculated and are found to be independent of film thickness of 105-350 nm. Different dispersion and absorption parameters are determined for the films.     

Structural, optical and electrical properties of ZnO:Al thin films for optoelectronic applications

Undoped and aluminum-doped ZnO thin films are prepared by the sol–gel spin-coating process. Zinc acetate dihydrate, ethanol and mono-ethanolamine are used as precursor, solvent and stabilizer, respectively. The atomic percentage of dopant in solution were [Al/Zn] = 1 %, 2 % and 3 %. The effect of Al doping on the optical and electrical properties of ZnO films was investigated by X-ray diffraction (XRD), Four-Point probe technique and UV–visible spectrophotometery. The results from the X-ray diffraction show that the pure ZnO thin films had a polycrystalline structure of the hexagonal Wurtzite Type. A minimum resistivity of $3.3 \times 10^{-3} \Omega \cdot \mathrm{cm}$ was obtained for the film doped with 2 mol % Al. Optical transmissions reveal a good transmittance within the visible wavelength spectrum region for all of the films. The value of the band gap is enhanced from 3.21 eV (undoped ZnO) to 3.273 eV (Al/Zn = 3 %), the increase in the band gap can be explained by the Burstein–Moss effect.     

Thermal annealing effect on structural and optical properties of 2,9-Bis [2-(4-chlorophenyl)ethyl] anthrax [2,1,9-def:6,5,10-d′e′f′] diisoquinoline-1,3,8,10 (2H,9H) tetrone (Ch-diisoQ) thin films

Thin films of 2,9-Bis [2-(4-chlorophenyl)ethyl] anthrax [2,1,9-def:6,5,10-d′e′f′] diisoquinoline-1,3,8,10 (2H,9H) tetrone (Ch-diisoQ) were prepared by thermal evaporation technique. Structural properties of these (as-prepared and annealed at 373, 423, 473 and 523 K) films were determined by X-ray diffraction and scanning electron microscopy, which showed that the grain sizes increasing by the annealing effect. The transmittance and reflectance of all Ch-diisoQ thin films were measured in the range 200–2500 nm. Some optical constants such as optical band gap (E _g ), dispersion energy (E _d ), single oscillator energy (E _o ) and optical dielectric constant at a higher frequency (ε _∞ ) were calculated at different annealing temperatures. The optical band gap of the samples is decreased with the increase of annealing temperatures due to the increasing of the π-dislocation. Finally, the values of the optical susceptibility, χ⁽³⁾, were found to be annealing dependence.     

High frequency impedance spectroscopy study on Gd-doped CeO<Subscript>2</Subscript> thin films

The gadolinia-doped ceria (GDC) thin films were deposited by pulsed laser deposition. Samples with special geometry were prepared which allowed us to characterize GDC film in across-plane direction. The electrical properties of the films were investigated by means of impedance spectroscopy in the frequency range of 10 Hz to 10 GHz and 380–600 K temperature interval. The data analysis was performed by using appropriate equivalent circuit. The equivalent circuit modeled thin GDC film itself, platinum metal connections (traces) in the dielectric medium of sapphire substrate and interfaces between the film and platinum electrodes. Hence, several factors influenced the impedance spectra, namely the properties of substrate, the oxygen-ion transport in the film, ion blocking at the interface between the film and the electrode, and metal traces. The electrical properties of GDC thin films were compared with these of bulk ceramics and showed similar conductivity and dielectric permittivity values. The study also revealed that measurement data at electrical field frequencies of up to 10 GHz were particularly important to correctly estimate electrical properties of GDC thin films, because at high temperatures the electric response of GDC film shifts to high frequencies (higher than 1 MHz at 600 K). The thin film sample preparation for high frequency measurements and fitting of impedance data by using relatively simple equivalent circuit model is presented.     

Research on adhesion strength and optical properties of SiC films obtained via RF magnetron sputtering

SiC is widely used in various mechanical applications as a protective film because of its strength, thermal stability and good mechanical hardness. Here, amorphous SiC thin films with AlN as a buffer layer were deposited on glass and Si substrates through RF magnetron sputtering at different RF powers. The influence of the AlN buffer layer thickness on the morphological and the mechanical properties of the composite films was investigated. Results demonstrate that the AlN buffer layer can effectively improve the adhesion strength of SiC thin films, which has increased gradually from 26.78 N to 37.66 N. The transmittance of SiC thin films was measured using a UV–Vis–NIR spectrophotometer over a spectral range of 300–1200 nm. The average transmittance of SiC films decreases with increasing RF power, and their optical band gap values have varied from 3.31 eV to 3.50 eV.     

Synthesis and characterization of DSSC by using Pt nano-counter electrode: photosensor applications

Pt electrode prepared by chemical method has been employed as counter electrode in dye-sensitized solar cell. TiO₂ nanomaterial was deposited on fluorine-doped tin oxide substrate to be used as photoanode. Structure of the TiO₂ and Pt films was investigated by atomic force microscope. The effect of illumination intensity on the photovoltaic parameters such as open circuit voltage, short circuit current density, output power, fill factor and efficiency of these cells was investigated in the range 2.5–130 mW/cm^?2. The cell efficiency is stable above 70 mW/cm². The fill factor is almost constant all over the studied range of illumination intensity. Impedance spectroscopy of the studied device as the summary measurements of the capacitance–voltage, conductance–voltage and series resistance–voltage characteristics were investigated in a wide range of frequencies (5 kHz–1 MHz). At low frequencies, the capacitance has positive values with peak around the origin due to the interfaces. At 200 and 300 kHz, the capacitance is inverted to negative with further increasing of the positive biasing voltage. Above 400 kHz, C–V profile shows complete negative behavior. Also, the impedance–voltage and phase–voltage characteristics were investigated. This cell shows a new promising device for photosensor applications due to high sensitivity in low and high illuminations.     

Investigation of characteristic properties of Pr-doped SnO2 thin films

In the present work, an investigation study on the crystal structure, surface morphology, electrical conductivity and optical transparency of spray-deposited Pr-doped SnO₂ was made as a function of Pr doping content. The X-ray diffraction studies indicated that the films were grown at the (2 1 1) preferential orientation. The values of crystallite size and strain were determined using Williamson–Hall method and they varied between 71.47 and 208.76 nm, and 1.98 × 10^?3 – 2.78 × 10^?3. As seen from Scanning Electron Microscope micrographs, the films were composed of homogenous dispersed pyramidal-shaped grains. The n-type conductivity of films was confirmed with Hall Effect measurements, and the best electrical parameters were found for 3 at.% Pr doping level. The highest optical band gap and transmittance values were observed for undoped SnO₂ sample. The highest figure of merit (Φ), which is a significant parameter to interpret the usage efficiency of conductive and transparent materials in the optoelectronic and solar cell applications, was calculated to be 2.85 × 10^?5 Ω^?1 for 1 at.% Pr doping content. As a result of this study, it may be concluded that Pr-doped SnO₂ films with above properties can be used as a transparent conductor in various optoelectronic applications.     

Impact of chloride treatment on the physical properties of polycrystalline thin CdTe films for solar cell applications

This report presents the microstructural, optoelectrical and surface morphological properties of e-beam evaporated thin CdTe films with the activation of post-chloride treatment. The thin films having thickness 800 nm were deposited onto glass and ITO substrates subsequently processed with CdCl₂ treatment at various temperatures and then subjected to different characterization tools to investigate the physical properties. The films were found to be polycrystalline in nature having a cubic phase with preferred orientation (111) up to 320 °C and completely oxidized at 470 °C while the ohmic nature of films is confirmed by I–V characteristics. The absorbance is found to be higher in the visible range and lowest transmittance is observed for film processed at 170 °C. The surface morphology reveals that films have uniform surface with improved grain growth and elemental analysis confirms the deposition and treatment. The optimized results attract attention to use the processed films at 170 °C as an effective absorber-layer in CdTe based solar cells.     

Effects of deposition temperature and hydrogen flow rate on the properties of the Al-doped ZnO thin films and amorphous silicon thin-film solar cells

A compound of 98 mol% ZnO and 1 mol% Al₂O₃ (AZO, Al:Zn = 98:2) was sintered at 1350 °C as a target and the AZO thin films were deposited on glass using a radio frequency magnetron sputtering system. The effects of deposition temperature (from room temperature to ～300 °C) on the optical transmission spectrum of the AZO thin films were studied. The Burstein–Moss shift was observed and used to prove that defects in the AZO thin films decreased with increasing deposition temperature. The variations in the optical band gap (E _g) values of the AZO thin films were evaluated from plots of (αhv)²=c(hν?E _g), revealing that the measured E _g values increased with increasing deposition temperature. The effects of the H₂ flow rate during deposition (0 %～11.76 %, deposition temperature of 200 °C) on the crystallization, morphology, resistivity, carrier concentration, carrier mobility, and optical transmission spectrum of the AZO thin films were measured. The chemical structures of the Ar-deposited and 2 % H₂-flow rate-deposited AZO thin films (both were deposited at 200 °C) were investigated by XPS to clarify the mechanism of improvement in resistivity. The prepared AZO thin films were also used as transparent electrodes to fabricate amorphous silicon thin-film solar cells, and their properties were also measured.