Annealing temperature effect on the structural, optical and electrical properties of ZnS thin films

Zinc sulfide thin films were prepared on glass substrates at room temperature using a chemical bath deposition method. The obtained films were annealed at temperatures ranging from 100 to 500 °C in steps of 100 °C for 1 h. The films were characterized by X-ray diffraction (XRD), Raman spectroscopy, energy dispersive X-ray analysis (EDX), optical absorption spectra, and electrical measurements. X-ray diffraction analysis indicates that the deposited films have an amorphous structure, but after being annealed at 500 °C, they change to slightly polycrystalline. The optical constants such as the refractive index (n_r), the extinction coefficient (k), and the real (ε₁) and imaginary (ε₂) parts of the dielectric constant are calculated depending on the annealing temperature. Aside from the ohmic characteristics of the I-V curve, a nonlinear I-V curve owing to the Schottky contact is also found, and the barrier heights (?_bn) for Au/n-ZnS and In/n-ZnS heterojunctions are calculated. The conductivity type was identified by the hot-probe technique.     

Optical and electrical properties of thermally evaporated In49Se48Sn3 films

Nearly stoichiometric thin films of In₄₉Se₄₈Sn₃ were deposited at room temperature, by conventional thermal evaporation of the presynthesized materials, onto precleaned glass substrates. The microstructural studies on the as-deposited and annealed films, using transmission electron microscopy and diffraction (TEMD), revealed that the as-deposited films are amorphous in nature, while those annealed at 498 K are crystalline. The optical properties of the investigated films were determined from the transmittance and reflectance data, in the spectral range 650-2500 nm. An analysis of the optical absorption spectra revealed a non-direct energy gap characterizing the amorphous films, while both allowed and forbidden direct energy gaps characterized the crystalline films. The electrical resistance of the deposited films was carried out during heating and cooling cycles in the temperature range 300-600 K. The results show an irreproducible behavior, while after crystallization the results become reproducible. The analysis of the temperature dependence of the resistance (ln(R) vs. 1000/T) for crystalline films shows two straight lines corresponding to both extrinsic and intrinsic conduction. The room temperature I-V characteristics of the as-deposited films sandwiched between similar Ag metal electrodes shows an ohmic behavior, while non-ohmic behavior attributed to space charge limited conduction has been observed when the films are sandwiched between dissimilar Ag/Al metal electrodes.     

Structural, optical and electrical properties of ZnO/Zn2GeO4 porous-like thin film and wires

Zinc oxide/zinc germanium oxide (ZnO/Zn₂GeO₄) porous-like thin film and wires has been fabricated by simple thermal evaporation method at temperature about 1120 °C for 2.5 h. The structural and optical properties of the porous-like-thin film and wires have been investigated by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD) and photoluminescence (PL) spectroscopy. Metal semiconductor metal (MSM) photodetector structure was used to evaluate the electrical characteristics by using current-voltage (I-V) measurements. Room temperature photoluminescence spectrum of the sample shows one prominent ultraviolet peak at 378 nm and a shoulder at 370 nm. In addition, broad visible blue emission peak at wavelength 480 nm and green emission peak at 500 nm are also observed. Strong photoelectric properties of the MSM in the UV demonstrated that the porous-like-thin film and wires contribute to its photosensitivity and therefore making ZnO/Zn₂GeO₄ wires potential photodetector in the shorter wavelength applications.     

The influence of oxidation temperature on structural, optical and electrical properties of thermally oxidized bismuth oxide films

Monoclinic bismuth oxide (Bi₂O₃) films have been prepared by thermal oxidation of vacuum evaporated bismuth thin films onto the glass substrates. In order to obtain the single phase Bi₂O₃, the oxidation temperature was varied in the range of 423-573 K by an interval of 50 K. The as-deposited bismuth and oxidized Bi₂O₃ films were characterized for their structural, surface morphological, optical and electrical properties by means of X-ray diffraction, scanning electron microscopy (SEM), optical absorption and electrical resistivity measurements, respectively. The X-ray analyses revealed the formation of polycrystalline mixed phases of Bi₂O₃ (monoclinic, α-Bi₂O₃ and tetragonal, β-Bi₂O₃) at oxidation temperatures up to 523 K, while at an oxidation temperature of 573 K, a single-phase monoclinic α-Bi₂O₃ was formed. From SEM images, it was observed that of as-deposited Bi films consisted of the well-defined isolated crystals of different shapes while after thermal oxidation the smaller dispersed grains were found to be merged to form bigger grains. The changes in the optical properties of Bi₂O₃ films obtained by thermal oxidation at various temperatures were studied from optical absorption spectra. The electrical resistivity measurement depicted semiconducting nature of Bi₂O₃ with high electrical resistivity at room temperature.     

Broadband photoluminescence from pulsed laser deposited Er2O3 films

Photoluminescence (PL) with the bandwidth of 45 nm (1523-1568 nm at the level of 3 dB) was observed in amorphous Er₂O₃ films grown on to the quartz substrate by pulsed laser ablation of erbium oxide stoichiometric target. Optical transmission spectrum has been fitted to Swanepoel formula to determine the dispersion of refractive index and to extract resonance absorption peaks at 980 and 1535 nm. The maximum gain coefficient of 800 dB/cm at 1535 nm was estimated using McCumber theory and experimental spectrum of the resonance absorption. In 5.7 mm-long waveguide amplifier a theory predicts the spectral gain of 20 dB with 1.4 dB peak-to-peak flatness in the bandwidth of 31 nm (1532-1563 nm) when 73% of Er³⁺ ions are excited from the ground state to the ⁴I_13/2 laser level. Strong broadband PL at room temperature and inherently flat spectral gain promise Er₂O₃ films for ultra-short high-gain optical waveguide amplifiers and integrated light circuits.     

Optical and gas sensing properties of thick TiO2 films grown by laser deposition

In this work the optical and the gas sensing properties of thick TiO₂ waveguide films, produced by pulsed laser deposition, were investigated by m-line spectroscopy. The films were deposited on (0 0 1) SiO₂ substrates at temperature of 100 °C. The thickness of the films was measured to be in the range from 650 to 1900 nm and the roughness increases from 5 to 14.6 nm. High quality mode spectra, consisted of thin and bright TE and TM modes, were observed in the films with thickness up to 1200 nm. All the films revealed anisotropic optical properties. Gas sensitivity of the films to CO₂ was examined at room temperature on the basis of the variations of the refractive index. CO₂ concentration of 3 × 10⁴ ppm was detected, which corresponds to a refractive index variation of about 1 × 10⁻⁴. The crystal structure and the optical transmittance of the films were also presented and discussed.     

Dependence of intermediated noble metals on the optical and electrical properties of ITO/metal/ITO multilayers

Sn doped In₂O₃ (ITO) single layer and a sandwich structure of ITO/metal/ITO (IMI) multilayer films were deposited on a polycarbonate substrate using radio-frequency and direct-current magnetron sputtering process without substrate heating. The intermediated metal films in the IMI structure were Au and Cu films and the thickness of each layer in the IMI films was kept constant at 50 nm/10 nm/40 nm. In this study, the ITO/Au/ITO films show the lowest resistivity of 5.6 × 10⁻⁵ Ω cm.However the films show the lower optical transmission of 71% at 550 nm than that (81%) of as deposited ITO films. The ITO/Cu/ITO films show an optical transmittance of 54% and electrical resistivity of 1.5 × 10⁻⁴ Ω cm. Only the ITO/Au/ITO films showed the diffraction peaks in the XRD pattern. The figure of merit indicated that the ITO/Au/ITO films performed better in a transparent conducting electrode than in ITO single layer films and ITO/Cu/ITO films.     

Effects of the substrate temperature on the properties of CuIn5S8 thin films

Structural, optical and electrical properties of CuIn₅S₈ thin films grown by thermal evaporation have been studied relating the effects of substrate heating conditions of these properties. The CuIn₅S₈ thin films were carried out at substrate temperatures in the temperature range 100-300 °C. The effects of heated substrate on their physico-chemical properties were investigated using X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), optical transmission and hot probe method. X-ray diffraction revealed that the films are strong preferred orientation along the (3 1 1) plane upon substrate temperature 200 °C and amorphous for the substrate temperatures below 200 °C. No secondary phases are observed for all the films. The composition is greatly affected by heated substrate. From the optical transmission and reflection, an important absorption coefficient exceeds 10⁵ cm⁻¹ at 800 nm was found. As increasing the substrate temperature, the optical energy band gap decreases from 1.70 eV for the unheated films to 1.25 eV for the deposited films at 300 °C. It was found that CuIn₅S₈ thin film is an n-type semiconductor at 250° C.     

Nanocrystalline formation and optical properties of germanium thin films prepared by physical vapor deposition

Amorphous and nanocrystalline germanium thin films were prepared on glass substrates by physical vapor deposition (PVD). The influence of thermal annealing on the characteristics of the Ge thin films has been investigated. X-ray diffraction (XRD) and SEM show amorphous structure of films deposited at room temperature. After thermal annealing, the crystallinity was improved when the annealing temperature increases. The Ge thin films annealed at different temperatures in air were nanocrystalline, having the face-centered cubic structure with preferred orientation along the 〈1 1 1〉 direction. The nanostructural parameters have been evaluated by using a single-order Voigt profile analysis. Moreover, the analysis of the optical transmission and reflection behavior was carried out. The values of direct and indirect band gap energies for amorphous and nanocrystalline phases are 0.86±0.02, 0.65±0.02 and 0.79±0.02, 0.61±0.02 eV, respectively. In addition, the complex optical functions for the wavelength range 600-2200 nm are reported. The refractive index of the nanocrystalline phase drops from 4.80±0.03 to 2.04±0.02, and amorphous phase changes from 5.18±0.03 to 2.42±0.02 for the whole wavelength range. The dielectric functions ε₁ and ε₂ of the deposited films were recorded as a function of wavelength within the range from 600 to 2200 nm.     

Planar quarter wave stacks prepared from chalcogenide Ge-Se and polymer polystyrene thin films

Planar quarter wave stacks based on amorphous chalcogenide Ge-Se alternating with polymer polystyrene (PS) thin films are reported as Bragg reflectors for near-infrared region. Chalcogenide films were prepared using a thermal evaporation (TE) while polymer films were deposited using a spin-coating technique. The film thicknesses, d∼165 nm for Ge₂₅Se₇₅ (n=2.35) and d∼250 nm for polymer film (n=1.53), were calculated to center the reflection band round 1550 nm, whose wavelengths are used in telecommunication. Optical properties of prepared multilayer stacks were determined in the range 400-2200 nm using spectral ellipsometry, optical transmission and reflection measurements. Total reflection for normal incidence of unpolarized light was observed from 1530 to 1740 nm for 8 Ge-Se+7 PS thin film stacks prepared on silicon wafer. In addition to total reflection of light with normal incidence, the omnidirectional total reflection of TE-polarized light from 8 Ge-Se+7 PS thin film stacks was observed. Reflection band maxima shifted with varying incident angles, i.e., 1420-1680 nm for 45° deflection from the normal and 1300-1630 nm for 70° deflection from the normal.     

Optical and electrical properties of plasma-oxidation derived HfO2 gate dielectric films

High-k gate dielectric HfO₂ thin films have been deposited on Si(1 0 0) by using plasma oxidation of sputtered metallic Hf thin films. The optical and electrical properties in relation to postdeposition annealing temperatures are investigated by spectroscopic ellipsometry (SE) and capacitance-voltage (C-V) characteristics in detail. X-ray diffraction (XRD) measurement shows that the as-deposited HfO₂ films are basically amorphous. Based on a parameterized Tauc-Lorentz dispersion mode, excellent agreement has been found between the experimental and the simulated spectra, and the optical constants of the as-deposited and annealed films related to the annealing temperature are systematically extracted. Increases in the refractive index n and extinction coefficient k, with increasing annealing temperature are observed due to the formation of more closely packed thin films and the enhancement of scattering effect in the targeted HfO₂ film. Change of the complex dielectric function and reduction of optical band gap with an increase in annealing temperature are discussed. The extracted direct band gap related to the structure varies from 5.77, 5.65, and 5.56 eV for the as-deposited and annealed thin films at 700 and 800 °C, respectively. It has been found from the C-V measurement the decrease of accumulation capacitance values upon annealing, which can be contributed to the growth of the interfacial layer with lower dielectric constant upon postannealing. The flat-band voltage shifts negatively due to positive charge generated during postannealing.     

Thickness dependence of optical parameters for ZnTe thin films deposited by electron beam gun evaporation technique

Zinc telluride thin films with different thicknesses have been deposited by electron beam gun evaporation system onto glass substrates at room temperature. X-ray and electron diffraction techniques have been employed to determine the crystal structure and the particle size of the deposited films. The stoichiometry of the deposited films was confirmed by means of energy-dispersive X-ray spectrometry. The optical transmission and reflection spectrum of the deposited films have been recorded in the wavelength optical range 450-2500 nm. The variation of the optical parameters, i.e. refractive index, n, extinction coefficient, k, with thickness of the deposited films has been investigated. The refractive index dispersion in the transmission and low absorption region is adequately described by the single-oscillator model, whereby the values of the oscillator strength, oscillator position, dispersion parameter as well as the high-frequency dielectric constant were calculated for different film thickness. Graphical representations of the surface and volume energy loss function were also presented.     

Optical absorption and emission properties of Nd in TeO2-WO3 and TeO2-WO3-CdO glasses

Effects of WO₃ and CdO on the spectroscopic properties of Nd³⁺ doped tellurite glasses were investigated. The optical band gaps and Urbach energies of the samples were determined using the dependence of the absorption coefficient on the photon energy. The Urbach energies were found to vary from 0.18 to 0.25 eV as the WO₃ content in the binary glasses decreased from 20.0 to 10.0 mol% while the optical band gap of the same glasses did not show an appreciable dependence on the glass composition. Judd-Ofelt (Ω_t) parameters were calculated from the optical absorption spectra measured at room temperature. In all the glasses the J-O parameters follow the same trend as Ω₂>Ω₆>Ω₄. The J-O intensity parameters were used to compute the radiative properties such as the radiative transition probabilities (A_ed), branching ratios (β) and radiative lifetimes (τ_r) for all the possible fluorescence bands. The fluorescence spectra obtained upon 805.2 nm excitation exhibited an intense emission band centered at 1064 nm (⁴F_3/2→⁴I_11/2) and two weak bands at 910 nm (⁴F_3/2→⁴I_9/2), and 1340 nm (⁴F_3/2→⁴I_13/2). The stimulated emission cross-section for the 1064 nm emission was determined using the emission spectra. The highest gain bandwidth (σ_e×Δλ_P) was determined to be 155.4 for the 0.79TeO₂-0.15WO₃-0.05CdO ternary glass composition, which could be more useful as promising material for the design and development of fiber amplifiers and lasers.     

Effects of co-substitution on the electrical properties of BiFeO3 thin films prepared by chemical solution deposition

Ferroelectric BiFeO₃ thin films with Nd-Cr (or Sm-Cr) co-substitution (denoted by BNdFCr and BSmFCr, respectively) were deposited on the Pt(2 0 0)/TiO₂/SiO₂/Si(1 0 0) substrates by a chemical solution deposition method. X-ray diffraction patterns revealed the formation of BNdFCr and BSmFCr thin films without any secondary phases. The co-substituted BNdFCr (or BSmFCr) thin films, which were annealed at 550 °C for 30 min in N₂ atmosphere, exhibited enhanced electrical properties compared to BFO thin films with the remanent polarization (2P_r) and coercive electric field (2E_c) of 196, 188 μC/cm² and 600, 570 kV/cm with the electric field of 800 kV/cm, respectively. The leakage current densities of BNdFCr and BSmFCr thin films measured at room temperature were approximately three orders of magnitude lower than that of BFO thin film, and the leakage current at room temperature of the thin films exhibited three distinctive conduction behaviors. Furthermore, the values of pulse polarizations [i.e., +(P*-P^{^}) or −(P*-P^{^})] of BNdFCr and BSmFCr thin films were reasonably unchanged up to 1.4 × 10¹⁰ switching cycles.     

Synthesis of bamboo-leaf-shaped ZnO nanostructures by oxidation of Zn/SiO2 composite films deposited with radio frequency magnetron co-sputtering

Bamboo-leaf-shaped ZnO nanostructures were synthesized by oxidation of metal Zn/SiO₂ matrix composite thin films deposited on Si(1 1 1) substrates with radio frequency magnetron co-sputtering. The synthesized bamboo-leaf-shaped ZnO are single crystalline in nature with widths ranging from 30 to 60 nm and lengths of up to 5-10 μm, room temperature photoluminescence spectrum of the nanostructures shows a strong and sharp UV emission band at 372 nm and a weak and broad green emission band at about 520 nm which indicates relatively excellent crystallization and optical quality of the ZnO nanostructures synthesized by this novel method.     

Effects of thermal oxidation temperature on vacuum evaporated tin dioxide film

In order to investigate the effect of thermal oxidation temperature on tin dioxide (SnO₂), tin dioxide films were obtained on quartz substrates by vacuum evaporation of tin metal. The films were characterized by X-ray diffraction (XRD) analyses, scanning electron microscopy (SEM), temperature dependent electrical resistivity measurement and optical absorption spectroscopy. The SEM images showed that the films are dense, continuous and are composed of nanoparticles and particle sizes are increased after thermal oxidation. From the X-ray measurement results, the films indicated two strong reflection peaks of tetragonal structure in the orientations of (1 0 1) and (2 0 0) at 2θ = 33.89° and 37.95°, respectively. Intensity of the peaks increased with increasing thermal oxidation temperature. We found resistivity values of about 10⁻⁴ Ω-cm. Optical absorption spectra of the films in the UV–Vis spectral range revealed that optical band gap (E_g) value of the films increases with increasing thermal oxidation temperature.     

Effect of some preparative parameters on optical properties of spray deposited iridium oxide thin films

Optical properties of iridium oxide films fabricated by the spray pyrolysis technique (SPT) have been investigated. The transmission and reflection spectra of the sprayed films were measured by using a double-beam spectrophotometer in the wavelength range from 200 to 2500 nm. Influences of the preparative parameters; namely, substrate temperature (350-500 °C) and solution molarity (0.005-0.03 M), on the optical characteristics were examined. The solution molarity of the iridium chloride solution was varied so as to prepare iridium oxide thin films with thicknesses ranging from 160 to 325 nm. Some important characteristics of optical absorption, such as optical dispersion energies, the dielectric constant, the ratio of the number of charge carriers to the effective mass, the single oscillator wavelength, and the average value of the oscillator strength, were evaluated. The value of the refractive index was found to depend on the chemical composition as well as the degree of stoichiometry of IrO₂. The values obtained for the high frequency dielectric constant through two procedures are in the range of 2.8-3.9 and 3.3-4.6 over the relevant ranges of the substrate temperature and solution molarity, respectively. Analysis of the energy dispersion curve of the absorption coefficient indicated a direct optical transition with the bandgap energy ranging between 2.61 and 2.51 eV when the substrate temperature increases from 350 to 500 °C.     

Structural, optical properties and VCNR mechanisms in vacuum evaporated iodine doped ZnSe thin films

Iodine doped ZnSe thin films were prepared onto uncoated and aluminium (Al) coated glass substrates using vacuum evaporation technique under a vacuum of 3 × 10⁻⁵ Torr. The composition, structural, optical and electrical properties of the deposited films were analyzed using Rutherford backscattering spectrometry (RBS), X-ray diffraction (XRD), spectroscopic ellipsometry (SE) and study of I-V characteristics, respectively. In the RBS analysis, the composition of the deposited film is calculated as ZnSeI_0.003. The X-ray diffractograms reveals the cubic structure of the film oriented along (1 1 1) direction. The structural parameters such as crystallite size, strain and dislocation density values are calculated as 32.98 nm, 1.193 × 10⁻³ lin⁻² m⁻⁴ and 9.55 × 10¹⁴ lin/m², respectively. Spectroscopic ellipsometric (SE) measurements were also presented for the prepared iodine doped ZnSe thin films. The optical band gap value of the deposited films was calculated as 2.681 eV by using the optical transmittance measurements and the results are discussed. In the electrical studies, the deposited films exhibit the VCNR conduction mechanism. The iodine doped ZnSe films show the non-linear I-V characteristics and switching phenomena.     

Optical properties of methane to 288 GPa at 300 K

Optical properties of solid methane (CH₄) were studied at high pressure and room temperature using a diamond anvil cell. Reflectivity and transmission measurements were used to measure the refractive index to 288 GPa. Fabry-Perot interferometery was used to measure the sample thickness to 172 GPa. This data was fitted to the derived expression of thickness vs. pressure that was then used to calculate the thickness to 288 GPa. This in turn was combined with optical absorption experiments to obtain the absorption coefficient and hence the extinction coefficient k^*. From combined reflection and absorption experiments the refractive index n=n_s+ik^* was obtained. The index of refraction and the ratio of molar refraction to molar volume showed a large increase between 208 and 288 GPa. This behavior indicated that a phase transformation of insulator-semiconductor might have occurred in solid CH₄ by 288 GPa.     

Molecular control over Ag/p-Si diode by organic layer

Electrical transport properties of Ag metal-fluorescein sodium salt (FSS) organic layer-silicon junction have been investigated. The current-voltage (I-V) characteristics of the diode show rectifying behavior consistent with a potential barrier formed at the interface. The diode indicates a non-ideal I-V behavior with an ideality factor higher than unity. The ideality factor of the Ag/FSS/p-Si diode decreases with increasing temperature and the barrier height increases with increasing temperature. The barrier height (φ_b=0.98 eV) obtained from the capacitance-voltage (C-V) curve is higher than barrier height (φ_b=0.72 eV) derived from the I-V measurements. The barrier height of the Ag/FSS/p-Si Schottky diode at the room temperature is significantly larger than that of the Ag/p-Si Schottky diode. It is evaluated that the FSS organic layer controls electrical charge transport properties of Ag/p-Si diode by excluding effects of the SiO₂ residual oxides on the hybrid diode.