Optical constants and electrical conductivity of Ge20Se60Sb20 thin films

Optical absorption and electrical resistivity of amorphous Ge₂₀Se₆₀Sb₂₀ films are investigated as a function of the thermal annealing. The dependence of the optical absorption coefficient on the photon energy is ascribed by the relation (h) = B(h–E_o)². Increasing the annealing temperature from 423 K to 553 K, decreases the optical gap of the film from 1.25 eV to 0.78 eV. The effect of annealing temperature on high frequency dielectric constant () and carrier concentration (N) was also studied. As a result of annealing the film at 533 K, the electrical resistivity and activation energy for conduction decreased from 5.7 × 10⁷ to 2.9 × 10² ·cm and from 0.94 to 0.34 eV, respectively. The crystalline structures resulting from heat treatment at different elevated temperatures have been studied by X-ray Diffraction (XRD). The optical and electrical changes were attributed to the amorphous-crystalline transformations in the chalcogenide films.     

Optical and structural properties of (Ba, Sr)TiO3 thin films grown by radio-frequency magnetron sputtering

We studied the structural and optical properties of (Ba, Sr)TiO₃ (BST) films deposited on the transparent substrates at various temperatures of 350–650°C and annealed at 450–650°C. Improved crystallization can be observed on 650°C annealed film whose substrate temperature is 350°C. The refractive index increased from 2.17 to 2.59 at =410 nm for the BST films deposited at 350–650°C and it varied from 2.17 to 2.25 after annealing up to 650°C. In addition, the refractive-index dispersion data related to the short-range-order structure of BST films obeyed the single-oscillation energy model. The indirect energy gap of the films deposited on Al₂O₃ and quartz substrates was found to be about 3.5 eV. According to the analysis of reflectance data, the optical inhomogeneity of films can be reduced by depositing the films at intermediate temperatures 450–550°C.     

Optical band gap and refractive index of c-BN thin films synthesized by radio frequency bias sputtering

Boron nitrogen (BN) films with the different cubic phase content were deposited on Si and fused silica substrates by radio frequency bias sputtering from a hexagonal BN target by using a two-stage deposition process. The BN films were characterized by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and UV-visible transmittance and reflection measurements. The optical absorption coefficient and the refractive index n were calculated from the transmittance and reflection spectra. With increasing the c-BN content the absorption edge shifts to the higher energy, indicating that the optical band gap of the BN films increases with cubic BN content. The optical absorption behavior of BN films shows characteristics of amorphous materials. The dependence of on the photon energy was fitted by the Urbach tail model and the band-to-band transition model at the two different energy regions, and the optical band gap of the BN films were obtained from the fits. In addition, the refractive index indicates obvious difference for the BN films with different cubic phase content.     

Effects of annealing temperatures on optical and electrical properties of vacuum evaporated Ga15Se77In8 chalcogenide thin films

The optical constants (absorption coefficient, optical band gap, refractive index, extinction coefficient, real and imaginary parts of dielectric constants) of amorphous and thermally annealed thin films of Ga₁₅Se₇₇In₈ chalcogenide glasses with thickness 4000 Å have been investigated from absorption and reflection spectra as a function of photon energy in the wave length region 400-800 nm. Thin films of Ga₁₅Se₇₇In₈ chalcogenide glasses were thermally annealed for 2 h at three different annealing temperatures 333 K, 348 K and 363 K, which are in between the glass transition and crystallization temperature of Ga₁₅Se₇₇In₈ glasses. Analysis of the optical absorption data shows that the rule of non-direct transitions predominates. It was found that the optical band gap decreases with increasing annealing temperature. It has been observed that the value of absorption coefficient and extinction coefficient increases while the values of refractive index decrease with increasing annealing temperature. The decrease in optical band gap is explained on the basis of the change in nature of films, from amorphous to crystalline state. The dc conductivity of amorphous and thermally annealed thin films of Ga₁₅Se₇₇In₈ chalcogenide glasses is also reported for the temperature range 298-393 K. It has been observed that the conduction is due to thermally assisted tunneling of the carriers in the localized states near the band edges. The dc conductivity was observed to increase with the corresponding decrease in activation energy on increasing annealing temperature in the present system. These results were analyzed in terms of the Davis-Mott model.     

Photo- and thermo-induced changes in the properties of thin amorphous As-S films

Changes in transmittance, refractive index, transmissivity in the infrared spectral region, and activation energy of the dissolution process were studied for thin films of the system As _x S_100–x (28.6 x45) as they result from illumination and annealing at temperatures of T _g . It is assumed that the irreversible changes occurring in the layers after treatment are accompanied by an increase in the concentration of As-S bonds. This leads to an increase in dissolution rate, a decrease in the activation energy of the process, and considerable changes in the absorption peaks at 370 and 310 cm^–1 obtained by infrared spectroscopy. It is shown that the photo- and thermoinduced changes in as-deposited chalcogenide films follow identical courses. The results obtained are explained from the viewpoint of the structural changes occurring in chalcogenide films.     

Preparation and properties of electrodeposited Hg1-xCdxSe films

Hg_1-xCd_xSe (0.87 < x < 1) films were electrodeposited potentiostatically onto ITO glass substrates by varying the Hg content in the aqueous electrolyte with the pH adjusted to 1.5–2 at room temperature. The as-deposited and the as-grown and annealed films showed hexagonal structure with c-axes perpendicular to the substrate. The band gap (direct allowed transition) energies as determined from the optical absorption measurements, varied between 1.7 eV for x=1, and 1.2 eV for x=0.88. All of the samples showed n-type conductivity. The carrier concentration increased and the resistivity decreased with the increase of the Hg content in the solution. The resistivity activation energy of the sample, E, decreased with increasing mole fraction of Hg, and E became 0 at higher Hg concentrations (x < 0.88).     

The Distribution of the Energy Gap and Josephson IcRn Product in Bi2Sr2CaCu2O8+x by Tunneling Spectroscopy

We present direct measurements of the density of states by tunneling spectroscopy on slightly overdoped Bi₂Sr₂CaCu₂O_8+x (Bi2212) single crystals at low temperature using break-junction and point-contact techniques. We find that (i) the variation of the gap magnitude, , between 20 and 36 meV is likely to be intrinsic to Bi2212, and (ii) there is a correlation between the maximum value of the Josephson I _c R _n product and the gap magnitude: I _c R _n decreases with the increase of . The maximum I _c R _n value of 26 mV is observed at = 20.5 meV. For = 36.5 meV, the maximum measured value of I _c R _n is 7.3 mV. We conclude that (i) the distribution of the Josephson I _c R _n product as a function of gap magnitude cannot be explained by the presence of a single energy gap in Bi2212, and (ii) the coherence energy scale in Bi2212 has the maximum Josephson strength.     

Structural and optical properties of CdGa2Se4 thin films

CdGa₂Se₄ thin films were prepared by vapour deposition onto either room temperature or preheated quartz and glass substrates (T _S) or they were deposited at room temperature and then annealed at about (T _A) 623 K. The films thus prepared were crystalline with a thiogallate tetragonal structure. The optical constants (the refractive index n and the absorption index, k) were determined for CdGa₂Se₄ films deposited onto quartz substrates held at either room temperature or at T _S = 573 K. These constants were also determined for preannealed films (T _A = 623 K). Plots of (hv)² = f(hv) and (hv)^1/2 = g(hv) were linear, indicating the existence of both direct and indirect optical transitions. It was found that the values of E _g ^d and E _g ^ind for as-deposited CdGa₂Se₄ films were 2.46 and 1.91 eV, respectively. The corresponding values for the annealed films and the films deposited at T _S = 573 K were 2.56 and 2.06 eV, respectively.     

Effect of Bismuth Ions on the Optical Absorption in Gd3Ga5O12〈Bi〉 Epitaxial Films

Single-crystal gadolinium gallium garnet films containing Bi impurity are grown on (111) Gd₃Ga₅O₁₂ substrates by liquid-phase epitaxy from Bi₂O₃–B₂O₃ fluxes. The absorption spectra of the films are measured from 0.2 to 1.5 m. The effect of Bi³⁺ impurity on the optical absorption in the films is examined.     

Electrical conductivity and optical properties of ZnO films annealed in hydrogen atmosphere after chemical vapor deposition

The d.c. electrical conductivity and optical properties of polycrystalline zinc oxide films (220–450 nm thick) annealed in hydrogen after chemical vapor deposition are investigated. A minimum film resistivity after the annealing gives 0.31 cm for the film as-deposited at a substrate temperature of 823 K. From the temperature dependence of conductivity, band conduction is confirmed for the films at temperatures above 250 K. The effect of grain-boundary scattering is due to thermionic emission of electrons over grain boundary barriers. At temperatures below 250 K, variable-range hopping transport is found to be dominant. The films are transparent in the wavelength range 400 to 1000 nm and have sharp ultraviolet absorption edges at 380 nm. The absorption edge analysis reveals the optical band gap energy for the films to be 3.18–3.23 eV. The Urbach tail analysis gives the width of localized states E_e=0.06-0.14eV.     

Distribution characteristics of mechanical properties and correlation between the respective properties on S35C carbon steel

Mechanical properties of tensile strength, , upper yield stress, _SU, lower yield stress, _SL elongation, , area reduction, , Vickers hardness, H _v, and impact absorbed energy, E, were examined using 50 specimens of S35C carbon steel, which were machined from two bars supplied from the same charged and heat-treated material. Distribution characteristics of these properties are discussed, and the correlation between each pair of them is investigated from a statistical viewpoint. The main conclusions obtained are summarized as follows; distribution characteristics of _B, _SL, , , H _v and E are well approximated by a normal distribution, but those of asu are not approximated as well by this type of distribution. In the latter case, a Weibull distribution is preferable to represent the distribution pattern. No significant correlation was observed between each pair of the above mechanical properties. Consequently, individual properties have the inherent distribution characteristics independent of the other properties.     

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

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

Photo-induced changes in the optical properties of amorphous As-Ge-S thin films

Changes in the transmission, absorption edge and refractive coefficient in the UV-VIS and the transmission in the IR spectrum of thin As-Ge-S films after irradiation with an argon laser with =488 nm were studied. X-ray microanalysis showed that the composition of the films (with small variations) corresponded to that of the initial substances. Films with a defined concentration of the elements could also be deposited by evaporation of As₂S₃ and GeS₂ from two sources. The optical properties of thin films prepared by thermal evaporation, flash evaporation and coevaporation from two crucibles have been compared. It was found that depending on the component content, both photodarkening and photobleaching coatings in a wide region of can be obtained in thin As-Ge-S films. The results have been explained from the viewpoint of the photostructural changes in chalcogenide layers.     

Electrical properties of non c-axis oriented SrBi2(Ta0.95V0.05)2O9 thin films

Pulsed laser deposition technique was used to grow off c-axis oriented SrBi₂(Ta_0.95V_0.05)₂O₉ (SBTV) ferroelectric thin films. X-ray diffraction studies revealed the c-axis suppression in the films grown at lower substrate temperature (350°C) followed by annealing at higher temperatures (650°C). In-plane lattice parameters of the films were decreased with increase in annealing temperature. SBTV films annealed at 750°C exhibited enhanced ferroelectric properties with remanent polarization (2P _r) of 31.5 C/cm² and coercive field (E _c) of 157 kV/cm. The dielectric permmitivity of the films increased with increase in annealing temperature and it was attributed to the grain size dependence. The films annealed at 750°C showed maximum value of dielectric permittivity 172 with a tangential loss of 0.1, at 100 kHz. Higher value of dissipation factor at lower annealing temperature is explained in terms of space charge accumulation at grain boundaries. The leakage current densities of the films follow ohmic behavior at low field regime and space charge limited current dominates at higher fields.     

Some studies of the optical properties of molybdenum-phosphate glasses

A series of binary MoO₃-P₂O₅ and ternary MoO₃-In₂O₃-P₂O₅ glasses was prepared and their optical properties were investigated. The optical absorption edge of the glasses was measured for specimens in the form of thin blown films. It was found that the fundamental absorption edge of these glasses usually occurs in the ultraviolet region. The linear variation of ()^1/2 with where is the absorption coefficient and is the incident photon energy, is taken as evidence of non-direct interband transitions. The linear dependence of optical gap with molybdenum content indicates that the molybdenum content controls the absorption phenomena in this glassy system. The infrared spectra of all the glasses appeared to be almost the same, indicating that the infrared bands arise primarily from the vibrations of the phosphate and molybdate groups. The structure of molybdenum phosphate glasses is discussed in terms of the formation of mixed phosphate and MoO₄ tetrahedra.     

Absorption Spectra of SbSeI and BiSeI Crystals

The absorption, total density of states, and dielectric permittivity (₂) spectra for SbSeI and BiSeI crystals are calculated in the range 0–4.5 eV for 110 K and the E || c and E c polarizations and in the range 0–13 eV for 300 K. The ₂ spectra are decomposed into elementary components, and the principal parameters of the components are evaluated: energy position, half width, area, and oscillator strength. The optical spectra of SbSeI and BiSeI are shown to be similar in the energy position of transitions and to differ markedly in their polarization and strength.     

Characterization of p-In2Se3 thin films

Indium selenide thin films were deposited onto glass substrates kept at 150 °C by thermal evaporation of -In₂Se₃. Some of the films were annealed at 150 °C and 200 °C and they all were found to exhibit p-type conductivity without intentional doping. Scanning electron microscopy (SEM) established that the films have an atomic content of In₅₁Se₄₉. X-ray diffraction (XRD) indicated that the as-grown films were amorphous in nature and became polycrystalline -In₂Se₃ films after annealing. The analysis of conductivity temperature-dependence measurements in the range 320–100 K revealed that thermal excitation and thermionic emission of the carriers are the predominant conduction mechanisms above 200 K in the amorphous and polycrystalline samples, respectively. The carrier transport below 200 K is due to variable range hopping in all the samples. Hall measurements revealed that the mobility of the polycrystalline films is limited by the scattering of the charged carriers through the grain boundaries above 200 K. © 2001 Kluwer Academic Publishers     

Preparation of alumina films by the sol-gel method

This review describes our study on preparation of alumina films by a sol-gel process and their several applications that have been investigated since 1986. Alumina films were prepared from alkoxide or inorganic salt. Both as-prepared alumina films were transparent in ultraviolet, visible and near infrared regions. The alumina from inorganic salt (inorganic alumina) was structureless even after annealed at 300–700°C in air, while the alumina from alkoxide (alkoxide alumina) was in pseudo-boehmite at an annealing temperature lower than 400°C and was in - or -type at 400–700°C. Both alumina films became opaque after annealed at temperatures above 1000°C. The inorganic alumina film annealed at 800°C showed a gas permeability that was influenced by physico-chemical properties of penetrant and alumina. Composite films of alumina and poly(vinyl alcohol) (PVA) were hydrophilic but insoluble in water, and removal of PVA from the composite films by annealing at 600°C led to formation of transparent alumina films. Such properties enabled us to use a counter diffusion method for fabricating -Fe₂O₃-doped alumina films. Alumina films doped with organic dyes such as laser dyes, hole-burning dyes and non-linear optical dyes, which were fabricated by gelation of dye-added alumina sol, exhibited laser emission, hole-spectra and second- or third-harmonic generation properties, respectively. Hydrogenation of alkene was catalyzed by Ni nanoparticles doped alumina films that were prepared by gelation of Ni²⁺ solution-added alumina sol and annealing the Ni²⁺-doped alumina gel in hydrogen gas. Nonlinear optical properties were observed for alumina films doped with CdS, Au and Ag nanoparticles, which were fabricated by gelation of Cd²⁺, HAuCl₄ and AgNO₃ solution-added alumina sols and annealing the Cd²⁺-doped alumina gel in H₂S gas and the Ag⁺- and Au³⁺-doped alumina gels in H₂ gas. Rare earth metal ion-doped alumina films, which were prepared by gelation of rare earth metal ion solution-added alumina sol and annealed the ion-doped alumina gel, exhibited not only normal luminescence but also up-conversion emission, energy transfer type luminescence and long lasting luminescence.     

Effect of Composition Variations on Electrical and Optical Properties of La1−x (Ca, Sr) x MnO3 Thin Films

Thin films of La _0.67 Ca _0.33 MnO ₃₊ (d 200 nm) grown at 750° C on MgO(100) substrates by pulsed laser deposition were annealed in various oxygen atmospheres. The LaF ₃ , CaF ₂ and Mn overlayers (d 5-10 nm) have been evaporated onto the films in order to saturate the compound by La, Ca or Mn during subsequent annealing at 900° C in air. Further, the pulsed injection CVD method has been utilized to prepare series of La _1–x Sr _x MnO ₃ films with x = 0÷0.5 on LaAlO ₃ (100). The effect of composition variations on electrical resistivity and magnetoresistance of the films as well as on their optical transmission and reflection spectra in the energy range between 0.2 and 4.0 eV has been investigated.     

Effect of heat treatment on the structural and optical properties of CuInTe2 thin films

The CuInTe2 thin films were prepared by thermal vacuum evaporation of the bulk compound. The structural and optical properties in the temperature range 300–47 K of thin films grown on glass substrates and annealed in vacuum were studied. The films were investigated by X-ray diffraction and electron microscope techniques. The calculated lattice constants for CuInTe₂ powder were found to bea=0.619 nm andc –1,234 nm. From the reflection and transmission data, the optical constants, refractive indexn, absorption index,k, and the absorption coefficient, , werw computed. The optical energy gap was determined for CuInTe₂ thin films heat treated at different temparatures for different periods of time. It was found thatE _g increases with both increasing temperature and time of annealing.