Effect of laser irradiation on the electrical properties of amorphous germanium films

Amorphous films of germanium were grown using a vacuum evaporation technique, on glass substrates kept at room temperature. As-grown films were irradiated with Q-Switched Nd-YAG laser pulses (=1.06 m, 20nsec, 10 to 50Jcm^–2). The d.c. conductivity measurements were made in the temperature range 77 to 300 K. It was observed that the effect of laser irradiation was similar to the effect caused by the thermal annealing of the films. The d.c. conductivity data were analysed in the light of Mott's theory of a variable range hopping conduction process.     

Effect of gamma irradiation on the optical properties of CR-39 polymer

The UV-Visible absorption spectra of virgin and gamma irradiated (20–800 kGy) CR-39 polymer have been deduced by using Shimadzu Double beam Double Monochromator UV-Visible Spectrophotometer (UV-2550). The existence of the peaks, their shifting and broadening as a result of gamma irradiation has been discussed. Finally the indirect and direct band gap in virgin and gamma irradiated CR-39 has been determined. The values of indirect band gap have been found to be lower than the corresponding values of direct band gap.     

Effect of structural defects on optical properties of amorphous selenium films

Thickness of film, energy of incident photons and glass transition temperature all affect the structural bonding between neighbours and are considered to be the main factors in studying the optical properties of amorphous selenium films. The results indicate that in the lowtemperature range (T <T _g), a shift in the absorption edge to lower photon energies with increasing film thickness occurs. Increasing the thickness is accompanied by a decrease in the optical energy gap,E _g ^opt , with a gradient of 5×10^–4eV nm^–1. In the high-temperature range (T >T _g), the value ofE _g ^opt for a given thickness decreases by more than 50% due to pronounced modulation of the structural defects under incidence of isoenergetic photons of 1.8 eV. The isothermal curves ofT,R=f(t), atT >T _g, take place via three time-dependent stages. These results are interpreted and are correlated with the temperature dependence of the morphological changes declaring the formation of spherulites having a lamellar structure. The kinetic parameters controlling the structural transition are computed and the results are discussed.     

Effect of Bi doping on the structure and conduction mechanism of amorphous GeSe films

This paper examines the effect of Bi doping on the short-range order in amorphous (GeSe)_{1 ? x} Bi _x (0 ≤ x ≤ 0.15) films and their electrical properties. Electron diffraction results demonstrate that the structure of the films can be described by a model typical of GeSe-Bi₂Se₃ solid solutions. Bi doping changes the charge transport mechanism and leads to type inversion in the amorphous (GeSe)_{1 ? x} Bi _x films.     

Influence of annealing on the optical properties of amorphous germanium films

The influence of annealing on the optical, electrical and structural properties of thin amorphous Ge films deposited under well-defined conditions has been investigated. The results below the onset of recrystallization are interpreted as due to a progressive elimination of defects and an evolution of the films towards an “ideal” amorphous state. Various mechanisms are discussed in relation with various structural models.     

Optical constants of thermally evaporated amorphous GeSe3 thin films

The optical transmission spectra of amorphous Ge-Se films of chemical composition GeSe₃, prepared by thermal evaporation, are measured overthe 300 nm to 2500 nm spectral region. A simple, straightforward procedure suggested by Swanepoel, which is based on the use of interference fringes, has been applied in order to derive the real and imaginary parts of the complex refractive index, and also the film thickness. Furthermore, thickness measurements made by a surface-profiling stylus are also carried out to cross-check the results obtained by the present optical method, employing only T(). The dispersion of n is discussed in terms of the single-oscillator Wemple and DiDomenico model, and the optical band gap E _g ^opt has been determined from the absorption coefficient values, using the Tauc procedure.     

Effect of gamma radiation on optical and electrical properties of tellurium dioxide thin films

Gamma radiation induced changes in the optical and electrical properties of tellurium dioxide (TeO₂) thin films, prepared by thermal evaporation, have been studied in detail. The optical characterization of the as-deposited thin films and that of the thin films exposed to various levels of gamma radiation dose clearly show that the optical bandgap decreases with increase in the gamma radiation dose up to a certain dose. At gamma radiation doses above this value, however, the optical bandgap has been found to increase. On the other hand, the current vs voltage plots for the as-deposited thin films and those for the thin films exposed to various levels of gamma radiation dose show that the current increases with the gamma radiation dose up to a certain dose and that the value of this particular dose depends upon the thickness of the film. The current has, however, been found to decrease with further increase in gamma radiation dose. The observed changes in both the optical and electrical properties indicate that TeO₂ thin films can be used as the real time gamma radiation dosimeter up to a certain dose, a quantity that depends upon the thickness of the film.     

Effect of high-energy electron-beam irradiation on the optical properties of ion-beam-sputtered silicon oxynitride thin films

Silicon oxynitride thin films are prepared by ion-beam sputtering, and the optical properties and surface chemical composition are studied by spectrophotometric and x-ray photoelectron spectroscopy, respectively. It is seen that the films sputtered by use of nitrogen alone as the sputtering species from a silicon nitride target are completely transparent (k < 0.005) and have a refractive-index dispersion from 1.85 to 1.71 over the visible and near-infrared spectral regions, and the films show distinct spectral lines that are due to silicon, Si(2s), nitrogen, N(1s), and oxygen, O(1s). Sputter deposition of argon and of argon and nitrogen produces silicon-rich silicon oxynitride films that are absorbent and have high refractive indices. These films have a direct electronic transition, with a threshold energy of 1.75 eV. Electron irradiation transforms optically transparent silicon oxynitride films into silicon-rich silicon oxynitride films that have higher refractive indices and are optically absorbing owing to the presence of nonsaturated silicon in the irradiated films. The degradation in current responsivity of silicon photodetectors, under electron irradiation, is within 3% over the wavelength region from 450 to 750 nm, which is entirely due to the degradation of optical properties of silicon oxynitride antireflection coatings.     

Electronic and optical properties of granular amorphous carbon films

Amorphous carbon (a-C〈N〉) films on glass substrates are obtained by magnetron sputtering of a graphite target in nitrogen. The temperature dependence of the electric conductivity (lnσ≈T ^1/2 at temperatures T<280 K) of the films is typical of a granular structure. The results of measurements of the thermo emf, conductivity, and optical absorption of the a-C〈N〉 films suggest that the granular structure comprises nanodimensional clusters of γ-carbon phase with metallic conductivity distributed in a graphitelike carbon matrix. The concentration of such clusters in the matrix increases with the substrate temperature.     

Effect of gamma irradiation on the electrical and optical properties and conduction mechanism of α-SiO2

The electrical and optical properties of gamma-irradiated α-SiO₂ crystals are studied in broad dose and temperature ranges, and their lattice dynamics is analyzed using IR absorption spectroscopy. The radiation effect on the electrical conductivity of the crystals is shown to be a nonlinear function of temperature and gamma dose, characteristic of percolation systems at low temperatures. The conductivity of the crystals is shown to be proportional to T ^?1/2 in a broad temperature range. The mechanism of conduction in the crystals is discussed in terms of percolation theory.     

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.     

Influence of ultraviolet irradiation on the optical properties of amorphous Sb10Se90 thin films

Amorphous Sb₁₀Se₉₀ thin films were prepared by thermal evaporation of the bulk glass. The changes in the optical properties (transmittance, optical gap, absorption coefficient, refractive index and extinction coefficient) have been measured in the wavelength range 500-900 nm of virgin and ultraviolet (UV) illuminated films. Analysis of the optical absorption data shows that the rule of non-direct transitions predominates. It is found that the optical energy gap decreases (photo-darkening) and the refractive index increases with the increase of UV exposure time. The dispersion of the refractive index (n) has been discussed in terms of Wemple-Didomenico single oscillator model. The oscillator energy E₀ and the dispersion energy E_d have been determined and discussed in terms of UV exposure time. The photo-darkening was discussed in terms of some of the current literature models.     

Effect of laser irradiation on structural,electrical and optical properties of SnO2 films

Thin films of SnO₂ were prepared using a spray pyrolysis technique. Films were irradiated with Nd:YAG laser pulses of various energy densities (2–50 mJ cm^–2) with varying number of pulses from 1–50. X-ray diffraction studies were made to investigate the structural changes due to laser irradiation. An improvement in crystallinity and an increase in grain size were observed in laser-irradiated films. Hall coefficient and Hall mobility studies were made in the temperature range 77–300 K for the as-grown as well as laser-irradiated films. An increase in mobility and a decrease in carrier concentration were observed in the films after laser irradiation. Optical transmission studies revealed that the refractive index increased as a result of laser irradiation.     

Electrical and optical properties of amorphous indium zinc oxide films

Valence electron control and electron transport mechanisms on the amorphous indium zinc oxide (IZO) films were investigated. The amorphous IZO films were deposited by dc magnetron sputtering using an oxide ceramic IZO target (89.3 wt.% In₂O₃ and 10.7 wt.% ZnO). N-type impurity dopings, such as Sn, Al or F, could not lead to the increase in carrier density in the IZO. Whereas, H₂ introduction into the IZO deposition process was confirmed to be effective to increase carrier density. By 30% H₂ introduction into the deposition process, carrier density increased from 3.08 × 10²⁰ to 7.65 × 10²⁰ cm^− 3, which must be originated in generations of oxygen vacancies or interstitial Zn²⁺ ions. Decrease in the transmittance in the near infrared region and increase in the optical band gap were observed with the H₂ introduction, which corresponded to the increase in carrier density. The lowest resistivity of 3.39 × 10^− 4 Ω cm was obtained by 10% H₂ introduction without substrate heating during the deposition.     

Influence of gamma radiation on the optical properties of ZnSe nanocrystalline thin films

The effect of gamma (γ) irradiation on the absorption spectra and the optical energy bandwidth of ZnSe nanocrystalline thin films have been studied. Thin films of different thicknesses from 20 to 120 nm were deposited by Inert gas condensation technique at constant temperature of 300 K and under pressure 2 × 10⁻³ Torr of Argon gas flow. The optical transmission (T) and optical reflection (R) in the wavelength range 190–2,500 nm of ZnSe nanocrystalline thin films were measure for unirradiated and irradiated films. The dependence of the absorption coefficient α on photon energy hν was determined for different γ-doses irradiated films. The ZnSe thin films show direct allowed interband transition by γ-doses. Both the absorption coefficient (α) and optical energy bandwidth were found to be γ-dose dependent. The optical energy band width has been decreased by irradiated of γ-doses. The E_gn values of irradiated thin films by 34.5 Gy of γ-doses were recovered to nearly their initial values after 100 days at 300 K.     

Effect of gamma irradiation on properties of hardened cement paste

Carbonation of hydrated cement paste (HCP) under γ-irradiation is researched in this paper. It is supposed that radiation-induced carbonation takes part simultaneously with “natural” carbonation. “Natural” carbonation is governed by diffusion and therefore takes part in the material close to surface only, whereas radiation-induced carbonation manifests in all irradiated material. The hypothesis has been tested by means of three sets of experiments. Within these experiments the following changes were investigated: (a) changes of composition of hydrated cement paste (transformation of portlandite to calcite), (b) changes of porous space [changes of average pore diameter (APD)], (c) changes of mechanical properties (hardness). HCP was analysed in the surface layer as well as in the centre of samples. The results show clearly that radiation at least accelerates carbonation driven by diffusion and support a hypothesis that besides natural carbonation there is also independent carbonation caused by γ-irradiation.     

Influence of substrate temperature on the electrical and optical properties of amorphous germanium films

The influence of substrate temperature on electrical and optical properties of the amorphous germanium films deposited under well-defined conditions has been investigated. DC electrical conductivity in the temperature range of 80–573°K has been measured. In the low temperature region Mott’sT ^−1/4 law of conductivity is obeyed. The estimated values ofT ₀ andN show significant decrease with change inT _s in steps of 50°K. Similar results are seen in annealed films. The values of activation energy and optical energy increase withT _s.     

Model calculations on the influence of dangling bonds on the optical properties of amorphous silicon films

The spectra of the optical constants of amorphous silicon films in the range 0.04hv5.6 eV, especially the very large infrared refractive indices obtained with high deposition rates, are fitted by the classical oscillator model. The oscillators considered are the three strongest single-crystal oscillators and an additional oscillator the existence of which can be ascribed either to dangling bonds in the microcrystal model or to an average non-covalent share of the bonds in the random network model. The sum of the four oscillator strengths is nearly independent of the degree of amorphousness. The calculated oscillator strength of the additional oscillator is proportional to the measured concentration of unpaired spins. The energy states of this oscillator in the E(k) diagram are placed along the axis Γ-L, and are parallel to the edges of the valence and conduction bands at a distance of 0.7±0.1 eV from the valence band.