Nanostructure and enhancement of the optical properties of Tb-doped NiO for photodiode applications

In the present work, pure and 1, 2.5, 5 and 10% Tb-doped NiO nanostructures were fabricated in the form of thin-films by the sol-gel spin coating process. The prepared structures were identified by an X-ray diffraction pattern and atomic force microscopy. The results of the X-ray diffraction indicate that the prepared films are polycrystalline with a cubic lattice face-centered for wholly Tb-doped concentration films. The surface topography of the films was studied by atomic force microscopy, and surface mapping was introduced to check the quality of the surface for optical investigations. The measured optical transmission indicated a high transmission that exceeds 80% through the visible region depending on the Tb-doping concentrations. It is affirmed that the measured optical bandgap and the index of refraction are strongly influenced by the Tb-doping concentrations. The parameters of nonlinearity were also critically affected by the Tb-doping concentrations. This innovative result can hopefully be applied in an industrialized approach for the field of photodiode devices.     

Electrical properties of film heterojunctions of cadmium selenide and amorphous selenium

Results are presented from a study of the volt-ampere characteristics of polycrystalline layers of cadmium selenide and amorphous layers of selenium, as well as the electrical and photoelectric characteristics of CdSe-Se heterojunctions. The experimental data and a theoretical examination of heterojunctions composed of a crystalline semiconductor and an amorphous semiconductor are used to propose an energy-band model for heterojunctions.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 65–70, November, 1990.     

Electrical properties of bilayer heterojunctions in a strong magnetic field

The electrical properties of bilayer heterojunctions in a strong magnetic field at low temperatures have been considered. It has been shown that both the ohmic and Hall conductivities decrease exponentially due to the formation of neutral pairs if the electric fields in the two layers are parallel. In the antiparallel fields, the Hall conductivity is still determined by the activation energy of the excited electrons and decreases exponentially, but the ohmic conductivity decreases much slower, proportional to the temperature square.     

Controlling the infrared optical properties of rf-sputtered NiO films for applications of infrared window

In this paper, we will focus on an IR transmittance enhancement technique from the window material point of view by using metal oxides, especially nickel oxide (NiO). At first, anti-reflection (AR) coatings were modeled by using the optical properties of NiO films. The transmittance of the model was predicted using Swanepoel’s model and verified with NiO film prepared by rf magnetron sputtering. Also, post-deposition annealing was performed and was found to change the optical properties of the NiO film. Therefore, we analyzed the annealing effect on the IR optical properties of the NiO film. Furthermore, we confirmed the durability of the NiO film and verified the possibility of this material being used in infrared optics.     

Electrical and optical properties of transition-metal oxides

Abstract

Transition-metal oxides can be insulators, semiconductors, metals, or undergo semiconductor-metal transitions. The nonmetallic materials are characterized by a primarily localized optical spectrum but a band-like electrical conductivity. However, a pure band approach predicts metallic rather than nonmetallic behavior, and so cannot be used without serious modification. Agreement with the optical and electrical results can be obtained by requiring the d electrons to be almost completely localized. The primarily p-type semiconduction which occurs must then take place in the 2p band associated with the oxygen ions. A method for representing the strongly-correlated localized levels on an effective one-electron density-of-states diagram is discussed.     

Electrical and optical properties of chalcopyrite compounds

Optical and electrical properties of Zn- and Cd-modified Cu₂SnSe₄ amorphous films have been studied. The results show that Zn and Cd incorporation decreases the thermal activation energy, the pre-exponential factor and the optical gap. Variation in the refractive index and extinction coefficient with the wavelength has been also reported. The relations between the optical gap and the chemical composition in the investigated films have been discussed in terms of the average heat of atomization. The effect of γ-radiation up to 71.25 Mrad dose on the optical gap was also studied.     

Electrical and optical properties of nanowires based solar cell with radial p-n junction

In our studies the absorption, transmittance and reflectance spectra for periodic nanostructures with different parameters were calculated by the FDTD (Finite-Difference Time-Domain) method. It is shown that the proportion of reflected light in periodic structures is smaller than in case of thin films. The experimental results showed the light reflectance in the spectral range of 400–900 nm lower than 1% and it was significantly lower in comparison with surface texturing by pyramids or porous silicon.Silicon nanowires on p-type Si substrate were formed by the Metal-Assisted Chemical Etching method (MacEtch). At solar cells with radial p-n junction formation the thermal diffusion of phosphorus has been used at 790 °C. Such low temperature ensures the formation of an ultra-shallow p-n junction. Investigation of the photoelectrical properties of solar cells was carried out under light illumination with an intensity of 100 mW/cm². The obtained parameters of NWs' solar cell were I_sc = 22 mA/cm², U_oc = 0.62 V, FF = 0.51 for an overall efficiency η = 7%. The relatively low efficiency of obtained SiNWs solar cells is attributed to the excessive surface recombination at high surface areas of SiNWs and high series resistance.     

Far infrared optical properties of SnIISnIVS3

The far infrared reflection spectra of mixed valence semiconductor Sn^IISn^IV have been recorded and analysed to yield the optical properties for all principal symmetry directions.     

Electrical and optical properties of gallium phosphide films

The electrical and optical properties of gallium phosphide films, prepared by the explosive evaporation and three-temperature methods, are studied. It is shown that film properties are strongly dependent on method of preparation and substrate temperature. Gallium phosphide films prepared by explosive evaporation having perfect structure possess the best electrical and optical properties.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, No. 6, pp. 54–58, June, 1971.     

Electrical and optical properties of titanium dioxide films

A method is described for producing insulating films of titanium dioxide by vacuum evaporation. Photomicrographs showing the growth of crystallites in the layer are presented, and X-ray and electron diffraction data are given. Sputtering regimes by means of which it is possible to produce compact layers of specific resistance 10¹³ ohm · · cm, dielectric strength 10⁶V/cm, and dielectric constant of 30 are given.By investigating optical density spectra and temperature variation of electrical conductivity for these specimens values were obtained for the optical and thermal forbidden band widths in titanium dioxide; these were 4.2 and 3.9 eV respectively. It was found that insulating films of titanium dioxide were completely transparent over a wide range of wavelengths from 300 to 1000 m. Using the same investigations in layers with electrical conductivity greater than 10^–13/ohm · · cm defects were discovered, which were connected with oxygen deficiency and gave three impurity energy levels in the forbidden band of titanium dioxide.In conclusion the authors would like to express their gratitude to Prof. K. V. Shalimova under whose guidance the work was executed.     

Electrical and optical properties of electron-irradiated ZnGeP2

Conclusions and summary The following conclusions are drawn from the reported study:The electrophysical properties of ZnGeP₂ crystals and their optical transparency in the range hG are attributable to the presence of a density-dominant (10¹⁷–10¹⁹ cm^–3) deep [E_v+(0.5–0.6) eV] growth defect associated predominantly with Zn vacancy clusters.Irradiation by high-energy electrons induces a shift of the Fermi level in the direction of E_G/2 and increases the resistivity of ZnGeP₂ to values of approximately 10¹² ·cm at 300 K. Irradiation with high-energy electrons is an effective technique for the optical bleaching of p-ZnGeP₂. The reversible modification of the optical absorption spectra of p-ZnGeP₂ in connection with irradiation and subsequent annealing indicates that the absorption step in the vicinity of h 0.6 eV is not attributable to light absorption by germanium inclusions, but to optical transition from the valence band to the growth-defect level E_v+(0.5–0.6) eV.Enhancement of the optical transmissivity of p-ZnGeP₂ in the range hG can be achieved in two wayss 1) as the result of a decrease in the density of centers with the level E_v+0.6 eV by variation of the growth conditions or subsequent annealing; 2) by shifting the Fermi level above the energy position E_v+0.6 eV through the irradiation-induced injection of compensating donor centers.The injection of radiation defects is an effective technique for controlling the electrical and optical parameters of the compound ZnGeP₂.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 122–130, August, 1986.     

Mechanical and optical properties of silver-halide infrared transmitting fibers

This article presents a review of the optical and mechanical properties of infrared transmitting fibers extruded from single crystals of silver-halides at the Applied Physics Group in Tel-Aviv University during the last decade. The optical properties of Agcl_xBr_1-x crystals and fibers include the spectral transmission window, laser power transmission, the change of the power distribution traveling along the fiber, and the laser-induced breakdown. The mechanical properties include the investigation of the ultimate tensile strength (UTS), hardness, and the elastic strain limits of these fibers and their composition dependence. The mechanical properties that involve single and multiple bending of fibers in the plastic and the elastic strain limits are also described.     

Electrical and photovoltaic properties of Cd1−x Zn x S/p-GaAs heterojunctions

Cd_1?x Zn _x S/p-GaAs heterojunctions for solar cell applications have been prepared by growing single crystal Cd_1?x Zn _x S epitaxial layers on (111)GaAs substrates through a vapour phase chemical transport method using the close-spaced geometry and H₂ as a transport agent. Electrical and photovoltaic properties of the heterojunctions have been investigated and discussed in connection with the main features of the growth technique. AM1 power conversion efficiencies up to 6.2% have been measured and possible improvements have been examined.     

Electrical and optical properties of parabolic semiconducting quantum wells

We investigate theoretically the optical and electrical properties of parabolic semiconducting quantum well structures. In our calculations, we assume that the confinement of the carriers is in an infinite parabolic well. We show that the carrier mobility in the plane perpendicular to the direction of confinements is directly proportional to the harmonic oscillator length λ whose value depends upon the partitioning of the band gap discontinuity between the conduction and valence bands. We have also calculated the linewidth for intra-subband resonances which should occur for electromagnetic radiation polarized in the direction of carrier confinement and show that the linewidth is inversely proportional to λ and directly proportional to the temperature when the linewidth is dominated by acoustic phonon scattering. The absorption coefficient for interband optical transitions shows equally spaced steps as a function of photon energy where the value of the spacing between adjacent steps depends upon the partitioning of the band gap discontinuity. Carrier freeze-out in the intrinsic conduction occurs due to the presence of zero point energies in the conduction and valence bands arising from the carrier confinement. These zero point energies also are found to depend upon the partitioning of the band gap discontinuities. Therefore, information about the partitioning of the energy band gap discontinuity between the conduction and valence bands can be obtained by measuring these various optical and electrical transport properties of a parabolic quantum well semiconducting structure under those conditions when the model of an infinite parabolic well approximates the real system.     

Electrical and optical properties of semiconducting camphoric carbon films

In situ variation in resistance of camphoric carbon versus time of pyrolysis, temperature of pyrolysis and effect of sintering are studied to perceive the time required for the completion of pyrolysis and the activation energy from the electrical conductance plot. Variation in the electrical conductance versus temperature and activation energies derived from these measurements, are reproducible when film is thermally treated below 750 °C. Thermal treatment above 750 °C changes the anatomy of the film causing a change in the conductance profile as well as decreases its band gap to 0.1 eV. Camphor pyrolyzed at 650 °C gives semiconducting carbon with optical band gaps 1 eV (direct) and 0.8 eV (indirect). Increase in pyrolysis temperature also shifts G-band of Raman spectrum from 1605 to 1586 cm⁻¹ i.e., towards value corresponding to graphitic carbon. SEM micrograph of camphoric film shows absence of any carbon nanobeads or fibers as normally observed with camphoric carbon pyrolysed in this temperature range.     

Visible,near-infrared and infrared optical properties of silica aerogels

Silica aerogel is an excellent thermal insulation material with a low thermal conductivity and a high porosity and has attracted great concern in applications. This paper was to experimentally investigate the optical properties of optically thick silica aerogel in the visible, near-infrared and infrared spectrum region. The fiber-loaded silica aerogel sample was prepared through sol–gel technique and supercritical drying process. Silica fibers were added into the aerogel during the preparation procedure to strength the skeleton of aerogel. As a comparison with the fiber-load silica aerogel, a silica fiber composite sample with the same chemical component and different physical structure was also prepared. A simplified two-flux model neglecting the boundary effect was used to describe the radiation propagation characteristics inside the samples. The spectral normal-hemispherical reflectances, transmittances, and normal emittances of silica aerogel and silica fiber samples were measured and compared in the wavelengths of 0.38–15 μm. Then the spectral optical constants of samples were determined using the experimental data. The spectral absorption and scattering coefficients of silica aerogel were within (0.01 cm⁻¹, 31.0 cm⁻¹) and (1.4 cm⁻¹, 25.8 cm⁻¹). The results showed that the spectrum region where the scattering coefficient is low usually corresponds to a high absorption coefficient. In addition, the total radiation properties of samples were predicted at high temperatures. The analysis of optical properties of silica aerogel is necessary to provide valuable data in applications.     

Si-PIN photodiode readout for a scintillating optical fiber dosimeter

For more than a decade plastic optical fiber based dosimeters have been developed for medical applications. PMT's have been widely used as the readout photodetector but for a number of applications, Si-PIN photodiodes are a good alternative. They are robust, present good stability over time and have enough sensitivity so that an electrometer can be used as a measuring device. This work describes the tests made with the S9195 Si-PIN photodiode from Hamamatsu used as the readout photodetector for a scintillating optical fiber dosimeter using a BCF-60 polystyrene optical fiber.