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Article Citation - WoS: 9Citation - Scopus: 9Optical Band Gap and Dispersion of Optical Constants of Cu-Ga Thin Films(Elsevier Gmbh, 2019) Isik, M.; Gullu, H. H.; Coskun, E.; Gasanly, N. M.Thermally deposited Cu-Ga-S thin films were optically characterized by means of experimental techniques of transmission measurements. The analyses of transmittance spectra were accomplished by derivative spectrophotometry analyses to get gap energies of thin films. The transmittance spectra of thin films annealed at different temperatures presented interference fringes which were analyzed by Swanepoel envelope method. The wavelength dependencies of optical parameters; refractive index (n), real part of complex dielectric function (epsilon(re)) and extinction coefficient (k) were reported in the weak absorption region. The photon energy dependencies of n and epsilon(re) were analyzed using single-oscillator and Spitzer-Fan models, respectively.Article Citation - WoS: 3Citation - Scopus: 4Optical Properties of Cu3in5< Single Crystals by Spectroscopic Ellipsometry(Elsevier Gmbh, 2018) Isik, M.; Nasser, H.; Ahmedova, F.; Guseinov, A.; Gasanly, N. M.Cu3In5S9 single crystals were investigated by structural methods of x-ray diffraction and energy dispersive spectroscopy and optical techniques of ellipsometry and reflection carried out at room temperature. The spectral dependencies of optical constants; dielectric function, refractive index and extinction coefficient, were plotted in the range of 1.2-6.2 eV from ellipsometric data. The spectra of optical constants obtained from ellipsometry analyses and reflectance spectra presented a sharp change around 1.55 and 1.50 eV, respectively, which are associated with band gap energy of the crystal. The critical point (interband transition) energies were also found from the analyses of second-energy derivative of real and imaginary components of dielectric function. The analyses indicated the presence of four critical points at 2.73, 135, 4.04 and 4.98 eV.Article Citation - WoS: 5Citation - Scopus: 5Structural and Optical Properties of Thermally Evaporated (gase)0.75-(gas)0.25 Thin Films(Elsevier Gmbh, 2021) Isik, M.; Işık, Mehmet; Emir, C.; Gasanly, N. M.; Işık, Mehmet; Department of Electrical & Electronics Engineering; Department of Electrical & Electronics EngineeringGaSe and GaS binary semiconducting compounds are layered structured and have been an attractive research interest in two-dimensional material research area. The present paper aims at growing (GaSe)0.75 - (GaS)0.25 (or simply GaSe0.75S0.25) thin film and investigating its structural and optical properties. Thin films were prepared by thermal evaporation technique using evaporation source of its single crystal grown by Bridgman method. The structural properties were revealed using x-ray diffraction (XRD), energy dispersive spectroscopy (EDS), scanning electron microscopy (SEM) and atomic force microscopy (AFM) techniques. XRD pattern and EDS analyses indicated that thin films annealed at 300 ?C were successfully deposited and its structural characteristics are well-consistent with its single crystal form. Surface morphology was studied by means of SEM and AFM measurements. Optical properties were investigated by transmission and Raman spectroscopy techniques. Raman spectrum exhibited three peaks around 172, 242 and 342 cm-1. Analyses of transmission spectrum revealed the direct band gap energy as 2.34 eV. The mixed compounds of GaSe0.75S0.25 were prepared for the first time in a thin film form and the results of the present paper would provide valuable information to research area in which layered compounds have been studied in detail.Article Citation - WoS: 3Citation - Scopus: 4Effects of Ge Substrate on the Structural and Optical Conductivity Parameters of Bi2o3< Thin Films(Elsevier Gmbh, 2019) Alharbi, S. R.; Qasrawi, A. F.In this article the structural, optical and dielectric properties of a 200 nm thick Bi2O3 thin films which are deposited onto amorphous germanium substrate are reported. Both of the Ge and Bi2O3 thin films are prepared by the thermal evaporation technique under vacuum pressure of 10 s mbar. Bi2O3 thin films are found to prefer the monoclinic nature of structure with larger values of microstrain, dislocation density, stacking faults and smaller grain sizes upon replacement of the glass substrate by germanium. Optically, significant redshift in the energy band gap is observed when the films are grown onto Ge. The Ge/Bi2O3 heterojunctions exhibit a conduction and valence band offsets of value of 0.81 and 1.38 eV, respectively. In addition to the enhancement in the dielectric constant near the IR region, the Drude-Lorentz modeling of the Ge/Bi2O3 heterojunctions has shown remarkable effect of the Ge substrate on the optical conductivity parameters of Bi2O3. Particularly, the drift mobility increased by about one order of magnitude, the free hole density decreased by (similar to)24 times and the plasmon frequency ranges extended from 5.21 to 11.0 GHz to 2.59-12.80 GHz when germanium substrate is used. The optical features of the heterojunction nominate it for visible light communication technology.Article Citation - WoS: 7Citation - Scopus: 7Enhancing the Optoelectronic Performance of As2se3< Thin Films Via Ag Slabs Sandwiching(Elsevier Gmbh, 2020) Qasrawi, A. F.; Alharbi, Seham ReefIn this work, the effects of insertion of Ag slabs of thicknesses of 50, 100 and 200 nm between layers of arsenic selenide are reported. The glassy structured As2Se3 is characterized by X-ray diffraction, energy dispersive X-ray spectroscopy, scanning electron microscopy, ultraviolet-visible light spectrophotometry and impedance spectroscopy techniques. While the two stacked layers of As2Se3 exhibited high absorption and energy band gap values that nominate them for optoelectronic applications, the Ag slabs enhanced the light absorbability by 3.98, 5.77, 6.13 times and shrunk the energy band gap by 1.16 %, 7.40 % and 13.8 % for Ag slabs of thicknesses of 50, 100 and 200 nm, respectively. In addition, even though the As2Se3/As2Se3 layers exhibited negative capacitance effect in the frequency domain of 0.01-1.80 GHz, the insertion of Ag slabs removed the negative capacitance effect and forced the capacitance spectra to exhibit resonance at critical frequency of value of 0.23 GHz. The modeling of the capacitance spectra have shown that the geometrical capacitance is increased by one order of magnitude upon Ag slabs insertion. The dynamic capacitance is limited by electrons (holes) plasmonic interaction at the interface between the As2Se3/Ag/As2Se3 layers. Furthermore, the capacitance- voltage characteristics of the As2Se3/Ag/As2Se3 films confirmed the suitability of the devices to exhibit MOS device features. The characteristics of the stacked layers of As2Se3 indicate their multi-functionality as an optical absorbers/receivers and as microwave cavities.Article Citation - WoS: 1Citation - Scopus: 1Temperature -Dependent Optical and Electrical Characterization of Cu-Ga Thin Films and Their Diode Characteristics on N-Si(Elsevier Gmbh, 2020) Gullu, H. H.; Isik, M.; Gasanly, N. M.; Parlak, M.In this paper, optical and electrical properties of thermally deposited Cu-Ga-S thin films were investigated using temperature-dependent optical transmission and electrical conductivity measurements. The analysis of the transmission spectra resulted in formation of three direct optical transitions due to the possible valence band splitting in the structure. The band gap values were calculated by means of absorption coefficient and incident photon energy was found in decreasing behavior as the temperature rises. The measured current-voltage values were used to extract the conductivity values which stand in the range of 1.73-2.62 (x104 O-1 cm-1) depending on the ambient temperature. These dark conductivity values were modeled by thermionic emission mechanism. The conductivity activation energies in the structures were calculated as 6.4, 14.5 and 40.7 meV according to the effects of grain boundary potentials. In addition, the films deposited on n-Si wafer showed a diode characteristic under the applied bias voltage between indium (In) front and silver (Ag) back contacts. From current-voltage measurements across the Si-based diode, about four orders of magnitude rectification was observed and the results were analyzed to determine the main diode parameters at dark and room temperature conditions.Article Citation - WoS: 4Citation - Scopus: 5Stability of Discrete-Time Systems Joined With a Saturation Operator on the State-Space: Yet Another Version of Liu-michel's Criterion(Elsevier Gmbh, 2012) Singh, VimalA novel criterion for the global asymptotic stability of fixed-point state-space digital filters using saturation arithmetic is presented. The criterion, which is basically a new version of an earlier criterion due to Liu and Michel, is a generalization and improvement over a recently reported criterion. The generalization is due to the fact that the use of even unsymmetric Lyapunov matrix P is permitted. An example illustrating the improvement realized from the present criterion is given. (C) 2011 Elsevier GmbH. All rights reserved.Article Citation - WoS: 4Citation - Scopus: 3Effect of Au/Ge Substrate on the Properties of Gase(Elsevier Gmbh, 2018) Qasrawi, A. F.; Abdallah, Maisam M. A.In this work, the effect of glass/Ge and Au/Ge substrate on the structural, optical and electrical properties of the GaSe thin films is investigated by means of X-ray diffraction, ultraviolet-visible light spectrophotometry and impedance spectroscopy techniques, respectively. While the glass/Ge, glass/GaSe and glass/Ge/GaSe are observed to exhibit amorphous nature of structure, the Au/Ge, and Au/Ge/GaSe are of polycrystalline nature. The formation of the Ge/GaSe interface exhibited high conduction band offset of value of 0.90 eV and enhanced the light absorbability of GaSe at 1.47 eV by 80 times. In addition, the modeling of the dielectric spectra for the Ge/GaSe interface revealed optical conductivity parameters presented by scattering time at femtosecond level and improvement of the drift mobility. Moreover, the impedance spectroscopy measurements have shown that with the increasing frequency, the Au/Ge/GaSe/Yb interface exhibit increasing trend of variation in the resistance causing high impedance mode associated with negative capacitance values below 1300 MHz. The effect is completely reversed in the higher range of frequency. These features of the Ge/GaSe interface nominate it as plasmonic interface, microwave cavities and as voltage amplifiers in low power nanoscale devices. (C) 2018 Elsevier GmbH. All rights reserved.Article Citation - WoS: 12Citation - Scopus: 14Engineering the Structural, Optical and Dielectric Properties of Znse Thin Films Via Aluminum Nanosandwiching(Elsevier Gmbh, 2019) Qasrawi, A. F.; Alsabe, Ansam M.In this work, two stacked layers of ZnSe thin films are nanosandwiched with aluminum slabs of variable thickness in the range of 10-100 nm. The films which are studied by the X-ray diffraction and ultra-violet visible light spectroscopy techniques exhibit interesting features presented by extension of the cubic lattice parameter, increase in the grain size and reduction in both of the microstrains and defect density. The Al nanosandwiching successfully engineered the energy band gap through narrowing it from 2.84 to 1.85 eV. In addition, the Al nanosandwiching is observed to form interbands that widens upon increasing the Al layer thickness. It also changed the electronic transition nature from direct allowed to direct forbidden type. Moreover, remarkable enhancement in the light absorbability by 796 times is observed near 1.72 eV for two stacked ZnSe layers nanosandwiched with Al slab of thickness of 100 nm. The dielectric constant is also increased three times and the dielectric tenability vary in the range of 3.0-1.2 eV. The nonlinearity in the dielectric spectra and the engineering of the band gap that become more pronounced in the presence of Al slabs make the ZnSe more attractive for nonlinear optical applications.Article Citation - WoS: 8Citation - Scopus: 9Thermoluminescence in Gallium Sesquisulfide Single Crystals: Usual and Unusual Heating Rate Dependencies(Elsevier Gmbh, 2018) Guler, I; Isik, M.; Gasanova, L.; Mahammadov, A.; Gasanly, N.Thermoluminescence (TL) experiments were conducted for Ga2S3 crystals to obtain information about trapping parameters. TL measurements were performed from 10 to 300 K with varying heating rates in the range of 0.2-0.8 K/s. Two TL glow peaks centered at 44K (peak A) and 91 K (peak B) were observed at heating rate of beta=0.5 K/s. For peak A, TL intensity decreased whereas that for peak B increased with elevating the heating rates that means anomalous heating rate occurred for peak B. TL glow curves were analyzed using initial rise method to find activation energies of traps. Distribution of trap centers was investigated using T-max - T-stop method. Quasi-continuous distributions with increasing activation energies from 40 to 135 meV and 193 to 460 meV were attributed to trap centers A and B, respectively. (C) 2018 Elsevier GmbH. All rights reserved.
