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Article Citation - WoS: 14Citation - Scopus: 15Structural and Optical Properties of Ga2se3< Crystals by Spectroscopic Ellipsometry(Springer, 2019) Guler, I.; Isik, M.; Gasanly, N. M.; Gasanova, L. G.; Babayeva, R. F.Optical and crystalline structure properties of Ga2Se3 crystals were analyzed utilizing ellipsometry and x-ray diffraction (XRD) experiments, respectively. Components of the complex dielectric function (epsilon=epsilon(1)+i epsilon(2)) and refractive index (N=n+ik) of Ga2Se3 crystals were spectrally plotted from ellipsometric measurements conducted from 1.2eV to 6.2eV at 300K. From the analyses of second-energy derivatives of epsilon(1) and epsilon(2), interband transition energies (critical points) were determined. Absorption coefficient-photon energy dependency allowed us to achieve a band gap energy of 2.02eV. Wemple and DiDomenico single effective oscillator and Spitzer-Fan models were accomplished and various optical parameters of the crystal were reported in the present work.Article Citation - WoS: 5Citation - Scopus: 4Properties of Se/Inse Thin-Film Interface(Springer, 2016) Qasrawi, A. F.; Qasrawı, Atef Fayez Hasan; Kayed, T. S.; Elsayed, Khaled A.; Kayed, Tarek Said; Qasrawı, Atef Fayez Hasan; Kayed, Tarek Said; Department of Electrical & Electronics Engineering; Department of Electrical & Electronics EngineeringSe, InSe, and Se/InSe thin films have been prepared by the physical vapor deposition technique at pressure of similar to 10(-5) torr. The structural, optical, and electrical properties of the films and Se/InSe interface were investigated by means of x-ray diffraction (XRD) analysis, ultraviolet-visible spectroscopy, and current-voltage (I-V) characteristics. XRD analysis indicated that the prepared InSe films were amorphous while the Se films were polycrystalline having hexagonal structure with unit cell parameters of a = 4.3544 and c = 4.9494 . Spectral reflectance and transmittance analysis showed that both Se and InSe films exhibited indirect allowed transitions with energy bandgaps of 1.92 eV and 1.34 eV, respectively. The Se/InSe interface exhibited two energy bandgaps of 0.98 eV and 1.73 eV above and below 2.2 eV, respectively. Dielectric constant values were also calculated from reflectance spectra for the three layers in the frequency range of 500 THz to 272 THz. The dielectric constant exhibited a promising feature suggesting use of the Se/InSe interface as an optical resonator. Moreover, the Au/Se/InSe/Ag heterojunction showed some rectifying properties that could be used in standard optoelectronic devices. The ideality factor and height of the energy barrier to charge carrier motion in this device were found to be 1.72 and 0.66 eV, respectively.Article Citation - WoS: 3Citation - Scopus: 4In Situ Observation of Heat-Assisted Hexagonal-Orthorhombic Phase Transitions in Se/Ag Sandwiched Structures and Their Effects on Optical Properties(Springer, 2019) Qasrawi, A. F.; Aloushi, Hadil D.In this work, two selenium layers of 500-nm thickness, nano-sandwiched with Ag nanosheets of 100-nm thickness (Se/Ag/Se), are subjected to in situ monitoring of the structural and optical transitions during heating over a temperature range of 303-473 K by x-ray diffraction and ultraviolet-visible light spectrophotometry, respectively. The Se/Ag/Se thin films are observed to exhibit a transformation from an amorphous to a polycrystalline phase at 343 K. Increasing the temperature above 363 K enhances the crystallinity of the hexagonal phase, reduces the microstrain, increases the crystallite size and reduces the defect density. Accordingly, the optical absorption spectra are redshifted upon heating. The redshift is accompanied by a transition in the energy band gap from 2.03 eV to 1.85 eV as the material structural phase is transformed from amorphous to polycrystalline. Increasing the temperature causes the energy band gap to shrink. Another permanent phase transformation from hexagonal to orthorhombic is detected when the Se/Ag/Se system is allowed to cool. Scanning electron microscopy images show that the phase transformation converts the grains of Se/Ag/Se films from wire-shaped to nanotubes. The second phase transformation causes a blueshift in the absorption coefficient spectra and increases the energy band gap. The structural and optical parameter enhancements achieved via heating render the Se thin films more suitable for optoelectronic applications.
