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Article Citation - WoS: 7Citation - Scopus: 7In situ monitoring of the permanent crystallization, phase transformations and the associated optical and electrical enhancements upon heating of Se thin films(Elsevier Science Bv, 2019) Qasrawi, A. F.; Aloushi, Hadil D.In this work, the in situ structural transformations from amorphous to polycrystalline upon heating and the associated enhancements in the structural parameters of selenium thin films are studied by means of X-ray diffraction technique. The Se thin films which are grown onto ultrasonically cleaned glass substrate by the thermal evaporation technique under vacuum pressure of 10(-5) mbar exhibits structural transformation from amorphous to polycrystalline near 353 K. The films completed the formation of the structure which includes both of the hexagonal and monoclinic phases at 363 K. It is observed that the hexagonal phase dominates over the monoclinic as temperature is raised. Consistently, the thermally assisted crystallization process is accompanied with increase in the crystallite size, decrease in the microstrain, decrease in defect density and decrease in the percentage of stacking faults. The scanning electron microscopy measurements also confirmed the crystallinity of selenium after heating. The time dependent reputations of the crystallization test has shown that the achieved phase transitions and enhancements in structural parameters are permanent in selenium. Optically, the crystallization process is observed to be associated with redshift in the absorption spectra and in the value of the energy band gap. Electrically, the in situ monitoring of the electrical conductivity during the heating cycle has shown that the electrical conductivity stabilizes and exhibit a decrease in the acceptor levels from 566 to 321 meV after the crystallization was achieved.Article Citation - WoS: 9Citation - Scopus: 10Spectroscopic Ellipsometry Investigation of Optical Properties of Β-ga2s3< Single Crystals(Elsevier Science Bv, 2018) Isik, M.; Gasanly, N. M.; Gasanova, L.Ga2S3 single crystals were studied by x-ray diffraction (XRD), energy dispersive spectroscopy and spectroscopic ellipsometry measurements. XRD pattern of the sample is well-matched with reported hexagonal structure of beta-Ga2S3 . The spectra of real and imaginary parts of complex dielectric function (epsilon = epsilon(1) + epsilon(2)) and refractive index (N = n + ik) were plotted in the 1.2-6.2 eV range according to results of ellipsometric data. The e 2 -spectrum and analyses of absorption coefficient pointed out that studied sample has band gap energy of 2.48 eV which is consistent with that of beta-Ga(2)S(3)2. Critical point energies of beta-Ga2S3 were also reported in the present study.Article Citation - Scopus: 1Infrared and Raman Scattering Spectra of Layered Structured Ga3inse4< Crystals(Elsevier Science Bv, 2013) Isik, M.; Gasanly, N. M.; Korkmaz, F.The infrared reflectivity and transmittance and Raman scattering in Ga3InSe4 layered crystals were investigated in the frequency ranges of 100-400, 400-4000 and 25-500 cm(-1). The refractive and absorption indices, the frequencies of transverse and longitudinal optical modes, high- and low-frequency dielectric constants were obtained from the analysis of the IR reflectivity spectra. The bands observed in IR transmittance spectra were interpreted in terms of two-phonon absorption processes. (C) 2012 Elsevier B.V. All rights reserved.Article Citation - WoS: 4Citation - Scopus: 4Band Offsets and Optical Conduction in the Cdse/Gase Interface(Elsevier Science Bv, 2016) Kayed, T. S.; Qasrawi, A. F.; Elsayed, Khaled A.In this work, the design and characterization of CdSe/GaSe heterojunction is considered. The CdSe/GaSe thin film interface was prepared by the physical vapor deposition technique. Systematic structural and optical analysis were performed to explore the crystalline nature, the optical band gaps, the conduction and valence band offsets, the dielectric spectra, and the frequency dependent optical conductivity at terahertz frequencies. The X-ray diffraction analysis revealed a polycrystalline interface that is mostly dominated by the hexagonal CdSe oriented in the (002) direction. It was also found that the CdSe/GaSe interface exhibits conduction and valence band offsets of 1.35 and 1.23/1.14 eV, respectively. The dielectric spectra displayed two dielectric resonance peaks at 530 and 445 THz. Moreover, the computational fittings of the optical conductivity of the interface revealed a free carrier scattering time of 0.41 (fs) for a free carrier density of 7.0 x 10(18) (cm(-3)). The field effect mobility for the CdSe/GaSe interface was found to be 5.22 (cm(2)/Vs). The remarkable features of this device having large band offsets and qualitative optical conduction dominated by a scattering time in the order of femtoseconds in addition to the dielectric property nominate the device to be used in optoelectronic technology. (C) 2016 Elsevier B.V. All rights reserved.Article Citation - WoS: 3Citation - Scopus: 3Temperature and Excitation Intensity Tuned Photoluminescence in Ga0.75in0.25< Crystals(Elsevier Science Bv, 2013) Isik, M.; Guler, I.; Gasanly, N. M.Photoluminescence (PL) spectra of Ga0.75In0.25Se layered single crystals have been studied in the wavelength range of 580-670 nm and temperature range of 7-59 K. Two PL emission bands centered at 613 nm (2.02 eV, A-band) and 623 nm (1.99 eV, B-band) were revealed at T = 7K. The excitation laser intensity dependence of the emission bands have been studied in the 0.06-1.40 W cm(-2) range. Radiative transitions from shallow donor levels located at E-A = 0.11 and E-B = 0.15 eV below the bottom of conduction band to single shallow acceptor level located at 0.01 eV above the valence band are suggested to be responsible for the observed A- and B-bands. A simple model was proposed to interpret the recombination processes in Ga0.75In0.25Se single crystals. (c) 2012 Elsevier B.V. All rights reserved.Article Citation - WoS: 9Citation - Scopus: 8Multiphonon Absorption Processes in Layered Structured Tlgas2, Tlins2 and Tlgase2 Single Crystals(Elsevier Science Bv, 2013) Isik, M.; Gasanly, N. M.; Korkmaz, F.The infrared transmittance and Raman scattering spectra in TlGaS2, TlInS2 and TlGaSe2 layered single crystals grown by Bridgman method were studied in the frequency ranges of 400-1500 and 10-400 cm(-1), respectively. Three, three and five bands observed at room temperature in IR transmittance spectra of TlGaS2, TlInS2 and TlGaSe2, respectively, were interpreted in terms of multiphonon absorption processes. (C) 2013 Elsevier By. All rights reserved.Article Citation - WoS: 5Citation - Scopus: 5Optical properties of (Ga2Se3)0.75 - (Ga2S3)0.25 single crystals by spectroscopic ellipsometry(Elsevier Science Bv, 2019) Isik, M.; Gasanly, N. M.; Gasanova, L.Structural and optical properties of 75 mol % Ga2Se3 - 25 mol % Ga2S3 system of single crystals were investigated by experimental techniques of x-ray diffraction (XRD), energy dispersive spectroscopy, Raman spectroscopy and ellipsometry. XRD pattern indicated that the studied compound has crystalline nature with cubic structure. Vibrational modes in the crystal were revealed using Raman spectroscopy experiments in the 90-450 cm(-1) frequency range and nine modes were observed in the spectrum. Ellipsometry measurements were utilized in the 1.2-6.2 eV range to get spectral dependencies of optical constants; complex dielectric function, refractive index and extinction coefficient. Under the light of fundamental expressions and models, refractive index and extinction coefficient spectra were analyzed to get various optical parameters of the single crystal.
