Güllü, Hasan Hüseyin

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Gullu,H.H.
H.,Güllü
H.H.Güllü
G., Hasan Huseyin
Güllü, Hasan Hüseyin
H., Gullu
G.,Hasan Huseyin
H.H.Gullu
Hasan Hüseyin, Güllü
G.,Hasan Hüseyin
Hasan Huseyin, Gullu
Gullu, Hasan Huseyin
Güllü,H.H.
Gullu, H. H.
Gullu, Hasan H.
Job Title
Doktor Öğretim Üyesi
Email Address
hasan.gullu@atilim.edu.tr
Main Affiliation
Department of Electrical & Electronics Engineering
Status
Former Staff
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Scholarly Output

55

Articles

52

Citation Count

631

Supervised Theses

1

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2018 - 201952020 - 20219
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Author: Gasanly, N. M.

Scholarly Output Search Results

Now showing 1 - 10 of 14
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    Article
    Citation - WoS: 14
    Citation - Scopus: 14
    Temperature-Dependent Optical Characteristics of Sputtered Ga-Doped Zno Thin Films
    (Elsevier, 2021) Gullu, H. H.; Isik, M.; Gasanly, N. M.; Parlak, M.; Department of Electrical & Electronics Engineering
    The present paper reports structural and optical properties of gallium (Ga) doped ZnO thin films (GZO) grown by magnetron sputtering technique. The crystalline properties were determined from X-ray diffraction measurements and analyses pointed out the crystalline structure as hexagonal, crystalline size as 43 nm and strain as 6.9 x 10(-5). Derivative spectroscopy analyses showed that band gap energy of GZO thin films decreases from 3.50 eV (10 K) to 3.45 eV (300 K). Temperature-band gap energy dependency was analyzed using Varshni and O'DonnellChen models. The absolute zero band gap energy, the rate of change of band gap energy with temperature and phonon energy were found as 3.50 eV, -2.8 x 10(-4) eV/K and 15 meV, respectively. The room temperature band gap and Urbach energies were also determined as 3.43 eV and 102 meV, respectively, from the absorption analysis.
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    Article
    Citation - WoS: 19
    Citation - Scopus: 23
    Temperature Dependence of Band Gaps in Sputtered Snse Thin Films
    (Pergamon-elsevier Science Ltd, 2019) Delice, S.; Isik, M.; Gullu, H. H.; Terlemezoglu, M.; Surucu, O. Bayrakli; Parlak, M.; Gasanly, N. M.; Electrical-Electronics Engineering; Department of Electrical & Electronics Engineering
    Temperature-dependent transmission experiments were performed for tin selenide (SnSe) thin films deposited by rf magnetron sputtering method in between 10 and 300 K and in the wavelength region of 400-1000 nm. Transmission spectra exhibited sharp decrease near the absorption edge around 900 nm. The transmittance spectra were analyzed using Tauc relation and first derivative spectroscopy techniques to get band gap energy of the SnSe thin films. Both of the applied methods resulted in existence of two band gaps with energies around 1.34 and 1.56 eV. The origin of these band gaps was investigated and it was assigned to the splitting of valence band into two bands due to spin-orbit interaction. Alteration of these band gap values due to varying sample temperature of the thin films were also explored in the study. It was seen that the gap energy values increased almost linearly with decreasing temperature as expected according to theoretical knowledge.
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    Article
    Citation - WoS: 3
    Citation - Scopus: 4
    Analysis of Temperature-Dependent Transmittance Spectra of Zn0.5in0.5< (zis) Thin Films
    (Springer, 2019) Isik, M.; Gullu, H. H.; Delice, S.; Gasanly, N. M.; Parlak, M.; Department of Electrical & Electronics Engineering
    Temperature-dependent transmission experiments of ZnInSe thin films deposited by thermal evaporation method were performed in the spectral range of 550-950nm and in temperature range of 10-300K. Transmission spectra shifted towards higher wavelengths (lower energies) with increasing temperature. Transmission data were analyzed using Tauc relation and derivative spectroscopy. Analysis with Tauc relation was resulted in three different energy levels for the room temperature band gap values of material as 1.594, 1.735 and 1.830eV. The spectrum of first wavelength derivative of transmittance exhibited two maxima positions at 1.632 and 1.814eV and one minima around 1.741eV. The determined energies from both methods were in good agreement with each other. The presence of three band gap energy levels were associated to valence band splitting due to crystal-field and spin-orbit splitting. Temperature dependence of the band gap energies were also analyzed using Varshni relation and gap energy value at absolute zero and the rate of change of gap energy with temperature were determined.
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    Article
    Citation - WoS: 3
    Citation - Scopus: 6
    Structural and Optical Properties of Thermally Evaporated Cu-Ga (cgs) Thin Films
    (Elsevier, 2018) Gullu, H. H.; Isik, M.; Gasanly, N. M.; Department of Electrical & Electronics Engineering
    The structural and optical properties of thermally evaporated Cu-Ga-S (CGS) thin films were investigated by Xray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), atomic force microscopy (AFM) and optical transmittance measurements. The effect of annealing temperature on the results of applied techniques was also studied in the present paper. EDS results revealed that each of the elements, Cu, Ga and S are presented in the films and Cu and Ga concentration increases whereas S concentration decreases within the films as annealing temperature is increased. XRD pattern exhibited four diffraction peaks which are well-matched with those of tetragonal CuGaS2 compound. AFM images were recorded to get knowledge about the surface morphology and roughness of deposited thin films. Transmittance measurements were applied in the wavelength region of 300-1000 nm. Analyses of the absorption coefficient derived from transmittance data resulted in presence of three distinct transition regions in each thin films with direct transition type. Crystal-field and spin-orbit splitting energies existing due to valence band splitting were also calculated using quasicubic model.
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    Article
    Citation - WoS: 9
    Citation - Scopus: 9
    Optical 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.; Department of Electrical & Electronics Engineering
    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.
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    Article
    Citation - WoS: 19
    Citation - Scopus: 20
    Synthesis and Temperature-Tuned Band Gap Characteristics of Magnetron Sputtered Znte Thin Films
    (Elsevier, 2020) Isik, M.; Gullu, H. H.; Parlak, M.; Gasanly, N. M.; Department of Electrical & Electronics Engineering
    Zinc telluride (ZnTe) is one of the attractive semiconducting compounds used in various optoelectronic devices. The usage of ZnTe in optoelectronic applications directs researchers to search its optical characteristics in great detail. For this purpose, structural and optical properties of magnetron sputtered ZnTe thin films were studied by means of x-ray diffraction and transmission spectroscopy measurements. Structural analyses indicated that ZnTe thin films having cubic crystalline structure were successfully grown on soda-lime glass substrates. Transmittance spectra in the 400-1000 nm were recorded in between 10 and 300 K temperature region. The analyses of absorption coefficient spectra resulted in band gap energies decreasing from around 2.31 (10 K) to 2.26 eV (300 K). Temperature dependency of gap energy was studied by Varshni and O'Donnell-Chen relations to determine various optical parameters like absolute zero temperature band gap energy, change of gap energy with temperature, phonon energy.
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    Article
    Citation - WoS: 1
    Citation - Scopus: 1
    Temperature -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.; Department of Electrical & Electronics Engineering
    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.
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    Article
    Citation - WoS: 12
    Citation - Scopus: 13
    Investigation of Band Gap Energy Versus Temperature for Sns 2 Thin Films Grown by Rf-Magnetron Sputtering
    (Elsevier, 2020) Isik, M.; Gullu, H. H.; Terlemezoglu, M.; Surucu, O. Bayrakli; Parlak, M.; Gasanly, N. M.; Electrical-Electronics Engineering; Department of Electrical & Electronics Engineering
    [No Abstract Available]
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    Article
    Citation - WoS: 7
    Citation - Scopus: 8
    Temperature Effects on Optical Characteristics of Cdse Thin Films
    (Elsevier Sci Ltd, 2021) Gullu, H. H.; Isik, M.; Surucu, O.; Gasanly, N. M.; Parlak, M.; Electrical-Electronics Engineering; Department of Electrical & Electronics Engineering
    CdSe is one of the significant members of II-VI type semiconducting family and it has a wide range of technological applications in which optoelectronic devices take a special position. The present paper reports the structural and optical characteristics of thermally evaporated CdSe thin films. XRD pattern exhibited preferential orientation along (111) plane while atomic composition analyses resulted in the ratio of Cd/Se as closer to 1.0. Temperature-dependent band gap characteristics of CdSe thin films were investigated for the first time by carrying out transmission experiments in the 10-300 K range. The analyses showed that direct band gap energy of the compound decreases from 1.750 (at 10 K) to 1.705 eV (at 300 K). Varshni model was successfully applied to the temperature-band gap energy dependency and various optical constants were determined. Raman spectrum of CdSe thin films was also presented to understand the vibrational characteristics of the compound. The present paper would provide worthwhile data to researchers especially studying on optoelectronic device applications of CdSe thin films.
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    Conference Object
    Citation - WoS: 4
    Citation - Scopus: 3
    Temperature-dependent material characterization of CuZnSe2 thin films
    (Elsevier Science Sa, 2020) Gullu, H. H.; Surucu, O.; Terlemezoglu, M.; Isik, M.; Ercelebi, C.; Gasanly, N. M.; Parlak, M.; Electrical-Electronics Engineering; Department of Electrical & Electronics Engineering
    In the present work, CuZnSe2 (CZSe) thin films were co-deposited by magnetron sputtering of ZnSe and Cu targets. The structural analyses resulted in the stoichiometric elemental composition and polycrystalline nature without secondary phase contribution in the film structure. Optical and electrical properties of CZSe thin films were investigated using temperature-dependent optical transmission and electrical conductivity measurements. The band gap energy values were obtained using transmittance spectra under the light of expression relating absorption coefficient to incident photon energy. Band gap energy values were found in decreasing behavior from 2.31 to 2.27 eV with increase in temperature from 10 to 300 K. Temperature-band gap dependency was evaluated by Varshni and O'Donnell models to detail the optical parameters of the thin films. The experimental dark and photoconductivity values were investigated by thermionic emission model over the grain boundary potential. Room temperature conductivity values were obtained in between 0.91 and 4.65 ( x 10(-4) Omega(-1)cm(-1)) under various illumination intensities. Three different linear conductivity regions were observed in the temperature dependent profile. These linear regions were analyzed to extract the activation energy values.