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Article Citation - WoS: 10Citation - Scopus: 10Temperature Effects on Optical Characteristics of Cdse Thin Films(Elsevier Sci Ltd, 2021) Gullu, H. H.; Isik, M.; Surucu, O.; Gasanly, N. M.; Parlak, M.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.Article Citation - WoS: 4Citation - Scopus: 4Growth and Optical Characterization of Sn0.6sb0.4< Layer Single Crystals for Optoelectronic Applications(Elsevier Sci Ltd, 2022) Bektas, T.; Terlemezoglu, M.; Surucu, O.; Isik, M.; Parlak, M.SnSe compound is an attractive semiconductor material due to its usage in photovoltaic applications. The sub-stitution of Sb in the SnSe compound presents a remarkable advantage especially in point of tuning optical characteristics. The present paper reports the structural and optical properties of Sn1-xSbxSe (x = 0.4) layered single crystals grown by the vertical Bridgman method. To the best of our knowledge, this work is the first investigation of the Sn0.6Sb0.4Se crystal grown with the vertical Bridgman technique. X-ray diffraction (XRD) pattern of the grown crystal indicated the well crystalline structure of the grown crystals. Lattice strain and interplanar spacing of the crystal structure were determined using the XRD pattern. Scanning electron micro-scope images allowed to the observation of the layer crystal structure. The layer crystalline structure shows 2D material properties and provides 2D applications. Optical properties were revealed by carrying out Raman, ellipsometry and transmission measurements. Raman modes, refractive index, extinction coefficient, and dielectric spectra, band gap energy of the crystal were presented throughout the paper. The obtained results indicated that Sn1-xSbxSe (x = 0.4) layer single crystals may be an alternative potential for photovoltaic and optoelectronic applications.Article Citation - WoS: 22Citation - Scopus: 24Synthesis and Temperature-Tuned Band Gap Characteristics of Magnetron Sputtered Znte Thin Films(Elsevier, 2020) Isik, M.; Gullu, H. H.; Parlak, M.; Gasanly, N. M.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.Article Citation - WoS: 9Citation - Scopus: 9Temperature Effects on Optical Characteristics of Thermally Evaporated Cusbse2 Thin Films for Solar Cell Applications(Elsevier, 2022) Surucu, O.; Isik, M.; Terlemezoglu, M.; Bektas, T.; Gasanly, N. M.; Parlak, M.CuSbSe2 thin film was deposited by co-evaporation of binary CuSe and Sb2Se3 sources. The structural and morphological properties of the deposited thin film were investigated with X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray analysis measurements. XRD pattern indicated that deposited thin film has an orthorhombic crystalline structure with the preferential orientation of (013) direction. SEM image presented that the thin film surface is almost uniform. The optical characteristics of the deposited CuSbSe2 thin film were investigated in detail by performing room temperature Raman, temperature-dependent transmittance spectroscopy, and photoluminescence techniques. Raman spectrum exhibited one mode at around 210 cm(-1) associated with A(g) vibrational mode. The derivative spectroscopy technique was used to obtain the band gap energy of the films. Temperature dependence of band gap energy was investigated by considering the Varshni model. The rate of change of band gap energy, absolute zero value of gap energy, and Debye temperature were determined as 1.3 x 10(-4) eV/K, 1.21 eV, and 297 +/- 51 K, respectively. The photoluminescence spectrum indicated the room temperature direct band gap energy as 1.30 eV.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: 10Citation - Scopus: 10Temperature Dependent Band Gap in Sns2x< (x=0.5) Thin Films(Elsevier Sci Ltd, 2020) Delice, S.; Isik, M.; Gullu, H. H.; Terlemezoglu, M.; Surucu, O. Bayrakli; Gasanly, N. M.; Parlak, M.Structural and optical properties of SnS2xSe(2-2x) thin films grown by magnetron sputtering method were investigated for composition of x = 0.5 (SnSSe) in the present study. X-ray diffraction, energy dispersive X-ray spectroscopy, atomic force microscopy and scanning electron microscopy methods were used for structural characterization while temperature-dependent transmission measurements carried out at various temperatures in between 10 and 300 K were accomplished for optical investigations. X-ray diffraction pattern of studied composition presented peaks at positions which are between those of SnSe2 and SnS2. Transmittance spectra recorded at all applied temperatures were analyzed using well-known Tauc relation. Analyses revealed the direct band gap energy value of SnSSe thin films as 1.75 eV at room temperature. Change of band gap energy as a response to varying temperature were discussed in the study by utilizing Varshni relation. It was shown that variation of gap energy values was well-matched with the Varshni's empirical formula. Energy band gap at absolute zero and rate of change of band gap with temperature were found to be 1.783 eV and -2.1 x 10(-4) eV K-1, respectively.Article Citation - WoS: 42Citation - Scopus: 47Structural and Temperature-Dependent Optical Properties of Thermally Evaporated Cds Thin Films(Elsevier Sci Ltd, 2019) Isik, M.; Gullu, H. H.; Delice, S.; Parlak, M.; Gasanly, N. M.In this work, structural and temperature dependent optical properties of thermally evaporated CdS thin films were investigated. X-ray diffraction, energy dispersive spectroscopy and Raman spectroscopy experiments were carried out to characterize the thin films and obtain information about the crystal structure, atomic composition, surface morphology and vibrational modes. Temperature-dependent transmission measurements were performed in between 10 and 300 K and in the spectral range of 400-1050 nm. The analyses of transmittance spectra were accomplished by two different methods called as the absorption coefficient and the derivative spectrophotometry analyses. All evaluated band gap energy values at each studied temperature were in good agreement with each other depending on the applied analyses techniques. Room temperature gap energy values were found around 2.39 eV and 2.40 eV from absorption coefficient and derivative spectrophotometry analyses, respectively. Band gap energy depending on the sample temperature was studied under the light of two different models to investigate average phonon energy, electron phonon coupling parameter and the rate of change of band gap energy with temperature.Article Citation - WoS: 16Citation - Scopus: 16Temperature-Dependent Optical Characteristics of Sputtered Ga-Doped Zno Thin Films(Elsevier, 2021) Gullu, H. H.; Isik, M.; Gasanly, N. M.; Parlak, M.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.Article Citation - WoS: 21Citation - Scopus: 24Temperature 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.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.Article Citation - WoS: 51Citation - Scopus: 46Temperature-Dependent Optical Characteristics of Sputtered Nio Thin Films(Springer Heidelberg, 2022) Terlemezoglu, M.; Surucu, O.; Isik, M.; Gasanly, N. M.; Parlak, M.In this work, nickel oxide thin films were deposited by radio frequency magnetron sputtering technique. X-ray diffraction (XRD), scanning electron microscopy and energy-dispersive X-ray analysis methods were applied to reveal the structural and morphological properties of sputtered thin films. The XRD pattern of films confirmed the presence of the cubic phase of nickel oxide with the preferential orientation of (200) direction. The surface morphology of thin films was observed as almost uniform and smooth. Optical aspects of sputtered film were studied by employing the room temperature Raman and temperature-dependent transmittance spectroscopy techniques in the range of 10-300 K. Tauc relation and derivative spectroscopy techniques were applied to obtain the band gap energy of the films. In addition, the relation between the band gap energy and the temperature was investigated in detail considering the Varshni optical model. The absolute zero band gap energy, rate of change of band gap energy, and Debye temperature were obtained as 3.57 eV, - 2.77 x 10(-4) eV/K and 393 K, respectively.
