Güllü, Hasan Hüseyin
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Name Variants
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.
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
ORCID ID
Scopus Author ID
Turkish CoHE Profile ID
Google Scholar ID
WoS Researcher ID
Scholarly Output
54
Articles
51
Citation Count
631
Supervised Theses
1
54 results
Scholarly Output Search Results
Now showing 1 - 10 of 54
Article Citation Count: 9CZTSSe thin films fabricated by single step deposition for superstrate solar cell applications(Springer, 2019) Sürücü, Özge; Surucu, O. Bayrakli; Güllü, Hasan Hüseyin; Gullu, H. H.; Ciftpinar, E. H.; Ercelebi, C.; Parlak, M.; Electrical-Electronics Engineering; Department of Electrical & Electronics EngineeringThe focus of this study is the characterization of Cu2ZnSn(S,Se)(4) (CZTSSe) thin films and fabrication of CZTSSe solar cell in superstrate configuration. In this work, superstrate-type configuration of glass/ITO/CdS/CZTSSe/Au was entirely fabricated by totally vacuum-based process. CZTSSe absorber layers were grown by RF magnetron sputtering technique using stacked layer procedure. SnS, CuSe and ZnSe solid targets were used as precursors and no additional step like the selenization process was applied. The structural and morphological properties of deposited CZTSSe layers were analyzed using X-ray diffraction (XRD), Raman scattering, scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy analysis (EDS) measurements. The optical and electrical properties of the CZTSSe thin films were investigated by UV-Vis spectroscopy, Hall-Effect and photoconductivity measurements. In addition, the device performance of the fabricated superstrate solar cell was examined.Article Citation Count: 34Structural and temperature-dependent optical properties of thermally evaporated CdS thin films(Elsevier Sci Ltd, 2019) Işık, Mehmet; Gullu, H. H.; Güllü, Hasan Hüseyin; Parlak, M.; Gasanly, N. M.; Department of Electrical & Electronics EngineeringIn 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 Count: 28Temperature and frequency effects on electrical and dielectric properties of n-4H SiC based metal-insulator-semiconductor (MIS) diode interlayered with Si3N4 thin film(Springer, 2020) Güllü, Hasan Hüseyin; Yildiz, D. E.; Department of Electrical & Electronics EngineeringEffects of frequency and temperature variations on the electrical properties of Au/Si3N4/n-4H SiC diode were investigated. The diode responses to the change in frequency with applied AC signal of varying frequencies and to the change in temperature controlled by cryogenic control system were discussed with considering possible deviation from ideality and effects of interface states at the junction. Depending on its capacitive and conductive characteristics, internal parasitic resistances were associated with the observed dielectric behaviors of the diode. With the use of Si3N4 layer, the values of complex dielectric constant were extracted and this parameter was found to be in a strong dependence of interface changes in low frequency region whereas this variation was very low at higher frequencies. In addition, there is a slight decrease in the dielectric constant with increasing temperature whereas the values of dielectric loss give a remarkable response to the temperature at forward bias region. Depending on these profiles, AC conductivity values were found in decreasing behavior with both frequency and temperature. From the temperature dependent behaviors, activation energies were calculated from the corresponding Arrhenius plots. Together with the series resistance of the diode and density of interface states, interface polarization was found in a dominant role in both complex dielectric and electric modulus characteristics of the diode.Article Citation Count: 0Annealing Effect on Dark Electrical Conductivity and Photoconductivity of Ga-In-Se Thin Films(Polish Acad Sciences inst Physics, 2018) Işık, Mehmet; Gullu, H. H.; Güllü, Hasan Hüseyin; Department of Electrical & Electronics EngineeringDark-conductivity and photoconductivity properties of thermally evaporated Ga-In-Se (GIS) thin films were investigated in the temperature range of 80-430 K. All measurements were performed on as-grown and annealed GIS thin films at 300 and 400 degrees C to get information about the effect of the annealing temperature on the conductivity properties. Room temperature conductivity was obtained as 1.8 x 10(-8) Omega(-1) cm(-1) for as-grown films and increased to 3.6 x 10(-4) Omega(-1) cm(-1) for annealed films at 400 degrees C. Analysis of the dark-conductivity data of as-grown films revealed nearly intrinsic type of conductivity with 1.70 eV band gap energy. Temperature dependent dark conductivity curves exhibited two regions in the 260-360 and 370-430 K for both of annealed GIS films. Conductivity activation energies were found as 0.05, 0.16 and 0.05, 0.56 eV for films annealed at temperatures of 300 and 400 degrees C, respectively. The dependence of photoconductivity on illumination intensity was also studied in the range from 17 to 113 mW/cm(2).Article Citation Count: 2Optical and Nanomechanical Properties of Ga2Se3Single Crystals and Thin Films(Springer, 2021) Güllü, Hasan Hüseyin; Emir, Cansu; Işık, Mehmet; Gasanly, Nizami; Department of Electrical & Electronics EngineeringThe optical and nanomechanical properties of Ga(2)Se(3)single crystals and thin films were investigated using reflection, transmission, and nanoindentation measurements. The reflection spectrum recorded in the 525- to 1100-nm range was analyzed to get the band gap energy of the crystal structure, and derivative analysis of the spectrum resulted in band gap energy of 1.92 eV which was attributed to indirect transition. The band gap energy of thermally evaporated Ga(2)Se(3)thin film was determined from the analysis of the transmittance spectrum. The absorption coefficient analysis presented the direct band gap energy as 2.60 eV. The refractive index was investigated in the transparent region using the Wemple-DiDomenico single-oscillator model. Nanoindentation measurements were carried out on the crystal and thin film structures of Ga2Se3. Nanohardness and elastic modulus of the Ga(2)Se(3)single crystals and thin films were calculated following the Oliver-Pharr analysis method.Article Citation Count: 5Influence of temperature on optical properties of electron-beam-evaporated ZnSe thin film(Iop Publishing Ltd, 2020) Işık, Mehmet; Isik, M.; Güllü, Hasan Hüseyin; Parlak, M.; Department of Electrical & Electronics EngineeringStructural and optical properties of ZnSe thin films grown by electron-beam evaporation technique were reported in the present paper. X-ray diffraction pattern exhibited a single peak around 27 degrees which is well-suited with cubic phase of the films. Energy dispersive X-ray spectroscopy analyses resulted in atomic composition ratio of Zn/Se nearly 1.0 which corresponds to the chemical formula of ZnSe. Transmission experiments were performed at various temperatures in between 10 and 300 K. The analyses of the transmission data showed that direct band gap energy of the ZnSe thin films increases from 2.72 to 2.83 eV as temperature was reduced to 10 K from room temperature. The Varshni and O'Donnell-Chen models giving the temperature-band gap energy relation were used to get various optical parameters of the evaporated thin films. Analyses resulted in absolute zero temperature band gap energy as 2.83 eV, temperature coefficient as -5.8 x 10(-4) eV K-1 and average phonon energy as 16 meV. Urbach tail state energies were also calculated using absorption coefficient in the low photon energy region as increasing from 173 meV (300 K) to 181 meV (10 K) with decreasing ambient temperature.Article Citation Count: 7Effects of Si nanowire on the device properties of n-ZnSe/p-Si heterostructure(Springer, 2019) Güllü, Hasan Hüseyin; Gullu, H. H.; Colakoglu, T.; Emir, C.; Bozdogan, E.; Parlak, M.; Department of Electrical & Electronics EngineeringThe semiconductor nanowire (NW) technology has raised attention owing to its one-dimensional geometry as a solution for lattice mismatch in the fabricated heterostructures. Although, SiNWs have been investigated for various device technologies, there is no published work on the p-n junction formed by deposition of ZnSe thin film on these NW structures, in which this film layer has significant optical and electrical properties in optoelectronics applications. The aim of this study is determining the device properties of n-ZnSe/SiNW heterojunction and obtaining the enhancement in the device application of the NW structure on Si surface with comparing to planar surface. SiNW was produced by metal assisted etching method as a cost-efficient process, and the ZnSe film was deposited on SiNW and planar Si substrates by thermal evaporation of elemental sources. The optical band gap of the deposited ZnSe film was determined as 2.7eV which is in a good agreement with literature. The ideality factor and series resistance values of the ZnSe/SiNW and ZnSe/Si heterojunctions were calculated as 3.12, 461 , and 4.52, 7.26x103, respectively. As a result of utilizing SiNW structure, a spectacular improvement in terms of the physical parameters related to device properties was achieved.Article Citation Count: 0Material and device properties of Si-based Cu0.5Ag0.5InSe2 thin-film heterojunction diode(Springer, 2020) Işık, Mehmet; Isik, M.; Güllü, Hasan Hüseyin; Parlak, M.; Gasanly, N. M.; Department of Electrical & Electronics EngineeringCu0.5Ag0.5InSe2 (CAIS) thin films were deposited on a glass substrate by sequential sputtering of Cu, Ag, and In2Se3-stacked film layers. Structural characterization showed that the deposited CAIS film satisfies nearly the stoichiometric form with uniform and homogeneous surface structure. The single-phase polycrystalline behavior without any secondary-phase formation was observed from the diffraction profile. The optical properties were investigated using temperature-dependent transmission measurements in the wavelength region of 600-1100 nm and in between 10 and 300 K. In the region of interest, the transmission spectra shifted towards the higher wavelengths as a result of an increase in the sample temperature. The analysis of the absorption data based on the transmission spectra resulted in absorption coefficient values of around 10(5) cm(-1) and the presence of direct allowed optical transition. From the Tauc plots, CAIS samples were found to have three distinct direct optical transitions depending on the possible splitting in the valence band. The obtained room temperature uppermost band gap energy value of 1.09 eV was found in the energy limit of ternary analogues (CuInSe2 and AgInSe2), and also in a good agreement with the previous works in the literature. The dependency of the band gap energy on the temperature was analyzed using fundamental relations. In addition, the electrical characteristics of the film layer were discussed in four-contact conductivity measurements, and room temperature conductivity was observed as 0.8 ohm(-1) cm(-1). Additionally, two activation energy values were found in the temperature-dependent conductivity profile. As a diode application, CAIS/Si heterojunction was fabricated and the main diode parameters were extracted at dark and room temperature conditions.Article Citation Count: 8Temperature dependent band gap in SnS2xSe(2-2x) (x=0.5) thin films(Elsevier Sci Ltd, 2020) Sürücü, Özge; Isik, M.; Işık, Mehmet; Terlemezoglu, M.; Güllü, Hasan Hüseyin; Gasanly, N. M.; Parlak, M.; Electrical-Electronics Engineering; Department of Electrical & Electronics EngineeringStructural 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 Count: 6Temperature dependence of electrical properties in Cu0.5Ag0.5InSe2/Si heterostructure(Springer, 2018) Güllü, Hasan Hüseyin; Parlak, M.; Department of Electrical & Electronics EngineeringThe polycrystalline Cu0.5Ag0.5InSe2 thin film was deposited on mono-crystalline n-Si wafer by sequential thermal evaporation of elemental sources. p-Cu0.5Ag0.5InSe2/n-Si heterojunction diode was fabricated and the current-voltage characteristics of the diode at various temperatures were investigated to determine the main diode parameters and dark current transport mechanism. The studied diode structure showed a rectifying behavior with a barrier height of 0.63 eV at room temperature. Series and shunt resistance values were calculated by parasitic resistance relations in high bias regions. Considering the ideality factor values between 1.7 and 2.8, dominant transport characteristics were detailed for forward and reverse voltages. The analysis of the forward current-voltage behavior reveals field emission can be the possible current conduction mechanism. At the reverse bias region, around 10(1) number of tunneling step and about 10(5) density of traps were found to act a role in the process in leakage current flow.
