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.
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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ORCID ID
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WoS Researcher ID
Sustainable Development Goals
14
LIFE BELOW WATER
0
Research Products
2
ZERO HUNGER
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11
SUSTAINABLE CITIES AND COMMUNITIES
0
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1
NO POVERTY
0
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12
RESPONSIBLE CONSUMPTION AND PRODUCTION
0
Research Products
7
AFFORDABLE AND CLEAN ENERGY
5
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5
GENDER EQUALITY
0
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3
GOOD HEALTH AND WELL-BEING
0
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9
INDUSTRY, INNOVATION AND INFRASTRUCTURE
0
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13
CLIMATE ACTION
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6
CLEAN WATER AND SANITATION
0
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10
REDUCED INEQUALITIES
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4
QUALITY EDUCATION
0
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15
LIFE ON LAND
0
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16
PEACE, JUSTICE AND STRONG INSTITUTIONS
0
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17
PARTNERSHIPS FOR THE GOALS
0
Research Products
8
DECENT WORK AND ECONOMIC GROWTH
0
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This researcher does not have a Scopus ID.
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Scholarly Output
55
Articles
52
Views / Downloads
7/0
Supervised MSc Theses
1
Supervised PhD Theses
0
WoS Citation Count
873
Scopus Citation Count
899
WoS h-index
16
Scopus h-index
16
Patents
0
Projects
0
WoS Citations per Publication
15.87
Scopus Citations per Publication
16.35
Open Access Source
8
Supervised Theses
1
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| Journal | Count |
|---|---|
| Journal of Materials Science: Materials in Electronics | 16 |
| Physica B: Condensed Matter | 7 |
| Bulletin of Materials Science | 3 |
| Materials Science in Semiconductor Processing | 3 |
| Optik | 3 |
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Competency Cloud
52 results
Scholarly Output Search Results
Now showing 1 - 10 of 52
Article Citation - WoS: 2Citation - Scopus: 3Electrical Characterization of Zninse2 Thin-Film Heterojunction(Springer, 2019) Gullu, H. H.; Parlak, M.ZnInSe2/Cu0.5Ag0.5InSe2 diode structures have been fabricated by thermal evaporation of stacked layers on indium tin oxide-coated glass substrates. Temperature-dependent dark current-voltage measurements were carried out to extract the diode parameters and to determine the dominant conduction mechanisms in the forward- and reverse-bias regions. The heterostructure showed three order of magnitude rectifying behavior with a barrier height of 0.72 eV and ideality factor of 2.16 at room temperature. In the high forward-bias region, the series and shunt resistances were calculated with the help of parasitic resistance relations, yielding room-temperature values of 9.54 x 10(2) Omega cm(2) and 1.23 x 10(3) Omega cm(2), respectively. According to the analysis of the current flow in the forward-bias region, abnormal thermionic emission due to the variation of the ideality factor with temperature and space-charge-limited current processes were determined to be the dominant conduction mechanisms in this heterostructure. In the reverse-bias region, the tunneling mechanism was found to be effective in the leakage current flow with trap density of 10(6) cm(-3). Spectral photocurrent measurements were carried out to investigate the spectral working range of the device structure. The main photocurrent peaks observed in the spectrum corresponded to the band-edge values of the active thin-film layers.Article Citation - WoS: 1Citation - Scopus: 1Structural and Optical Properties of Thermally Evaporated Ga-In Thin Films(World Scientific Publ Co Pte Ltd, 2014) Isik, Mehmet; Gullu, Hasan HuseyinIn this paper, structural and optical properties of Ga-In-Se (GIS) thin films deposited by thermal evaporation technique have been investigated. The effect of annealing was also studied for samples annealed at temperatures between 300 degrees C and 500 degrees C. X-ray diffraction, energy dispersive X-ray analysis and scanning electron microscopy have been used for structural characterization. It was reported that increase of annealing temperature results with better crystallization and chemical composition of the films were almost same. Optical properties of the films were studied by transmission measurements in the wavelength range of 320-1100 nm. The direct bandgap transitions with energies in the range of 1.52 eV and 1.65 eV were revealed for the investigated GIS films. Photon energy dependence of absorption coefficient showed that there exist three distinct transition regions for films annealed at 400 degrees C and 500 degrees C. The quasicubic model was applied for these transitions to calculate crystal-field splitting and spin-orbit splitting energy values.Article Citation - WoS: 77Citation - Scopus: 79Electrical Properties of Al/Pcbm:zno Heterojunction for Photodiode Application(Elsevier Science Sa, 2020) Gullu, H. H.; Yildiz, D. E.; Kocyigit, A.; Yildirim, M.In this paper, the electrical characteristics of spin-coated PCBM:ZnO interlayered Al/PCBM:ZnO/Si diode are investigated under the aim of photodiode application. Under dark condition, the diode shows about four orders in magnitude rectification rate and diode illumination results in efficient rectification with increase in intensity. The analysis of current-voltage curve results a non-ideal diode characteristics according to the thermionic emission model due to the existence of parasitic resistances and interface states. The measured current-voltage values are used to extract the barrier height and ideality factor under dark and illumination conditions. Under illumination, photo-generated carriers contribute to the current flow and linear photo-conductivity behavior in photo-current measurements with illumination shows the possible use of hybrid PCBM:ZnO layer in Si-based photodiodes. In addition, change in the series and shunt resistance values under illumination is found to be effective in this light-sensing behavior of the diode. This characteristic is also observed from the typical on/off illumination switching behavior for the photodiodes in transient photo-current, photo-capacitance and photo-conductance measurements with the quick response to the illumination. The deviations from ideality are also discussed by means of distribution of interface states and series resistance depending on the applied frequency and bias voltage. (C) 2020 Elsevier B.V. All rights reserved.Article Citation - WoS: 42Citation - Scopus: 41Analysis of Forward and Reverse Biased Current-Voltage Characteristics of Al/Al2< Schottky Diode With Atomic Layer Deposited Al2o3< Thin Film Interlayer(Springer, 2019) Gullu, H. H.; Yildiz, D. E.The dark current-voltage (I-V) characteristics of Al/Al2O3/n-Si Schottky diode are investigated in a wide temperature range of 260-360 K. The diode shows four orders of magnitude rectification. In forward and reverse bias regions, the temperature-dependent I-Vcharacteristics are detailed in terms of diode parameters and dominant conduction mechanisms. Due to the existence of Al2O3 film layer and series resistance in the diode structure, current flow under the forward bias is observed in a deviation from pure exponential characteristics. The diode parameters are estimated from thermionic emission model with non-unity ideality factor, and this non-ideal behavior is resulted in the ideality factors greater than two. In addition to these values, zero-bias barrier height is found to be strongly temperature dependent, and this variation indicates a presence of inhomogeneties in the barrier according to Gaussian distribution (GD) approximation. This fact is investigated plotting characteristic plot of this model and by extracting mean barrier height with its standard deviation. In order to complete the work on the forward I-V region, the carrier transport characteristics of the diode are explained on the basis of thermionic emission mechanism with a GD of the harrier heights. In accordance with this approximation, the conventional Richardson plot exhibits non-linearity behavior and modified current relation based on GD model is used to calculate mean barrier height and Richardson constant. In addition, the values of parasitic resistances are determined using Ohm's law as a function of temperature for all bias voltage spectra. In the reverse bias region, Poole-Frenkel effect is found to be dominant on the conduction associated with the barrier lowering, and barrier height in the emission process from the trapped states, and high-frequency dielectric constant of Al2O3 film layer is calculated.Article Citation - WoS: 11Citation - Scopus: 8Fabrication and Characterization of Tio2 Thin Film for Device Applications(World Scientific Publ Co Pte Ltd, 2019) Hosseini, A.; Gullu, H. H.; Coskun, E.; Parlak, M.; Ercelebi, C.Titanium oxide (TiO2) film was deposited by rectification factor (RF) magnetron sputtering technique on glass substrates and p-Si (111) wafers to fabricate n-TiO2/p-Si heterojunction devices for the investigation of material and device properties, respectively. The structural, surface morphology, optical and electrical properties of TiO(2 )film were characterized by means of scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), UV-visual (UV-Vis) spectral and dark current-voltage (I-V) measurement analyses. The deposited film layer was found to be homogeneous structure with crack-free surface. The bandgap value of TiO2 film was determined as 3.6 eV and transmission was around 65-85% in the spectral range of 320-1100 nm. The conductivity type of the deposited film was determined as n-type by hot probe method. These values make TiO2 film a suitable candidate as the n-type window layer in possible diode applications. TiO2 film was also deposited on p-Si (111) wafer to obtain Al/n-TiO2/p-Si/Al heterojunction device structure. The dark I-V characteristic was studied to determine the possible conduction mechanisms and diode parameters.Article Deposition and Characterization of Znsnse2 Thin-Films Deposited by Using Sintered Stoichiometric Powder(2019) Sürücü, Özge Bayraklı; Güllü, Hasan HüseyinIn this work, ZnSnSe2 (ZTSe) thin films were deposited using crystalline powder grown by vertical Bridgman-Stockbarger technique. The deposition process was carried out by means of e-beam evaporation on the well-cleaned soda lime glass substrates and keeping them at the substrate temperature of 200°C. The structural, optical and electrical properties of ternary ZTSe thin films were investigated depending on the annealing temperature at 250 and 300°C. X-ray diffraction analysis showed that as-grown films were in amorphous structure, however annealing at 250°C triggered the crystallization on the preferred ternary structure and annealing at 300°C resulted in the changes from amorphous to the polycrystalline structure. Using the compositional analysis, the detail information about the stoichiometry and the segregation mechanisms of the constituent elements in the structure were determined for both as-grown and annealed samples. In addition, they were morphologically characterized using scanning electron microscopy technique. The electrical properties were analyzed using temperature dependent dark- and photo-conductivity measurements. From the variation of electrical conductivity as a function of the ambient temperature, the current transport mechanisms and corresponding activation energies at specific temperature intervals for each sample were determined. The optical properties for the ZTSe thin films were studied depending on the structural changes with annealing.Article Citation - WoS: 144Citation - Scopus: 147CaXH3 (X = Mn, Fe, Co) perovskite-type hydrides for hydrogen storage applications(Wiley, 2020) Surucu, Gokhan; Gencer, Aysenur; Candan, Abdullah; Gullu, Hasan H.; Isik, MehmetHydrogen storage is one of the attractive research interests in recent years due to the advantages of hydrogen to be used as energy source. The studies on hydrogen storage applications focus mainly on investigation of hydrogen storage capabilities of newly introduced compounds. The present paper aims at characterization of CaXH3 (X: Mn, Fe, or Co) perovskite-type hydrides for the first time to understand their potential contribution to the hydrogen storage applications. CaXH3 compounds have been investigated by density functional theory studies to reveal their various characteristics and hydrogen storage properties. CaXH3 compounds have been optimized in cubic crystal structure and the lattice constants of studied compounds have been obtained as 3.60, 3.50, and 3.48 angstrom for X: Mn, Fe, and Co compounds, respectively. The optimized structures have negative formation enthalpies pointing out that studied compounds are thermodynamically stable and could be synthesized experimentally. The gravimetric hydrogen storage densities of X: Mn, Fe, and Co compounds were found in as 3.09, 3.06, and 2.97 wt%, respectively. The revealed values for hydrogen storage densities indicate that CaXH3 compounds may be potential candidates for hydrogen storage applications. Moreover, various mechanical parameters of interest compounds like elastic constants, bulk modulus, and Poisson's ratio have been reported throughout the study. These compounds were found mechanically stable with satisfying Born stability criteria. Further analyses based on Cauchy pressure and Pugh criterion, showed that they have brittleness nature and relatively hard materials. In addition, the electronic characteristics, band structures, and associated partial density of states of CaXH3 hydrides have been revealed. The dynamic stability behavior of them was verified based on the phonon dispersion curves.Article Citation - WoS: 1Citation - Scopus: 1Material Characterization of Thermally Evaporated Znsn2te4< Thin Films(Elsevier Gmbh, Urban & Fischer verlag, 2019) Gullu, H. H.Polycrystalline and stoichiometric ZnSn2Te4 (ZST) thin films were deposited on glass substrates by sequential evaporation of elemental powder sources. The deposited films were annealed in nitrogen atmosphere at annealing temperature ranging 100-300 degrees C. Under post-annealing treatments, the composition, structural, surface morphological, optical and electrical characteristics of the films were investigated. Annealing treatments lead to maintain the structural characteristics with the possible change in atomic concentration of the constituent elements in limit of detection and crystallinity of the films increased with increasing annealing temperature. Grainy surface morphology was observed in as-grown and annealed films and densely packed appearance of the surface of the samples indicates uniform deposition of the film over the entire substrate surface. Under the aim of visible light harvesting in the applications of thin film photovoltaics, normal-incidence transmittance measurements were performed and the direct band gap values were found in the range of 1.8-2.1 eV. Temperature dependent conductivity characteristics of the films were investigated under dark condition and the observed conductivity profiles were found in Arrhenius behavior with temperature dominated by the thermionic emission model.Article Citation - WoS: 3Citation - Scopus: 6Structural and Optical Properties of Thermally Evaporated Cu-Ga (cgs) Thin Films(Elsevier, 2018) Gullu, H. H.; Isik, M.; Gasanly, N. M.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.Article $cuınse_2$ ve $cugase_2$ İnce Filmlerin Özellikleri Üzerine Karşılaştırmalı Çalışma(2019) Candan, İdris; Güllü, Hasan HüseyinCu(In1-xGax)Se2 (CIGS) yarıiletken ince filmlerin iki kenar noktası olan x=0 ($CuInSe_2$) ve x=1 ($CuGaSe_2$) ince filmleri, Cu, InSe ve GaSe hedeflerden saçtırma yöntemi ile 250 oC sıcaklıkta soda lime cam alttaşlar üzerine kaplandı. In ve Ga oranı ve üretim sonrası ısıl işlemin CuInSe2 (CIS) ve CuGaSe2 (CGS) ince filmlerin özellikleri üzerine etkileri araştırıldı. Üretilmiş filmlerin yapısal özelliklerini incelemek için X-ışını kırınımı (XRD) ve örneklerin bileşenleri enerji dağılımlı X-ışını kırınımı analizi (EDXA) yöntemi kullanılarak analiz edildi. İnce film örneklerinin Raman aktif modlarının tayini için oda sıcaklığında Raman spektroskopi ölçümleri yapıldı. 400 oC sıcaklıkta ısıl işlem uygulanmış CIS ve CGS ince film örneklerinin en aktif modları (A1 modu) en yoğun çizgilerin sırayla 178 cm^{-1} ve 185 $cm^{-1}$ olduğu gözlendi. Bu mod kalkopirit yapıların Raman spektroskopisinde gözlemlenen en güçlü moddur. Isıl işlem uygulanmamış ve 350 oC’ta ısıl işlem uygulanmış CGS örneklerinde 486 $cm^{-1}$ çizgisi gözlenmiş olmasına rağmen bu çizginin yoğunluğu artan ısıl işlem sıcaklığı ile ters orantılı olarak azaldığı ve 400 oC uygulanan ısıl işlem sonrası tamamen yok olduğu gözlenmiştir. Üretilen CIS ve CGS ince filmlerin optik geçirgenlik ölçümleri sonucunda ısıl işlem uygulanmayan filmler ve at 400 oC sıcaklıkta ısıl işlem uygulanan filmler için optik bant aralıklarındaki değişim değerleri CIS için 1.28 eV ile 1.45 eV, CGS için 1.68 eV ile 1.75 eV aralıklarında değiştiği hesaplandı. Numunelerin oda sıcaklığındaki elektriksel iletkenlikleri ısıl işlem öncesi ve 400 oC ısıl işlem sonrasında n-CIS için sırayla 8.6x$10^{-3}$ ve 13.6x$10^{-2}$ $\\;{(Ω.cm)}^{-1}$ , p-CGS için sırayla 1.6 and 1.9 $\\;{(Ω.cm)}^{-1}$ olarak ölçüldü.
