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
Main Affiliation
Department of Electrical & Electronics Engineering
Status
Former Staff
Website
ORCID ID
Scopus Author ID
Turkish CoHE Profile ID
Google Scholar ID
WoS Researcher ID
Sustainable Development Goals
2
ZERO HUNGER
0
Research Products
14
LIFE BELOW WATER
0
Research Products
17
PARTNERSHIPS FOR THE GOALS
0
Research Products
5
GENDER EQUALITY
0
Research Products
16
PEACE, JUSTICE AND STRONG INSTITUTIONS
0
Research Products
8
DECENT WORK AND ECONOMIC GROWTH
0
Research Products
4
QUALITY EDUCATION
0
Research Products
6
CLEAN WATER AND SANITATION
0
Research Products
7
AFFORDABLE AND CLEAN ENERGY
5
Research Products
10
REDUCED INEQUALITIES
0
Research Products
11
SUSTAINABLE CITIES AND COMMUNITIES
0
Research Products
9
INDUSTRY, INNOVATION AND INFRASTRUCTURE
0
Research Products
1
NO POVERTY
0
Research Products
3
GOOD HEALTH AND WELL-BEING
0
Research Products
12
RESPONSIBLE CONSUMPTION AND PRODUCTION
0
Research Products
13
CLIMATE ACTION
0
Research Products
15
LIFE ON LAND
0
Research Products
This researcher does not have a Scopus ID.
This researcher does not have a WoS ID.
Scholarly Output
55
Articles
52
Views / Downloads
7/0
Supervised MSc Theses
1
Supervised PhD Theses
0
WoS Citation Count
877
Scopus Citation Count
899
WoS h-index
16
Scopus h-index
16
Patents
0
Projects
0
WoS Citations per Publication
15.95
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 |
Current Page: 1 / 5
Scopus Quartile Distribution
Competency Cloud
26 results
Scholarly Output Search Results
Now showing 1 - 10 of 26
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: 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 Citation - WoS: 25Citation - Scopus: 25First Principles Study on the Structural, Electronic, Mechanical and Lattice Dynamical Properties of Xrhsb (x = Ti and Zr) Paramagnet Half-Heusler Antimonides(Iop Publishing Ltd, 2019) Surucu, Gokhan; Candan, Abdullah; Erkisi, Aytac; Gencer, Aysenur; Gullu, Hasan HuseyinThe half-Heusler TiRhSb and ZrRhSb alloys in the formation of face-centered cubic MgAgAs-type structure, which conforms to the F (4) over bar 3m space group with 216 as the space number, have been investigated using Generalized Gradient Approximation (GGA) implemented in Density Functional Theory (DFT). The calculated formation enthalpies and the plotted energy-volume curves of different types of structural phases (alpha, beta, and gamma) in these alloys indicate that the gamma-phase structure is the best energetically suitable structure. In addition, TiRhSb and ZrRhSb alloys have been found as paramagnetic (PM) with the investigation of antiferromagnetic (AFM), ferromagnetic (FM), and paramagnetic (PM) orders in the most stable gamma-phase structure. Therefore, their electronic, mechanical, and dynamical properties have been examined in the gamma structural phase and paramagnetic order. These alloys have semiconducting nature due to the observed same band gaps in both the majority and minority spin channels of the calculated spin-polarised electronic band structure. These calculated band gaps are 0.75 eV for gamma-TiRhSb and 1.18 eV for gamma-ZrRhSb. The predicted elastic constants indicate that the alloys in this study are mechanically stable and show nearly isotropic behavior in the gamma structural phase. Also, the minimum and the diffuson thermal conductivites have been determined for these alloys. Finally, the calculated phonon dispersion spectras for the gamma-TiRhSb and gamma-ZrRhSb half-Heusler antimonide alloys show the dynamic stability of these systems.Article Citation - WoS: 1Deposition and Characterization of ZnSnSe2 Thin-Films Deposited by Using Sintered Stoichiometric Powder(Gazi Univ, 2019) Bayrakli Surucu, Ozge; Gullu, Hasan HuseyinIn 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 degrees C. The structural, optical and electrical properties of ternary ZTSe thin films were investigated depending on the annealing temperature at 250 and 300 degrees C. X-ray diffraction analysis showed that as-grown films were in amorphous structure, however annealing at 250 degrees C triggered the crystallization on the preferred ternary structure and annealing at 300 degrees 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: 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.Conference Object Citation - WoS: 10Citation - Scopus: 10Investigation of Carrier Transport Mechanisms in the Cu-Zn Based Hetero-Structure Grown by Sputtering Technique(Canadian Science Publishing, 2018) Gullu, H. H.; Terlemezoglu, M.; Bayrakli, O.; Yildiz, D. E.; Parlak, M.In this paper, we present results of the electrical characterization of n-Si/p-Cu-Zn-Se hetero-structure. Sputtered film was found in Se-rich behavior with tetragonal polycrystalline nature along with (112) preferred orientation. The band gap energy for direct optical transitions was obtained as 2.65 eV. The results of the conductivity measurements indicated p-type behavior and carrier transport mechanism was modelled according to thermionic emission theory. Detailed electrical characterization of this structure was carried out with the help of temperature-dependent current-voltage measurements in the temperature range of 220-360 K, room temperature, and frequency-dependent capacitance-voltage and conductance-voltage measurements. The anomaly in current-voltage characteristics was related to barrier height inhomogeneity at the interface and modified by the assumption of Gaussian distribution of barrier height, in which mean barrier height and standard deviation at zero bias were found as 2.11 and 0.24 eV, respectively. Moreover, Richardson constant value was determined as 141.95 Acm(-2)K(-2) by means of modified Richardson plot.Article Citation - WoS: 6Citation - Scopus: 7Construction of Self-Assembled Vertical Nanoflakes on Cztsse Thin Films(Iop Publishing Ltd, 2019) Terlemezoglu, M.; Surucu, O. Bayrakli; Colakoglu, T.; Abak, M. K.; Gullu, H. H.; Ercelebi, C.; Parlak, M.Cu2ZnSn(S, Se)(4) (CZTSSe) is a promising alternative absorber material to achieve high power conversion efficiencies, besides its property of involving low-cost and earth-abundant elements when compared to Cu(In, Ga) Se-2 (CIGS) and cadmium telluride (CdTe), to be used in solar cell technology. In this study, a novel fabrication technique was developed by utilizing RF sputtering deposition of CZTSSe thin films having a surface decorated with self-assembled nanoflakes. The formation of nanoflakes was investigated by detailed spectroscopic method of analysis in the effect of each stacked layer deposition in an optimized sequence and the size of nanoflakes by an accurate control of sputtering process including film thickness. Moreover, the effects of substrate temperature on the formation of nanoflakes on the film surface were discussed at a fixed deposition route. One of the main advantages arising from the film surface with self-assembled nanoflakes is the efficient light trapping which decreases the surface reflectance. As a result of the detailed production and characterization studies, it was observed that there was a possibility of repeatable and controllable fabrication sequence for the preparation of CZTSSe thin films with self-textured surfaces yielding low surface reflectance.
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