5 results
Search Results
Now showing 1 - 5 of 5
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.Article Citation - WoS: 2Citation - Scopus: 1Investigation of Conductivity Characteristics of Zn-In Thin Films(World Scientific Publ Co Pte Ltd, 2020) Gullu, H. H.; Parlak, M.Zn-In-Se thin films were fabricated on the ultrasonically cleaned glass substrates masked with clover-shaped geometry by thermal evaporation of its elemental sources. Temperature-dependent conductivity characteristics of the films were investigated under dark and illuminated conditions. The semiconductor type of the films was found as n-type by thermal probe test. According to the van der Pauw technique, the dark electrical conductivity analyses showed that the variations of conductivity of unannealed and annealed at 300 degrees C samples are in exponential dependence of temperature. These conductivity profiles were found to be dominated by the thermionic emission at high temperature region whereas their behaviors at low temperatures were modeled by hopping theory. On the contrary, as a result of the further annealing temperatures, the surface of the samples showed semi-metallic characteristics with deviating from expected Arrhenius behavior. In addition, the temperature-dependent photoconductivity of the films was analyzed under different illumination intensities and the results were explained by the supra-linear characteristic based on the two-center recombination model.Article Citation - WoS: 10Citation - Scopus: 7Fabrication 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: 5Citation - Scopus: 6Influence of Temperature on Optical Properties of Electron-Beam Znse Thin Film(Iop Publishing Ltd, 2020) Gullu, H. H.; Isik, M.; Gasanly, N. M.; Parlak, M.Structural 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.
