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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: 3Citation - Scopus: 3Fabrication of Cdsexte1-X Thin Films by Sequential Growth Using Double Sources(Elsevier, 2021) Demir, M.; Gullu, H. H.; Terlemezoglu, M.; Parlak, M.CdSexTe(1-x) (CST) ternary thin films were fabricated by stacking thermally evaporated CdSe and electron beam evaporated CdTe layers. The final structure was achieved in a stoichiometric form of approximately Cd:Se:Te = 50:25:25. The post-annealing processes at 300, 400, and 450 degrees C were applied to trigger the compound formation of CST thin films. The X-ray diffraction (XRD) profiles revealed that CdTe and CdSe have major peaks at 23.9 degrees and 25.5 degrees corresponds to (111) direction in cubic zinc-blend structure. Raman modes of CdTe were observed at 140 and 168 cm(-1), while Raman modes of CdSe films were detected at 208 and 417 cm(-1). The post-annealing process was found to be an effective method in order to combine both diffraction peaks and the vibrational modes of CdTe and CdSe, consequently to form CST ternary alloy. Transmission spectroscopy analysis revealed that CST films have direct band gap value of 1.6 eV.Article Citation - WoS: 11Citation - Scopus: 13Optical and Structural Characteristics of Electrodeposited Cd1-xznx< Nanostructured Thin Films(Elsevier, 2021) Erturk, K.; Isik, M.; Terlemezoglu, M.; Gasanly, N. M.The structural and optical characteristics of Cd1-xZnxS (CdZnS) thin films grown by the electrodeposition method were investigated in the present paper. The crystalline structure of the grown CdZnS thin film was determined as cubic wurtzite due to observed diffraction peaks associated with (111) and (220) planes. Atomic compositional ratios of the constituent elements were obtained using energy dispersive spectroscopy and doping concentration of the Zn was found as 5% (x similar to 0.05). Scanning electron microscopy image of the studied thin film indicated that grown film is nanostructured. Raman spectra of CdS and CdZnS thin films were measured and it was seen that observed longitudinal optical modes for CdZnS present a blue-shift. Temperature-dependent band gap energy characteristics of the thin films were studied performing transmission experiments in the 10-300 K temperature range. The analyses of the recorded transmittance spectra showed that direct band gap energy of the films decreases from 2.56 eV (10 K) to 2.51 eV (300 K) with the increase of temperature. The band gap energy vs. temperature dependency was studied applying well-known Varshni optical model and various optical parameters of the films were reported according to the results of the applied model.Article Citation - WoS: 8Citation - Scopus: 7Structural and Optical Characteristics of Thermally Evaporated Tlgase2 Thin Films(Elsevier, 2022) Isik, M.; Işık, Mehmet; Karatay, A.; Gasanly, N. M.; Işık, Mehmet; Department of Electrical & Electronics Engineering; Department of Electrical & Electronics EngineeringThe present paper reports the structural and optical properties of thermally evaporated TlGaSe2 thin films. X-ray diffraction pattern of evaporated film presented two diffraction peaks around 24.15 and 36.00 degrees which are associated with planes of monoclinic unit cell. Surface morphology of the TlGaSe2 thin films was investigated by scanning electron and atomic force microscopy techniques. Although there was observed some ignorable amount of clusters of quasi-spherical shape in the scanning electron microscope image, the film surface was observed almost uniform. Raman spectrum exhibited six peaks around 253, 356, 488, 800, 1053 and 1440 cm(-1) associated with possible vibrational mode combinations. Band gap energy of the thin film was determined as 3.01 eV from the analyses of transmission spectrum. Transmission spectrum presented strong Urbach tail and analyses of corresponding region resulted in Urbach energy of 0.66 eV. The structural and optical properties of deposited TlGaSe2 thin films were compared with those of single crystal. This comparison would provide valuable information about influence of thickness on the studied compounds.Article Citation - WoS: 5Citation - Scopus: 5Improvement of Electrical Characteristics of Snse/Si Heterostructure by Integration of Si Nanowires(Elsevier, 2021) Coskun, E.; Gullu, H. H.; Emir, C.; Parlak, M.In this study, the effects of the nanowire geometry on Si wafer substrate were investigated for the SnSe/Si-nanowire heterojunction device and the obtained results were compared with the one fabricated on planar Si surface. Nanowires on Si surface were produced by metal-assisted etching method and the SnSe film layer was deposited by thermal evaporation technique. On both Si and glass surfaces, deposited film shows polycrystalline and single SnSe phase. From optical transmission measurements, optical band gap of this film was determined as 1.36 eV in a good agreement with the literature. All SnSe/Si heterostructures were found in a p-n diode behavior and the ideality factor and series resistance values were calculated as 2.40, 547 Omega, and 3.71, 1.57 x 10(3) Omega, for SnSe/Si-nanowire and SnSe/Si heterojunctions, respectively. As a result, an improvement in device characteristics concerning the planar Si structure was found by utilizing Si nanowire structure.Article Citation - WoS: 25Citation - Scopus: 26Determination of Current Transport Characteristics in Au-cu/Cuo Schottky Diodes(Elsevier, 2019) Surucu, O. Bayrakli; Gullu, H. H.; Terlemezoglu, M.; Yildiz, D. E.; Parlak, M.In this study, the material properties of CuO thin films fabricated by sputtering technique and electrical properties of CuO/n-Si structure were reported. Temperature-dependent current-voltage (I-V) measurement was carried out to determine the detail electrical characteristics of this structure. The anomaly in thermionic emission (TE) model related to barrier height inhomogeneity at the interface was obtained from the forward bias I-V analysis. The current transport mechanism at the junction was determined under the assumption of TE with Gaussian distribution of barrier height. In this analysis, standard deviation and mean zero bias barrier height were evaluated as 0.176 and 1.48 eV, respectively. Depending on the change in the diode parameters with temperature, Richardson constant was recalculated as 110.20 Acm(-2)K(-2) with the help of modified Richardson plot. In addition, density of states at the interface were determined by using the forward bias I-V results.
