Master Degree / Yüksek Lisans Tezleri
Permanent URI for this collectionhttps://hdl.handle.net/11147/3008
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Master Thesis Defect Reduction Study of Molecular Beam Epitaxially Grown Cdte Thin Flims by Ex-Situ Annealing(Izmir Institute of Technology, 2015) Bakali, Emine; Selamet, YusufMolecular Beam Epitaxy (MBE) grown CdTe thin films were annealed in this study to decrease the number density of defects. For annealing, a system was designed and constructed. During anneals; anneal temperature, anneal time, anneal cycle and hydrogen gas effects were analyzed. The effects of annealing parameters were analyzed by Scanning Electron Microscope (SEM), Atomic Force Microscope (AFM), Everson Etch method, resonance Raman spectroscopy and Photoluminescence measurement. In our studies, dislocation density decreased for 5 min. annealing when annealing temperature increased. Dislocation density decreased with increasing annealing time. Besides, dislocation density decreased when cycle number increased. Te precipitation decreased with annealing. Raman mode at 144 cm-1 was investigated and that mode was decided as Te E mode. Also I2LO/ILO ratio decreased with increasing annealing temperature and annealing time. I2LO/ILO ratio were approached to 1 at 80oK due to so called ‘resonance Raman scattering’. Extra peaks were also observed by Raman scattering. On the surface, small pits occurred when annealing temperature increased. Surface roughness decreased with increasing cycle number.Master Thesis Applications of Transparent Conductive Indium Tin Oxide Films in Automotive and Vitrifications Industries(Izmir Institute of Technology, 2009) Tuna, Öcal; Selamet, Yusuf; Selamet, YusufDue to its unique electrical and optical properties, highly doped n-type Indium tin oxide used for various applications such as smart glass, LCDs, OLEDs, solar cells and car windows. In this study Indium Tin Oxide (ITO) thin films were grown by both DC and RF magnetron sputtering techniques. To know deposition rate of ITO, system was calibrated for both DCMS and RFMS and then ITO were grown on glass substrate with the thickness of 70 nm and 40 nm by changing substrate temperature. The effect of substrate temperature, film thickness and sputtering method on structural, electrical and optical properties were investigated. Wan der Pauw method was used for electrical characterization and to use this method properly, we patterned ITO thin films by photolithography and Ion beam etching techniques. The results show that substrate temperature and film thickness substantially affects the film properties, especially crystallization and resistivity. The thin films grown at the lower than 150 oC showed amorphous structure. However, crystallization was detected with the further increase of substrate temperature. Substrate temperature and film thickness increment were lead to increase band gap of ITO which can be explained by BMS. Band gap of ITO was calculated to be about 3.64 eV at the substrate temperature of 150 oC, and it widened with substrate temperature increment. From electrical measurements the resistivity at room temperature was obtained 1.28*10 and 1.29*10 cm, for DC and RF sputtered films, respectively. We also measured temperature dependence resistivity and the Hall coefficient of the films, and we calculated carrier concentration and Hall mobility.Master Thesis Influence of Ni Thin Flim Structural Properties Over Graphene Growth by Cvd(Izmir Institute of Technology, 2013) Özçeri, Elif; Selamet, YusufThis thesis work focused on the effect of polycrystalline Nickel (Ni) TM thin film structure on the growth graphene by chemical vapor deposition (CVD). TM films were deposited by magnetron sputtering technique on Si/SiO2 substrates. To grow 1-2 layer graphene on Ni thin film catalyst by methane decomposition thermal CVD method was carried out using various growth parameters. To reduce the TM film surface roughness and grow larger size graphene layers on Ni film, Si/SiO2 substrates were coated by a thin Al2O3 buffer layers and Cr adhesive layers by magnetron sputtering. Ni film crystal structure and surface roughness, which affected the number of graphene layers, were examined by X-ray Diffraction (XRD) and Atomic Force Microscopy (AFM) techniques, respectively. The thickness and columnar structure of the films were measured from Surface Profiler and Scanning Electron Microscopy (SEM) images. Ni films were annealed at 800 oC, 900 oC and 950 oC in order to improve their crystal quality and to evaluate the effect of the crystallinity on graphene growth at atmospheric pressure. Samples were studied using XRD and AFM also to assess their crystal quality after the annealing process. It was observed that the calculated grain sizes depended on the film thickness and the annealing temperature. Surface roughness of the films was increased by increasing film thickness. A sole thin Al2O3 buffer layer reduced the surface roughness significantly. However, sole Cr adhesive layer or Cr/Al2O3 buffer layers did not reduce the surface roughness, but increased the crystallinity of Ni films in (111) direction. Argon, Hydrogen or a mixture of these two gases was added to methane during graphene growth at ambient pressure by CVD. The Raman spectroscopy was utilized in order to determine the number of the layers and quality of graphene growth over the Ni catalyst film.Master Thesis Growth and Characterization of Aluminum Doped Transparent and Conductive Zinc Oxidethin Flims(Izmir Institute of Technology, 2010) Ataç, Derya; Selamet, YusufThis thesis focuses on fabrication, characterization and understanding physical properties of transparent and conductive Al doped zinc oxide (ZnO) thin films. Films were deposited by magnetron sputtering technique, using separate ZnO and Al targets. SiO2 and glass (microscope slides) were used as substrates. Growths were performed at room temperature in Ar environment at a constant pressure of 3 mTorr. Films were characterized by atomic force microscope, x-ray diffractometer, scanning electron microscope, UV-vis spectroscophotometer and four point probe electrical measurements. Using transmission data, band gaps of the films and using four point probe measurements, resistivities of films were calculated. Firstly properties of pure ZnO films were studied. They were found to be highly transparent; however their resistivity was very high that we could not measure with our instrument. Therefore, ZnO films were uniformly doped with Al. It was seen that decreasing Al content was improving electrical and optical properties. Al concentration of the films was decreased firstly by decreasing deposition power of Al. After that, content was further decreased by depositing stacks of doped and undoped layers (modulation doping). Following that, modulation doped films were deposited with applying RF bias power to substrates. All films were annealed at 300oC for 1 hour in vacuum. The lowest resistivity obtained in this study was 1.68x10-3 .cm. Transmittance and band gap of the corresponding film were 80% and 4.1 eV respectively. The film was fabricated by modulation doping accompanied with substrate bias of 10 W, followed by annealing at 300oC in vacuum.