Master Degree / Yüksek Lisans Tezleri
Permanent URI for this collectionhttps://hdl.handle.net/11147/3008
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Master Thesis Grafen Silisyum Karbür Tabanlı Quadrant Fotodedektör Aygıt Geliştirilmesi(2025) Reyhan, Ahmet Yusuf; Çelebi, Cem; Ünverdi, ÖzhanBu tez çalışmasında, Kimyasal Buhar Biriktirme yöntemi ile üretilen p-tipi grafen ve n-tipi Silisyum Bu tez çalışmasında Grafen/Silisyum Karbür aygıt mimarisine sahip kendinden beslemeli, Schottky eklemli ve ultraviyole bölgede çalışacak kadran fotodedektör aygıt tasarlanmış ve karakterize edilmiştir. Çalışmanın amacı kapsamında kimyasal buhar biriktirme metodu ile sentez edilmiş p-tipi çift katmanlı grafen malzemesinin kadran fotodedektör mimarisine uyumluluğunu değerlendirilmiş ve ışık pozisyonunu algılama kapasitesini deneysel metodlar ile incelenmiştir. Aygıtın n-tipi eklemini oluşturan silisyum karbür alttaşın üzerinde termal buharlaştırma metodu ile kadran aygıtın elektrotları ve yapısı oluşturulmuştur. Çift katmanlı p-tipi grafen bu yapının üzerine transfer edilerek p-i-n eklemlerine sahip kendinden beslemeli aygıt yapısı tamamlanmıştır. Büyütülmüş çift katmanlı grafenin varlığı Raman spektroskobisi metodu ile doğrulanmıştır. Aygıtın karanlık koşullarda akım-gerilim özellikleri ölçülerek, karanlık akım, Schottky bariyer yüksekliği ve idealite faktörleri hesaplanmıştır. Cihazın 250 – 300 nanometre dalga boyundaki ultraviyole ışınına karşı tepkiselliği ölçülmüştür. Son olarak pozisyonlama hassasiyeti sensörün aktif bölgesinde seçilen bir aramada tarama yaparak belirlenmiştir. Bu çalışma gelecekte geliştirilebilecek Grafen/Silisyum Karbür mimarisine sahip kadran fotodedektörler için bir giriş niteliği taşımaktadır.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 Terahertz Wave Sensitive Superconducting Bolometric Detector(Izmir Institute of Technology, 2015) Semerci, Tuğçe; Özyüzer, Lütfi; Özdemir Köklü, MehtapTerahertz (THz) waves has varied properties than other part of the electromagnetic spectrum which between microwave and infrared and has 0.3-10 THz frequency range and 3-0.03 mm wavelength. There are many areas to utilize from THz radiation that defense industry particularly security part such as detecting of unknown materials, poison or explosive matters. Additionally, THz waves can pass through leather, fabric and paper despite of metal and water and there is no enough energy to ionize the atoms in THz radiation. That’s why, THz radiation is not hazardous for human. Many detectors are developed to use these benefit of THz radiation. Bolometric detector is preferred between these detectors to detect the radiation above 1 THz frequency. Bi2Sr2CaCu2O8+δ (Bi2212) single crystal was used in literature for the first time to detect the THz waves with superconducting bolometers with our study. In this study, epoxy was used to transfer Bi2212 single crystal onto the sapphire substrate. Intended thickness was acquired by scotch tape via cleaved crystal mechanically. Edge of crystals were cut pyramid shape to provide each layer to contact with gold, crystal and silver epoxy. 150-200 nm crystals were shadowed by aluminum foil to deposit roughly 200 nm gold. Then clean room process was implemented to prepare our samples to electron beam lithography. Log-periodic antenna and four point contact structure was placed onto the crystals then UV light, developer and ion beam etching system were performed. Cryostat was designed and produced to measure electrical and bolometric measurements. Resistance-temperature in a-b axis gave the around 90 K as critical temperature. Bolometric measurement was done via superconducting transition region to decide the selected temperature to measure the change of resistance by sending signal from Stefan-Boltzmann Lamp in specific seconds. Change of resistance was observed from resistance-time measurement for bolometric measurement. Response time was calculated approaching 825 ms from the result of bolometric measurement. Our measurement set-up has limitation to read right data. Lock-in-amplifier may use to more accurate result.