Master Degree / Yüksek Lisans Tezleri

Permanent URI for this collectionhttps://hdl.handle.net/11147/3008

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Access Right: Open AccessAuthor: search.filters.author.Ateş, Serkan

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Now showing 1 - 5 of 5
  • Master Thesis
    B92 Based Quantum Key Distribution With Faint Pulsed Laser
    (01. Izmir Institute of Technology, 2021) Mutlu, Görkem; Ateş, Serkan; Çakır, Özgür
    In quantum key distribution (QKD), photons are used to share the key between the transmitter and receiver, and in principle, single photon sources should be used to create a secure communication channel. Nowadays, attenuated laser sources are used in many studies. While it is practical to use attenuated laser pulses for QKD system, it poses many safety issues due to the possibility of multiple photons in the laser pulses. In addition, the key rate is waived to increase the level of security. However, the use of single photon sources is not as easy and practical as using attenuated laser sources. Today, studies of single photon sources to be used for QKD continue. In order for these single photon sources to be used actively, a photon source that operates at room temperature, operates in a wide band-gap range for different areas of use (underwater, optical fiber-based and free space) and can be excited at high speed is required. Since hBN defect centers are a material that can produce single photons at room temperature and have a wide band gap, it seems very ideal for these studies. In this thesis, studies have been carried out on the realization of the protocol, which is a part of QKD, with solid-state materials that produce single photons. In the studies, a key was produced with a faint pulsed laser. Also, data is encrypted using the key of the transmitter. Then the data is successfully decrypted with the key measured by the receiver.
  • Master Thesis
    Optical Spectroscopy of Single Defects in Hexagonal Boron Nitride
    (01. Izmir Institute of Technology, 2021) Birinci, Ayşenur; Ateş, Serkan
    Single photon sources are main component for several applications in quantum information technologies. Hexagonal boron nitride (hBN) is a suitable material to create heterostructures with two dimensional materials. It is a popular two dimensional material and single photon source due to having stable and bright emission in visible range. In this thesis, optical properties of single defects in bulk hBN were investigated. Defects have been selected using the micro-Photoluminescence setup, and it was observed that the defects have high degree of polarization and show typical optical saturation behavior. Time-resolved photoluminescence measurements were done by time-correlated single photon counting. Single photon nature of generated light from individual defects were demonstrated using Hanbury-Brown and Twiss interferometer.
  • Master Thesis
    Molecular Beam Epitaxial Growth of Znse on (211)b Gaas
    (Izmir Institute of Technology, 2017) Yavaş, Begüm; Ateş, Serkan; Özçelik, Serdar
    The Mercury Cadmium Telluride (Hg1-xCdxTe) play important role for infrared (IR) focal plane array application. It is grown on variety alternative substrates which are Si, Ge, GaAs or GaSb. When GaAs is compared with the others alternative substrate, it is more preferable due to having good surface polarity and also easily commercially available of high quality. When HgCdTe epilayer is grown directly on the GaAs substrate, there exist some dislocations in the epilayer due to large lattice mismatch between HgCdTe and GaAs substrate.The CdTe semiconductor is grown like a buffer layer to reduce dislocation in the HgCdTe epilayer grown on GaAs or other alternative substrate [1].The crystal quality of CdTe buffer layer directly affected HgCdTe epilayer. Therefore, CdTe needed to be low defect density.Because of %14.6 lattice mismatch between CdTe and GaAs [2], some defects are observed in CdTe buffer layer. ZnSe epilayer can be used to decrease lattice mismatch between CdTe and alternative substrate. When ZnSe interlayers are grown with high quality, CdTe affects positively. The aim of this theses is the growth of ZnSe epilayer films on (211) GaAs substrates by molecular beam epitaxy (MBE). The effect of growth temperature, VI/II flux ratio and deoxidation process with In and As were studied in this study. Crystal qualities of films were investigated by using X-ray diffraction. The surface morphology of ZnSe films were analyzed by atomic force microscopy and Nomarski microscopy. Vibrational phonon modes, thermal and elastic strains of ZnSe epilayer were observed by using Raman spectroscopy.
  • Master Thesis
    Temperature Dependence of Zero Phonon Line Emission From Defects in Hexagonal Boron Nitride and Design of Photon-Pair Source
    (Izmir Institute of Technology, 2017) Polat, Nahit; Ateş, Serkan
    This thesis presents studies of the defect centers in hBN and design of nonlinear waveguide. The multilayer hBN flakes and Si3N4 waveguide are available materials in modern nanophotonics applications. The color centers in hBN are consisted of quantized states because each defect center has different saturation power and dipole polarization. The line shape of emission from defect centers is directly depended photon vibrations and temperature of sample. Moreover, phonon bands in the color centers affect the wavelength of emission and we statistically worked on the phonon effects on ZPL. The Si3N4 waveguide can be more efficient chip scale photon pair sources to create entangled photons in visible band. The zero dispersion wavelength calculations give an efficient waveguide geometry as 650×600 nm2 for 780 nm pump wavelength.
  • Master Thesis
    Visible Photon Emission From Defects in Hexagonal Boron Nitride Flakes
    (Izmir Institute of Technology, 2017) Fırat, Volkan; Ateş, Serkan; Ateş, Serkan
    Geniş band aralığına sahip kristallerde bulunan renk merkezleri, band aralığı içerisinde kesikli enerji seviyeleri oluşturur. Bir çok kuantum optik ve kuantum bilgi uygulamaları için gerekli olan tek-fotonlar bu kesikli enerji seviyeleri kullanılarak elde edilebilir. Bu çalışmada, çok katmalı hekzagonal bor nitrür (hBN) pulları içinde, tavlama tekniği kullanılarak optik-aktif kusurlar oluşturuldu. Farklı tavlama sıcaklıklarında (500, 750 ve 850°C) yedi örnek ve kıyaslama için iki tavlanmamıs¸ örnek hazırlandı. hBN geniş band aralığı sayesinde görünür bölgede ışıma yapan kusurları barındırabilir. hBN pulları içerisindeki noktasal kusurları bulmak için mikro-fotolüminesans haritalama yapıldı. Daha sonra uyarma gücüne, polarizasyona ve sıcaklığa bağlı ölçümler yapıldı. Ölçümler sonucunda kusurların ortalama 0.5 m boyutlarında olduğu, göreceli olarak düşük uyarma güçlerinde doyuma ulaştıkları, dipole özellik gösterdikleri, 0.8 meV kadar dar genişlikte sıfır-fonon çizgisine sahip oldukları gözlemlendi. Bu sonuçlar kesikli enerji seviyelerine sahip, optik-aktif kusurların oluştuğunu göstermektedir.