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      • Theses - Department of Physics
      • Dept. of Physics - Master's degree
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      Low dimensional structures for optical and electrical applications

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      Author
      Akça, İmran
      Advisor
      Aydınlı, Atilla
      Date
      2008
      Publisher
      Bilkent University
      Language
      English
      Type
      Thesis
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      Abstract
      Low dimensional structures such as quantum dots have been particularly attractive because of their fundamental physical properties and their potential applications in various devices in integrated optics and microelectronics. This thesis presents optical and electrical applications of low dimensional structures. For this purpose we have studied silicon and germanium nanocrystals for flash memory applications and InAs quantum dots for optical modulators. As a quantum dot, nanocrystals can be used as storage media for carriers in flash memories. Performance of a nanocrystal memory device can be expressed in terms of write/erase speed, carrier retention time and cycling durability. Charge and discharge dynamics of PECVD grown nanocrystals were studied. Electron and hole charge and discharge currents were observed to differ significantly and strongly depend on annealing conditions chosen for the formation of nanocrystals. Our experimental results revealed that, discharge currents were dominated by the interface layer acting as a quantum well for holes and route for direct tunneling for electrons. On the other hand, possibility of obtaining quantum dots with enhanced electro-optic and/or electro-absorption coefficients makes them attractive for use in light modulation. Therefore, waveguides of multilayer InAs quantum dots were studied. Electro-optic measurements were conducted at 1.5 µm and clear Fabry-Perot resonances were obtained. The voltage dependent Fabry-Perot measurements revealed that 6 V was sufficient for full on/off modulation. Electroabsorption measurements were conducted at both 1.3 and 1.5 µm. Since the structure lases at 1285 nm, high absorption values at 1309 nm were obtained. The absorption spectrum of the samples was also studied under applied electric field. Absorption spectra of all samples shift to lower photon energies with increasing electric field.
      Keywords
      Silicon nanocrystals
      optical waveguides
      electro-absorption modulation
      electro-optic modulation
      quantum dots
      nonvolatile memories
      Germanium nanocrystals
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      http://hdl.handle.net/11693/14723
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      • Dept. of Physics - Master's degree 160
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