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Transport Properties in Heterostructures of 2D Layers of Graphene with WS2 and hBN Quantum Dots

Razzaghi, Zahra | 2019

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 52209 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Simchi, Abdolreza
  7. Abstract:
  8. Graphene based photodetectors which are modified with quantum dots, are the new generation of detectors. In these supplies an integration of graphene’s unique characteristics like high conductivity and mobility and the high light absorption of quantum dots, are used.In this research graphene by chemical vapor deposition in centimetric large scales, tungsten disulfide quantum dots, boron nitride and graphene quantum dots and 2D tungsten disulfide have been synthesized. In the next step each of them were characterized to modify the quality of used layers in heterostructure.Based on the characteristic tests, quantum dots aspect ratios were 1 to 5 nanometers. Also tungsten disulfide was obtained with approximate scale of 20 micrometers while it was few layer and quasicrystal. After transferring the graphene to silicon wafer with oxide layer, and depositing contacts on it, quantum dots were spin coated on the surface and the photodetector manufacturing was completed. Finally the behavior of the hemterostructure was studied under light illumination and in the dark situation.It was fortunately observed that disulfide quantum dots enhance 4 order of magnitude the responsivity of graphene-based photodetectors to light at room temperature and visible wavelength. Moreover, boron nitride nanoparticles by preventing the carriers’ scattering, 1.5 order of magnitude increased the responsivity. Also, the results showed that the combination of WS2 and graphene quantum dots have a breief reinforcement. On the other hand graphene photodetectors showed a photoresponsivity of 1.7 and 2.7 µAW-1 respectively in the exposure of blue and red light. In conclusion, depending on the type and size of quantum dots, the outputs of graphene-based photodetectors would change, and according to the device’s purpose, it should be optimized
  9. Keywords:
  10. Chemical Vapor Deposition (CVD) ; Photodetector ; Quantum Dot ; Graphene ; Tungsten Disulfide ; Boron - Nitride

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