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Fabrication and Characterization of a Graphene-Silicon Heterostructure-Based Photodetector

Montazeri Shatori, Arefeh | 2025

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 58364 (04)
  4. University: Sharif University of Technology
  5. Department: Physics
  6. Advisor(s): Akhavan, Omid; Kazemi Sheykh Shabani, Asieh Sadat
  7. Abstract:
  8. Graphene, owing to its high electrical conductivity, optical transparency with broadband absorption, and superior carrier mobility, is considered one of the key materials in the development of next-generation hybrid photodetectors. In this study, graphene–silicon heterostructure photodetectors were designed, fabricated, and characterized using monolayer graphene grown by chemical vapor deposition (CVD). The current–voltage responses of seven samples were evaluated under dark conditions and under visible lasers illumination (450–650nm) to ensure reproducibility and accuracy of the results. The findings revealed that laser illumination, particularly at the green wavelength, significantly enhanced photocurrent and improved detection performance. Subsequently, the effect of graphene functionalization with hydrogen, fluorine, nitrogen, and oxygen plasmas was investigated to induce an energy bandgap in graphene and to study the influence of functional groups on the optoelectronic performance of the photodetectors, including spectral responsivity, photocurrent, external quantum efficiency, and response time. For instance, in a diode-contact photodetector (sample 6), the dark current of about 2100μA increased from 5000μA to 23000μA μA under green laser illumination after hydrogen functionalization. In the same sample with ohmic contact, the dark current was about 3900 μA, which, after functionalization, rose from 12000μA to 20000μA under green laser exposure, demonstrating the pronounced effect of both functionalization and optical excitation. To confirm surface uniformity, quality, and the presence of functional groups, the samples were characterized using atomic force microscopy (AFM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and Raman spectroscopy. Overall, the results indicate that laser illumination and controlled functionalization (depending on the gas type and treatment conditions) can significantly improve the performance of graphene–silicon photodetectors, and that optimized design parameters can remarkably enhance both sensitivity and response speed
  9. Keywords:
  10. Photodetector ; Functionalization ; Optoelectronic Network ; Characterization ; Graphene Heterostructure ; Graphene-Silicon Heterostructure

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