Investigation of Photodetectors Based on Mechanically Exfoliated Graphene

Student: Wafaa Gebril

Degree: Ph.D., July 2021

Major Professor: Dr. Omar Manasreh

Research Area(s):

Nanoscience & Engineering

Photonics

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Background/Relevance

  • Rapid growth in photodetector applications in terms of scale and diversity increases the demand for more research attention in this area to overcome the existing limitations.
  • Many novel nanostructured materials such as quantum dots and graphene have emerged as promising candidates for high performance optoelectronics. These materials have shown unique size-dependent optical properties comparing with the corresponding bulk materials.
  • In this work, photodetectors based on graphene and colloidal nanocrystals were investigated and characterized.

Approach

  • PbSe, CdSe and Ag nanocrystals were synthesized using a published wet chemical growth methods.
  • Mechanically exfoliated and CVD methods were used to obtain graphene and transform it on Si/SiO2 substrates.
  • The prepared nanomaterials were characterized using Optical microscopy and Raman spectroscopy.
  • Patterning interdigital devices and single channel device using Standard optical photolithography.
  • Depositing the electrodes metals using Electron-beam evaporator.
  • Characterizing the fabricated devices using Keithley 4200 SCS.

Key Results

  • The transfer curve of the graphene phototransistor shows a photoresponse at negative gate voltages due to the photogating.
  • The Ag NP enhanced the absorption in CdSe NC because of the plasmonic effect, as shown in their absorbance spectra.
  • PbSe NC increase the photocurrent when used on graphene in graphene photodetector.

Conclusions

  • The hybrid graphene/PbSe photodetector demonstrated that the QDs were the light absorber of the device and achieved high responsivity and ditectivity.
  • In graphene-based phototransistors, the photogating effect introduced by the p-doped Si/SiO2 substrate was exploited to generate a photoresponse, and the devices showed high and tunable responsivity.
  • By adding a Ag NP layer to the CdSe NC a photodetector, an enhancement was obtained in both responsivity and detectivity due to the plasmonic effect of the Ag NPs.

Future Work

  • The graphene/PbSe photodetector can be more investigated with different ligands that connect the PbSe NC. Various types of substrates can be investigated in the graphene-based phototransistor.