Improvement in Photodetection Characteristics of Graphene/p-Silicon Heterojunction Photodetector by PMMA/Graphene Cladding Layer

摘要

This work evaluates the photodetection characteristics of graphene/p-silicon (Gr/p-Si) heterojunction photodetector having Polymethyl Methacrylate (PMMA) as cladding layer. The graphene film was deposited on copper (Cu) by using the atmospheric pressure chemical vapor deposition method, whereas the PMMA layer was deposited on the Gr/Cu by the spin coating technique. The fabricated heterojunction was characterized by Raman spectroscopy, UV-visible spectroscopy and field emission scanning electron microscopy. The photodetection characteristics of the heterojunction photodetector were assessed through a current-voltage digital source system (Keithley 2400). The results showed that the addition of PMMA/Gr layer to Gr/p-Si enhanced the photodetection performance of the device upon the incident of light emitting diodes with various wavelengths (395nm, 405nm, 470nm, 605nm, 625nm, 880nm and 940nm). Among all these wavelengths, light emitting diodes with 470 and 395nm wavelengths were found to display better photodetection performance. For the 470nm illumination case, the quantum efficiency and responsivity of the fabricated device were increased by approximate to 7 times, the sensitivity was increased by approximate to 12 times whereas the current gain was increased by approximate to 6 times. The enhancement of quantum efficiency and responsivity is attributed to the use of a PMMA/Gr layer that increased the light absorption, reduced the light reflectivity, changed the graphene band structures and decreased the device dark current. For the case of 395nm illumination at 5V, the gain was approximate to 9, the responsivity was approximate to 5.052 A/W and the quantum efficiency was approximate to 15.86W/A while the sensitivity at 4V was 650%.