High Photoresponsivity of Vertical Graphene Nanosheets/P-Si Enhanced by Electron Trapping at Edge Quantum Wells

• Published in: Journal of physical chemistry. C 2021-03, Vol.125 (9), p.5392-5398
• Main Authors: Gao, Siyan, Liu, Liang, Lin, Zezhou, Zhang, Xi, Diao, Dongfeng
• Format: Article
• Language: English
• Subjects: C: Physical Properties of Materials and Interfaces
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/acs.jpcc.1c00137

Graphene has been considered as a promising candidate of next-generation photodetectors, but it presents low responsivity due to the lack of trapping centers. We proposed a vertical graphene nanosheets/p-Si photodetector by introducing edge quantum wells (QWs) as the electron trapping centers. A high responsivity has been achieved both in experiments and in time-dependent density functional theory calculations. Our research reveals that (i) the high density of edges makes the band gap of three-size complexes increase from 0.665 and 0.806 eV to 1.016 eV; (ii) empty edge states locate above lowest unoccupied molecular orbitals (LUMOs), providing unoccupied states for photoelectron transitions; (iii) exciton absorption peaks, corresponding to the transitions from Si p orbitals to the edge states of graphene nanosheets, exhibit a blue shift from 1581 to 790 nm with the increase in the density of edges from 31.25 to 58.33%; (iv) as the density of the edges increases, the experimental photoresponsivity increases from 3.66 A/W to 61.52 A/W, and the calculated relative oscillation resonance increases from 1 to 28%. The high density of edges that trap photoexcited electrons enhances the photoresponsivity. The principle clarified here lays the foundation for the edge quantum modulation of two-dimensional (2D) material applications.