Photonics Research, 2020, 8(1): 01000039, Published Online: Nov. 7, 2019

### Bipolar phototransistor in a vertical Au/graphene/MoS2 van der Waals heterojunction with photocurrent enhancement

Author Affiliations

#### 3School of Microelectronics, Tianjin University, Tianjin 300072, China

Abstract
Bipolar phototransistors have higher optical responsivity than photodiodes and play an important role in the field of photoelectric conversion. Two-dimensional materials offer a good optical responsivity and have the potential advantages of heterogeneous integration, but mass-production is difficult. In this study, a bipolar phototransistor is presented based on a vertical Au/graphene/$MoS2$ van der Waals heterojunction that can be mass-produced with a silicon semiconductor process using a simple photolithography process. Au is used as the emitter, which is a functional material used not just for the electrodes, $MoS2$ is used for the collector, and graphene in used for the base of the bipolar phototransistor. In the bipolar phototransistor, the electric field of the dipole formed by the Au and graphene contact is in the same direction as the external electric field and thus enhances the photocurrent, and a maximum photocurrent gain of 18 is demonstrated. A mechanism for enhancing the photocurrent of the graphene/$MoS2$ photodiode by contacting Au with graphene is also described. Additionally, the maximum responsivity is calculated to be 16,458 A/W, and the generation speed of the photocurrent is $1.48×10?4$ A/s.
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