Feng-Xia Liang, Xing-Yuan Zhao, Jing-Jing Jiang, Ji-Gang Hu, * Wei-Qiang Xie, Jun Lv*, Zhi-Xiang Zhang, Di Wu, Lin-Bao Luo,* 

Abstract: In this study, we demonstrated a highly sensitive and self-driven near infrared (NIR) light photodetector based on PdSe₂/pyramid Si heterojunction arrays, which were fabricated through simple selenization of pre-deposited Pd nanofilm on black Si. The as-fabricated hybrid device exhibits excellent photoresponse performances in terms of a large On/off ratio of 1.6×10⁵, a responsivity of 456 mA W^-1 and a high specific detectivity of up to 9.97×10¹³ Jones under 980 nm illumination at zero bias. Such a relatively high sensitivity can be ascribed to the light trapping effect of the pyramid microstructure, which was confirmed by numerical modelling based on finite-difference time domain (FDTD). On the other hand, thanks to the broad optical absorption properties of PdSe₂, the as-fabricated device also exhibits obvious sensitivity to other NIR illuminations with wavelength of 1300, 1550 and 1650 nm, which is beyond the photoresponse range of Si-based devices. It is also found that the PdSe₂/pyramid Si heterojunction device can also function as an NIR light sensor, which can readily record both “tree” and “house” images produced by 980 and 1300 nm illumination, respectively. We believe the present multilayer PdSe2 /pyramid Si heterojunction device holds great promise in future infrared optoelectronic systems.