High-performance near-infrared PtSe 2 /n-Ge heterojunction photodetector with ultrathin Al 2 O 3 passivation interlayer

Two-dimensional (2D) materials are being intensively exploited for broadband-responsive photodetectors (PDs). However, the broadband-responsive PDs based on 2D materials normally suffer from poor response to infrared wavelengths. Here, we report the excellent photoresponse performance of vertical PtSe 2 /ultrathin Al 2 O 3 /Ge PD under near-infrared illumination. We directly selenize Pt film deposited on Al 2 O 3 /Ge to form PtSe 2 layer. The ultrathin Al 2 O 3 passivation layer plays the role of surface modification, effectively weakening recombination of the photogenerated carriers. Under 1550-nm illumination, the PtSe 2 /ultrathin Al 2 O 3 /Ge PD with a working area of 50 µm × 50 µm at zero bias obtains a large responsivity of 4.09 A W −1 , and fast rise/fall times of 32.6/18.9 µs, respectively. And under an external electric field of −5 V, the responsivity and response speed of the PtSe 2 /ultrathin Al 2 O 3 /Ge PD can be as high as 38.18 A W −1 and as fast as 9.6/7.7 µs, respectively. We find that the working area has a great influence on the photoresponse characteristics. Furthermore, we demonstrate the PtSe 2 /ultrathin Al 2 O 3 /Ge PDs array shows outstanding violet, visible, and infrared imaging capability at room temperature. Our study suggests that the PtSe 2 /ultrathin Al 2 O 3 /Ge heterojunction has great application prospects for the design of emerging broadband optoelectronic devices with superior performance for near-infrared response.