Unipolar Barrier Photodetectors Based on Van Der Waals Heterostructure with Ultra-High Light On/Off Ratio and Fast Speed.

Abstract

Unipolar barrier architecture is designed to enhance the photodetector's sensitivity by inducing highly asymmetrical barriers, a higher barrier for blocking majority carriers to depressing dark current, and a low minority carrier barrier without impeding the photocurrent flow through the channel. Depressed dark current without block photocurrent is highly desired for uncooled Long-wave infrared (LWIR) photodetection, which can enhance the sensitivity of the photodetector. Here, an excellent unipolar barrier photodetector based on multi-layer (ML) graphene (G) is developed, WSe₂, and PtSe₂ (G-WSe₂-PtSe₂) van der Waals (vdW) heterostructure, in which extremely low dark current of 1.61×10^-13 A, a record high light on/off ≈10⁹ are demonstrated at 0 V. Notably, the device exhibits ultrafast response speed with rise time τ_r = 699 ns and decay time τ_d = 452 ns and high-power conversion efficiency (η) of 4.87%. The heterostructure demonstrates a broadband photoresponse from 365 nm to LWIR 10.6 µm at room temperature. Notably, the G-WSe₂-PtSe₂ nBn device demonstrates high photoresponsivity (R) of 1.8 AW^-1 with 10.6 µm laser at 1 V bias in ambient air. This unipolar barrier device architecture offers an alternative way for highly sensitive free space communication.