image: Figure | Bipolar-barrier tunnel heterostructure of 2D BP/MoTe2/BP for MIR photodetection. a, Schematic of device structure. b, Schematic of band structure. Under mid-infrared light illumination, the effective barrier height in the valence bands of BP/MoTe2 heterostructure decreases compared to the dark condition, promoting quantum tunneling of photo hole carriers and resulting in significant tunneling photocurrents.
Credit: Fakun Wang, Song Zhu et al.
MIR photodetectors play a crucial role in modern optoelectronic technology, with widespread applications in key fields such as military, healthcare, and communication. Achieving high specific detectivity has always been a central goal in the research of mid-infrared photodetectors. However, high dark current remains a major obstacle to the stable operation of these detectors at room temperature.
Barrier heterostructures based on emerging two-dimensional (2D) materials have made some progress in suppressing dark current, primarily by blocking the flow of majority carriers to reduce dark current. However, they still face challenges in achieving satisfactory room-temperature mid-infrared photodetection performance. This is mainly due to the significant contribution of minority carriers to dark current caused by thermal excitation and bias. Additionally, the photon capture efficiency of nanoscale 2D materials is limited, further restricting the photoconversion efficiency, making it challenging to achieve high performance at room temperature.
In a new paper published in Light: Science & Applications, a team of scientists, led by Professor Qi Jie Wang from Nanyang Technological University, Singapore, have proposed an innovative design for MIR photodetection—a bipolar-barrier tunnel heterostructure. This design addresses the issues of high dark current and low optical absorption in 2D barrier heterostructures, achieving outstanding room-temperature specific detectivity. The heterostructure is composed of black phosphorus (BP)/MoTe2/BP, stacked on an Au reflector. The MoTe2 layer forms a bipolar barrier, effectively suppressing the majority holes and minority electrons in the p-type BP layer, minimizing dark current by blocking thermally excited and bias-induced carrier leakage, while facilitating efficient tunneling of photogenerated carriers via trap-assisted photogating mechanisms. In addition, the Au reflector enhances optical absorption through interference effects. As a result, the heterostructure achieves remarkable performance metrics, including a room-temperature specific detectivity of ∼3.0 × 1010 cm Hz0.5 W−1, a high responsivity of ∼4 A W−1, and an external quantum efficiency of ∼140% within the MIR range, laying a solid foundation for the development of high-performance infrared optoelectronic devices.
Article Title
Bipolar-barrier tunnel heterostructures for high-sensitivity mid-wave infrared photodetection