Avalanche-Enhanced Infrared Photodetection via Interlayer Absorption in a WSe ₂ /MoS ₂ Heterostructure

Infrared photodetectors are crucial for a broad range of emerging optical applications. Type-II band alignment in two-dimensional (2D) heterostructures whose constituent layers possess visible-range bandgaps enables sub-bandgap infrared photoresponse via interlayer optical transitions. However, the responsivity of such devices remains limited by intrinsically weak optical absorption associated with interlayer transitions. Here, we demonstrate an interlayer-absorption avalanche photodiode based on a WSe 2 /MoS 2 heterostructure, harnessing avalanche multiplication to overcome the weak interlayer absorption. Sub-bandgap infrared illumination (1,064 nm) generates photocurrent through interlayer absorption within the heterostructure, while avalanche multiplication is induced in an adjacent WSe 2 region. As a result, the device exhibits a 63-fold enhancement in responsivity, reaching 1 mA/W. These results establish avalanche multiplication as an effective internal-gain mechanism for interlayer-absorption photodetectors, highlighting a scalable route toward sensitive infrared detection using 2D semiconductor platforms.