Photogeneration at a Dirac/Charge-Compensated Semimetal Heterojunction based on Graphene and WTe₂

The unique photocurrent characteristics of pure semimetal heterojunctions composed of atomically thin materials remains a new frontier in optoelectronics. A novel pairing of a Dirac semimetal and a charge-compensated semimetal provides an opportunity to investigate photogeneration when photo-thermoelectric, photovoltaic, and other important photogeneration effects coexist. We employ near-infrared scanning photocurrent microscopy to investigate the dynamics of photoexcited electrons that control the electrical and optical conductivities at the interface to clarify the heterojunction band alignment between WTe₂ and graphene, which have charge compensated electron-hole bands and a Dirac point, respectively. Our findings highlight the important role that the photo-thermoelectric effect plays in the photocurrent distribution, alongside other phenomena such as the photovoltaic effect that have been seen earlier in p-n junctions. Our measurements not only define the essential photocurrent and band alignment characteristics of this combined Dirac-Weyl system but also provide valuable insights for the design and enhancement of highly sensitive infrared sensors based on van der Waals heterostructures. These discoveries pave the way for exciting advancements in the field of quantum optoelectronics.