  A variety of fabrication methods for van der Waals heterostructures have been
demonstrated; however, their wafer-scale deposition remains a challenge. Here
we report few-layer van der Waals PtS2/PtSe2 heterojunction photodiodes
fabricated on a 2" SiO2/Si substrate that is only limited by the size of work
chamber of the growth equipment, offering throughputs necessary for practical
applications. Theoretical simulation results show that the bandgap of PtS2 is
shrunk to half of its original size in the PtS2/PtSe2 heterostructures, while
PtSe2 exhibits a limited response to the coupling. Both PtSe2 and PtS2 layers
in the coupled system are still semiconductors. Dynamic photovoltaic switching
in the heterojunctions is observed at zero-volt state under laser illuminations
of 532 to 2200 nm wavelengths. The PtS2/PtSe2 photodiodes show excellent
characteristics in terms of a high photoresponsivity of 361 mAW-1, an external
quantum efficiency (EQE) of 84%, and a fast response speed (66 ms). The
wafer-scale production of 2D photodiodes in this work accelerates the
possibility of 2D materials for practical applications in the next-generation
energy-efficient electronics.
