Record-High Work-Function p-Type CuBiP₂ Se₆ Atomic Layers for High-Photoresponse van der Waals Vertical...

The notable lack of intrinsic p-type 2D layered semiconductors has hindered the engineering of 2D devices for complementary metal oxide semiconductors (CMOSs). Herein, a novel quaternary intrinsic p-type 2D semiconductor, CuBiP₂ Se₆ atomic layers, is introduced into the 2D family. The semiconductor displays a high work function of 5.26 eV, a moderate hole mobility of 1.72 cm² V^-1 s^-1 , and an ultrahigh on/off current exceeding 10⁶ at room temperature. To date, 5.26 eV is the highest work-function recorded in p-type 2D materials, indicating the ultrastable p-type behavior of CuBiP₂ Se₆ . Additionally, a multilayer graphene/CuBiP₂ Se₆ /multilayer graphene (MLG/CBPS/MLG)-based fully vertical van der Waals heterostructure phototransistor is designed and fabricated. This device exhibits outstanding optoelectronic performance with a responsivity (R) of 4.9 × 10⁴ A W^-1 , an external quantum efficiency (EQE) of 1.5 × 10⁷ %, a detectivity (D) of 1.14 × 10¹³ Jones, and a broad working wavelength (400-1100 nm), respectively. This is comparable to state-of-the-art 2D devices. Such excellent performance is attributed to the ultrashort transmit length and nondestructive/defect-free contacts. This leads to faster response speed and eliminates Fermi-level pinning effects. Moreover, ultrahigh responsivity and detectivity endow the device with applaudable imaging sensing capability. These results make CuBiP₂ Se₆ an ideal p-type candidate material for next-generation CMOSs logic devices.