Record‐High Work‐Function p‐Type CuBiP ₂ Se ₆ Atomic Layers for High‐Photoresponse van der Waals Vertical Heterostructure Phototransistor

Abstract 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, CuBiP ₂ Se ₆ 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 cm ² V ⁻¹ s ⁻¹ , and an ultrahigh on/off current exceeding 10 ⁶ 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 CuBiP ₂ Se ₆ . Additionally, a multilayer graphene/CuBiP ₂ Se ₆ /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 × 10 ⁴ A W ⁻¹ , an external quantum efficiency (EQE) of 1.5 × 10 ⁷ %, a detectivity ( D ) of 1.14 × 10 ¹³ 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 CuBiP ₂ Se ₆ an ideal p‐type candidate material for next‐generation CMOSs logic devices.