Electronic structure properties of PbX (X = S, Se)/graphene van der Waals heterojunctions: A first-principles study

Abstract

Van der Waals heterojunctions (vdWHs) exhibit richer physical properties compared to their individual components, making them advantageous for emerging optoelectronic applications such as infrared photodetection. Due to the high infrared absorption coefficient of lead sulfide (PbS) and lead selenide (PbSe) as well as the ultra-high carrier mobility of graphene (Gr), the vdWH formed between these materials are suitable for fabricating high-performance infrared photodetectors. However, studies on the hybrid structures of PbS and PbSe with graphene have primarily focused on experimental outcomes, with insufficient theoretical discussion on the electronic structural characteristics. In this study, first-principles methods were employed to investigate the electronic structure properties of PbS/Gr and PbSe/Gr vdWHs, including their band structures, work functions, and charge density distributions. The results reveal that the band structure of each material remains largely unchanged upon forming the heterojunction, and the overall band structure of the heterojunction can be regarded as a superposition of the isolated components. Importantly, there is a significant overlap in the band structures of PbS and PbSe, individually, with that of graphene near the Fermi level, which facilitates the charges transport between them. Moreover, opposite local electric fields and inhomogeneous charge distribution were found at the heterojunction interface, suggesting an inspiring path to further optimize the charge transport at the nanoscale. Such findings are not only beneficial for improving the interface engineering of PbX (X = S, Se)/Gr-based photodetectors, but also provide illuminating insights into advancing the meticulous design of various optoelectronic devices with extensive vdWHs.