Intrinsic dipole-induced self-doping in Janus MXY-based (M = Mo, W; X = S; Y = Se, Te) p–n junctions

Abstract

Semiconductor p–n junctions are the most rudimentary building block in modern optoelectronic devices. Herein, we report and demonstrate, using first-principle calculations, that an intrinsic dipole induces self-doping in Janus MXY (M = Mo, W; X = S; Y = Se, Te) van der Waals p–n junctions. The stacked dipole moment in Janus MXY homostructures drives the electrons and holes transfer, forming self-doped p-type and n-type regions in the outermost layer, which is in stark distinction from previously applied electric fields. Furthermore, the doping level in G/MXY/G (G = graphene) heterostructures can be modulated by tuning the thickness of the Janus MXY. Taking the G/WSTe/G heterostructure as an example, the charge carrier density could be tunable to when the Janus WSTe thickness is stacked to a double layer. Interestingly, the interface dipole moment caused by the electrons transfer results in an asymmetric doping level in the top graphene and bottom graphene. Our work provides an intrinsic approach for designing self-doped p–n junctions.