Utilisation of janus material for controllable formation of graphene p–n junctions and superlattices

Abstract

Graphene-based device applications such as ultrafast transistors and photodetectors benefit from precise control over its carrier type and concentration as well as a combination of both high-quality p- and n-doped components with spatial control and seamless connection (p–n junctions/superlattices). However, this remains experimentally a challenge for an atom-scale control over the doping in graphene and the attendant formation of p–n junctions/superlattices. Here, we demonstrate that sandwiching a janus material (a functionalized graphene layer with one side by H atoms and another side by F atoms, defined as H–G–F) between MoSe₂ (BN) substrate and graphene allows us to effectively control the carrier type in graphene, where the janus material acts as an electron pump, facilitating the electron tunneling between MoSe₂ (BN) and graphene. Appropriate functionalization of the janus material would open the possibility of creating well ordered and atomically sharp graphene p–n junctions/superlattices in a single layer of graphene. Furthermore, upon applying an external electric field, the charge concentration in both n-type and p-type regions can be continuously tuned except for a platform area. A comprehensive and detailed picture built by density functional theory calculations sheds light on the physical mechanism of the observed doping course as well as its response to an external field. Our results not only introduce single-layer H–G–F as a new 2D Janus material with the ability of electron extraction, but also open up a new direction for local control over the properties of graphene without destroying its intrinsic structure.