Electronic properties of a two-dimensional van der Waals MoGe(2)N(4)/MoSi(2)N(4) heterobilayer: effect of the insertion of a graphene layer and interlayer coupling

van der Waals heterostructures (vdWHs) based on 2D layered materials with select properties are paving the way to integration at the atomic scale, and may give rise to new heterostructures exhibiting absolutely novel physics and versatility. Herein, we investigate the structural and contact types in a 2D vdW heterobilayer between MoGe(2)N(4) and MoSi(2)N(4) monolayers, and the monolayers in the presence of electrical graphene (GR) contact. In the ground state, the MoGe(2)N(4)/MoSi(2)N(4) heterobilayer forms type-II band alignment, which effectively promotes the separation of electrons and holes and provides opportunity for further electrons and holes. Thus, the MoGe(2)N(4)/MoSi(2)N(4) heterobilayer is promising for designing optoelectronic devices with significantly suppressed carrier-recombination. Interestingly, the insertion of the GR contact to a MoGe(2)N(4)/MoSi(2)N(4) heterobilayer gives rise to the formation of a metal/semiconductor contact. Depending on the GR position relative to the MoGe(2)N(4)/MoSi(2)N(4) heterobilayer, the GR-based heterostructure can form either an n-type or p-type Schottky contact. Intriguingly, the contact barriers in the GR contacted MoGe(2)N(4)/MoSi(2)N(4) heterobilayer are significantly smaller than those in the GR contacted with MoGe(2)N(4) or MoSi(2)N(4) monolayers, suggesting that the GR/MoGe(2)N(4)/MoSi(2)N(4) heterostructure offers an effective pathway to reduce the Schottky barrier, which is highly beneficial for improving the charge injection efficiency of the contact heterostructures. More interestingly, by controlling the interlayer coupling through stacking, both the Schottky barriers and contact types in the GR/MoGe(2)N(4)/MoSi(2)N(4) heterostructure can be manipulated. Our findings could provide theoretical insight into the design of nanodevices based on a GR and MoGe(2)N(4)/MoSi(2)N(4) heterobilayer.