Effective modulation of ohmic contact and carrier concentration in a graphene-MgX (X=S,Se) van der Waals heterojunction with tunable band-gap opening via strain and electric field

The development of low contact resistance at metal-semiconductor interfaces in next-generation transistors is being prioritized to improve device performance. By using density functional theory, an intrinsic Ohmic contact between a wide band gap semiconductor MgS and semimetal graphene is predicted herewith theoretically. The zero Schottky barriers in graphene/MgS van der Waals heterostructure (vdWH) can facilitate a high charge injection efficiency, whereas Ohmic contact can be induced in graphene/MgSe under small external perturbation. A comprehensive investigation of the modulation in the electronic contact properties is conducted under the application of vertical compressive strain and a perpendicular electric field to understand their role in the transport mechanism. Under vertical compressive strain, a band gap of \ensuremath{\sim}0.62 eV in graphene has been opened up. While under perpendicular electric field, the hole carrier concentration in graphene is found to be increased up to $\ensuremath{\sim}{10}^{14}\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{--2}$. Moreover, this work circumvents the prevalent approaches in inducing an Ohmic contact and addresses solutions to very fundamental challenges in pristine graphene, i.e., band gap opening and its tunability, and modulation of carrier concentration. These interesting properties of vdWHs can open up new avenues for constructing these heterojunctions for multifunctional graphene-based field-effect transistors.