Controlling the Schottky barrier atMoS2/metal contacts by inserting a BN monolayer

Making a metal contact to the two-dimensional semiconductor ${\mathrm{MoS}}_{2}$ without creating a Schottky barrier is a challenge. Using density functional calculations we show that, although the Schottky barrier for electrons obeys the Schottky-Mott rule for high work function $(\ensuremath{\gtrsim}4.7$ eV) metals, the Fermi level is pinned at 0.1--0.3 eV below the conduction band edge of ${\mathrm{MoS}}_{2}$ for low work function metals, due to the metal-${\mathrm{MoS}}_{2}$ interaction. Inserting a boron nitride (BN) monolayer between the metal and the ${\mathrm{MoS}}_{2}$ disrupts this interaction, and restores the ${\mathrm{MoS}}_{2}$ electronic structure. Moreover, a BN layer decreases the metal work function of Co and Ni by $\ensuremath{\sim}2$ eV, and enables a lineup of the Fermi level with the ${\mathrm{MoS}}_{2}$ conduction band. Surface modification by adsorbing a single BN layer is a practical method to attain vanishing Schottky barrier heights.