Electron Excess Doping and Effective Schottky Barrier Reduction on the MoS₂/h-BN Heterostructure.

Abstract

Layered hexagonal boron nitride (h-BN) thin film is a dielectric that surpasses carrier mobility by reducing charge scattering with silicon oxide in diverse electronics formed with graphene and transition metal dichalcogenides. However, the h-BN effect on electron doping concentration and Schottky barrier is little known. Here, we report that use of h-BN thin film as a substrate for monolayer MoS₂ can induce ∼6.5 × 10¹¹ cm^-2 electron doping at room temperature which was determined using theoretical flat band model and interface trap density. The saturated excess electron concentration of MoS₂ on h-BN was found to be ∼5 × 10¹³ cm^-2 at high temperature and was significantly reduced at low temperature. Further, the inserted h-BN enables us to reduce the Coulombic charge scattering in MoS₂/h-BN and lower the effective Schottky barrier height by a factor of 3, which gives rise to four times enhanced the field-effect carrier mobility and an emergence of metal-insulator transition at a much lower charge density of ∼1.0 × 10¹² cm^-2 (T = 25 K). The reduced effective Schottky barrier height in MoS₂/h-BN is attributed to the decreased effective work function of MoS₂ arisen from h-BN induced n-doping and the reduced effective metal work function due to dipole moments originated from fixed charges in SiO₂.