Optimization of graphene-MoS₂ barristor by 3-aminopropyltriethoxysilane (APTES)

We theoretically and experimentally investigated the influence of the Fermi level position of graphene relative to the Dirac point on the performance of a graphene/MoS₂ heterojunction barristor. A large Fermi level modulation (ΔE_F = 0.28 eV) of graphene, when the V_GS is changed between -20 V and +20 V, was theoretically predicted when the Fermi level is located at the Dirac point. For reference, ΔE_F = 0.11 eV when the Fermi level is far from the Dirac point. This prediction was experimentally proven using two kinds of barristors with pristine (strongly p-type) and 2.4% APTES-treated (intrinsic) graphene. The on/off-current ratio was improved by a factor of 32 (a 2.1-fold increase in the on-current density and a 15-fold increase in the off-current density) in the APTES-treated device, as compared to the control. Using a temperature-dependent current-voltage measurement, we quantitatively confirmed the larger modulation of the barrier height in the APTES-treated barristor (ΔE_F = 0.27 eV) compared to that of the control device (ΔE_F = 0.14 eV). This study can be used to guide the design and optimization of graphene-based heterojunction devices.