Bilayer-Graphene-on-MoS$$_2$$ Heterostructures: Channel Bandgap, Transconductance, and Noise

Abstract

Graphene-MoS\(_2\) hybrid structure shows extremely large photoresponse (Chap. 6). However, zero-bandgap in monolayer graphene permits large background current (\(I_{d}\) = \(I_{DS}\) in dark). It is seen that a bilayer graphene (BLG) can be utilized to make a BLG-on-MoS\(_2\) field effect transistor (FET), which helps reducing \(I_{d}\). Reduction in \(I_{d}\) occurs because of a band-gap opening in BLG channel in presence of external electric field (Sect. 2.1.2). A dual gated structure is used to control the bandgap (\(E_g\)) and Fermi energy (\(E_F\)) independently, giving full regulation over the lowest current in off-state and the channel conductance of the FET respectively. A larger \(E_g\) reduces the dark current (\(I_d < 10\) nA) and improves the field control tunability (on/off ratio) of channel conductance. Large on/off ratio helps in attaining high photogating effect, which further helps in achieving large photoresponsivity value (\(\sim \) \(10^9\) A W\(^{-1}\)) while operating at low source-drain bias (\(V_{DS}\)= 50 mV).