Two-dimensional BN buffer for plasma enhanced atomic layer deposition of Al₂O₃ gate dielectrics on graphene field effect transistors

Here, we investigate the use of few-layer metal organic chemical vapor deposition (MOCVD) grown BN as a two-dimensional buffer layer for plasma enhanced atomic layer deposition (PE-ALD) of Al₂O₃ on graphene for top gated field effect transistors (FETs). The reactive nature of PE-ALD enables deposition of thin (2 nm) dielectrics directly on graphene and other two-dimensional materials without the need for a seed or functionalization layer; however, this also leads to significant oxidation of the graphene layer as observed by Raman. In FETs, we find this oxidation destroys conductivity in the graphene channel. By transferring thin (1.6 nm) MOCVD BN layers on top of graphene channels prior to PE-ALD, the graphene is protected from oxidation enabling BN/Al₂O₃ layers as thin as 4 nm. Raman and X-ray photoelectron spectroscopy on BN films show no significant oxidation caused by PE-ALD of Al₂O₃. Inserting the BN layer creates an atomically abrupt interface significantly reducing interface charges between the graphene and Al₂O₃ as compared to use of a 2 nm Al buffer layer. This results in a much smaller Dirac voltage (- 1 V) and hysteresis (0.9 V) when compared to FETs with the Al layer (V_Dirac = - 6.1 V and hysteresis = 2.9 V).