Two-Dimensional Materials Inserted at the Metal/Semiconductor Interface: Attractive Candidates for Semiconductor Device Contacts.

Metal-semiconductor junctions are indispensable in semiconductor devices, but they have recently become a major limiting factor precluding device performance improvement. Here, we report the modification of a metal/n-type Si Schottky contact barrier by the introduction of two-dimensional (2D) materials of either graphene or hexagonal boron nitride (h-BN) at the interface. We realized the lowest specific contact resistivities (ρ) of 3.30 nΩ cm (lightly doped n-type Si, ∼ 10/cm) and 1.47 nΩ cm (heavily doped n-type Si, ∼ 10/cm) via 2D material insertion are approaching the theoretical limit of 1.3 nΩ cm. We demonstrated the role of the 2D materials at the interface in achieving a low ρ value by the following mechanisms: (a) 2D materials effectively form dipoles at the metal-2D material (M/2D) interface, thereby reducing the metal work function and changing the pinning point, and (b) the fully metalized M/2D system shifts the pinning point toward the Si conduction band, thus decreasing the Schottky barrier. As a result, the fully metalized M/2D system using atomically thin and well-defined 2D materials shows a significantly reduced ρ. The proposed 2D material insertion technique can be used to obtain extremely low contact resistivities in metal/n-type Si systems and will help to achieve major performance improvements in semiconductor technologies.