Black phosphorus n-MOSFETs with record transconductance

Two-dimensional (2D) materials have attracted a great deal of attention for use in a variety of electronic and photonic applications. The layered crystal structure in these materials offers an ultra-thin or even monolayer body thickness, which could reduce short channel effects allowing improved transistor scaling compared to conventional bulk materials. In order to use these 2D materials in complementary logic circuits, it would be desirable to have high performance p-FETs and n-FETs made using the same semiconductor channel. Transition metal dichalcogenides (TMDs) are the most widely studied 2D materials and inverters based on these materials have already been reported. Although these inverters show high voltage gain, their performance is eventually limited by the low mobility in these materials. Recently, the 2D material black phosphorus (BP) has been studied which promises improved performance due to its high electron and hole mobility and thickness-dependent band gap. However, black phosphorus tends to be naturally p-type, and while high-performance BP p-FETs have been demonstrated, achieving high-performance n-FETs has proven to be difficult. In this work, we report Al₂O₃-passivated black phosphorus n-FETs with record transconductance of 45 μS/μm, a value that is over 10 times higher than the previous best values. These result suggest strong evidence that black phosphorus is a promising material for 2D CMOS applications.