  The layered semiconductor black phosphorus has attracted attention as a 2D
atomic crystal that can be prepared in ultra-thin layers for operation as field
effect transistors. Despite the susceptibility of black phosphorus to
photo-oxidation, improvements to the electronic quality of black phosphorus
devices has culminated in the observation of the quantum Hall effect. In this
work, we demonstrate the room temperature operation of a dual gated black
phosphorus transistor operating as a velocity modulated transistor, whereby
modification of hole density distribution within a black phosphorus quantum
well leads to a two-fold modulation of hole mobility. Simultaneous modulation
of Schottky barrier resistance leads to a four-fold modulation of transcon-
ductance at a fixed hole density. Our work explicitly demonstrates the critical
role of charge density distribution upon charge carrier transport within 2D
atomic crystals.
