  In this letter, a new approach to chemically dope black phosphorus (BP) is
presented, which significantly enhances the device performance of BP
field-effect transistors for an initial period of 18 h, before degrading to
previously reported levels. By applying
2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ), low ON-state
resistance of 3.2 ohm.mm and high field-effect mobility of 229 cm2/Vs are
achieved with a record high drain current of 532 mA/mm at a moderate channel
length of 1.5 {\mu}m.
