  The ability to detect light over a broad spectral range is central for
practical optoelectronic applications, and has been successfully demonstrated
with photodetectors of two-dimensional layered crystals such as graphene and
MoS2. However, polarization sensitivity within such a photodetector remains
elusive. Here we demonstrate a linear-dichroic broadband photodetector with
layered black phosphorus transistors, using the strong intrinsic linear
dichroism arising from the in-plane optical anisotropy with respect to the
atom-buckled direction, which is polarization sensitive over a broad bandwidth
from 400 nm to 3750 nm. Especially, a perpendicular build-in electric field
induced by gating in black phosphorus transistors can spatially separate the
photo-generated electrons and holes in the channel, effectively reducing their
recombination rate, and thus enhancing the efficiency and performance for
linear dichroism photodetection. This provides new functionality using
anisotropic layered black phosphorus, thereby enabling novel optical and
optoelectronic device applications.
