  We report on a room-temperature photodetector utilizing semimetal bismuth
nanowire arrays coupled with graphene. The structural flatness and high
electron mobility of graphene exhibit great potential for future generations of
electronic materials. Bismuth nanowire arrays coupled with graphene have strong
absorption because of light trapping. Bismuth (Bi), as a semimetal, complements
graphene's gapless and mobility characteristics. Bi also features a long
screening length (4 nm) comparable to semiconductors. Raman spectroscopy is
used to characterize the charge transfer between graphene and Bi. The analyzed
spectrum includes the visible (350 nm) through the near infrared (980 nm) and
well into the telecommunication band (1550 nm). Because of photocarrier pair
generation and transfer at the interface, the photocurrent generated by the
interface built-in field is robust without sacrificing the detection spectrum.
We observe a power-law frequency dependence of the photoresponse over three
order of magnitude of excitation frequency consistent with a wide distribution
of diffusion times. These key properties may enable application of the
junctions of graphene with Bi in detector and light harvesting applications.

Mesoscale and Nanoscale Physics