William S.
Whitney1, Michelle C. Sherrott2,3,
Deep Jariwala2,3,
Wei-Hsiang Lin2, Hans A. Bechtel4,
George R.
Rossman5, Harry A.
Atwater2,3
We report
the infrared optical response of thin black phosphorus under
field-effect
modulation, and interpret the observed spectral shifts as a combination
of an
ambipolar Burstein-Moss (BM) bandgap shift due to band-filling and
Pauli-blocking
under gate control, together with a quantum confined Franz-Keldysh
(QCFK)
effect, which have been proposed theoretically to occur for BP flakes
under
electric field modulation. Modulation amplitudes as high as 15% are
observed
for 25 nm layers, suggesting the potential for use of black phosphorus
as an
active material in mid-infrared optoelectronic modulator applications.