We
report the integration of a black phosphorus (BP) photodetector
on a silicon planar photonic crystal cavity for improving the performance.
Benefiting from the cavity-enhanced light–BP interaction, the
device has a compact footprint, promising high responsivity, low dark
current, and high speed. With an on-resonance excitation, the photodetection
is enhanced by 36 times over that obtained with the off-resonance
excitation. Under a bias of 0.5 V, the photodetector has a responsivity
of ∼125 mA W–1 with a dark current lower
than 20 nA thanks to the short BP channel. Relying on BP’s
high carrier mobility and the compact device structure, a high speed
with a 3 dB bandwidth exceeding ∼1.42 GHz is obtained, which
is limited by our instrument response. Our results indicate the BP
photodetector integrated on a planar photonic crystal cavity has potential
for constructing a compact on-chip photodetector of photonic integrated
circuits.