Black Phosphorus Photodetector Enhanced by a Planar Photonic Crystal Cavity

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.