Avalanche Carrier Multiplication in Multilayer Black Phosphorus and Avalanche Photodetector

A highly sensitive avalanche photodetector (APD) is fabricated by utilizing the avalanche multiplication mechanism in black phosphorus (BP), where a strong avalanche multiplication of electron–hole pairs is observed. Owing to the small bandgap (0.33 eV) of the multilayer BP, the carrier multiplication occurs at a significantly lower electric field than those of other 2D semiconductor materials. In order to further enhance the quantum efficiency and increase the signal-to-noise (S/N) ratio, Au nanoparticles (NPs) are integrated on the BP surface, which improves the light absorption by plasmonic effects. The BP–Au-NPs structure effectively reduces both dark current (≈10 times lower) and onset of avalanche electric field, leading to higher carrier multiplication, photogain, quantum efficiency, and S/N ratio. For the BP–Au-NPs APD, it is obtained that the external quantum efficiency (EQE) is 382 and the responsivity is 160 A W^-1 at an electric field of 5 kV cm^-1 (V_d ≈ 3.5 V, note that for the BP APD, EQE = 4.77 and responsivity = 2 A W^-1 obtained at the same electric field). The significantly increased performance of the BP APD is promising for low-power-consumption, high-sensitivity, and low-noise photodevice applications, which can enable high-performance optical communication and imaging systems.