Efficient Responsivity Enhancement of Surface-Illuminated InGaAs Avalanche Photodiode by Photon Trapping on the SOI Substrate

The short-wave infrared avalanche photodiodes (SWIR-APDs) with high signal-to-noise ratio (SNR) and high bandwidth are essential components for optical interconnections and large-scale photonic integrated circuits (PICs). However, most surface-illuminated APDs rely on the use of a relatively thick absorber for high absorption efficiency, sacrificing the bandwidth and dark current. To address the challenge, we reported InGaAs APDs with a photon-trapping (PT) structure on the silicon-on-insulator (SOI) substrate using a ~250-nm absorber, featuring a record-high responsivity of 0.75 A/W at unit gain with a wavelength of 1626 nm, equivalent to an external quantum efficiency (EQE) of 57.2%, and a low dark current of 51.3 nA at 90% of the breakdown voltage. A broad operation window from −4 to −24.1 V is achieved, with high detectivities of $9.34\times 10^{{10}}$ Jones at −4 V and $3.43\times 10^{{12}}$ Jones at −24.1 V. The work exhibits the dramatic advantage of the PT structure in photon responsivity enhancement with 2.5 times and the feasibility of InGaAs-based APD to integrate with silicon PICs, paving the way for high-efficiency and high-speed detectors targeting a broad range of emerging applications.