Active Area Uniformity of InGaAs/InP Single-Photon Avalanche Diodes

We present a detailed characterization of the active area uniformity of InGaAs/InP Single-Photon Avalanche Diodes (SPADs) from two different design iterations. Nonuniformity of the electric field within the device active area has been measured through 2-D scans of detection efficiency and timing response to a pulsed laser. Additionally, we measured the near-infrared luminescence emitted by hot carriers during the avalanche. The nonuniformity is stronger at lower excess bias, with much higher and nonuniform electric field at the edge of the active area than expected, and it is fainter at higher excess bias, due to the saturation of the avalanche triggering efficiency. The main drawbacks are that the detection efficiency is position dependent when the SPAD is not fiber pigtailed and that the temporal response is worse, because of the nonuniform delay in the avalanche build-up across the SPAD active area.