Identification of stress factors and degradation mechanisms inducing DCR drift in SPADs

The reliability of Single-Photon Avalanche Diodes (SPADs) is addressed by measurement of Dark Count Rate (DCR) drift as a function of stress time (Delta DCR). The degradation mechanisms are analyzed performing stress-conditions at various temperatures, voltages, and irradiances. Measurement and simulation of current are performed to reinforce the degradation assumptions. Potential degradation locations are investigated by comparison of initial and post ageing DCR at different temperatures together with simulations covering defect position and number in the device. Different variations of manufacturing processes are also studied to further confirm defect positions. All the results have allowed identification of the plausible degradation mechanisms, including Hot-Carrier Degradation (HCD) and charge accumulation at the upper interface occurring in SPADs over a wide range of stress conditions.