A TCAD and Spectroscopy Study of Dark Count Mechanisms in Single-Photon Avalanche Diodes

It is shown through dark count rate spectroscopy (DCRS) and TCAD-simulations that in single-photon avalanche diodes (SPADs), the majority of low dark count rate (DCR) devices in modern CMOS arrays are free of deep-level traps and that DCR can therefore be explained by saturation current and band-to-band tunneling (BTBT). The DCRS performed on the Megaframe 32 × 32 show that the activation energies for the high DCR devices are consistent with a single type of defect at ≈ 0.44 eV, thought to be the E-center, in differing electric fields. Calibrated TCAD-simulated reverse bias leakage currents are orders of magnitude lower than those measured due to the lack of parasitic leakage paths but give theoretical DCRS that are close to the measured values for four different SPAD designs and predict the voltage dependence at high fields. The coefficients for Kane´s indirect tunneling model in the [100] direction are determined as A ≈ 2×10¹⁵ cm^-3/s and B ≈ 2.39×10⁷ V/cm through TCAD calibration, DCR measurement, and theory. It is found that indirect BTBT dominates the DCR of SPADs with low breakdown voltages.