Photodetection characterization of SPADs fabricated in 0.35µm PIN photodiode and high voltage CMOS technologies

Given the doping profiles available in different CMOS technologies, different single-photon avalanche diode (SPAD) structures could be designed. A good insight into the effect of various doping profiles on the electric field distribution within the device is crucial for optimizing the photodetection performance. In this paper, we present an experimental and simulation characterization of the photon detection probability (PDP) for two reach-through SPADs with different doping profiles, and study the effect of the electric field distribution on the PDP performance. We use a comprehensive model to evaluate the PDP up to an excess bias voltage of 13.2V. In addition, it is shown that the SPAD with a thicker high-field region, despite having the lower maximum value of the electric field, shows higher carrier avalanche triggering probabilities and, consequently, a higher PDP (67% at 13.2 V excess bias and a wavelength of 642 nm). The PDP at the wavelength of the absolute transmission maximum of the isolation and passivation stack at 665 nm is even 84% at 13.2 V excess bias. The presented results and discussions can offer a better insight to the designer to achieve higher PDP for other SPAD structures by optimizing the electric field profile using doping modifications.