ABSTRACT
This chapter introduces some of the fundamental parameters in proportional avalanche photodiodes and single photon avalanche diode (SPADs) that are relevant when one wants to build large arrays of photon-counting pixels. It focuses on wide-spectrum SPADs that also have the feature of being isolated from the substrate, thus enabling low crosstalk. SPADs for time-resolved imaging have evolved over the years, which were aided by novel designs and fabrication process enhancements. As the multipixel-based complementary metal–oxide semiconductor SPAD imager gets adopted in various applications, the need to enhance the performance of the device is also increasing. The designs are usually afflicted by a relatively high dark noise, characterized in SPADs by the dark count rate, mainly due to band-to-band tunneling and trap-assisted tunneling that results from reduced annealing and drive-in diffusion steps. Timing resolution relates to the uncertainty of the response of a SPAD to a short excitation pulse, usually achieved through a laser source.
