Analysis of single photon detection in avalanche photodetectors with multi-gain-stage multiplication region

We report the design and analysis of a single photon avalanche detector (SPAD) with cascaded multiplication stages with asymmetric gain series for near-IR applications. The asymmetric gain profile allows us to selectively enhance the ionization coefficient for injected electrons and suppress the hole-initiated ionization by repetition of high and low field layers. The low field layer acts as a carrier relaxation region, which inhibits avalanche feedback between stages; hence, it is expected to have a lower dark count rate (DCR). The gain stage consists of three distinct layers with different electric fields, which can be adjusted by geometrical and mole fraction design. In this paper we study the effect of these layers' field and thickness on the single photon quantum efficiency (SPQE) and DCR of the proposed SPAD. Our results show that the high-field layer can better influence the performance of the detector rather than the others. In comparison with a conventional SPAD with a uniform multiplication region, our proposed structure shows lower DCR for a same SPQE.