Fig. 7

a Schematic of the waveguide-coupled low-voltage Si-Ge vertical SACM APD integrated with a distributed Bragg reflector and b Reflectivity versus number of period for two DBR designs. Inset is the reflectivity spectra for the two types of DBRs with 2, 4, and 6 periods, respectively [100]; c Schematic of the waveguide-coupled low-voltage Si-Ge vertical SACM APD integrated with a loop reflector and d Reflectivity spectrum of the loop reflector [101]