A photodetector includes a Geiger mode avalanche photodiode, which includes a body of semiconductor material, which is delimited by a front surface. The avalanche photodiode further includes: a cathode region having a first type of conductivity, which forms the front surface; and an anode region having a second type of conductivity, which extends in the cathode region starting from the front surface. The photodetector further includes: a dielectric region, arranged on the front surface; a quenching resistor, which extends on the dielectric region, is electrically connected to the anode region, and is laterally spaced apart with respect to the anode region; and an optical-isolation region, which extends through the dielectric region and laterally delimits a portion of the dielectric region, the anode region extending underneath the portion of the dielectric region, the optical-isolation region being moreover interposed between the portion of the dielectric region and the quenching resistor.