An avalanche photodetector (APD) includes a photo converter for signals to be demodulated into free charge carriers; and at least one avalanche amplifier for the free charge carriers. The photo converter and the avalanche amplifier are located next to each other on the same substrate and are in direct contact with each other. The avalanche amplifier includes a contact layer and a multiplier layer. The multiplier layer is made of a semiconductor of the same conductivity type as the photo converter and faces the substrate abutting the photo converter on one side. A first electrode is on the contact layer of the avalanche amplifier, while the second electrode is on a bottom of the substrate.