Pie photodetector

An apparatus comprising:

• a semiconductor disk;
• a first doped region disposed within the semiconductor disk such that the first doped region extends across a center of the semiconductor disk, wherein the first doped region has a first doping type;
• and
• a first absorption region disposed on the first doped region such that a portion of the first doped region is positioned between the center of the semiconductor disk and the first absorption region along a radius of the semiconductor disk, wherein the first absorption region extends around a periphery of an exposed portion of the first doped region that extends across a radial center of the semiconductor disk, wherein the first absorption region comprises a second doped region with a second doping type different from the first doping type, and wherein the first absorption region is arranged to absorb an optical signal as the optical signal travels along an inner circumference of the semiconductor disk.