Provided is a manufacturing method of a photo detector. The method includes: forming a first single crystal semiconductor layer and an optical waveguide protruding from the first single crystal semiconductor layer; forming an insulation layer on the first single crystal semiconductor layer to cover the optical waveguide; forming an opening by etching the insulation layer to expose the top surface of the optical waveguide; forming a second single crystal semiconductor layer from the top surface of the exposed optical waveguide, in the opening; and selectively forming a poly semiconductor layer from the top surface of the second single crystal semiconductor layer, the poly semiconductor layer being doped with dopants.