The present disclosure relates to semiconductor structures and, more particularly, to photodiodes and/or PIN diode structures and methods of manufacture. The structure includes: a spiral fin structure comprising semiconductor substrate material and dielectric material; a photosensitive semiconductor material over sidewalls and a top surface of the spiral fin structure, the photosensitive semiconductor material positioned to capture laterally emitted incident light; a doped semiconductor material above the photosensitive semiconductor material; and contacts electrically contacting the semiconductor substrate material and the doped semiconductor material from a top surface thereof.