The present disclosure relates to semiconductor structures and, more particularly, to photodiodes and/or PIN diode structures and methods of manufacture. The structure includes: at least one fin including substrate material, the at least one fin including sidewalls and a top surface; a trench on opposing sides of the at least one fin; a first semiconductor material lining the sidewalls and the top surface of the at least one fin, and a bottom surface of the trench; a photosensitive semiconductor material on the first semiconductor material and at least partially filling the trench; and a third semiconductor material on the photosensitive semiconductor material.