LATERAL PHOTODIODE

PURPOSE:To reduce an unnecessary part in which light is not directed to a circular spot of incident light, and to decrease a parasitic capacity by composing two or more electrodes in which the arcuate parts of the electrodes are opposed concentrically in the same plane to form the shape of a photodetector in a circular shape. CONSTITUTION:After Si is ion implanted on a GaAs substrate 8 to form an active layer 7 of a photodiode, a first electrode 1 having one arcuate part 1a and a second electrode 2 having two arcuate parts 2d, 2c opposing on a concentric circle with the arcuate part 1a are formed by patterning on the layer 7, and a photodetector 13 is formed in a circular shape. Thus, an unnecessary part irradiated with no light is removed to reduce its capacity, and the end part 2d of the photodiode is effectively operated as an electrode. Accordingly, the diameter of the parts of the shanks 1b, 2b of a comb can be reduced, thereby decreasing its parasitic capacity.