A photodiode comprises an optical detection portion for detecting an
optical signal and outputting a photoelectric conversion signal. The
optical detection portion has a semiconductor substrate of a first
conductive type and semiconductor layers of a second conductive type
formed in spaced-apart relation in a surface of the semiconductor
subtrate. A depletion layer is formed in the semiconductor subtrate by
application of a reverse bias to the photodiode so as to surround the
semiconductor layers. An etched surface portion of the depletion layer is
disposed between the semiconductor layers so that an interface level
region of the surface of the semiconductor substrate does not exist
between the semiconductor layers.
