A photodetector that utilizes the photovoltaic effect, that is, the
generation of an electromotive force by irradiation of light.
Since an interface potential exists across a barrier such as a PN junction
in a semiconductor, an electric field is generated around the barrier.
If a photon with an energy greater than the energy gap between the valence
band and the conduction band hits the interface, it creates an electron
and a hole, which are parted from each other by the interface electric
field, producing a potential (photovoltaic force). High voltage can be
produced by integrating multiple photovoltaic cells by silicon micromachining
technology. The photovoltaic cell is used for photodiodes, phototransistors,
and solar batteries.