Other modes of operation

Avalanche photodiodes have a similar[1] structure to regular photodiodes,BUF460AV

 but they are[1] operated with much higher reverse bias. This allows each photo-generated carrier to be multiplied by avalancheBLV33

 breakdown, resulting in internal gain within the photodiode, which increases the effective responsivity of the device.Phototransistors also consist of a photodiodeML4800CS

 with internal gain. A phototransistor is in essence nothing more than[1] a bipolar transistor that is encased in a transparent case so that light can reach the base-collector junction.MG400G1UL1

 The electrons that are generated by photons in the base-collector junction are injected into the base, and this photodiode current is amplified by the transistor's current gain. Note that while phototransistorsSTY34NB50

 have a higher responsivity for light they are not[1] able to detect low levels of light any better than photodiodes.Phototransistors also have significantly longer response times.