Group items tagged

Reverse bias induces only little current (known as saturation or back current) along its direction. But a more important effect of reverse bias is widening of the depletion layer (therefore expanding the reaction volume) and strengthening the photocurrent. Circuits based on this effect are more sensitive to light than ones based on the photovoltaic effect and also tend to have lower capacitance, which improves the speed of their time response. On the other hand, the photovoltaic mode tends to exhibit less electronic noise.

Photodiodes can be used under either zero bias (photovoltaic mode) or reverse bias (photoconductive mode)

The current through a photodiode is directly proportional to the light intensity

The photodiode and phototransistor can be both photovoltaic (generators of potential difference) and photoconductive (modifiers of an electric current), depending on the application.

A reverse-biased photodiode operates in what is called photoconductive mode, since the conduction of the semiconductor junction varies with the illuminating light intensity.  If the reverse-biased voltage is relatively large (i.e. several volts) the reverse-biased photodiode will have a very fast response time (much faster than an LDR) and is suitable for detecting light signals that vary down to a time scale of a fraction of a microsecond.