Editing Photodiode (section)

===Photoconductive mode===

In photoconductive mode the diode is [[p–n junction#Reverse bias|reverse biased]], that is, with the cathode driven positive with respect to the anode.  This reduces the response time because the additional reverse bias increases the width of the depletion layer, which decreases the junction's [[capacitance]] and increases the region with an electric field that will cause electrons to be quickly collected. The reverse bias also creates [[Dark current (physics)|dark current]] without much change in the photocurrent.

Although this mode is faster, the photoconductive mode can exhibit more electronic noise due to dark current or avalanche effects.<ref>{{cite web | url =http://www.pacer.co.uk/Assets/Pacer/User/Photodiodes.pdf | title =Photodiode Application Notes – Excelitas – see note 4 | access-date =2014-11-13 | archive-url =https://web.archive.org/web/20141113175955/http://www.pacer.co.uk/Assets/Pacer/User/Photodiodes.pdf | archive-date =2014-11-13 | url-status =dead }}</ref> The leakage current of a good PIN diode is so low (&lt;1 nA) that the [[Johnson–Nyquist noise]] of the load resistance in a typical circuit often dominates.