Why should a photodiode be operated in reverse bias?
When reverse biased, current will only flow through the photodiode with incident light creating photocurrent. The reverse bias causes the potential across the depletion region to increase and the width of the depletion region to increase. This is ideal for creating a large area to absorb the maximum amount of photons.
What is the photoconductive effect?
An internal photoelectric effect in which some nonmetallic materials exhibit a marked increase in electrical conductivity upon absorption of photon energy. The incident photons excite electrons into the conduction band where they move more freely, resulting in increased electrical conductivity.
Why do you use reverse bias in a photodiode?
Finally, reverse bias also extends a photodiode’s range of linear operation. If you’re concerned about maintaining accurate measurements with high illuminance, you can use photoconductive mode and then choose the reverse-bias voltage according to your system requirements.
What kind of bias is used in photovoltaic mode?
Photovoltaic mode employs zero bias and minimizes dark current. The next article in the Introduction to Photodiodes series covers several different photodiode semiconductor technologies.
What is the difference between photovoltaic and photoconductive mode?
Photovoltaic mode: The circuit is held at zero volts across the photodiode, since point A is held at the same potential as point B by the operational amplifier. This eliminates the possibility of dark current. Photoconductive mode: The photodiode is reversed biased, thus improving the bandwidth while lowering the junction capacitance.
What is the reverse current in a photodiode?
The same thing happens in a photodiode, but the reverse current is called dark current. Higher reverse-bias voltage leads to more dark current, so by using the op-amp to hold the photodiode at approximately zero bias, we virtually eliminate dark current.