Let’s talk about Photodiode operation in circuits.
The operating principle of a photodiode is when a large-energy photon strikes the diode, creating a pair of electrons. This mechanism is also called the internal photoelectric effect. If absorption occurs at the junction of the depletion region, the bearers are removed from the junction through the embedded electrical field of the exhaustion region.
Therefore, the holes in the region are moving towards the anode, and the electrons are moving towards the cathode and a photoconductor is generated. The entire diode current is the sum of the absence of light and photographic flux. Therefore, the absence of current must be reduced to maximize the sensitivity of the device.
Photodiodes consist of a p-n junction or a pin junction. When the incident light of sufficient energy strikes the junction, an electron is excited. This electron is called a free electron; along with this electron, a positively charged electron hole is also created. This mechanism is called an internal photoelectric effect.
When light absorption occurs in the region of junction depletion, these carriers are removed from the intersection with the region’s integrated electric field. This results in a photographic flow due to the movement of the holes to the anode and the electrons to the cathode.
In addition to photocurrent, a certain amount of dark current is generated by electron flow with or without light. The total current produced by the device is the sum of the current and the dark current.
To get maximum sensitivity from the device, it is essential to minimize the dark current. There are mainly two modes of operation of the photodiode, namely photovoltaic and photoconductive modes.
In photovoltaic mode, the diode is operated under zero polarization, while in photoconductive mode it works in reverse bias. Another type of diode operation is the avalanche photodiode, which is nothing more than a stronger bias.