Introduction to Photodiode:
After reading this article the reader will be able to learn about the basics of the Photodiode, working and the basic construction of the Photodiode, difference between the photodiode and the simple PN junction diode and final the applications of the photodiode. So sit back, keep reading and enjoy learning.
What is Photodiode
Photodiode is the two terminal passive element which converts light in to electrical current. The basic construction of the Photodiode is similar to that of the simple PN junction diode however it is optimized to respond to light. As described earlier that the PN junction is sensitive to light thus the PN junction of the photodiode is exposed to light, it is covered with the transparent window thus the light can reach the photo sensitive part of the PN junction. The photodiodes have a quite slow response thus most of the Photodiodes are now manufactured with PIN Junction instead of the PN junction in order to improve the response time.
The schematic symbol of the photodiode is as shown in the following image:
Construction of the Photodiode:
As mentioned earlier that the photodiode is basically the PN junction diode with PN the junction exposed to the light and in order to improve the response time of the photodiode the PIN junction rather than PN junction is employed in the photodiode. PIN junction is a PN junction with an intrinsic semiconductor sandwiched between N-type and P-type regions. The PIN junction of the photodiode is as shown in the following image:
The P-type region of the Photodiode is doped with Acceptor ions, N-type region is doped with Donor ions whereas the intrinsic part of the photodiode is the pure semiconductor that is no impurity is added in to the Intrinsic part of the photodiode therefore the term intrinsic.
Working of the Photodiode:
The photodiode works on the photoelectric effect; that is when the photon of the sufficient energy is absorbed an electron-hole pair is formed.
When the photon of sufficient energy is absorbed an electron-hole is generated and if the absorption occurred near the depletion region or one diffusion length from the depletion region the electrons move towards the cathode and holes towards the anode due to inner electric field This current is called the photocurrent.
Dark current is the current that flows through the photodiode in the absence of light. There are many reasons for it, I will not discuss them here as it is out of the scope of this article. It is desirable to keep the dark current as low as possible.
An important point to notice here is that the photodiode not only detect the visible light but some photodiodes are also capable detecting electromagnetic waves out of the visible spectrum.
I hope this article(Introduction to Photodiode) would be helpful for you; I have discussed the basics of the photodiode in this article. That is all for now in the next article I will come up with more interesting engineering topics. Till then stay connected, keep reading and enjoy learning.