Pin Diode

What is Pin Diode?

A PIN diode is a type of semiconductor device with a broad undoped intrinsic semiconductor region between the regions of a p-type semiconductor and an n-type semiconductor. The regions of p-type and n-type semiconductors are heavily doped because they are utilized for ohmic contacts.

The wide intrinsic region is similar to that of an ordinary p–n diode. The wide intrinsic region makes the PIN diode a typical function of a diode; however, it makes it suitable for applications viz: attenuators, fast switches, photodetectors, and high-voltage power electronics devices. 

Pin Diode Symbol

A pin diode symbol is shown below:

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Pin Diode Working

The term PIN diode gets its name from the idea that involves three main layers. Instead of just having P-type and N-type layered semiconductors, it has three layers such as

• P-type layer

• Intrinsic layer (in the middle)

• N-type layer

The working principle of the PIN diode is exactly the same as that of the working of a normal diode. The main difference can be seen in the depletion region because this layer normally exists between both the P & N regions in a reverse-biased or unbiased diode, which is larger. 

In a given PN junction diode, the P region comprises holes as it has been developed and doped to make sure that it contains a majority of holes. Similarly, the N-region has been created and doped to hold excess electrons.

The layer between the P & N regions includes no charge carriers so as many electrons and holes can merge. Since the depletion region of the diode has no charge carriers, it works as an insulator. The depletion region is present within a PIN diode; however, when the PIN diode is forward-biased, the carriers come into the depletion region, and as the two types of carriers get together, the flow of current starts.

When the PIN diode is connected in forwarding biased condition, the charge carriers are very much higher than the level of intrinsic carrier’s intensity. Because of this reason, the electric field and the high-level injection level extend core into the region; this electric field generated assists in speeding up the moving of charge carriers from the P to N region, which consequences or helps in the quicker operation of the PIN diode, making it an appropriate and suitable functioning device for high-frequency operations.

Pin Diode Applications 

You may find applications of a pin diode in the following areas:

We use a PIN diode as a high voltage rectifier. The intrinsic layer in this diode offers a partition between both the layers P and N layers, therefore, allowing higher reverse voltages to be tolerated.

We use a PIN diode as an ideal radio frequency switch. The intrinsic layer residing between the P & N layers increases the space between them; this, in turn, also reduces the capacitance between both the regions, thus raising the level of isolation when the PIN diode is reverse biased.

The PIN diode is employed as a photodetector to transform the light into the current that takes place in the depletion layer of a photodiode, and therefore, rising the depletion layer by inserting the intrinsic layer. The intrinsic layers help to progress or to enhance the performance by increasing the volume in where light variation occurs.

Pin diode is an ideal element to provide electronics switching in applications or areas of electronics. A pin diode is primarily useful for RF design applications and also for offering the switching, or an attenuating element in RF  attenuators and RF switches. This diode is capable of providing much higher levels of consistency than RF relays that are frequently the only other alternative/option.

The main applications of the PIN diode that we discussed in the above context are limited; however, they can also be applied in some other areas.

Pin Diode Characteristics

A pin diode fully obeys the diode equation for small frequency signals. At higher frequencies, the PIN diode appears like a perfect resistor. There is a bulk of stored charge in the intrinsic region and at small frequencies, the charge can be detached and the diode gets switched OFF.

At higher frequencies, there is insufficient time to eliminate the charge, so the PIN diode doesn’t get switched OFF, which means the diode has a reduced reverse recovery time. A PIN diode properly biased also performs as a variable resistor. So, the high-frequency resistance may vary over a broad range, i.e., from 0.1 Ω-10 kΩ in some cases.

The design of the PIN-diode has some specialty. On increasing the magnitudes of the intrinsic region, the diode appears to be a resistor at minor frequencies. It readily affects the time required to switch off the diode & its shunt capacitance. Therefore, it is advised to choose a device with the most suitable properties for a specific use.