PIN Diode - Definition, Symbol, Construction, Working, Characteristics and Applications

The PIN diode is a unique combination of P-N junction diodes. It is a diode with an undoped intrinsic semiconductor region between p-type and n-type semiconductor region. It was first used in 1952 as a high-power and low-frequency rectifier. In addition, the PIN diode is a type of photodetector (which converts light energy into electrical energy) and has microwave applications.

Read on to learn more about PIN diode’s construction, working and applications.

PIN Diode

PIN means Positive- Intrinsic-Negative. Thus, the highly resistive I layer is arranged between P, and N. P and N are semiconductor layers. The intrinsic layer induces a high electric field due to the movement of electrons and holes. Therefore, the direction of the electric field will be from N to P. Due to the high electric field, the diode responds to small signals.

PIN Diode Symbol

The below figure represents the structure of the PIN diode. PIN diodes have two terminals – anode (positive) and cathode (negative).

PIN Diode Construction

A PIN diode has three layers, including an intrinsic layer sandwiched between N-type and P-type semiconductor layers. The N-type layer is created when a pentavalent impurity is covered in the semiconductor area. In contrast, the P-type layer is created when the trivalent impurity is formed in the semiconductor area. The middle layer, i.e., the intrinsic layer, comprises an undoped semiconductor.

PIN diodes can be constructed by two methods- planner structure and mesa structure.

Planner structure: In the intrinsic part, a narrow epitaxial section is imposed to create the p-region; similarly, the n-region is formed in the other section. The intrinsic section has a very large resistivity, around 0.1 ohm-m.

Mesa structure:  In the intrinsic part, the sections of semiconductors which are previously covered are grown to produce PIN diodes.

The following figure shows the construction of the PIN diode:

The intrinsic region contains no charge because holes and electrons merge at the depletion region of the diode. Hence, this section has no charge carriers and behaves as an insulator.

Working of PIN diode

The working of the PIN diode is similar to the P-N junction diode, but the PIN diode has an intrinsic region, and this region works as a depletion layer between the layers P and N.

In an unbiased PIN diode, charge carriers will distribute, i.e., charges of the depletion region try to transmit to the basic part. It will continue until the charges become equivalent in the depletion region.

Let us consider that the N region and intrinsic layer form the depletion region. So, the electron and hole distribution will make the depletion section within the N-I region. In the N region, a thin depletion layer will be induced, and in the intrinsic region, a thick depletion layer of opposite polarity will be induced because the basic level of the N region is greater than the intrinsic section.

There are two types of PIN diode bias states – Forward and reverse biased conditions.

Forward Biased PIN Diode

When the PIN diode is connected in the forward bias, charge carriers enter the intrinsic region from the N and P regions. The width of the depletion layer decreases because of applied forward potential, and resistance provided by diodes in no-bias conditions starts decreasing. As the forward voltage increases, more charge carriers get injected into the intrinsic region. In forward bias, the PIN diode works as a variable resistance device.

Reversed Biased PIN Diode

When the diode is connected in the reverse bias, the reverse voltage will be supplied to the diode, and the width of the depletion layer starts increasing. On further increasing reverse voltage, the width of the depletion layer will increase until all the charge carriers are swept away from the intrinsic region. The specific voltage is known as swept out voltage. Generally, its value is around -2 volt.

The device works as a capacitor in reverse bias, where P and N serve as two parallel surfaces of capacitor plates. If the value of reverse voltage is very high, then a thin depletion layer can be formed in the P region.

Characteristics of PIN Diode

PIN diodes have some key characteristics that make them useful for certain applications:

• They have a PN junction like a regular diode but also have a heavily doped intrinsic region between the P and N regions. This intrinsic region can be modulated by an applied reverse bias voltage.
• When a reverse bias is applied, the intrinsic region becomes depleted of carriers and the diode acts as a high resistance. This allows PIN diodes to be used as switches or modulators.
• PIN diodes can switch from a low to high impedance state, and vice versa, very quickly. This makes them useful for high-speed applications like RF switching and modulation.
• They have a very wide bandwidth, from DC to GHz frequencies. This again makes them useful for RF applications.
• They can handle high voltages in the reverse bias state and high currents in the forward bias state. This gives them a wide dynamic range.
• They have a fast reverse recovery time, which means they can switch states quickly.

Application of PIN diode

PIN diodes have a wide range of applications in various fields. Some of them are as follows:

• PIN diodes can be used as a high-voltage rectifier because the sizable intrinsic region between the P and N regions can tolerate an extensive range of high reverse voltage.
• PIN diodes are used in photodetectors to convert light energy into electrical energy. Because of the large depletion layer, the volume of light conversion increases and improves the performance of the diode.
• PIN diodes are also used in photovoltaic cells.
• PIN diodes are used in fibre optics network cables and switches.
• PIN diodes also have applications in detecting X-rays and gamma-ray photons.
• PIN diodes have low capacitance, so they are used in radio frequencies, microwave switches, and microwave variable attenuators.

Advantages and Disadvantages of PIN Diode

Some important advantages and disadvantages of PIN diodes are as follows. 

Advantages of PIN Diodes

• PIN diodes have low noise.
• PIN diodes have low dark current means very low electric current flows through the diode when no photons enter the diode.
• PIN diodes have very low bias voltage and very high reverse bias voltage.
• PIN diodes have large depletion regions and low junction capacitance.

Disadvantages of PIN diodes

• PIN diodes are significantly less sensitive.
• PIN diodes have a slower response time than other diodes.
• Pin diodes have a high reverse recovery time due to significant power loss.

We hope this article will clear readers’ concepts related to PIN diode. You can also check out other interesting Physics topics for a better understanding. For more conceptual understanding and better scores, download the Testbook app today. Testbook will help readers to create a better learning experience.