P-N Junction Definition, history, advantages, and applications

P-N Junction

What is the p-n junction?

A P-N junction is a combination of two different doped semiconductor materials (extrinsic semiconductors). When an electrical potential is applied to the P-N junction as forward biased, it allows the electrical current to pass through the depletion layer in one way.

When the applied potential is revered, the current will not pass. In this article, the materials used for the P-N junction will be explained as well as the history, advantages, disadvantages, and applications of the P-N junction. The details of the P-N properties, energy bands, operation, and biasing will be explained later.

What is the P–Type semiconductors?

P-type extrinsic semiconductors are intrinsic semiconductor atoms like Silicon or Germanium doped (planted) with a trivalent acceptor impurity element with three electrons in its valance orbits (B, Ga, In, Al). The three electrons that exist in the valance orbits are bonding with the neighbor silicon atoms by a valance bond while the fourth bond is not completed and has a hole (positive charge).

An electron jumps from the neighbor atom to occupy and combine with the hole leaving a hole in its original position. Because of the number of holes from the dopant and the generated holes in the original intrinsic, the majority carriers are holes and the minority carriers are the electrons.

The number of holes is larger than the number of electrons. As the jumped electron doesn’t have enough energy to move in the conduction band, its energy level is far away from the conduction band and will be directly above the valance band energy level. When the electron jumps to the empty position, the charge of the Boron atom is negative.

What is the N-type semiconductors?

N-type extrinsic semiconductors are intrinsic semiconductor atoms like Silicon or Germanium doped (planted) with a pentavalent donor impurity with five electrons in its valence orbits. These elements are atoms like Arsenic (AS) or phosphor (P) called donors. These five electrons from the donor are bonded with the intrinsic neighbor atoms through a covalent bond.

For example, when the Silicon atom is doped by a phosphor atom, the silicon’s four electrons in its valance are covalent with four electrons of the phosphor donor atom and there will be a free electron in the lattice. The conduction band has a large number of electrons which are the majority carriers and the valance band has a small number of holes known as minority carriers.

The number of electrons is larger than the number of holes. Looking at the energy band structure, the donor energy level (ED) is slightly below the conduction band (EC) and as a result, the required energy to move the donor electron to the conduction band is less than the energy required to move the covalent bond electron from the valance band.

When the donor electron is excited by a small amount of energy like thermal energy, the donor electron will move to the conduction band and a positive charge ion will be left behind. The free electron in the conduction band is a free electron doesn’t leave a hole behind the valance band.

History of the P-N junction.

The first discovery of the P-N junction was by an American scientist called Russell Ohi. After two years in 1941, a Soviet physicist discovered the P-N Junction in Cu2O and photosensors (light sensors). In 1950, an American inventor explained the modern P-N junction Theory called William Shockley.

What are the advantages of the P-N junction?

Because of the construction of the P-N junction and the special characteristics of its components, it includes all the advantages of the semiconductor materials besides the advantages of the P-N junction itself. It is the revolution and the most common material for electronics components manufacturing. There are main three parameters considered advantages of the P-N junction which include the advantages of its applications (which are countless). These advantages are:

Controlling its behavior when used in electronic circuits. As per the holes majority carriers in P-Type and the electrons majority carriers in N-Type, and when these two types form the P-N junction connected, it can control the flow of current in one direction only and not allow it to flow in the other direction (it will be explained in details below).

Sizing of the products and applications of the P-N junction were recently having a rapid development in nanoelectronics and all processes technology (depositing, patterning, etching) of the electronics fabrication making use of huge components in a very small size of integrated circuits, micro, and Nano-electronics with perfect performance.

Area utilizing. Sizing the components used in electronics manufacturers enables the designers to add more applications and functions, and the originals improve.

The previous three items controlling, sizing, and area utilizing led to a significant impact on cost saving.

Disadvantages of the P-N junction.

In some applications when used in high power applications, it dissipates more power and generates more heat which are unwanted parameters in electronic circuits.

What are the application of the P-N Junction?

It is used as a solar cell ware converting sunlight to electricity. The rule of P-N Junction is that the depletion layer (barrier potential) inside the solar cell prevents the free-generated electrons by the photovoltaic effect from being diffused.

Used in the rectifier circuit where the alternative current is converted to the direct current. It is used in rectifier circuits based on its property that allows the current to pass in one direction.

Used in avalanche diode for electronic circuit protection against over-high voltage and surges. When it is reversed bias.

Used in LED applications (light emitting diode). It emits energy in the form of visible light (photons) when the current passes through the P-N junction at the forward bias while no light when it is reversed. The LED light is more efficient than the normal light bulbs.

Used in Photodiodes where the process in LED is reversed. When the photodiode absorbs energy from light, a current will pass through it when reverse-biased.

Used As a Zener diode for voltage regulation and voltage stability. It fixes the voltage across its terminals when connected in parallel with the load. When it is biased and the voltage exceeds the predetermined knee curve, it will fix the voltage across its terminals.