Semiconductors & Semiconductor Diodes

Materials with conductivity intermediate between conductors (usually metals) and non-conductors or insulators are referred to as semiconductor materials (such as ceramics). Semiconductors, such as gallium arsenide, or pure elements such as germanium or silicon can be used as semiconductors.

For example, gallium arsenide, germanium, and silicon are all types of semiconductor materials. Gallium  arsenide is utilised in solar cells, laser diodes, and other applications, while silicon is employed in electronic circuit construction.

Semiconductors contain holes and electrons.

Carriers of charge in semiconductors include holes and electrons, which are responsible for the flow of current. Atoms with positively charged electric charge carriers (valence electrons) are called holes, whereas electrons are negatively charged particles. When measured in terms of magnitude, both electrons and holes are equal, yet their polarities are opposite.

Electron and hole mobility are both important.

It is true that electrons have a higher mobility in a semiconductor than holes do. Their differences in band structures and scattering mechanisms are the primary reasons for this.

Conduction band is where electrons move, whereas the valence band is where holes move. Because of their constrained movement, holes are unable to travel as freely as electrons in the presence of an electric field. Hole formation in semiconductors is caused by electrons being elevated from their inner to higher shells, which is caused by an electron being elevated from their inner to higher shells. Holes have poorer mobility than electrons because they are subjected to a larger atomic force by the nucleus.

Semiconductors and the Band Theory

It was during the quantum revolution in science that the band theory was first proposed. Energy bands were found by Walter Heitler and Fritz London. The electrons in an atom, as we all know, are present in a variety of energy levels across the atom . A Band Gap is defined as the space between consecutive bands that represent a range of energies that do not include an electron.

Semiconductors have two distinct bands: the conduction band and the valence band.

Valence Band:

It is an energy band that includes the energy levels of valence electrons. That particular energy band is the most heavily populated. The bandgap of semiconductors is narrower as compared to that of insulators. It enables electrons in the valence band to transition into the conduction band when they are exposed to external energy, allowing them to conduct electricity.

Conduction Band:

It is the lowest unoccupied band in the electromagnetic spectrum that comprises the energy levels of charge carriers that are either positive (holes) or negative (free electrons) in nature. Due to the presence of conducting electrons, current is generated. Although it has a high energy level, the conduction band is almost always empty in nature. In semiconductors, electrons from the valence band are accepted by the conduction band.

What is the Fermi Level in Semiconductors and how does it work?

Between the valence and conduction bands, there is a Fermi level (denoted by the symbol EF). At absolute zero, it is the molecular orbital with the largest percentage of its occupied energy level being utilised. This state is defined by the fact that the charge carriers each have their own quantum state and do not interact with one another in most instances. The charge carriers will begin to occupy states above the Fermi level when the temperature climbs above absolute zero.

The density of empty states increases in a p-type semiconductor, indicating that the semiconductor is becoming more conductive. Thus, the lower energy levels may accommodate a greater number of electrons. On the other hand, the density of states increases in an n-type semiconductor, allowing for the accommodation of more electrons at higher energies.

Semiconductors Have Specific Characteristics

Electrical current can be conducted by semiconductors in a favourable environment or under favourable conditions. In addition to its unique feature, it is a superb material for conducting electricity in a controlled manner when the situation calls for it.

In contrast to conductors, charge carriers in semiconductors are created solely as a result of the presence of external energy (such as electricity) (thermal agitation). Because of this, a specific number of valence electrons leap across the energy gap and into the conduction band, resulting in an equal number of vacant energy states, or holes, in the valence electrons’ orbitals. Either electrons or holes cause conduction, and both are significant.

In what way does temperature affect the resistance of semiconductors?

In conductors and semiconductors, the difference in resistivity is related to the different densities of charge carriers in the two materials.

Due to the quick increase in the number of charge carriers associated with an increase in temperature, the resistivity of semiconductors falls with temperature, causing the fractional change, or temperature coefficient, to be negative.

Examples of some Important Characteristics of Semiconductors include:

When the temperature is zero Kelvin, a semiconductor behaves like an insulator. The material becomes a conductor when the temperature is raised. In order to take use of their extraordinary electrical properties, semiconductors can be manipulated via doping in order to produce semiconductor devices that are appropriate for energy conversion, switches, and amplifiers. Reduced losses of electrical energy. Miniaturised and light-weight, semiconductors are a good fit for many applications. In comparison to conductors, their resistivity is higher; yet, it is lower than that of insulants. With a rise in temperature, the resistance of semiconductor materials reduces, and vice versa.

In response to the increase in temperature, which is caused by collisions, a small number of electrons become unbound and free to move through the lattice, causing an absence in the spot where it was previously present (hole). During the conduction of electricity in a semiconductor, these free electrons and holes play a role. The number of charge carriers in both the negative and positive directions is equal. It is possible to ionise a few atoms in the lattice by applying heat energy, which results in a reduction in their conductivity.

Uses for Semiconductors are numerous.

Let’s take a look at how semiconductors are used in everyday life. Most electronic gadgets rely on semiconductors for their operation. Our lives would be drastically different if it weren’t for them!

Because of their dependability, compactness, low cost, and controlled conduction of electricity, they are well suited for usage in a wide variety of components and devices for a wide range of applications. Semiconductors are used in the manufacture of a wide variety of devices, including transistors, diodes, photosensors, microcontrollers, integrated chips, and many others.

Semiconductors are used in a variety of applications throughout daily life.

Semiconductor devices are used in the manufacture of temperature sensors.

In 3D printing machines, they are employed.

These elements are found in microchips and autonomous vehicles.

The term is found in calculators and other electronic equipment such as solar plates, computers, and computers.

Semiconductors are used in the production of transistors and MOSFETs, which are switches in electrical circuits.

Conclusion

Carriers of charge in semiconductors include holes and electrons, which are responsible for the flow of current. Atoms with positively charged electric charge carriers (valence electrons) are called holes, whereas electrons are negatively charged particles. Semiconductors are used in the manufacture of a wide variety of devices, including transistors, diodes, photosensors, microcontrollers, integrated chips, and many others. Conduction band is where electrons move, whereas the valence band is where holes move. Because of their constrained movement, holes are unable to travel as freely as electrons in the presence of an electric field.