Self-Instruct
Semiconductors play an essential role in modern electronics, from computer chips to solar panels. They are materials that have a conductivity between that of conductors and insulators. However, semiconductors can be classified into two main types: intrinsic semiconductor and extrinsic semiconductor.
Intrinsic Semiconductor
An intrinsic semiconductor is a pure semiconductor, meaning it has no impurities and is made up of one chemical element. This type of semiconductor is also referred to as an undoped semiconductor. An undoped semiconductor consists of valence electrons that are bound to atoms and are not free to move.
Intrinsic semiconductors have a valence band, which is a band of energy levels that contains electrons that are tightly bound to atoms. These electrons are not available for electrical conduction unless sufficient excited energy is supplied. Additionally, intrinsic semiconductors also have a conduction band, which is an empty band above the valence band where electrons have enough energy to break free from their atomic bonds and become free electrons.
At room temperature, a small number of electrons in an intrinsic semiconductor gain enough energy to break free from their bond with their atoms and move to the conduction band. This generates an equal number of holes (vacancies) in the valence band where electrons were originally bound. This process is known as intrinsic carrier generation and creates an equal number of electrons and holes. Therefore, intrinsic semiconductors are sometimes referred to as having "intrinsic carriers."
However, the number of free carriers generated by this process is small, even when the semiconductor is heated or illuminated by light. As a result, the conductivity of intrinsic semiconductors is low. The small conductivity of intrinsic semiconductors can be increased by doping with impurities, which is where extrinsic semiconductors come into play.
Extrinsic Semiconductor
An extrinsic semiconductor is a semiconductor that has been doped or mixed with impurities. The addition of impurities greatly enhances the electrical conductivity of the semiconductor. The impurities, referred to as dopants, are added to regulate the concentration of free carriers in extrinsic semiconductors.
Dopants introduce either more electrons or holes than the intrinsic semiconductor, depending on the type of dopant used. There are two main types of dopants used in extrinsic semiconductors: p-type and n-type dopants.
P-type doping is the process of adding impurities with fewer valence electrons than a semiconductor material. This creates a semiconductor with excess holes which means that they can move through the material. Boron is a common dopant used for p-type semiconductors.
N-type doping is the process of adding impurities with more valence electrons than a semiconductor material. This creates a semiconductor with extra electrons that are free to move. Phosphorus is a commonly used dopant for n-type semiconductors.
Doping an intrinsic semiconductor creates a region where electron concentration will be at the highest, the n-type semiconductor, and the region with a low electron concentration, the p-type semiconductor. When p-type and n-type semiconductors are in close proximity to each other, they form a p-n junction, which is a key building block of several electronic devices, including transistors and some solar cells.
Conclusion
Intrinsic and extrinsic semiconductors are fundamental to modern electronics. An intrinsic semiconductor is pure and has a low conductivity, while extrinsic semiconductors have been doped with impurities that alter their electrical properties for increased conductivity. This increase in conductivity is due to the regulation of electrons and holes within the semiconductor, which is dependent on the type of dopant used. Extrinsic semiconductors are key building blocks of several electronic devices and are important in the continued growth of technology.