An extrinsic semiconductor is a semiconductor that has been doped with a specific impurity that has the ability to profoundly alter its electrical properties, making it ideal for electronic (diodes, transistors, etc.) or optoelectronic applications. (light emitters and detectors).
A tiny amount of any suitable impurity is added to a pure material in this process, increasing its conductivity many times over. An extrinsic semiconductor is also known as impurity semiconductor or doped semiconductor.
The procedure of adding impurities is referred to as doping, and the atoms used as an impurity are referred to as dopants. The dopant added to the material is selected so that the pure semiconductor’s original lattice is not distorted.
Furthermore, the dopants fill only a few of the sites in the original semiconductor’s crystal, and the size of the dopant must be nearly equal to the size of the semiconductor atoms.
Two kinds of dopants are used in the process of doping a material such as tetravalent Si or Ge:
- Pentavalent elements, or atoms with valency 5, include arsenic (As), phosphorus (Pi), antimony (Sb), and others.
- Trivalent elements, or atoms with valency 3; for example, indium (In), aluminum (Al), boron (B), and so on.
A P – type semiconductor is an intrinsic semiconductor (like Si) to which an acceptor impurity (such as boron B in Si) has been deliberately added.
These impurities are known as acceptors because, once inserted into the crystalline lattice, they lack one or more electrons required for complete bonding with the remainder of the crystal.
Dopant density is always far greater than intrinsic carrier density in external semiconductors: NA>>ni. The hole density in a p-type material is then near the dopant density NA.
Also Read: What is Amorphous Semiconductor?
A N – Type semiconductor is an intrinsic semiconductor (e.g., silicon Si) with a deliberately introduced donor impurity (e.g., arsenic As in Si or Si in GaAs). Donor impurities are so named because they must contribute an additional electron to the conduction band in order to form all of the bonds with neighboring atoms.