Tag: electronic devices

In an extrinsic semiconductor, doped with an impurity. For example, an n-type semiconductor which is formed by doping n-type impurity so that number of electrons are more than the number of holes. So, the number density of holes is not equal to the number density of electrons. Because in an extrinsic semiconductor, one of the two carriers are in abundance and the other one is in majority.

In an intinsic semiconductor number density of electrons and holes are always equal. As the number of electrons generated in the conduction band is equal to the number of holes generated in the valance band.

A pure semiconductor is called an intrinsic semiconductor. It has thermally generated current carriers. Germanium and silicon are frequently used as semiconductors. The intrinsic semiconductor has no impurity added to them.

The conductivity of an extrinsic semiconductor is more than that of an intrinsic semiconductor. This is because, in an intrinsic (pure) semiconductor, the carriers are only thermally generated carriers. But in extrinsic semiconductors, which is doped with a p-type or n-type impurity to form p-type and n-type semiconductor so as to increase the number of holes or number of electrons in a semiconductor respectively. More the charge carriers, more is the conductivity.

Donor impurities are the ones that donate electrons to the semiconductor atom. For each donor atom added, there is one electron donated to the semiconductor atom. As a result, the electrons in such type of semiconductors are majority charge carriers. Therefore, this extrinsic semiconductor formed by adding donor impurities are called n-type semiconductors.

A transistor is a device which consists of a thin layer of one type of extrinsic semiconductor sandwiched between two thick layers of other types of extrinsic semiconductor. There are two types of transistors:

1. pnp transistor and,
2. npn transistor
   So, a transistor is made of extrinsic semiconductor.

A semiconductor diode consists of p-n junction having metallic contacts at both the ends. A single piece of a semiconductor material (either Si or Ge) with one portion doped with a pentavalent impurity and other portion doped with trivalent impurity behaves as a p-n junction. Means, extrinsic semiconductor or semiconductor doped with impurities of both p and n are used in p-n junction diode.

p type semiconductor has more number of holes than electrons.
P-type semiconductors are created by doping an intrinsic semiconductor with acceptor impurities like boron, aluminium and other group IIIA elements