P-Type Semiconductors

Description:

When Si or Ge crystal or intrinsic semiconductor is doped with measured quantity of trivalent impurity such as indium(In), boron (B), aluminum (Al), we get p type semiconductor.

The trivalent atom has three electrons in valence shell. Every trivalent dopant atom shares its 3 electrons with 3 neighboring Si atoms to form covalent bond. But, the bond between dopant atom and 4^th neighbor is not completed as trivalent atom has no more electron to share. Hence creating a vacancy that acts as a hole.

This hole has tendency to accept any electron in its close vicinity. For this reason, trivalent impurity is called as an acceptor type dopant.

At room temperature, an electron from neighboring atom can jump into the hole. This hole disappears and new hole is created at the position of displaced electron.

As this semiconductor has large number of holes and conductivity is because of positively charged holes, it is called p type semiconductor.

In P type semiconductor holes are majority charge carriers and electrons are minority charge carriers.

The number of holes is comparatively very large than the number of electrons.

n_h >> n_e

Though P type semiconductor has large numbers of holes, its net charge is zero.