Impurities in Electrons: Both silicon and germanium belong to group 14 of the periodic table, and have four valence electrons each. When silicon semiconductor or germanium is doped with an element from Group 15, such as, P, As, Sb or Bi, one extra electron per dopant atom gets introduced into the lattice. Semiconductor these extra electrons become de localized and enhance the conductivity of silicon n and p.
Silicon doped with a Group 15 element is called an n-type semiconductor. In n-type semiconductors, electricity is carried by the de localised free electrons. The letter n comes from negative: electrons being negatively charged.
Electron-deficient impurities: Doping pure silicon with a group 13 element, such as, B, Al ,Ga and In produces a lattice in which a four valence electron atoms (Si) are replaced by equal number atoms of the Group 13 elements consisting of only three valence electrons. This electron causes an electron vacancy or electron hole in the system.
Doping meaning an electron from the neighbouring atom jumps into an electron hole, creating an electron hole at its original position. These holes thus appear to move through the lattice like a positive charge in a direction opposite to that of the electrons. This electron causes an electron hole at its original position. These holes thus appear to move through the lattice like a positive charge in a direction apposite to that of the electrons. This electron causes an electron s.
The substances like silicon, germanium which have poor electrical conductance as low temperature but the conductance increases with the increase in temperature are called as semiconductors.
Their conductivity lies between metallic conductors and insulators.
The energy difference between valence band and conduction band is relatively small, hence the electrons from valence band can be excited to conduction band by heating.