Semiconducting materials

Semiconducting materials are those whose conductivity properties lie between conductors and insulators. Both insulators and semiconductors have energy between conduction band and valence band whereas in conductors energy gap is forbidden and conduction band and valence band overlaps. In insulators, valence band is completely filled while conduction band is entirely empty. Energy gap is large of the order of 3-7 eV. In insulators, valence electrons are very tightly bounded to the nuclei and requires very large electric field to free them from the attraction of nuclei. Diamond is a perfect insulator. Forbidden energy gap is around 1 eV in semiconductors. Silicon, Germanium, Graphite, GaAs etc. are examples of semiconducting materials. Semiconducting materials are widely used in amplifiers, rectifiers, power engineering and telecommunication engineering. Intrinsic semiconductor is a pure semiconductor. Extrinsic semiconductors are formed by adding impurity by the process of doping. At room temperature, energy gap of Silicon is 0.72 eV and Germanium 1.1 eV. Electron mobility is 2.5 and hole mobility 2.7 for Silicon. For Germanium, electron mobility is 1.66 and hole mobility 2.33. Semiconductor resistivity is affected by factors like temperature, voltage, electric field, illumination and impurities. GaAs is a direct bandgap semiconductor, where recombination of electrons and holes possible. This recombination results in light. This technology is employed in light emitting diodes (LED) and laser diodes.