Semiconductor Metal and Insulator Energy Band Diagram
At first, you have to know Insulators, Semiconductors & Conductors(Metal) regarding electrical conductivity theory & property by Energy Band. Electrical conduction properties of insulators almost NIL. No current could flow across insulators. Electrical conduction property of Metal is very high.A Huge amount of current could flow across Metal, so Metal is known as Conductor. Electrical current conductivity features and characteristics of Semiconductors is to exist between insulator & metal conductor, mean electrical conduction of semiconductor is greater than insulator and less than a metal conductor.we obtain medium level current flow across semiconductors.
Energy Band Diagram is explained by semiconductor physics & solid state physics:-
Energy Band Electrical Conductivity of Metals: Current conduction in Metals is opposite direction of motion of the free electron.Conduction Band & Valence Band are overlapped mutually in metal.Difference between Conduction Band & Valence Band is called Forbidden Bandgap. Band Gap does not exist so clearly, no forbidden higher energies available.When an electric field is applied to the metal, then few electrons start to transfer from valence band to conduction band.At this condition state, there is highly low extra energy is required to move the electron from valence band to conduction band.Therefore, electrical conduction of metal is greatest. Examples: (iron) Fe, Cu(copper)
Energy Band Insulation Conductivity: Difference between the conduction band and valence band is very large in insulators.Mean forbidden band gap is very high almost 6eV. There is no way to generate free electrons and transfer from valence band to conduction band. So, NO electrical conduction could be obtained in insulators.This is the theory of insulation. Example, Diamond.
Difference between the conduction band and valence band is small in semiconductors almost 1eV.The conductivity of a material is directly proportional to the concentration of free electrons.The number of free electrons in a semiconductor is more than insulator & less than a metal conductor.So, electrical conductivity is medium in semiconductor, mean more than insulator & less than metal.Practically, germanium and silicon are to be considered as a semiconductor material. Those have energy gap is 0.785eV for germanium & 1.21eV for silicon at 0 degree Kelvin. Normally, this magnitude of this energy cannot be acquired from an applied field. At low temperature, valence band remains full & conduction band remains empty. So, At low temperature, there is no sufficient thermal energy to break their covalent bond and release the free electron from their valence band. Secondarily, acquired thermal energy from heat by electrons is very low than band gap energy.So, at low-temperature germanium and silicon act as an insulator, no electrical conductivity acquired.
Normally, n-type semiconductors are preferred. Lets study, Intrinsic Semiconductors Theory
As the temperature is increased, the thermal energy breaks their covalent bond and release free electrons from their valence bands. Such exist electrons in the valence band acquire thermal energy from heat higher than the forbidden gap energy and free electrons are easily move into the conduction band. So, there is medium additional energy is required to move the electrons from valence band to conduction band. Thus, The required energy to release an electron from valence band is 0.66eV for germanium, 1.08eV for silicon and 1.58eV for gallium arsenide. Electrical conduction of semiconductor is average.
This is the difference between conductors semiconductors and insulators on the basis of energy band theory, Hence applications of the semiconductor are big.