Energy Band Theory

ELECTRONICS 

Is the branch of physics that deals with the emission and effects of electrons in materials.

  

CONDUCTORS, INSULATORS AND SEMICONDUCTORS

Materials can be classified as insulators, conductors and semiconductors depending to their electric conductivity. 

INSULATORS

Are materials which do not flow of electrical charges through it.

Examples of insulators are glass, mica, paraffin, hard rubber and plastics.

  

CONDUCTORS

Are materials which allow flow of electric charges through it. Examples of conductors are metals, and some non – metals such as graphite (carbon). Metals like Aluminium and copper wires

  

SEMICONDUCTORS

It is a substance with conduction properties between conductors (metals) and insulators.

 OR

Are material with an electrical conductance that is intermediate between that of an insulator and a conductor.

A semiconductor behaves as an insulator at very temperature but has a significant electrical conductance at room temperature.

Examples of semi-conductor are silicon, germanium, selenium, cadmium sulfide and gallium arsenide. Most common used semiconductors are Silicon and Germanium

  

ENERGY BANDS 

Is the series of allowed and forbidden energy bands that it contains.

  

ENERGY BAND THEORY 

Theoretical modal describing the states of electrons in solid materials that can have values of energy only within certain specific ranges

The energy band theory proposes the existence of continuous ranges of energy values (energy bands) which electrons may occupy (allowed) or may not occupy (forbidden). 

VALENCE BAND

Is the highest range of electron energies where electrons are normally present at the absolute zero temperature.

CONDUCTION BAND

Is the range of electron, sufficient to make the electrons free to accelerate under the influence of an applied electric field and thus constitute an electric current.

OR

Is the lowest range of vacant electronic states.

FERMI LEVEL

Is the maximum energy occupied by an electron at absolute zero temperature (0 K)

OR

Refers to the collection of electron energy levels at absolute zero temperature (0 K)

DIFFERENCES BETWEEN CONDUCTORS, SEMICONDUCTORS AND INSULATORS

CONDUCTORS	SEMICONDUCTORS	INSULATORS
(i)      Allow electric charges to flow through it at any temperature.	Have both properties of conductors and insulators.	Do not allow electric charges to flow through it any temperature.
(ii)     Conductivity, decrease in the increase of temperature.	Conductivity increase in the increase of temperature.	Temperature does not influence conductivity.
(iii)   Conduction band and valence band overlap.	Have narrow forbidden gap.	Have wide forbidden gap.

Note:-

At absolute zero temperature semiconductors is an insulator and it is conductor at room temperature.