conductor\semiconductor\insulator\energy_band_gap_theory

conductor\semiconductor\insulator\energy_ band_gap_theory

Metal(conductor) - They posses very low resistivity (high conductivity) .
Or Which type of material easily electric current passes through it.
   Ex-Gold(Au), silver(Ag), copper(Cu) ,Aluminium(Al) etc.
            Note-Silver is the best conductor of electricity.
Insulator –They have high resistivity (low conductivity).
or which type of material electric current does not passes through it. Ex-rubber, plastics, wood etc.
Semiconductor -It is a material which electrical current partial passes through it.
They have resistivity or conductivity intermediate to metal(conductor)and insulator.
     EX- 1. Elemental Semiconductor: Si and Ge.
             2.compound semiconductor:
                              inorganic -Cds , GaAs , CdSe ,InP etc.
                              organic – Anthracene , doped pthalocyanines etc
                              organic polymers-polypyrrole,polyaniline etc.
Note-
what is resistance?
which is opposes the flow of magnitude of electric current is called resistance.it's denoted by R.and SI unit is ohm(Ω).
what is Resistivity?
resistivity is the property of the material which defines the resistance of the material having specific dimension.

• it's denoted by ρ (rho).
• it's SI unit is Ω⋅m
• formula -here A is cross section area,L length of object

On the basic of energy band theory- 

According to Bohr’s theory, every shell of an atom contains a

 discrete amount of energy at different levels. Energy band theory 

explains the interaction of electrons between the outermost shell 

and the innermost shell. Based on the energy band theory, there are 

three different energy bands:

1.Valence band

2.Forbidden energy gap

3.Conduction band

Valence band –The energy band which includes the energy levels of

the valence electrons is called valance band.

forbidden energy gap(Eg )-The gap between the top of the valence 

band and bottom of the conduction band is called band gap or

 forbidden energy gap.

conduction band-The energy band above the valence band is called 

conduction band.

              

Insulator-which have band gap is more than 3eV(Eg>3eV).

Semiconductor-which have band gap is less than 3eV(Eg<3eV).

     conductor- conduction band and valence band is overlapped . here no band gap.

There are two type of semiconductor.

Intrinsic semiconductor- An intrinsic(pure) semiconductor, also called an undoped semiconductor or i-type semiconductor, is a pure semiconductor without any significant dopant species present.Ex- Si,Ge etc

      structure in 3 D form

           structure in 2 D form

Extrinsic Semiconductor-when a small amount , say , a few parts per million (ppm),of a suitable impurity is added  to the pure semiconductor , the conductivity of semiconductor is increases

   There are two types .

        1. n-type = electron majority charge carrier, hole is minority

                       charge carrier . i.e (Ne>Nh)

       

      2.P-type = hole is majority charge carrier, electron is 

               minority charge carrier. i.e (Nh>Ne)