Semiconductors and Doping

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

TYPES OF SEMICONDUCTORS

                                       i.            Intrinsic semiconductor.

                                     ii.            Extrinsic semiconductor.

INTRINSIC SEMICONDUCTORS

Are pure semiconductors that conductivity increases with the increase in temperature.

EXTRINSIC SEMICONDUCTORS

Are semiconductors that have been doped with impurities to modify the number of free charges carriers present.

                                 i.            N - type semiconductors.

                               ii.            P- type semiconductors

MECHANISM OF DOPING SEMICONDUCTORS

DOPING

Is the process of adding impurity atoms to a pure semiconductors crystal. 

DOPANTS

Are substances (impurity atoms) added to a pure semiconductor to alter its conductivity properties.                                                                                                                            

PRODUCTION OF N – TYPE SEMICONDUCTORS 

N- type semiconductors are semiconductors where the majority carriers are electrons .

Are produced when pure semiconductor added by a Pentavalent atom such as Phosphorus (P), Arsenic (As), Antimony (Sb) and Bismuth (Bi)

Impurity atoms producing n – type semiconductors are called DONOR” because donate electrons during doping.

Each of the four electrons of the silicon of the outer most shell is covalently bonded to one of the four adjacent pentavalent atom and one exited into the conduction band.

The majority carriers in n - type semiconductor are electrons.

PRODUCTION OF P – TYPE SEMICONDUCTORS 

P- type semiconductors are semiconductors where the majority carriers are holes.

Are produced when pure semiconductor added by a trivalent atom such as Boron (B), Aluminium (Al), Gallium (Ga), Indium (In) and Nitrogen (N)

Impurity atoms producing P – type semiconductors are called “ACCEPTOR” because creates a hole during doping.

The addition of trivalent impurities such as Boron, Aluminium or Gallium to an intrinsic semiconductor creates deficiencies of valence electrons, called “Holes”

The majority carriers in P - type semiconductor are Holes.