We know electronic devices have electronic and hole currents. The semiconductor materials have free electrons between their atoms. Every free electron leaves a hole behind it.These free electrons contribute in electricity. We can increase the number of free electrons or holes by adding a little amount of other elements in intrinsic (pure) form of semiconductor material (i.e Si or Ge). This also increases the conductivity of semiconductors.
What is Doping?
Doping is the process of adding some impurity in the semiconductor material.
A semiconductor material in its pure form is called intrinsic semiconductor. (See fig-1)
Fig-1: Intrinsic (Pure) form of Si
After adding impurity semiconductor material loses its intrinsic or pure form. This is known as extrinsic semiconductor. All p type and n type semiconductors are extrinsic semiconductors.
N type Semiconductor
Silicon (Si) is tetravalent atom.It has 4 electrons in the valence shell. It makes 4 covalent bonds with other Si atoms surrounding it as shown in fig-1 above.(see how do electronic devices work). We can increase the number of free electrons in intrinsic Si by adding a little amount of pentavalent atoms such as Arsenic (As), Bismuth (Bi), Antimony (Sb) etc. The pentavalent atoms have 5 electrons in their valence shell.
The 4 electrons of pentavalent atom make covalent bonds with other 4 Si atoms. But one electron in the valence shell is free. This electron goes into conduction band because it does not make any bond. (See fig-2)
Fig-2: N-Type Semiconductor
At any instant the piece of silicon material already have some free electrons in the conduction band. This impurity adds more electrons in the conduction band. As the number of electrons are more as compared to holes so this is called N-type semiconductor.
Majority Carriers: Free electrons are the majority carriers in n-type semiconductors
Minority Carriers: the number of holes are less as compared to electrons in n-type so the minority carriers are holes
P type semiconductor
Just like N type semiconductor where we add impurity from pentavalent atoms. In order to make p type semiconductor we add impurity from trivalent atoms such as indium (In), boron (B) etc. The trivalent atoms have three electrons in their valence shell. The three electrons make covalent bonds with other Si atoms surrounding it. Where as 4th bond leaves a whole. (See Fig-3)
Fig-3: P-type Semiconductor