23-01-2013, 12:06 PM
Types of Semiconductors
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Intrinsic Semiconductor
Semiconductor in pure form is known as Intrinsic Semiconductor.
Ex. Pure Germanium, Pure Silicon.
At room temp. no of electrons equal to no. of holes.
Extrinsic Semiconductor
When we add an impurity to pure semiconductor to increase the charge carriers then it becomes an Extrinsic Semiconductor.
In extrinsic semiconductor without breaking the covalent bonds we can increase the charge carriers.
N-type Semiconductor
Arsenic atom has 5 valence electrons.
Fifth electron is superfluous, becomes free electron and enters into conduction band.
Therefore pentavalent impurity donates one electron and becomes positive donor ion. Pentavalent impurity known as donor.
P-type Semiconductor
Gallium atom has 3 valence electrons.
It makes covalent bonds with adjacent three electrons of silicon atom.
There is a deficiency of one covalent bond and creates a hole.
Therefore trivalent impurity accepts one electron and becomes negative acceptor ion. Trivalent impurity known as acceptor.
Carriers in P-type Semiconductor
In addition to this, some of the covalent bonds break due temperature and electron hole pairs generates.
Holes are majority carriers and electrons are minority carriers.
Formation of pn diode
A P-N junction is formed , if donor impurities are introduced into one side ,and acceptor impurities
Into other side of a single crystal of semiconductor
Initially there are P type carriers to the left side of the junction and N type carriers to the right side as shown in figure 1
P-N Junction Diode- Reverse Bias
External bias voltage applied with +ve on n-side, −ve on p- side.
This RB bias aids the internal field.
The majority carriers i.e. holes on p-side, the electrons on n- side attracted by the negative and positive terminal of the supply respectively.
This widens the depletion layer width and strengthens the barrier potential.
Few hole-electron pairs are created due to thermal agitation (minority carriers).
As a result small current flows across the junction called as reverse saturation current I0 (uA for Germanium, nA for Silicon).
Behaves as a high impedance element.
[attachment=48145]
Intrinsic Semiconductor
Semiconductor in pure form is known as Intrinsic Semiconductor.
Ex. Pure Germanium, Pure Silicon.
At room temp. no of electrons equal to no. of holes.
Extrinsic Semiconductor
When we add an impurity to pure semiconductor to increase the charge carriers then it becomes an Extrinsic Semiconductor.
In extrinsic semiconductor without breaking the covalent bonds we can increase the charge carriers.
N-type Semiconductor
Arsenic atom has 5 valence electrons.
Fifth electron is superfluous, becomes free electron and enters into conduction band.
Therefore pentavalent impurity donates one electron and becomes positive donor ion. Pentavalent impurity known as donor.
P-type Semiconductor
Gallium atom has 3 valence electrons.
It makes covalent bonds with adjacent three electrons of silicon atom.
There is a deficiency of one covalent bond and creates a hole.
Therefore trivalent impurity accepts one electron and becomes negative acceptor ion. Trivalent impurity known as acceptor.
Carriers in P-type Semiconductor
In addition to this, some of the covalent bonds break due temperature and electron hole pairs generates.
Holes are majority carriers and electrons are minority carriers.
Formation of pn diode
A P-N junction is formed , if donor impurities are introduced into one side ,and acceptor impurities
Into other side of a single crystal of semiconductor
Initially there are P type carriers to the left side of the junction and N type carriers to the right side as shown in figure 1
P-N Junction Diode- Reverse Bias
External bias voltage applied with +ve on n-side, −ve on p- side.
This RB bias aids the internal field.
The majority carriers i.e. holes on p-side, the electrons on n- side attracted by the negative and positive terminal of the supply respectively.
This widens the depletion layer width and strengthens the barrier potential.
Few hole-electron pairs are created due to thermal agitation (minority carriers).
As a result small current flows across the junction called as reverse saturation current I0 (uA for Germanium, nA for Silicon).
Behaves as a high impedance element.