Semiconductor Electronics: Materials, Devices And Simple Circuits
Extrinsic Semiconductor
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Metals − Possess very low resistivity (or high conductivity)
Their resistivities lie in the range: (10–2 Ω m to 10–8 Ω m)
Their conductivities lie in the range: (102 S m–1 to 108 S m–1) -
Semi-conductors − Possess resistivity or conductivity intermediate to metals and insulators
Their resistivities lie in the range: (10–5 Ω m to 106 Ω m)
Their conductivities lie in the range: (105 S m–1 to 10–6 S m–1) -
Insulators − Possess high resistivity (or low conductivity)
Their resistivities lie in the range: (1011 Ω m to 1019 Ω m)
Their conductivities lie in the range: (10–11 S m–1 to 10–19 S m–1) -
Semi-conductors are of two types:
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Elemental semi-conductor − Example: Si and Ge
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Compound semi-conductor − Examples:
• Organic: doped pthalocyanines, anthracene, etc.
• Organic polymers: polypyrrole, polythiophene, etc.
• Inorganic: CdS, GaAs, CdSe, etc.
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Energy band diagram of metals or conductors
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Conduction band is partially filled and the valence band is partially empty or the conduction and valence band overlap.
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Due to overlap, electrons can easily move into the conduction band. This situation makes a large number of electrons available for electrical conduction.
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When the valence band is partially empty, electrons from their lower levels can move to higher levels making conduction possible.
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Energy band diagram for insulators
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Large band gap Eg exists. (Eg > 3 eV)
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Since there are no electrons in the conduction band, no electrical conduction is possible.
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The electron cannot be excited from the valence band to the conduction band by thermal excitation.
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Energy band diagram for semi-conductors
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Energy band gap Eg is small. (Eg < 3 eV)
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At room temperature, some electrons from valence band cross the energy gap and enter the conduction band.
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Metals − Possess very low resistivity (or high conductivity)
Their resistivities lie in the range: (10–2 Ω m to 10–8 Ω m)
Their conductivities lie in the range: (102 S m–1 to 108 S m–1) -
Semi-conductors − Possess resistivity or conductivity intermediate to metals and insulators
Their resistivities lie in the range: (10–5 Ω m to 106 Ω m)
Their conductivities lie in the range: (105 S m–1 to 10–6 S m–1) -
Insulators − Possess high resistivity (or low conductivity)
Their resistivities lie in the range: (1011 Ω m to 1019 Ω m)
Their conductivities lie in the range: (10–11 S m–1 to 10–19 S m–1) -
Semi-conductors are of two types:
-
Elemental semi-conductor − Example: Si and Ge
-
Compound semi-conductor − Examples:
• Organic: doped pthalocyanines, anthracene, etc.
• Organic polymers: polypyrrole, polythiophene, etc.
• Inorganic: CdS, GaAs, CdSe, etc.
-
Energy band diagram of metals or conductors
-
Conduction band is partially filled and the valence band is partially empty or the conduction and valence band overlap.
-
Due to overlap, electrons can easily move into the conduction band. This situation makes a large number of electrons available for electrical conduction.
-
When the valence band is partially empty, electrons from their lower levels can move to higher levels making conduction possible.
-
Energy band diagram for insulators
-
Large band gap Eg exists. (Eg > 3 eV)
-
Since there are no electrons in the conduction band, no electrical conduction is possible.
-
The electron cannot be excited from the valence band to the conduction band by thermal excitation.
-
Energy band diagram for semi-conductors
-
Energy band gap Eg is small. (Eg < 3 eV)
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At room temperature, some electrons from valence band cross the energy gap and enter the conduction band.
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A pure semi-conductor which is free of every impurity is called intrinsic semi-conductor.
Example − Ge and Si
The crystal structure of Ge/ Si in 2-D is shown above.
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In intrinsic semi-conductors, the number of free electrons ne is equal to the number of holes nh.
That is, ne = nh = ni
Where,
ni → Intrinsic carrier concentration
- An intrinsic semi-conductor will behave similar to an insulator at T = 0 K
- Eg is the energy band gap between valence band and conduction band.
- The value of Eg for Si and Ge are 1.1 eV and 0.7 eV, respectively.
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A pure semi-conductor which is free of every impurity is called intrinsic semi-conductor.
Example − Ge and Si
The crystal structure of Ge/ Si in 2-D is shown above.
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In intrinsic semi-conductors, the number of free electrons ne is equal to the number of holes nh.
That is, ne = nh = ni
Where,
ni → Intrinsic carrier concentration
- An intrinsic semi-conductor will behave similar to an insulator at T = 0 K
- Eg is the energy band gap between valence band and conduction band.
- The value of Eg for Si and Ge are 1.1 eV and 0.7 eV, respectively.
A semi-conductor with impurity atom added to it is called extrinsic semi-conductor.
Two types of extrinsic semi-conductors are:
n-type semi-conductor
p-type semi-conductor
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n-type semi-conductor
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Doped with pentavalent atoms such as arsenic or phosphorous or antimony or bismuth
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