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1. 1 ENGINEERING PHYSICS
Mr. Gouri Kumar Sahu
Sr. Lecturer in Physics.
1 ENGINEERING PHYSICS
Mr. Gouri Kumar Sahu
Sr. Lecturer in Physics.
ENGINERING PHYSICSENGINERING PHYSICSENGINERING PHYSICSENGINERING PHYSICSENGINERING PHYSICSENGINERING PHYSICSENGINERING PHYSICSENGINERING PHYSICS
Mr. Gouri Kumar Sahu
Senior Lecturer in Physics
C.U. T. M.

2. 2 ENGINEERING PHYSICS
Mr. Gouri Kumar Sahu
Sr. Lecturer in Physics.
2 ENGINEERING PHYSICS
Mr. Gouri Kumar Sahu
Sr. Lecturer in Physics.
SESSION-10
10.1 Extrinsic semiconductors
The semiconductors in which some impurity atoms are
embedded
Doping: Doping is the incorporation of [substitutional]
impurities into a semiconductor according to our requirements.
Impurities change the conductivity of the material so that it can
be fabricated into a device
Extrinsic semi conductors are basically of two types:
1. P-type semi conductors
2. N-type semi conductors

3. 3 ENGINEERING PHYSICS
Mr. Gouri Kumar Sahu
Sr. Lecturer in Physics.
3 ENGINEERING PHYSICS
Mr. Gouri Kumar Sahu
Sr. Lecturer in Physics.
SESSION-10
10.2 N-type Semi conductors
– Semiconductors doped by donor atoms( Penta-valent ) are
called n-type semiconductors
Let us consider a Silicon atom doped with donor atom.
– Substitute one Si (Group IV) atom with a Group V atom (e.g.
As or P)
– Si atoms have four valence electrons that participate in
covalent bonding
– When a Group V atom replaces a Si atom, it will use four of
its electrons to form the covalent bonding

4. 4 ENGINEERING PHYSICS
Mr. Gouri Kumar Sahu
Sr. Lecturer in Physics.
4 ENGINEERING PHYSICS
Mr. Gouri Kumar Sahu
Sr. Lecturer in Physics.
SESSION-10
10.2 N-type Semi conductors
The remaining electron will not be
very tightly bound, and can be
easily ionized at T > 0K
Ionized electron is free to conduct
– In term of the band structure,
this electron is now in the
conduction band
Such Group V impurities are called
Donors, since they “donate”
electrons into the Conduction
Band

5. 5 ENGINEERING PHYSICS
Mr. Gouri Kumar Sahu
Sr. Lecturer in Physics.
5 ENGINEERING PHYSICS
Mr. Gouri Kumar Sahu
Sr. Lecturer in Physics.
SESSION-10
10.2 N-type Semi conductors
Donors: Energy Levels
The Band Structure View
– Such impurities “create” an
energy level within the band gap,
close to the conduction band
A donor is similar to a hydrogen atom
– A positive charge with a single
electron within its potential
– Such impurities are called
hydrogenic donors
– They create so-called “shallow”
levels - the levels that are very
close to the conduction band, so
the energy required to ionize the
atom is small and a sizable
fraction of donor atoms will be
ionized at room temperature

6. 6 ENGINEERING PHYSICS
Mr. Gouri Kumar Sahu
Sr. Lecturer in Physics.
6 ENGINEERING PHYSICS
Mr. Gouri Kumar Sahu
Sr. Lecturer in Physics.
SESSION-10
10.2 N-type Semi conductors
Donors: Energy Levels
The Band Structure View
– Such impurities “create” an
energy level within the band gap,
close to the conduction band
A donor is similar to a hydrogen atom
– A positive charge with a single
electron within its potential
– Such impurities are called
hydrogenic donors
– They create so-called “shallow”
levels - the levels that are very
close to the conduction band, so
the energy required to ionize the
atom is small and a sizable
fraction of donor atoms will be
ionized at room temperature

7. 7 ENGINEERING PHYSICS
Mr. Gouri Kumar Sahu
Sr. Lecturer in Physics.
7 ENGINEERING PHYSICS
Mr. Gouri Kumar Sahu
Sr. Lecturer in Physics.
SESSION-10
10.2 N-type Semi conductors
This crystal has been doped with a pentavalent impurity.
The free electrons in n type silicon support the flow of
current. So, electrons are majority charge carriers

8. 8 ENGINEERING PHYSICS
Mr. Gouri Kumar Sahu
Sr. Lecturer in Physics.
8 ENGINEERING PHYSICS
Mr. Gouri Kumar Sahu
Sr. Lecturer in Physics.
END OF SESSION -10
SESSION-10
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