This document discusses semiconductors and is presented by Mr. Gouri Kumar Sahu, a senior lecturer in physics. It covers different types of semiconductors including elemental, compound, ternary and quaternary semiconductors. Semiconductors are classified as either pure/intrinsic or doped/extrinsic. Pure semiconductors have a small number of electrons that participate in conduction due to thermal energy. This leaves behind holes which act as positively charged carriers. Examples given are silicon and germanium.

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-9
9.1 Semiconductors
Elemental Semiconductors-each atom is of the same type such
as Ge, Si
– Compound semiconductors are made of two or more elements.
Common examples are GaAs or InP.
Belong to the III-V semiconductors
Ternary semiconductors: Al x Ga 1-x As
Quaternary materials :Ga x In (1-x) As y P (1-y)

3. 3 ENGINEERING PHYSICS
Mr. Gouri Kumar Sahu
Sr. Lecturer in Physics.
3 ENGINEERING PHYSICS
Mr. Gouri Kumar Sahu
Sr. Lecturer in Physics.
SESSION-9
9.2 Classification of Semiconductors
Semiconductors are of two types:
1. Pure or intrinsic semiconductors
2. Doped or extrinsic semiconductors

4. 4 ENGINEERING PHYSICS
Mr. Gouri Kumar Sahu
Sr. Lecturer in Physics.
4 ENGINEERING PHYSICS
Mr. Gouri Kumar Sahu
Sr. Lecturer in Physics.
SESSION-9
9.3Pure or intrinsic semiconductors
Intrinsic semiconductors: pure semiconductor material.
Elemental and compound semiconductors can be intrinsic semiconductors.
At room temperature, the thermal energy of the atoms allow a small number
of the electrons to participate in the conduction process.
The resistance of the material decreases with temperature.
When an electron gains enough energy to escape the electrostatic attraction
of its parent atom, it leaves behind a vacancy which may be filled be another
electron.
The vacancy produced can be thought of as a second carrier of positive
charge known as ‘hole’.

5. 5 ENGINEERING PHYSICS
Mr. Gouri Kumar Sahu
Sr. Lecturer in Physics.
5 ENGINEERING PHYSICS
Mr. Gouri Kumar Sahu
Sr. Lecturer in Physics.
SESSION-9
9.3 Pure or intrinsic semiconductors
Consider nominally pure
semiconductor at T = 0 K
There is no electrons in the
conduction band
At T > 0 K a small fraction of
electrons is thermally excited
into the conduction band,
“leaving” the same number of
holes in the valence band

6. 6 ENGINEERING PHYSICS
Mr. Gouri Kumar Sahu
Sr. Lecturer in Physics.
6 ENGINEERING PHYSICS
Mr. Gouri Kumar Sahu
Sr. Lecturer in Physics.
SESSION-9
9.3 Pure or intrinsic semiconductors
Electrons and holes contribute to
the current when a voltage is
applied
Let’s take EV = 0, then EC = EG
The number of electrons equals
the number of holes, ne = nh
The Fermi level lies in the middle
of the band gap

7. 7 ENGINEERING PHYSICS
Mr. Gouri Kumar Sahu
Sr. Lecturer in Physics.
7 ENGINEERING PHYSICS
Mr. Gouri Kumar Sahu
Sr. Lecturer in Physics.
SESSION-9
9.3 Pure or intrinsic semiconductors
Examples of the intrinsic
semiconductors=silicon and
germanium
Electronic configuration:
Germanium -1s22s22p63s23p6
3d104s24p2
Silicon: 1s2 2s2 2p6 3s2 3p2
These four valance electrons will
form covalent bonds, with the
neighbouring electrons of the
germanium atoms

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 -9
SESSION-9
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