This document is a lecture on semiconductor physics presented by Dr. Shilpa K.C. of Dr. Ambedkar Institute of Technology. It discusses energy bandgaps in semiconductors, including the differences between direct and indirect bandgap semiconductors. It also examines the band structure and energy diagrams of metals, semiconductors and insulators. Finally, it introduces the concept of holes and how their movement in the valence band allows current to flow, similar to the movement of electrons in the conduction band.

1. Dr. Ambedkar Institute of Technology
Electronics Devices (19EC31)
Class 4
Dr. Ambedkar Institute of
Technology
Dr. Shilpa K.C
Assistant
Professor
Dept. of
Electronics and
Communication
Engineering
Dr.AIT
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Prepared by Dr.Shilpa K.C, Dept of ECE

2. Dr. Ambedkar Institute of Technology
Energy Bandgap (Eg) Energy Bandgap
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Prepared by Dr.Shilpa K.C, Dept of ECE 2
Semiconductor BandGap
1.Energy difference (in electron volts)
between the top of the valence band
and the bottom of the
conduction band.
2. Type of Bandgap
• Direct Bandgap Semiconductor.
• Indirect Bandgap Semiconductor.

3. Dr. Ambedkar Institute of Technology
Direct Bandgap Semiconductor InDirect Bandgap Semiconductor
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Prepared by Dr.Shilpa K.C, Dept of ECE 3
Direct and Indirect BandGap Semiconductor

4. Dr. Ambedkar Institute of Technology
Direct and Indirect BandGap Semiconductor
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Prepared by Dr.Shilpa K.C, Dept of ECE 4
The material for which maximum of valence band and
minimum of conduction band donot occur at the same
value of k, k is Propogation Constant Ex. Si, Ge
The material for which maximum of valence band and
minimum of conduction band lie for same value of k ,
k is Propogation constant Ex.GaAs, GaN

5. Dr. Ambedkar Institute of Technology
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Direct and Indirect BandGap Semiconductor
E-k Diagrams

6. Dr. Ambedkar Institute of Technology
Direct Bandgap Semiconductor
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Prepared by Dr.Shilpa K.C, Dept of ECE 6
Direct and Indirect BandGap Semiconductor
1. Electrons falling from conduction band to an
Valence Band gives of lights(photon)
This process is called “ Recombination”.
2. Examples GaAs (Gallium Arsenide)
GaN (Gallium Nitride).
3. Examples light-emitting diodes (LEDs), and
laser diodes

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Energy Band Diagram

8. Dr. Ambedkar Institute of Technology
Insulator
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Metals, Semiconductors and Insulators
1. In Insulator - the Energy BandGap
(Eg ) is wider between Conduction
Band and Valence Band.
Diamond -- Eg = 5eV
2. If electric field applied, the electrons
in Valence Band (VB) cannot reach
Conduction Band.
Energy Diagram of Insulator

9. Dr. Ambedkar Institute of Technology
Metals
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Metals, Semiconductors and Insulators
Energy Diagram of Metals
1. In Metals, valence band and
conduction band overlap each
other. Therefore, there is no
forbidden gap in a conductor or
partially filled conduction band
2. A small amount of applied external
energy provides enough energy for
the valence band electrons to move
in to conduction band.

10. Dr. Ambedkar Institute of Technology
Semiconductor
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Prepared by Dr.Shilpa K.C, Dept of ECE 10
Metals, Semiconductors and Insulators
Energy Diagram of Semiconductor
1. In Semiconductor - the Energy
BandGap (Eg ) is smaller between
Conduction Band and Valence
Band than in insulators.
Si -- Eg = 1.1eV
2. At 0K, Semiconductor behave as
an Insulator.
3. At T> 0K, Semiconductor behave
as an Metal

11. Dr. Ambedkar Institute of Technology
Semiconductor
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Prepared by Dr.Shilpa K.C, Dept of ECE 11
Metals, Semiconductors and Insulators
Energy Diagram of Semiconductor
1. A small fraction of the electrons is
thermally excited into the
conduction band. These electrons
carry current just as in metals.
2. The smaller the gap the more
electrons in conduction band at a
given temperature.
3. Resistivity decreases with
temperature due to higher
concentration of electrons in
conduction band

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The Energy Band of
Metals, Semiconductors and Insulators

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Electrons and Holes

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The Valence Band in the Semiconductor
Valence Band in Semiconductor
• The valence band of with all
states filled (electrons) .
• The electron with wave vector kj
is matched with opposite wave
vector –kj .
• There is no net current in band
unless an electron is removed.

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The concept of Hole

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Mechanism of Hole movement
Hole Movement

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Movement of Holes in Valence Band
Electrons and Hole
directions

18. Dr. Ambedkar Institute of Technology
Thank You
Dr. Ambedkar
Institute of Technology
HAVE A NICE DAY
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Prepared by Dr.Shilpa K.C, Dept of ECE