Its easy and simple for Students to learn their desired topics.

1. Intrinsic and Extrinsic Semiconductor:
N – type and P – type Semiconductor:
Forward Biased and Reverse Biased.
PRESENTED BY :
• HAMID RAZA (BSP01183003)
• HAFIZ MUHAMMAD SAJJAD HUSSAIN (BSP01183067)
• ZULFIQAR MUSHTAQ (BSP01183013)
• OBAID UR REHMAN (BSP01183010)

2. Brief history of Semiconductor:
 Introduction:
The term semiconductor was first used by
Michael Faraday in 1833.
 Who noticed that resistance of silver sulfide
Decreases with the temperature.

3. Semiconductor:
 Semiconductor are materials whose electronic properties are
intermediate between those of Metals and Insulators.
 Example:
Silicon and Germanium etc.
 They have conductivity range of 10-4 to 10+4
 The interesting feature about semiconductor is that they are bipolar
and current is transported by two charge carriers of opposite sign.

4. Type of Semiconductor:

5. Intrinsic Semiconductor:
 A semiconductor which does not have any kind of impurities behave as an
Insulators at 0K and behave as a Conductors at higher temperature is known as
Intrinsic Semiconductor.
 Germanium and Silicon are the best examples
of intrinsic semiconductors.
 They posses diamond cubic crystalline structure.

6. Intrinsic semiconductors energy band
diagram:
 In intrinsic semiconductors the numbers of excited electron and the numbers of
holes are equal.
n = p
 The fermi level for the intrinsic semiconductors
lies in the middle of forbidden energy gap.

7. Extrinsic Semiconductor:
 The Extrinsic Semiconductors are those in which impurities of large
quantity are present. Usually, the impurities can be either 3rd group
elements or 5th group elements.
 Based on the impurities present in the extrinsic semiconductors, the
are classified into two categories.

8. Extrinsic semiconductors energy band
diagram:
 In extrinsic semiconductors, the numbers of electrons in the conduction
band and the numbers of holes in valence band are not equal.
n ≠ p
 The fermi level for the extrinsic semiconductors
lies close to the conduction band or valence band.

9. N-type Semiconductor:
 When we add a pentavalent impurity to pure semiconductor we get
n-type semiconductor.

10. N-type Semiconductor:
 Arsenic atom has 5 valance 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.

11. P-type Semiconductor:
 When we add a Trivalent impurity to pure semiconductor we get p-
type semiconductor.

12. P-type Semiconductor:
 Gallium atom has 3 valance 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.
 In addition to this, some of the covalent bonds break due
temperature and electron are minority carriers.

13. Comparison between n-type and p-type
semiconductors:
N-type
 Pentavalent impurities are added.
 Majority carriers are electrons.
 Minority carriers are holes.
 Fermi level is near the
conduction band
P-type
 Trivalent impurities are added.
 Majority carriers are holes.
 Minority carriers are electrons.
 Fermi level is near the valence
band

14. Forward Biasing:
 In forward P-type connected to positive terminal and N-
type connected to negative terminal of battery, applied
across the junction is said to be forward biased.
 Holes on P-side being positively charged particles are
repelled from the positively bias terminal and driven
towards the junction.
 The depletion region is reduced in width and barrier
potential is also reduced.

15. Reverse Biasing:
 In this bias P-type is connected to negative terminal
and N-type is connected to positive terminal of battery
junction is said to be reverse biased.
 In this biasing polarity has changed so minimum
charge will pass through depletion region(almost zero).
 The depletion region is widened.

16. Comparison:
Forward Bias
 The forward bias reduces the
strength of the potential barrier
due to which current can easily
flow.
 The Forward bias reduces the
strength of potential barrier.
 In forward biasing the voltage of
anode is greater than cathode.
 It operates as conductor
Reverse Bias
 The Reverse bias strengthens the
potential barrier and obstruct the
flow of charge carrier.
 The Reverse bias increase the
strength of the potential barrier.
 In Reverse bias the voltage of
cathode is greater than anode.
 It operates as insulator.

17. Graphical Representation:

18. Specially Designed
Application:
• Light Emitting Diodes:
The light emitting diode is a specially designed diode
which radiate light energy, when it is forward biased.
LED’s are used as small source of light or indicators
and optical fiber transmitter to send electrical signals.
Advantages of LED over filament lamp are:
• Small
• Long Life
• Economical
• High Operating Speed

19. Photodiode:
 A device which is used to convert light energy in to electrical energy
and is used to detect the intensity of light is known as photodiode
 It can detect both visible and invisible light.
 It is used in automatic switching circuits.

20. Photovoltaic Cell or Solar Cell:
 A semiconductor which converse the light energy
in to electrical energy when it is unbiased is known
as photovoltaic or solar cell.
In which incident light produces minority carriers in
the form of electron-hole pairs in p-type and
n-type regions.
Solar Cell is used for energy purposes, in satellite and
space vehicles