This document discusses key concepts related to PN junction diodes. It begins by defining a semiconductor as a material with conduction properties between metals and insulators. It then discusses intrinsic and extrinsic semiconductors, doping, and the charge carriers in pure, n-type, and p-type semiconductors. The document defines a junction diode as a structure formed by intimate contact of p-type and n-type semiconductors. It also discusses forward and reverse bias, knee voltage, reverse breakdown, Zener diodes, and their application as voltage regulators. Key diode parameters like barrier potential, reverse saturation current, static and dynamic resistance, and transition capacitance are also defined.

1. viva-voce questions
viva-voce questions
PN - JUNCTION DIODE
PN - JUNCTION DIODE

2. What is a semiconductor ?
It is a substance with conduction properties between metals and insulators.
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What is meant by intrinsic semiconductor ?
A pure semiconductor completely free from impurities is called intrinsic
semiconductor.

3. What do you mean by an extrinsic semiconductor ?
It is a semiconductor to which an impurity from group 13 or group 15 has been
added.
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What do you mean by a doped semiconductor ?
It is a semiconductor to which an impurity from group 13 or group 15 has been
added.

4. What is doping ?
It is the process of addition of impurity to a pure semiconductor in order to
alter its conduction properties.
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To which group does a (i) p-type, (ii) n type impurity belong ?
p-type impurity belongs to group 13 and n-type to group 15.

5. What are the charge carriers in a pure semiconductor.
A pure semiconductor has electrons and holes as charge carriers. Their
number densities are equal.
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What are the charge carriers in n-type semiconductor ?
In n-type semiconductor, electrons are majority charge carriers and holes are
minority charge carriers.

6. What is junction diode ?
A junction diode is formed when a p-type semiconductor is in intimate contact
with n-type semiconductor.
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What is meant by forward bias ?
A pn junction is said to be forward biased when p-region is connected to
positive terminal and n-region to the negative terminal of battery.

7. What is meant by reverse bias?
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What is knee voltage ?
A pn junction is said to be forward biased when n-region is connected to
positive terminal and p-region to the negative terminal of battery.
In a forward biased pn junction, the voltage at which there is a sudden increase
in current with a small increase in voltage is called knee voltage.

8. What do you mean by reverse breakdown ?
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What is a zener diode ?
For a certain value of reverse potential applied to a pn junction, there is a
sudden sharp increase in current. This is called reverse breakdown.
It is a diode specially designed to operate in reverse breakdown region.
The p and n regions are heavily doped and are separated by a very narrow
neutral region.

9. What is zener voltage ?
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Give an application of zener diode ?
The reverse breakdown voltage of zener diode is called zener voltage.
It is used as a voltage regulator.

10. Define the energy level in an atom?
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What is the SI unit of conductance?
Energy level in an atom is defined as the energy value of an electron in the
subshell of an atom.
SI unit of conductance is siemens (S).

11. Why n - type or penta valent impurities are called as Donor impurities?
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Why P – type or trivalent impurities are called as acceptor impurity?
n- type impurities will donate the excess negative charge carriers ( Electrons)
and therefore they are reffered to as donor impurities.
p- type impurities make available positive carriers because they create holes
which can accept electron, so these impurities are said to be as acceptor
impurity

12. What is depletion region in PN junction?
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Give the other names of depletion region?
The region around the junction from which the mobile charge carriers (
electrons and holes) are depleted is called as depletion region. since this
region has immobile ions, which are electrically charged , the depletion
region is also known as space charge region.
i). space charge region ii). Transition region

13. What is barrier potential?
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What is Reverse saturation current?
Because of the oppositely charged ions present on both sides of PN
junction an electric potential is established across the junction even
without any external voltage source which is termed as barrier potential.
The current due to the minority carriers in reverse bias is said to be reverse
saturation current. This current is independent of the value of the reverse bias
voltage.

14. Define drift current?
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When an electric field is applied across the semiconductor, the holes
move towards the negative terminal of the battery and electron move
towards the positive terminal of the battery. This drift movement of
charge carriers will result in a current termed as drift current.

15. Define the term diffusion current?
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A concentration gradient exists, if the number of either electrons or
holes is greater in one region of a semiconductor as compared to the
rest of the region. The holes and electron tend to move from region of
higher concentration to the region of lower concentration. This process
in called diffusion and the current produced due this movement is
diffusion current.

16. Define mean life time of a hole or and electron?
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The electron hole pair created due to thermal agitation woll disappear
as a result of recombination. Thus an average time for which a hole or
an electron exist before recombination can be said as the mean life time
of a hole or electron.

17. What is the static resistance of a diode?
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Static resistance R of a diode can be defined as the ratio of voltage V
across the diode to The current flowing through the diode.
R = V/ I
Where,
R - Static resistance of a diode
V - Voltage across the diode
I - current across the diode

18. Define dynamic resistance.
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Dynamic resistance of a diode can be defined as the ratio of change in
voltage across the diode to the change in current through the diode.

19. Define the term transition capacitance?
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When a PN junction is reverse biased, the depletion layer acts like a
dielectric material while P and N –type regions on either side which has
low resistance act as the plates. In this way a reverse biased PN
junction may be regarded as parallel plate capacitor and thus the
capacitance across this set up is called as the transition capacitance.

20. Thanks for Watching
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