This presentation describes to you the very basic introduction of PN junction diode. All the topics and contents are presented in such a manner that students can understand it very easily and prepare it for final exam. At the end of this presentation, a few multiple choice questions (MCQ) are also there to test your knowledge on a particular topic that would be discussed in presentation.

1. Diode Theory
Gujarat Technological University (GTU)
Branch: Electronics and Communication Engineering (ECE) Branch code : 11
Subject: Basic Electronics (3110016)
* Course would be applicable for all branches during 1st year of engineering

2. Types of semiconductor Materials
2
Intrinsic
Semiconductors
Extrinsic
P-type
N-type

3. Intrinsic Semiconductor
- Pure form of Ge and Si
- Very pure materials
- ne = nh
Types of Semiconductors
Extrinsic Semiconductor
- Impure materials
- P-type and N-type
3

4. “
4

5. P-type Semiconductors
A p-type semiconductor is an extrinsic type of
semiconductor. When a trivalent impurity (like Boron,
Aluminum etc.) is added to an intrinsic or pure
semiconductor (silicon or germanium), it is said to be a p-
type semiconductor.
Trivalent impurities such as boron (B), gallium (Ga),
indium (In), aluminum (Al) etc. are called acceptor
impurity. 5

6. P-type Semiconductors
⊹ p-type semiconductors are the impure or extrinsic
semiconductors.
⊹ Trivalent atoms are doped with intrinsic semiconductors to
produce p-type semiconductors.
⊹ Concentration of holes is greater than the concentration of
electrons in p-type semiconductors.
⊹ p-type semiconductors have greater conductivity than the
pure or intrinsic semiconductors.
6

7. N-type Semiconductors
⊹ An N-type semiconductor is a impurity mixed
semiconductor material used in electronics.
⊹ The pentavalent impure atoms
like phosphorus, arsenic, antimony or some other chemical
element are used to produce n-type semiconductors.
⊹ These impure atoms are called donor impurities because
they give free electrons to a semiconductor.
7

8. N-type semiconductor
⊹ n-type semiconductors are not the pure semiconductors.
They are extrinsic semiconductors.
⊹ To get n-type semiconductor, pentavalent atoms like Arsenic
(As), Phosphorus (P) are doped in an intrinsic semiconductor
like Si, Ge etc.
⊹ Majority carriers in n-type semiconductors are free electrons.
That means concentration of free electrons in n-type
semiconductor is greater than the concentration of holes.
8

9. 9

10. Formation of Depletion region in PN Diode
10

11. 11
Forward Biased Diode:
⊹ P-region is connected to positive terminal of battery and N-region is connected with
negative terminal.
⊹ Current flowing through forward biasing – IF (Forward current in few mA)
⊹ With increase in external vtg >>> Width of depletion region will reduce >>> Barrier
Potential decrease
⊹ RF = Forward resistance (10 to 100Ω )
⊹ VF = Vtg drop across the diode (0.7 for Si, 0.3 for Ge) (Due to barrier potential and
internal resistance)

12. 12
Reverse Biased Diode:
⊹ P-region is connected to -ve terminal of battery and N-region is connected with +ve
terminal.
⊹ Current flowing through reverse biasing – IS (Reverse current in few mA)
⊹ With increase in external vtg >>> Width of depletion region will increase >>> Barrier
Potential increase
⊹ Rr = Reverse biased resistance (few 100kΩ )

13. Fig-A – Forward biased diode Fig – b – Reverse Biased Diode
13

14. Breakdown Mechanism in Reverse Biased Diode
14

15. 15
Zener Breakdown Avalanche Breakdown
⊹ Occurs in heavily doped,
narrow depletion layers
⊹ Very strong E-field across
narrow layer (108 V/m)
⊹ Occurs due to heavy
electric field is applied
across the junction
⊹ Temp coeff -ve
⊹ Occurs in lightly doped,
wide depletion layers
⊹ E-field is not too strong
⊹ Occurs due to collision of
electrons inside PN
junction
⊹ Temp coeff +ve

16. 16
1. How many junction/s do a diode consist?
a) 0
b) 1
c) 2
d) 3
2. If the positive terminal of the battery is connected to the anode of the
diode, then it is known as
a) Forward biased
b) Reverse biased
c) Equilibrium
d) Schottky barrier
3. During reverse bias, a small current develops known as
a) Forward current
b) Reverse current
c) Reverse saturation current
d) Active current

17. 17
A PN junction has a thickness of the order
1.1 cm
2.1 mm
3.10-6 m
4.10-12 cm
In a semiconductor, current conduction is due to …
•Only holes
•Only free electrons
•Holes and free electrons
•None of the above

18. 18
A forward biased pn junction diode has a resistance of the
order of
•Ω
•kΩ
•MΩ
•None of the above
A pn junction acts as a ……….
•Controlled switch
•Bidirectional switch
•Unidirectional switch
•None of the above

19. 19

20. 20

21. 21

22. 22
Ideal Diode Equations

23. Boltzman’s Constant
⊹ k = 1.3806 ˟ 10-23 J/K
⊹ k = 8.617 ˟ 10-5 eV/K
23

24. Surface Mount Diode (SMD)
24
• Surface-mount technology (SMT) is a method in
which the electrical components are mounted
directly onto the surface of a printed circuit
board (PCB).
• Surface mounting was originally called "planar
mounting"

25. 25

26. 26
• A small outline transistor (SOT) is a family of surface
mount transistor commonly used in consumer electronics.
• The most common SOT are SOT23 variations, also
manufacturers offer the nearly identical thin small outline
transistor (TSOT) package, where lower height is important.
SOT Package

27. 27

28. Test Your knowledge on
Diode Theory

29. When PN junction is in forward bias, by
increasing the battery voltage -
A. Circuit resistance increases
B. Current through PN junction increases
C. Current through PN junction decreases
D. None of the above
29
1

30. When a PN junction is reverse biased
A. Holes and electrons tend to concentrate
towards the junction
B. The barrier tends to break down
C. Holes and electrons tend to move away
from the junction
D. None of these
30
2

31. A PN junction
A. Has low resistance in forward as well as
reverse directions
B. Has high resistance in forward as well as
reverse directions
C. Conductors in the forward direction only
D. Conducts in the reverse direction only
31
3

32. A PN junction is said to be forward-
biased when
A. The positive terminal of the battery is connected
to P-side and the negative side to the N-side
B. Junction is earthed
C. N-side is connected directly to the p-side
D. The positive terminal of the battery is connected
to N-side and the negative side to the P-side.
32
4

33. PN junction failure below 8 V is caused
primarily by
A. Avalanche breakdown
B. Zener breakdown
C. Either (a) or (b)
D. None of the above
33
5

34. How many junction/s do a diode consist?
A. 1
B. 2
C. 3
D. 0
34
6

35. During reverse bias, a small current
develops known as
A. Forward current
B. Reverse current
C. Reverse Saturation current
D. Zener current
35
7

36. If the voltage of the potential barrier is V0.
A voltage V is applied to the input, at
what moment will the barrier disappear?
A. V < V0
B. V = V0
C. V > V0
D. None
36
8

37. The most widely used semiconductor
material in an electronics devices is -
A. Germaniun
B. Silicon
C. Copper
D. Carbon
37
9

38. The leakage current of PN junction diode
is caused by -
A. Heat Energy
B. Chemical Energy
C. Barrier Potential
D. Majority carriers
38
10

39. The leakage current of PN junction diode
is caused by -
A. Heat Energy
B. Chemical Energy
C. Barrier Potential
D. Majority carriers
39
10

40. Electronics components which are made
of a semiconductor material are often
called ____ devices.
A. Silicon
B. Solid State
C. Germanium
D. Intrinsic
40
11

41. Any voltage that is connected across the
PN junction is called -
A. Barrier
B. Breakdown
C. Reverse
D. Bias
41
12

42. The area within a semiconductor diode
where no mobile current carrier exists
when it is formed is called ___ region.
A. Saturation
B. Depletion
C. Potential barrier
D. None
42
13

43. Major part of a current in an intrinsic
semiconductor is due to -
A. Conduction band electrons
B. Valence band electrons
C. Holes in valance bond
D. Thermally generated electrons
43
14

44. The process of adding impurities to a
pure semiconductor is known as -
A. Mixing
B. Refining
C. Diffusing
D. Doping
44
15

45. A forward resistance of a diode is
A. Few Ω
B. Few kΩ
C. Few MΩ
45
16

46. The arrowhead in the diode symbol
points the direction of -
A. Electron current
B. Conventional current
C. Reverse saturation current
D. None
46
17

47. When the diode current is large, the
bias is -
A. Forward
B. Inverse
C. Poor
D. Reverse
47
18

48. In reverse bias current through diode is
very ______
A. Large
B. Small
C. Moderate
D. Poor
48
19

49. Knee voltage of germanium diode is ____
than silicon diode.
A. Less
B. More
C. Very high
D. Can’t say
49
20

50. In the reverse breakdown region, the
power dissipation is -
A. Very small
B. Very high
C. Moderate
D. Can’t say
50
21

51. N-type silicon is obtained by doping
silicon with -
A. Germanium
B. Aluminium
C. Phosphorus
D. Boron
51
22

52. Consider the following type of semicondutors –
1. n-type 2. p-type
3. Intrinsic 4. Extrinsic
Which of these type of semicontuctors are
formed by doping germanium with gallium ?
A. 1 & 3
B. 2 & 4
C. 1 & 4
D. 2 & 3
52
23

53. Consider the following statements for PN
junction diode:
1. It is an active component
2. Depletion layer width decreases with forward
biasing
3. In reverse biasing case saturation current
increases with increasing temperature
Which of the statements given above are
correct?
A. 1 , 2 & 3
B. 1 & 2 only
C. 2 & 3 only
D. 1 & 3 only 53
24

54. For a germanium PN junction, the
maximum value of barrier potential is -
A. 0.3V
B. 0.7V
C. 1.3V
D. 1.7V
54
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