PN DIODE CHARACTERISTICS

1. EC 8351
Electronic Devices And
Circuits

2. Syllabus
UNIT I PN JUNCTION DEVICES
PN junction diode –structure, operation and V-I characteristics,
diffusion and transient capacitance - Rectifiers – Half Wave and Full
Wave Rectifier,– Display devices- LED, Laser diodes- Zener diode
characteristics-Zener Reverse characteristics – Zener as regulator
UNIT II TRANSISTORS
BJT, JFET, MOSFET- structure, operation, characteristics and Biasing
UJT, Thyristor and IGBT - Structure and characteristics.

3. UNIT III AMPLIFIERS
BJT small signal model – Analysis of CE, CB, CC amplifiers- Gain and
frequency response – MOSFET small signal model– Analysis of CS and
Source follower – Gain and frequency response- High frequency analysis.
UNIT IV MULTISTAGE AMPLIFIERS AND DIFFERENTIAL
AMPLIFIER
BIMOS cascade amplifier, Differential amplifier – Common mode and
Difference mode analysis – FET input stages – Single tuned amplifiers –
Gain and frequency response – Neutralization methods, power amplifiers
–Types (Qualitative analysis).
UNIT V FEEDBACK AMPLIFIERS AND OSCILLATORS
Advantages of negative feedback – voltage / current, series , Shunt
feedback –positive feedback – Condition for oscillations, phase shift –
Wien bridge, Hartley, Colpitts and Crystal oscillators.

4. Need of Electronics
Electronics is an applied form of science that deals
with electrons. It handles electric circuits
containing active elements, passive elements and other
underlying techniques making it as an important part of
engineering. The world is growing at a fast rate and it is
relevant for the technology enthusiast to upgrade with
latest changes happening in the society.

5. What is Electronics?
• “Electronics”, as the name implies relating to
electrons. The word electronics arrived from
electron mechanics (Behaviour of the electron when
it is subjected to externally applied fields).
• The definition of electronics technically says “Electronics
is an engineering branch that concerns with the flow
of current through semiconductor, gas or any form
of matter.

6. Applications of Electronics
1.Consumer Electronics
Office Gadgets, Home appliances, Audio and Video
Systems, Advanced Consumer Devices, Storage Devices
2.Industrial Electronics
Industrial automation and motion control, Machine learning,
motor drive control, Mechatronics and robotics, Power
converting technologies, Photo voltaic systems, Renewable
energy applications, Power electronics, and Biomechanics

7. • Medical applications
Stethoscope, Glucose meter, Pace Maker,etc.
• Meteorological and Oceanographic
Anemometer, Barometer, Hygrometer ,etc.
• Defence and Aerospace
Missile Launching systems, Rocket Launchers for space,Aircraft
systems, Cockpit controllers, etc.
• Automotive
Most parts of automobiles consists of electronic devices.

8. UNIT I
PN JUNCTION DEVICES

9. Types of Materials based on
conductivity

11. TYPES OF
SEMICONDUCTOR

12. Intrinsic Semiconductor
A semiconductor, which is in its extremely pure form, is known
as an intrinsic semiconductor. Silicon and germanium are the
most widely used intrinsic semiconductors.
Both silicon and germanium are
tetravalent, i.e. each has four
electrons (valence electrons) in
their outermost shell.
Each atom shares its four
valence electrons with its four
immediate neighbours, so that
each atom is involved in four
covalent bonds.

13. Intrinsic Semiconductor
semiconductor is
large number of
When the temperature of an intrinsic
increased, beyond room temperature a
electron-hole pairs are generated.
Since the electron and holes are generated in pairs so,
Free electron concentration (n) = concentration of holes (p)
= Intrinsic carrier concentration (ni)

14. Extrinsic Semiconductor
Pure semiconductors have negligible conductivity at room
temperature. To increase the conductivity of
semiconductor, some impurity is added. The
intrinsic
resulting
semiconductor is called impure or extrinsic semiconductor.
Impurities are added at the rate of ~ one atom per 106 to 1010
semiconductor atoms. The purpose of adding impurity is to
increase either the number of free electrons or holes in a
semiconductor.

15. Extrinsic Semiconductor
Two types of impurity atoms are added to the semiconductor
Atoms containing 5
valance electrons
(Pentavalent impurity atoms)
e.g. P, As, Sb, Bi
Atoms containing 3
valance electrons
(Trivalent impurity atoms)
e.g. Al, Ga, B, In
N-type semiconductor P-type semiconductor

16. Comparison of Intrinsic and
Extrinsic Semiconductor

18. PN Junction Formation

19. PN Junction Formation

20. PN Junction Formation

21. PN Junction Formation
P-Type semiconductor
having excessive holes
N-Type semiconductor
having excessive free
electrons
Junction
Acceptor
atoms
Donor
atoms

22. Charge Distribution
- +
- +
- +
P N
Positive and negative ions are
created when holes and free
electrons cross the junction and
move to the other side this charge is
called “space charge”
Diffusion
current flows
whenever P and
N materials are
joined together

23. The P-N Junction
•When initially joined
electrons from the
n-type migrate into the p-
type – less electron density
there
•When an electron fills a
hole – both the electron
and hole disappear as the
gap in the bond is filled
•This leaves a region with no free charge carriers – the depletion layer – this layer
acts as an insulator
Slide 10

24. Barrier Potential
P N
+
+
+
-
-
-
E
Depletion Region
Charges of opposite polarities establish “Electric
Field” also known as “Barrier Potential”. This
field prevents any further diffusion current
Barrier potential is also
known as “Junction
Potential” or “Diffusion
Potential”. It is denoted by Vo
Si -0.7 V
Ge-0.3 V

26. DIODE
(Formed Using P-N Junction)

27. DIODE
• A PN Junction is also called DIODE.
• Term diode from the Greek roots di , meaning 'two',
and ode, meaning 'path'.
• It is used in various electronics application.
• We will use this diode to form transistor and FET.
• Same diode are also used to form logic circuit

28. P-N Junction
diode

29. DIODE SYMBOL, SIGN

30. https://www.youtube.com/watch?v=ar7xDMR4P_U
https://www.youtube.com/watch?v=ar7xDMR4P_U

32. Forward Biased Junction
+
+
+
-
-
-
E
N
P
+ -
Opposing field due to battery
Depletion region
shrinks and drift
current begins to flow

33. Reverse Biased Junction
+
+
+
-
-
-
E
N
P
+
-
Supporting field due to battery
Depletion region
expands and opposes
flow of current

34. DIODE Characteristics

35. Drift and Diffusion currents

36. Drift Current
Drift current can be defined as the charge carrier’s moves in
a semiconductor because of the electric field. There are two
kinds of charge carriers in a semiconductor like holes and
electrons. Once the voltage is applied to a semiconductor,
then electrons move toward the +Ve terminal of a battery
whereas the holes travel toward the –Ve terminal of a
battery.
Here, holes are positively charged carriers whereas the
electrons are negatively charged carriers. Therefore, the
electrons attract by the +Ve terminal of a battery, whereas
the holes attract by the -Ve terminal of a battery.

37. Diffusion Current
The diffusion current can be defined as the flow of
charge carriers within a semiconductor travels from a
higher concentration region to a lower concentration
region. A higher concentration region is nothing but
where the number of electrons present in the
semiconductor. Similarly, a lower concentration region
is where the less number of electrons present in the
semiconductor.

41. Diode junction capacitances
• Transition capacitance (CT)
• Diffusion capacitance (CD)

42. Transition capacitance
• The amount of capacitance changed with increase
in voltage is called transition capacitance.
• The transition capacitance is also known
as depletion region capacitance, junction
capacitance or barrier capacitance.
• Transition capacitance is denoted as CT.
• The change of capacitance at the depletion
region can be defined as the change in electric
charge per change in voltage.

43. Transition capacitance
CT = dQ / dV
Where CT = Transition capacitance
dQ = Change in electric charge, dV = Change in voltage
The transition capacitance can be mathematically written
as CT = ε A / W,
Where ε = Permittivity of the semiconductor
A = Area of plates or p-type and n-type
regions
W = Width of depletion region

44. Diffusion capacitance
 When the junction is forward biased, a capacitance comes into
play , that is known as diffusion capacitance denoted as CD. It is
much greater than the transition capacitance.
 During forward bias, the potential barrier is reduced. The charge
carriers moves away from the junction and recombine.
 The density of the charge carriers is high near the junction and
reduces or decays as the distance increases.
 The change in charge with respect to applied voltage results in
capacitance called as diffusion capacitance.
 Diffusion capacitance is directly proportional to the electric
current or applied voltage.

45. Diffusion capacitance
CD = τ ID / η VT ,
where τ isthe mean life time of the charge carrier, ID is the
diode current and VT is the applied forward voltage, and η is
generation recombination factor.
The diffusion capacitance is directly proportional to the diode
current. In forward biased CD >> CT . And thus CT can be
neglected. The diffusion capacitance value will be in the range of
nano farads (nF) to micro farads (μF).

46. DIODE APPLICATIONS

48. HALF WAVE RECTIFIER

49. HALFWAVE RECTIFIER WITH
FILTER

52. RMS Value

53. 4.Efficiency

55. 5.Ripple Factor

56. 6. Transformer Utilization Factor(TUF)

57. 7. Peak Inverse Voltage(PIV)
• Peak Inverse Voltage (PIV) is the maximum voltage
that the diode can withstand during reverse bias
condition. If a voltage is applied more than the PIV,
the diode will be destroyed.
• For Half wave Rectifier,
PIV= Vm

58. FULL WAVE RECTIFIER

59. FULL WAVE RECTIFIER

60. FULL WAVE RECTIFIER

61. Derive the Parameters for Full wave rectifier

65. Efficiency
Pdc = Idc2 RL = (2Im / π)2 RL
Pac =Irms2 (rf + RL) =( Im / √2)2 (rf + RL)
Rectifier Efficiency (η) = Pdc / Pac
Put the values of Pdc and Pac from above equations,
therefore,
η =[ (2Im / π)2 * RL ] / [( Im / √2)2 * (rf + RL)]
= 0.812 RL / (rf + RL)
= 0.812 / (1+ rf /RL)
If rf is neglected as compared to RL then the efficiency of the
rectifier is maximum.
Therefore, η max =0.812 = 81.2%

69. BRIDGE RECTIFIER

70. BRIDGE RECTIFIER

71. RECTIFIER COMPARISON

72. Zener Diode

73. Introduction
 The zener diode is a silicon p-n junction devices that
differs from rectifier diodes because it is designed for
operation in the reverse-breakdown region.

74. Circuit of Zener
One Zener Diodeconnected with one resistanceand
battery.

75. Characteristics
 A Zenerdiode isalways reverseconnected
When forward biased, itscharacteristics are just likeof
ordinarydiode
 It has sharp breakdown voltage, called Zenervoltage

76. VI characteristics of Zener diode

77. Principle of Zener Diode
 The Working Principle of zener diode lies in the cause of
breakdown for a diode in reverse biased condition. Normally
there are two types of breakdown.
 1) Zener Breakdown
 2) Avalanche Breakdown.

78. Zener Breakdown
 This type of breakdown occurs for a reverse bias voltage between 2
to 8V.
 Even at low voltage, the electric field intensity is strong enough to
exert a force.
 The valence electrons of the atom such that they are separated from
the nuclei.
 This type of break down occurs normally for highly doped diode
with low breakdown voltage and larger electric field.
 As temperature increases, the valence electrons gain more energy to
disrupt from the covalent bond and the less amount of external
voltage is required.
 Thus zener breakdown voltage decreases with temperature.

79. Avalanche Breakdown
 This type of breakdown occurs at the reverse bias voltage
above 8V and higher.
 It occurs for lightly doped diode with large breakdown voltage.
 As minority charge carriers (electrons) flow across the device.
 They tend to collide with the electrons in the covalent bond and
cause the covalent bond to disrupt.

80. Avalanche Breakdown
 As voltage increases, the kinetic energy (velocity) of the
electrons also increases.
 The covalent bonds are more easily disrupted, causing an
increase in electron hole pairs.
 The avalanche breakdown voltage increases with temperature.

81. As Voltage Regulator

82. As Voltage Regulator
 In a DC circuit, Zener diode can be used as a voltage regulator
or to provide voltage reference.
 The main use of zener diode lies in the fact that the voltage
across a Zener diode remains constant for a larger change in
current.
 This makes it possible to use a Zener diode as a constant
voltage device or a voltage regulator.
 In any power supply circuit, a regulator is used to provide a
constant output (load) voltage.

83.  While designing a voltage regulator using zener diode
 The latter is chosen with respect to its maximum power rating.
 The maximum current through the device should be:-
 Imax = Power/Zener Voltage
 Since the input voltage and the required output voltage is
known.
 It is easier to choose a zener diode with a voltage
approximately equal to the load voltage, i.e. Vz ~=Vo.

84.  The value of the series resistor is chosen to be
R =(Vin – Vz)/(Izmin + IL), where IL = Load Voltage/Load
resistance.
 It is advisable to use a forward biased diode in series with the
Zener diode.
 This is because the Zener diode at higher voltage follows the
avalanche breakdown principle, having a positive temperature
of coefficient.
 Hence a negative temperature coefficient diode is used for
compensation.

85. 1
LightEmitting Diodes

86.  Introduction
 ConstructionofL
E
D
 Working
 Colors& Materials
 T
ypes
 Comparison
 Applications
 Advantages& Disadvantages
LightEmitting Diodes
2

87. • LEDisanacronym for Light EmittingDiode.
• ALight Emitting Diode(LED)isatwo LED
semiconductor light source.
• It isaPNJunctiondiode Which emits light when
activated by asuitable voltageis applied to theleads.
Introduction
3

88. • TheLEDconsistsof achip of
semiconductor material doped
with impurities to create aPN
junction.
• Thechipsare mounted in a
reflecting tray order to increase
the light output.
• Thecontacts are made on the
cathode side by meansof
conductive adhesiveand on the
anodeside via gold wire to thelead
frame.
• Theplastic caseenclosesthe chip
areaof the leadframe.
Constructionof LED
7

89. Working
• Whenthe negative end of acircuit
is hooked up to the N-type layer
and the positive end is hooked up
with P-type layer than electron
and holes start moving.
• If you try to run current the other
way,with the P-type side
connected to the negative end of
the circuit and the N-type side
connected to the positive end,
current will not flow.
• No current flows acrossthe
junction becausethe holes and
the electrons are eachmoving in
the wrong direction.
10

90. When currentflows
acrossa diode
Negative electrons move
one wayand positive
holes move the other
way
LED:HowIt Works
11

91. • Theholes exist at a
lower energy levelthan
the freeelectrons.
• Therefore when a
freeelectron falls, it
losesenergy.
LED:HowIt Works
12

92. • Thisenergy is emitted
ina form of a
photon, which
causeslight
• The color of the light
is determined by the
fall of the electron
and hence energy
level of the photon
LED:HowIt Works
13

93. Colors Colors
Name
WavelengthRange(nm) TypicalEfficiency(lm/W)
Red 620 - 645 72
Red–Orange 610 - 620 98
Green 520 - 550 93
Cyan
490 - 520
75
Blue 460 - 490 37
Efficiency& OperationalParameter
14

94. LEDsare produced in avariety of shapesand sizes.The
color of the plastic lens is often the sameasthe actual
color of light emitted.
Typesof LEDs
15

95.  TraditionalInorganicL
E
D
s
 Multi ColorL
E
D
• Bi-color
• Try-color
 OrganicL
E
D
 Miniature
 Highpower
Different sizeof LEDs: 8 mm, 5 mm and 3mm,
Modern high-power LEDssuchasthose usedfor lighting and
backlighting are generally found in SurfaceMount Technology(SMT)
(not shown here)
Somemain types is given below;
Typesof LEDs
16

96. • This type of LEDsmanufacturedfrom
inorganic materials.
• Someof the more widely used arecompound
semiconductor suchasAluminum Gallium
Arsenide(AlGaAr), Gallium Arsenide
Phosphide(GaArP), and many more.
Traditional InorganicLEDs
17

97. •Twodifferent LEDemitters
in one case.There are two
types of these.
•Onetype consists of twodies
connected to thesame
two color types oflight.
•Current flow in onedirection
emits one color, andcurrent
in the oppositedirection
emits the othercolor.
Multi ColorLED
18
Bi-color

98. • TheOLEDmostly used display technology computer monitors,
television , mobile phone Screenetc.
OrganicLightEmitting Diode(OLED)
19

99. OrganicLightEmitting Diode(OLED)
• Thesemiconductor in anOLEDisorganic which
meansit containscarbon.
•TheOLED
usesone of
two polymer
or small
molecule.
20

100. • 1.9 to 2.1V for Red,Orange&Yellow.
• 3.0 to 3.4V for Green &Blue.
• 2.9 to 4.2V for Violet, Pink, Purple &White.
Miniature
Miniature surface mount LEDsin most common sizes.Theycan much smaller than a
traditional 5mm lamp TypeLED.
21

101. Highpower
22
For example, the CREEXP-Gseries LEDachieved 105 lm/W in
2009, while Nichia released the 19 series withatypical efficacy of
140 lm/W in2010.

102. Comparison
24

103. LEDusesfall into Three maincategories
• Indicatorsand signals
• Lighting
• Data communicationandother signaling
Applications
25

104. The low energy consumption , low maintenance and small size
ofLEDs hasLEDto usesasstatus indicators and displays on a
variety of equipment and installations. the are used as
stadium airports and railway stations, trains, buses, trams,
and ferriesetc.
Indicatorsandsignals
26

105. LEDsare now used commonly in all market areasfrom commercial to
home use: standard lighting, stage, theatrical, architectural,and public
installations, and wherever artificial light isused.
Lighting
27

106. • Light canbe used to transmit data andanalog signals.
• Listening device in many theaters and similar spacesusearrays
of infrared LEDsto send sound to listenersreceivers.
• Light-emitting diodes are used to send data over manytypes
of fiber optics cable, from digital audio the very high bandwidth
fiber links that form the internet backbone.
Data communicationandother signaling
29

107. • Efficiency:LEDsemit more lumens per watt than incandescent
light bulbs.The efficiency of LEDlighting fixtures is not affected by
shapeand size,unlike fluorescent light bulbs ortubes.
• Color:LEDscanemit light of an intended color without using any
color filtersas traditional lighting methods need. Easilyavailable
manycolors.
• Size:LEDs canbe verysmall
smaller than 2mm
Advantages
30

108. • On/Off time: LEDslight up very quickly.A typical red indicatorLED
will achievefull brightness in underamicrosecond
• Cycling: LEDsare ideal for usessubject to frequent on-off cycling,
unlike incandescent and fluorescent lampsthatfail faster when High-
intensity dischargelamps that require along timebefore restarting.
• Lifetime: LEDscan have a relatively long useful life. One report
estimates 35,000 to 50,000 hours of useful life, though time to
complete failure maybelonger.
• Focus:Thesolid packageof the LEDcanbe designedto focusits light.
Incandescent and fluorescent sourcesoften require anexternal
reflector to collect light and direct it in ausablemanner.
Advantages
31

109. • Highinitial price: LEDsare currently more expensive,price per
lumen.
• LightQuality: Most cool-white LEDs havespectra that differ
significant from ablack body radiator like the sun oran incident
light.
• Temperaturedependence:Driving the LEDhard in high ambient
temperaturesmay
result to overheating of the led package,eventually leading to
device failure.
• Voltagesensitivity
• Nonreparation
Disadvantages
32

110. LASER DIODE

111. Introduction to Laser Diode
LASER stands for Light Amplification by Stimulated Emission of Radiation.
A laser diode is an electronic device, which converts electrical energy into
light energy to produce high-intensity coherent light.
Laser diode is very small in size and appearance.
It is similar to a transistor and has operation like LED but it emit coherent
light.
The material which often used in Laser diode is the gallium Arsenide (GaAs).
It is also called injection laser diode.
It works on forward biasing.

112. Symbol:

113. Laser diode construction
The laser diode is made of two doped gallium arsenide layers.
One doped gallium arsenide layer will produce an n-type
semiconductor whereas another doped gallium arsenide layer will
produce a p-type semiconductor. In laser diodes, selenium,
aluminum, and silicon are used as doping agents.
P-N junction
When a p-type layer is joined with the n-type layer, a p-n junction is
formed. The point at which the p-type and n-type layers are joined
is called p-n junction. The p-n junction separates the p-type and n-
type semiconductors.

114. Main steps required for producing a coherent
beam of light in laser diodes
Absorption of energy:
Absorption of energy is the process of absorbing energy from the external
energy sources.
In laser diodes, electrical energy or DC voltage is used as the external energy
source. When the DC voltage or electrical energy supplies enough energy to
the valence electrons or valence band electrons, they break bonding with the
parent atom and jumps into the higher energy level (conduction band). The
electrons in the conduction band are known as free electrons.

115. Cont…
When the valence electron leaves the valence shell, an empty space is
created at the point from which electron left. This empty space in the
valence shell is called a hole.
Thus, both free electrons and holes are generated as a pair because of the
absorption of energy from the external DC source.

116. Spontaneous emission:
Spontaneous emission is the process of emitting light or photons
naturally while electrons falling to the lower energy state.
In laser diodes, the valence band electrons or valence electrons are in
the lower energy state. Therefore, the holes generated after the
valence electrons left are also in the lower energy state.
On the other hand, the conduction band electrons or free electrons are in
the higher energy state. In simple words, free electrons have more energy
than holes.
The free electrons in the conduction band need to lose their extra energy
inorder to recombine with the holes in the valence band.
The free electrons in the conduction band will not stay for long period.
After a short period, the free electrons recombine with the lower energy
holes by releasing energy in the form of photons.

117. Cont…

118. Stimulated emission:
Stimulated emission is the process by which excited electrons or free
electrons are stimulated to fall into the lower energy state by releasing
energy in the form of light. The stimulated emission is an artificial process.
In stimulated emission, the excited electrons or free electrons need not wait
for the completion of their lifetime. Before the completion of their lifetime,
the incident or external photons will force the free electrons to recombine
with the holes. In stimulated emission, each incident photon will generate
two photons.
All the photons generated due to the stimulated emission will travel in the
same direction. As a result, a narrow beam of high-intensity laser light is
produced.

119. Cont…

120. How laser diode works?
When DC voltage is applied across the laser diode, the free
electrons move across the junction region from the n-type
material to the p-type material. In this process, some electrons
will directly interact with the valence electrons and excites
them to the higher energy level whereas some other electrons
will recombine with the holes in the p-type semiconductor and
releases energy in the form of light. This process of emission is
called spontaneous emission.
The photons generated due to spontaneous emission will travel
through the junction region and stimulate the excited electrons
(free electrons). As a result, more photons are released. This
process of light or photons emission is called stimulated
emission. The light generated due to stimulated emission will
moves parallel to the junction.

121. Cont…
The two ends of the laser diode structure are optically
reflective. One end is fully reflective whereas another
end is partially reflective. The fully reflective end will
reflect the light completely whereas the partially
reflective end will reflect most part of the light but
allows a small amount of light.
The light generated due to the stimulated emission is
escaped through the partially reflective end of the laser
diode to produce a narrow beam laser light.
All the photons generated due to the stimulated
emission will travel in the same direction. Therefore,
this light will travel to long distance without spreading
in the space.

122. Working Diagram

123. Advantages of laser diodes
Simple construction
Lightweight
Very cheap
Small size
Highly reliable compared to other types of lasers.
Longer operating life
High efficiency
Mirrors are not required in the semiconductor lasers.
Low power consumption

124. Disadvantages of laser diodes
Not suitable for the applications where high powers are required.
Semiconductor lasers are highly dependent on temperature.

125. Applications of laser diodes
Laser diodes are used in laser pointers.
Laser diodes are used in fiber optic communications.
Laser diodes are used in barcode readers.
Laser diodes are used in laser printing.
Laser diodes are used in laser scanning.
Laser diodes are used in range finder

126. PROBLEMS
1. An a.c. supply of 230 V is applied to a half-wave
rectifier circuit through a transformer of turn ratio
10 : 1. Find (i) the output d.c. voltage and (ii) the
peak inverse voltage. Assume the diode to be ideal.

128. 2. A crystal diode having internal resistance rf = 20Ω is used for half-
wave rectification. If the applied voltage v = 50 sin ω t and load
resistance RL= 800 Ω, find :
(i) Im, Idc, Irms (ii) a.c. power input and d.c. power output (iii) d.c.
output voltage (iv) efficiency of rectification.