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Subimtted by :- Dinesh Ghalot
INTRODUCTION TO
SEMICONDUCTOR DEVICES
PREREQUISITES

To understand this presentation, you should be
able to:
 Draw the structure of an atom, including
electrons, protons, and neutrons.
 Define resistance and conductance.
 Label an electronic schematic, indicating
current flow.
 Define Ohm’s and Kirchhoff’s laws.
 Describe the characteristics of DC and AC
(sine wave) voltages.
STUDENT LEARNING OUTCOMES
 Upon
completion of viewing this
presentation, you should be able to:
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Define active and passive components.
Name three main categories of active semiconductor
devices.
Name the two elements of a diode and state the primary
operational characteristics of a diode.
Define bias and name the two types of bias and their
effects on diode operation.
Explain the concept of a transistor.
Explain how a transistor can switch or amplify.
Define integrated circuit.
PASSIVE COMPONENTS
Semiconductor materials can be used to form
almost any kind of electronic component,
including passive components.
 Passive components like resistors, capacitors or
inductors are very common.
 A resistor is made with a piece of N or P-type
semiconductor material doped to the
appropriate resistance level.
 A capacitor is made with two plates of a
highly conductive semiconductor material
separated by a pure semiconductor material or
another insulator like glass silicon dioxide
(SiO2).
 An inductor is made by making a spiral of
highly conductive semiconductor material.

ACTIVE ELECTRONIC COMPONENTS
 An
active electronic component either
amplifies or switches.
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The most common active components are
diodes and transistors.
Both diodes and transistors are easy to
make with semiconductors
 With
semiconductor materials it is
possible to create complete circuits of
active and/or passive components wired
together.

These circuits are formed on a single chip
of silicon and are called integrated circuits
(ICs).
DIODES

A semiconductor diode is
formed with pieces of N
and P-type material are
joined.
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The P material is called the
anode.
The N material is called the
cathode.
The resulting structure is
called a PN junction.
A PN junction (or diode) is
a switch or component
through which electrons
will flow easily in one
direction but not in the
opposite direction.
BIASING A PN JUNCTION
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To get current to flow in PN
junction or diode, you have to
apply an external voltage
called bias.
With this connection, current
only flows freely from cathode
across the junction to the
anode.
You’d say the switch is closed
when electrons can flow
through the diode.
Note: The current flow may be
so high that an external
resistance R is usually needed
to minimize the current flow to
a level a diode can withstand.
This arrangement is called
forward bias.
REVERSE BIAS
A
diode with the
external voltage
polarity reversed is
called reverse bias.
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With this connection no
current will flow.
You’d say the switch is
open when electrons
can’t flow through the
diode.
DIODE SYMBOL
The PN junction forms a
diode.
 To represent the diode in
schematic diagrams, we
use the symbol shown on
the right.
 Note the designations for
the anode and cathode.

DIODE CURRENT FLOW

The direction of current flow (electrons) is shown by the
arrow.
A PRACTICAL DIODE
A
practical diode has two wire leads.
 Note the end with the band circling the
body is the cathode end.
Wire Leads
FORWARD AND REVERSE BIAS
 Examples
diodes:
of both forward and reverse biased
PRACTICAL DIODES
 Diodes,
like other electronic
components, are not perfect.
 Diodes have an upper current limit
that if exceeded will destroy the diode.
 You can get diodes with current limits
of a few milliamperes up to hundreds
or thousands of amperes.
 Diodes also have an upper voltage limit
when reverse biased.
 This is the reverse break down voltage
which may be only a few volts or
hundreds or thousands of volts.
DIODE VOLTAGE DROP

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Diodes also have a voltage drop
while they are conducting. This is
called forward voltage drop. It is in
the 0.5 to 0.9 volt range for silicon
diodes. A typical value is 0.7 volts.
The forward drop in a germanium
diode is in the 0.2 to 0.4 volt range.
Diodes also have a threshold
voltage approximately equal to the
forward voltage drop. This is the
minimum amount of forward
voltage that must be applied to get
the diode to conduct.
For example if you apply a forward
bias of less than abut 0.7 volts to a
silicon diode, it will not conduct.
As soon as the bias voltage rises
about 0.7 volts the diode will
conduct.
TRANSISTORS
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A transistor is a 3-terminal
semiconductor device that is
used to amplify or switch.
By applying an external DC
voltage, current will flow from
terminal 1 through the device
to terminal 3.
A resistor is used to set the
current level.
A voltage or current applied to
terminal 2 is used to control
how much current flows from
terminals 1 to 3.
A very small voltage or current
variation at terminal 2 can
produce a very large current
variation between terminals 1
and 3.
HOW TRANSISTORS SWITCH
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The transistor is connected in
series with a resistor.
With no (zero) voltage on
terminal 2, no current will flow
in the transistor. The
transistor acts like an open
switch. The output voltage is 3
volts as seen through the
resistor R.
If a large enough voltage is
applied to terminal 2, the
transistor will conduct heavily
and act like a very low
resistance between terminals 1
and 3. It then acts like a closed
switch. The output voltage is
near zero.
HOW A TRANSISTOR AMPLIFIES

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The circuit is the same as the
switch.
With a small voltage on
terminal 2, a large variation in
current from terminals 1 to 3
occurs.
For example, if a sine wave is
applied to the input, the
current through the transistor
will be a sine wave and it will
produce a sine wave voltage
across the resistor and the
transistor.
Since the current variation in
the transistor is very large, the
out put voltage is larger than
the smaller input voltage.
The transistor amplifier is said
to have gain.
HOW A TRANSISTOR AMPLIFIES (CONTINUED)
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A key point to note in the
amplifier is that the transistor
does not actually make the
input voltage bigger. Instead,
the small input controls the
larger current through the
device produced by the external
DC voltage.
The transistor just generates a
larger separate version of the
input voltage in the output.
TYPES OF TRANSISTORS
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There are two commonly used
types of transistors, metal
oxide semiconductor field effect
transistors (MOSFETs) and
bipolar junction transistors
(BJTs) called bipolars.
MOSFETs are the most widely
used although BJTs are still
used in selected applications.
There are sub categories of
each type and you will learn
how each works in a later
course.
INTEGRATED CIRCUITS
Integrated circuits (ICs)
are semiconductor devices
that are complete circuits
made up of transistors,
diodes, capacitors,
resistors and inductors.
 The complete circuit is
made on a single piece of
silicon called a chip.
 See Figure.
 Any circuit from a simple
amplifier to a quad core
microprocessor used in a
PC can be made.

 Most
electronic
equipment is made up
of a collection of ICs
and a small selection
of discrete passive
components like
resistors and
capacitors connected
together on a printed
circuit board (PCB).
 Figure shows a typical
board.
IN SUMMARY
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The simplest semiconductor device is a diode made by
forming a junction between a P and N-type semiconductor
material.
The diode will pass current from cathode to anode but not
in the other direction.
If the anode is made positive and the cathode negative, the
diode is said to be forward biased and current will flow.
The reverse condition is called reverse bias and no current
flows.
A three terminal (element) semiconductor device is called a
transistor. The voltage on one element controls the current
between the other two elements.
A transistor is used to switch voltages or currents or to
amplify small signals into larger ones.
MOSFETs and BJTs are the two major types of transistors