ELECTRONIC DEVICES

ELECTRONICS 1
Dr. Awadh Al-Kubati
University of Sana’a
Faculty of Engineering
Department of Biomedical Engineering

Course Description
• This course presents fundamental principles and concepts
of electronic devices and their applications in the design
and construction of electronic circuits for solving practical
problems in biomedical engineering. Course covers the
main principles of formatting semiconductor devices, such
as Diodes and Bipolar Junction Transistors (BJT). Also
focus on formation of the different types of the Field Effect
Transistors (FET) & their DC/AC analyses. Laboratory
experiments and MATLAB simulation work are carried for
different types of analog electronic elements to verify the
theoretical concepts and to develop problem-solving skills
related to electronic circuits and systems design and
implementation.

Outcomes
1. Understand the basic concepts of electronic devices: Fabrication,
characteristics and operation
2. Appreciate the properties and fundamental lows of electronic materials
and devices.
3. Have sufficient skills in both theoretical and practical sides in order to be
able to use electronic circuits in typical engineering applications.
4. Analyze of electronic circuits containing: diode, bipolar and FET
transistors and test them.
5. Build a simple electronics circuits using Lab and modern software
simulation tools.
6. Conduct experiments for evaluating the performance of electronic
components or systems with respect to specification, as well as to
analyze and interpret data.
7. Work effectively as a member of a group or individually to accomplish a
common goal.
8. d2 Purchase transferable skills of finding root causes and alternative
solutions of problems.

Course Contents
• Introduction
• P-N Junction Diode
• Bipolar Junction Transistor
• Field Effect transistor

GRADING SYSTEM
• Assignments → 10
• Quizzes 1 & 2 → 10
• Mid-Term Theoretical Exam → 20
• Mid-Term Practical Exam → 20
• Final Practical Exam → 30
• Final Theoretical Exam → 60

Chapter 1
Introduction to Semiconductor
ELECTRONIC DEVICES

Semiconductor Materials
• Definition: Semiconductors are a
special class of elements having a
conductivity between that of a good
conductor and that of an insulator

• Single crystal – Germanium (Ge) and
Silicon (Si)
• Compound Semiconductor – Gallium
Arsenide (GaAs), Cadmium Sulfide
(CdS), Gallium Nitride (GaN) and
Gallium Arsenide phosphide (GaAsP).
• Mostly used : Ge, Si and GaAs

• Ge – First discovered. Used as Diode in
1939, transistor in 1947. Sensitive to
changes in temperature – suffer reliability
problem.
• Si – Introduced in 1954 (as transistor), less
sensitive to temperature. Abundant materials
on earth. Over the time – its sensitive to
issue of speed.
• GaAs – in 1970 (transistor), 5x speed faster
than Si. Problem – difficult to manufacture,
expensive, had little design support at the
early stage.

Periodic Table
• Columns: Similar Valence Structure
Electropositive elements:
Readily give up electrons
to become + ions.
Electronegative elements:
Readily acquire electrons
to become - ions.
He
N e
Ar
Kr
Xe
Rn
inert
gases
accept
1e
accept
2e
give
up1e
give
up2e
give
up
3e
F
Li Be
Metal
Nonmetal
Intermediate
H
Na Cl
Br
I
At
O
S
Mg
Ca
Sr
Ba
Ra
K
Rb
Cs
Fr
Sc
Y
Se
Te
Po

Electropositive elements:
Readily give up electrons
to become + ions.
Electronegative elements:
Readily acquire electrons
to become - ions.

Semiconductors, Conductors &
Insulators
Conductors
• Material that easily conducts electrical current.
• The best conductors are single-element material (e.g copper, silver,
gold, aluminum, ect.)
• One valence electron very loosely bound to the atom- free electron
Insulators
• Material that does not conduct electric current under normal
conditions.
• Valence electron are tightly bound to the atom – less free electron
Semiconductors
• Material between conductors and insulators in its ability to conduct
electric current
• in its pure (intrinsic) state is neither a good conductor nor a good
insulator
• most commonly use semiconductor- silicon(Si), germanium(Ge), and
carbon(C).
• contains four valence electrons

Covalent Bonding &
Intrinsic Materials
• Atom = electron + proton + neutron
• Nucleus = neutrons + protons
Protons
(positive charge)
Neutrons
(uncharged)
Nucleus
(core of atom)
Electrons
(negative charge)
ATOM

Atomic Structure
No. of electron in each shell
Ne = 2(n)2
n = no of shell.

Covalent Bonding
Covalent bonding of the Silicon atom
Covalent bonding of the GaAs crystal

Intrinsic Carrier
Table 1.1
Intrinsic Carriers
Semiconductor Intrinsic Carriers
(per cubic centimeter)
GaAs 1.7 x 106
Si 1.5 x 1010
Ge 2.5 x 1013
• Intrinsic carriers – The free electrons in a material due to only
external causes.
• in other words Intrinsic carriers: are the electrons and holes that
participate in conduction>
• Ge has the highest number of carriers and GaAs has the lowest
intrinsic carriers.
• The term intrinsic is applied to any semiconductor material that has
carefully refined to reduce the number of impurities to a very low
level – essentially as pure as can be made available through
modern technology.

Relative Mobility Factor µn
Table 1.2
Relative Mobility Factor
Semiconduct
or
µn (cm2/V-s)
Si 1500
Ge 3900
GaAs 8500
• Relative mobility – the ability of the free carriers to move
throughout the material.
• GaAs has 5X the mobility of free carriers compared to Si, a
factor that results in response times using GaAs electronic
devices is 5X those of the same device made from Si.
• Ge has more than twice the mobility of electrons in Si, a factor
that results in the continued of Ge in high-speed radio
frequency applications.

Difference between Conductors
& Semiconductors
• Conductors – Resistance increases with the
increase in heat, because their vibration pattern
about relatively fixed location makes it increasingly
difficult for a sustained flow of carriers through the
material – positive temperature coefficient.
• Semiconductors – Exhibit an increased level of
conductivity with the application of heat. As the
temperature rises, an increasing number of valence
electron absorb sufficient thermal energy to break
the covalent bond and contribute to the number of
free carriers – negative temperature effects

Difference between Conductors, semiconductors
and insulators

Energy Level
Figure: Energy levels: conduction and valence bands of an
insulator, a semiconductor, and a conductor.

Extrinsic Materials : n-Type and
P-Type Materials
• The characteristics of a semiconductor material
can be altered significantly by the addition of a
specific purity atoms to relatively pure
semiconductor materials – this process is known
as doping process.
• A semiconductor that has been subjected to the
doping process is called an extrinsic materials.
• Extrinsic Materials are n-type material [five
valence electrons (pentavalent)] and p-type
material [three valence electrons atom
(trivalent)].

N-Type Materials
• n-Type material is created by introducing the impurity
(bendasing) elements that have five valence electrons
(pentavalent).
• There are antimony (Sb), Arsenic (As) and phosphorous (P).
Figure: Antimony impurity in n-type material
Diffused impurities with five
valence electrons are called
donor atoms

N-Type Materials
• The effect of this doping cause the energy level (called the
donor level) appears in the forbidden band with Eg significantly
less than intrinsic material.
• This cause less thermal energy to move free electron (due to
added impurity) into conduction band at room temperature.
Figure: Effect of donor impurities on the energy band structure

N-Type Material
• Pentavalent atoms is an n-type semiconductor (n stands for the
negative charge on electrons).
• The electrons are called the majority carrier in n-type materials.
• In n-type material there are also a few holes that are created when
electrons-holes pairs are thermally generated
• Holes in n-type materials are called minority carrier.

P-Type Material
• Si or Ge doped with impurities atoms having three valence
electrons.
• Mostly used are boron (B), gallium (Ga) and indium (In).
• The void (vacancy) is called ‘hole’ represented by small circle
or a ‘+’ sign.
Figure: Boron impurity in p-type
material.
Diffused impurities with three
valence electrons are called
acceptor atoms

P-Type Material
• In p-type materials the hole is the majority carrier
and the electron is the minority carrier.
• Holes can be thought as +ve charges because the
absence of electron leaves a net +ve charge on the
atom.

Difference between N & P -Types Material

Electron Vs Hole Flow
• With sufficient kinetic energy to break its covalent
bond, the electron will fills the void created by a
hole, then a vacancy or hole, will be created in the
covalent bond that released the electron.

Semiconductor Diode
Diode
• Simple construction of electronic device
• It is a joining between n-type and p-type
material (joining one with majority carrier
of electron to one with a majority carrier
of holes)

Forward Bias (VD > 0 V)
Figure: Forward-biased p–n junction. (a) Internal distribution of
charge under forward-bias conditions; (b) forward-bias polarity
and direction of resulting current.
(b)

Reverse Bias (VD < 0 V)
Figure: Reverse-biased p–n junction. (a) Internal distribution of charge
under reverse-bias conditions; (b) reverse-bias polarity and direction of
reverse saturation current.

Diode Characteristics Curve
Figure: Silicon semiconductor diode characteristics.

Ge, Si and GaAs
Figure: Comparison of Ge,
Si, and GaAs diodes.

Temperature Effects
Figure: Variation in Si diode
characteristics with
temperature change.

Ideal Vs Practical
• Semiconductor diode behaves in a
manner similar to mechanical switch
that can control the current flow
between it’s two terminal
• However, semiconductor diode different
from a mechanical switch in the sense
that it permit the current flow in one
direction

Ideal Vs Practical
Figure: Ideal semiconductor diode:
(a) forward-biased (b) reverse-biased.

=
=
= 0
5
0
mA
V
I
V
R
D
D
F


=
=
=
mA
V
I
V
R
D
D
R
0
20
(Short circuit equivalent –fwd bias, actual case R ≠ 0)
(Open circuit equivalent – Reverse bias, actual case
saturation current Is ≠ 0)
Figure: Ideal versus actual
semiconductor characteristics.

Resistance Levels
DC or Static Response
• Application of dc voltage will result in an operating
point on the characteristic curve will not change with
time.
D
D
D
I
V
R =
In general, the higher the current
through a diode, the lower is the
dc resistance level.
Figure: Determining the dc resistance
of a diode at a particular operating
point.

Resistance Levels
d
d
d
d
I
mV
I
V
r
26
=


=
Figure: Defining the dynamic or
ac resistance.
AC or Dynamic Response

Resistance Levels
d
d
av
I
V
r


=
Figure: Determining the average ac resistance
between indicated limits.
Average AC Response

Diode Equivalent Model
 
d
LIMIT
BIAS
F
d
LIMIT
F
BIAS
d
F
V
d
F
D
F
r
R
V
V
I
V
r
R
I
V
r
I
r
I
V
V
+
−
=
+
+
=
+
=
+
=
7
.
0
7
.
0
7
.
0
]
'
[ LIMIT
F
BIAS R
r
I
V R +
=

Piecewise-Linear Equivalent Circuit

Example 1
Determine the forward voltage (VF) and forward current [IF]. Also
find the voltage across the limiting resistor. Assumed rd’ = 10 at
the determined value of forward. If,VBIAS = 10v , RLIMIT = 1KΩ
V
k
mA
R
I
V
mV
mA
V
r
I
V
V
mA
k
V
V
r
R
V
V
I
LIMIT
F
R
d
F
F
d
LIMIT
BIAS
F
LIMIT
21
.
9
)
1
)(
21
.
9
(
792
)
10
)(
21
.
9
(
7
.
0
7
.
0
21
.
9
10
1
7
.
0
10
7
.
0
'
'
=

=
=
=

+
=
+
=
=

+

−
=
+
−
=

Example 2
Determine the Reverse voltage (VR). Also find the voltage across
the limiting resistor. Assumed IR = 1 µA.
Answer:
VRLIMIT =1mV
VR=4.999V

Diode Testing
• Analog MM (or Ohm meter testing)
Figure: Checking a diode with an
ohmmeter.

Diode Testing
• Digital MM
Figure: DMM diode test on a properly functioning diode.

Diode Testing – Defective diode
• Digital MM (Testing Defective Diode)
Diode failed open: get
open circuit reading
(2.6 V) or ‘OL’
Diode is shorted: get
0 V reading in both
forward and reverse
bias test.

Zener Diode
Figure: Characteristics of Zener
region.
Figure: Conduction direction: (a)
Zener diode (b) semiconductor diode
(c) resistive element.

Zener Region
• The Zener region is in
the diode’s reverse-
bias region.
• At some point the
reverse bias voltage is
so large the diode
breaks down and the
reverse current
increases dramatically.
• This maximum voltage
is called avalanche
(runtuhan) breakdown
voltage
• The current is called
avalanche current.

The term semiconductor arises from the
ability of these materials to conduct “part time.”
Their versatility lies in the fact that the
conductivity can be controlled to produce effects
such as amplification, rectification, oscillation,
signal mixing, and switching.
semiconductor

Metal oxides
Certain metal oxides have properties that make them useful in
the manufacture of semiconductor devices. When you hear about
MOS (pronounced “moss”) or CMOS (pronounced “sea moss”)
technology, you are hearing about metal-oxide semiconductor and
complementary metal-oxide semiconductor devices, respectively.
One advantage of MOS and CMOS devices is that they need
almost no power to function. They draw so little current that a
battery in a MOS or CMOS device lasts just about as long as it
would on the shelf. Another advantage is high speed. This allows
operation at high frequencies, and makes it possible to perform
many calculations per second.
Certain types of transistors, and many kinds of integrated
circuits, make use of this technology. In integrated circuits, MOS
and CMOS allows for a large number of discrete diodes and
transistors on a single chip. Engineers would say that MOS/CMOS
has high component density.
The biggest problem with MOS and CMOS is that the devices
are easily damaged by static electricity. Care must be used when
handling components of this type.

Selenium
Selenium has resistance that varies depending on the
intensity of light that falls on it.
All semiconductor materials exhibit this property, known as
photoconductivity, to a greater or lesser degree, but selenium is
especially affected. For this reason, selenium is useful for
making photocells.
Selenium is also used in certain types of rectifiers. This is a
device that converts ac to dc;

❖ The free holes “wish” to combine with the free electrons . .
• When we apply an external voltage that facilitates this combination
(a forward voltage, vD > 0), current flows easily.
• When we apply an external voltage that opposes this combination,
(a reverse voltage, vD < 0), current flow is essentially zero.
➢ When we “place” p-type semiconductor adjacent to n-type
semiconductor, the result is an element that easily allows current to
flow in one direction, but restricts current flow in the opposite direction .
. . this is our first nonlinear element:
Forward & Reverse Bias

typical diode i-v characteristic:
PSpice-generated i-v characteristic for a 1N750 diode showing
the various regions of operation
VF is called the forward knee voltage, or simply, the forward voltage.
• It is typically approximately 0.7 V, and has a temperature coefficient
of approximately -2 mV/K VB is called the breakdown voltage.
• It ranges from 3.3 V to kV, and is usually given as a positive value.
➢ Diodes intended for use in the breakdown region are called zener
diodes (or, less often, avalanche diodes).
➢ In the reverse bias region, |iD| ≈ 1 nA for low-power (“signal”) diodes.

Junction capacitance
Some P-N junctions can between conduction (in forward bias)
and nonconduction (in reverse bias) millions or billions of times
per second. Other junctions are slower. The main limiting factor
is the capacitance at the P-N junction during conditions of
reverse bias. The amount of capacitance depends on several
factors, including the operating voltage, the type of
semiconductor material, and the cross-sectional area of the P-N
junction.
By examining Fig. of reverse bias, we should notice that the
depletion region, sandwiched between two semiconducting
sections, resembles the dielectric of a capacitor. In fact, the
similarity is such that a reverse-biased P-N junction really is a
capacitor. Some semiconductor components are made with this
property specifically in mind.
The junction capacitance can be varied by changing the
reverse-bias voltage, because this voltage affects the width of
the depletion region. The greater the reverse voltage, the wider
the depletion region gets, and the smaller the capacitance
becomes.

Avalanche effect
The greater the reverse bias voltage, the “more determined an
insulator” a P-N junction gets—to a point. If the reverse bias goes past
this critical value, the voltage overcomes the ability of the junction to
prevent the flow of current, and the junction conducts as if it were
forward biased. This avalanche effect does not ruin the junction (unless
the voltage is extreme); it’s a temporary thing. When the voltage drops
back below the critical value, the junction behaves normally again.
Some components are designed to take advantage of the avalanche
effect. In other cases, avalanche effect limits the performance of a
circuit.
In a device designed for voltage regulation, called a Zener diode,
you’ll hear about the avalanche voltage or Zener voltage specification.
This might range from a couple of volts to well over 100 V. It’s important
in the design of voltage-regulating circuits in solid-state power supplies.
For rectifier diodes in power supplies, you’ll hear about the peak
inverse voltage (PIV) or peak reverse voltage (PRV) specification. It’s
important that rectifier diodes have PIV great enough so that avalanche
effect will not occur (or even come close to happening) during any part
of the ac cycle. Otherwise, the circuit efficiency will be compromised.

ELECTRONIC DEVICES

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