INTRODUCTION TO
ELECTRONIC DEVICES
MENJANA MINDA KREATIF DAN INOVATIF
Introduction
¾ What is…
•
•
•
Electronics?
Electronic Devices?
Electronic Systems?
introduction
El t
Electronics:
i
•
•
The branch of physics that deals with the
emission and effects of electrons ; and
the use of electronic devices.
Science of the motion of charges in a
gas,, vacuum or semiconductor.
g
Electronic devices:
• An electronic building block packaged in a
discrete form with two or more connecting
leads or metallic pads.
• Components are connected together to
create an electronic circuit with a particular
p
function.
– E.g.:
E g : an amplifier
amplifier, radio receiver
receiver, or oscillator
oscillator.
• Active components are sometimes called
devices.
Electronic systems:
• Composed of subsystems or electronic
circuits which may include amplifiers
circuits,
signal sources, power supplies etc…
– E.g.: Laptop, DVD players, iPOD, PDA,
mobile phones
What we are learning?
Electronic Devices:
™ Diodes
™ Transistor (BJT)
™ Transistor (FET)
CHAPTER 1
Semiconductor Material
Semiconductor Material
1.1
Atomic Structure
12
1.2
Materials Classification
1.3
Energy Band
1.4
Covalent Bonds
15
1.5
C d ti iin S
Conduction
Semiconductors
i
d t
1.6
p type
yp and n type
yp semiconductors
1 1 Atomic structure
1.1
• All matters on earth made of atoms (made
up
p of elements or combination of
elements).
• All atoms consist of electrons
electrons, protons
protons,
and neutrons.
• An atom is the smallest particle of an
element that retains the characteristics of
that element.
B h ’ At
Bohr’s
Atomic
i St
Structure
t
• According to Bohr,
atoms have a p
planetary
y
structure that consists of
a central nucleus,
surrounded
d db
by orbiting
biti
electrons. Nucleus
contains protons and
neutrons.
Electrons ((-))
orbits the nucleus
Nucleus :
Protons (+)
Neutrons
(neutral)
C t
Cont..
• Each type of atom has a certain number of
electrons and protons that distinguishes it from
atoms of other elements.
H: 1 proton
proton, 1
electron
He: 2 proton
proton, 2
neutron, 2 electron
H li
Helium
At
Atom
Each electron has its
own orbit which
corresponds to
different energy levels
levels.
Similar energy levels
( bi ) are grouped
(orbits)
d
into energy bands
called
ll d shells.
h ll
El t
Electron
Shells
Sh ll and
dO
Orbits
bit
• Each electron travels on its own orbit.
• The different orbit corresponds to different
energy level.
• In an atom, orbits are grouped into energy
bands known as shells.
shells
• Each shell has a fixed max no. of
electrons
l t
att allowed
ll
d energy llevels
l
The Energy Band Concept
• The number of electrons in
shell 1 - 4 can be
calculated as: Ne = 2n2
• Electron orbits the nucleus
at certain distances
• The
Th outermost
t
t shell
h ll iis
called the valence shell.
• Electrons on this shell are
called valence electrons
V l
Valence
El
Electrons
t
• The outermost shell is called the valence
shell and electrons at this layer are called
valence electrons.
electrons
• Valence electrons contribute to chemical
reactions and bonding within the structure of
a material and determine its electrical
properties.
• Maximum number of valence electron is 8.
• An atom is stable if it has 8 valence
electrons;
– eg:
g Neon ((10),
), Argon
g ((18),
), Krypton
yp
((36).
)
C t
Cont..
• The number of valence electrons determines
the abilityy of material to conduct current. The
less complete a shell is filled to capacity (max
8) the more conductive the material is.
• Iff an atom off a material carries 1 to 3 valence
electrons, the material is a conductor
because the atom has more tendency to lose
its valence electrons which become free
electrons. (Copper, Aluminium)
Cont…
Cont
• If an atom of a material carries 5 to 8 valence
electron, the material is an insulator because
the atom has more tendency to gain free
p
its shell. ((Argon,
g , Neon))
electrons to complete
• If an atom of a material carries 4 valence
alence
electrons, the material is a semiconductor
b
because
it iis nott easy ffor the
th atom
t
to
t lose
l
or
gain any electrons. (Silicon, Germanium)
C t
Cont…
A Silicon atom has 4 electrons in
its valence ring. This makes it a
semiconductor
semiconductor.
A Copper atom has only 1 electron
in its valence ring. This makes it a
good conductor.
Semiconductor Material
1.1
Atomic Structure
12
1.2
Materials Classification
Insulators, Conductors, and Semiconductor
1.3
Energy Band
14
1.4
C
Covalent
l tB
Bonds
d
1.5
Conduction in Semiconductors
1.6
p type and n type semiconductors
1 2 Materials Classification
1.2
•
•
•
•
Semiconductors, conductors and insulators
Semiconductors
How are they different?
What is the difference between silicon and
germanium semiconductor?
Why is Si more widely used compared to
Ge
Ge?
C t
Cont..
•
Conduction band and valence electrons
determines the electrical properties of a
material.
Conductor
•
A conductor is a material that easily conducts
electrical current.
•
The best conductors are (with one valence electron)
eg: copper, silver, gold and aluminium.
•
In a conductor, the valence band and the conductor
band overlaps
p ((≤ 0.01 eV).
) Onlyy a little energy
gy or
voltage is needed for the electron to jump into
conduction band.
Insulator
•
An insulator is a material that does not conduct
electrical current
c rrent under
nder normal circ
circumstances.
mstances
•
Energy gap in
E
i an iinsulator
l t iis very wide
id ( ≥ 6eV).
6 V)
Valence electron requires a large electric field to
gain enough energy to jump into conduction band
band.
Semiconductor
•
A semiconductor is between a conductor and
insulator.
•
A semiconductor in its p
pure ((intrinsic)) state is neither
a good conductor nor a good insulator.
•
Most common semiconductor are silicon,
germanium and carbon.
•
A semiconductor has a conductivity level between
the extreme of an insulator and a conductor.
Cont..
Cont
Compare silicon and germanium. Which one is better and
why?
Semiconductor Material
1.1
Atomic Structure
1.2
Materials Classification
1.3
1.4
Energy Band
- Energy Level
- Valence Band, Conduction Band, Energy
Gap
Covalent Bonds
15
1.5
Conduction in Semiconductors
1. 6
p type and n type semiconductors
1 3 Energy Band
1.3
„
ENERGY in an electron is of two types - kinetic
(energy of motion) and potential (energy of position).
„
Each material has its own set of permissible energy
levels for the electrons in its atomic structure.
structure
„
Energy
gy level in an atom is measured in ELECTRON
VOLT (eV): 1 eV = 1.602 x 10-19 J
„
Electrons that orbits within an energy level will have
similar amount of energy.
Energy Level
More energy
Less energy
Energy increases as the distance from the nucleus increases.
Energy Gap
„
When an electron acquires sufficient additional
energy, it can leave the valence shell and become a
f
free
electron
l t
and
d exists
i t iin th
the conduction
d ti b
band.
d
„
The energy difference between the valence band
and conduction band is called the energy gap.
„
Energy gap: the
E
h amount off energy that
h a valence
l
electron must have to jump into the conduction
band.
„
Once in conduction band, the electron is free to
move throughout the material and is not tied to any
atom.
Cont..
Cont
• Energy diagrams for the three types of materials:
Semiconductor Material
1.1
Atomic Structure
12
1.2
M t i l Cl
Materials
Classification
ifi ti
1.3
Energy
gy Band
1.4
Covalent Bonds
1.5
Conduction in Semiconductors
1.6
p type and n type semiconductors
Covalent Bonds
•
In a pure silicon or germanium crystal, the
four valence electrons of one atom form a
bonding arrangement with four adjoining
atoms.
•
This bonding of atoms
atoms, strengthened by the
sharing of electrons, is called covalent
bonding – is a method by which atoms
complete their valence shell by sharing
valence electrons with other atoms
Cont..
Cont
The atoms are
electrically stable
because their valence
shells are complete.
Cont..
Cont
Certain atoms will combine in this way to form a
crystal structure. Silicon and Germanium atoms
combine
bi iin thi
this way iin th
their
i iintrinsic
t i i or pure state.
t t
Covalent Bonds
in a silicon crystal
Review
1 In the atomic structure of a semiconductor,
1.
semiconductor within
which energy band do free electrons exist? Within
which energy band do valence electrons exist?
2. Why is current established more easily in a
semiconductor than in an insulator?
Previously..
Previously
™
™
™
™
™
™
™
™
™
Diodes and transistors are all made of semiconductor material.
Bohr model: electrons circle the nucleus. (planetary-type)
Atomic structure of a material determines its ability to conduct or
insulate.
The orbit paths (energy band) of the electrons surrounding the
nucleus are called shells.
Each shell has a defined number of electrons it will hold.
The outer shell is called the valence shell
shell.
The valence shell determines the ability of material to conduct
current.
Energy gap: difference in energy levels between the conduction
and valence bands. (forbidden band)
Covalent bonding is a bonding of two or more atoms by the
interaction of their valence electrons to form a crystal structure.
Semiconductor Material
1.1
Atomic Structure
12
1.2
Materials Classification
1.3
Energy Band
1.4
Covalent Bonds
15
1.5
C d ti iin S
Conduction
Semiconductors
i
d t
1.6
p type
yp and n type
yp semiconductors
15C
1.5
Conduction
d ti
iin Semiconductors
S i
d t
How is current produced in a semiconductor?
Conduction in Semiconductors
Unexcited (no external energy)
silicon atom. (0 K)
Electron Hole Pair
Electron-Hole
E it d silicon
Excited
ili
atom.
t
(R
(Room
t
temperature)
t )
Conduction Electrons and Holes
•
When an intrinsic silicon crystal gains sufficient heat (thermal
energy), some valence electrons could break their covalent
bonds to jump the gap into conduction band, becoming free
electrons.
electrons
•
Free electrons are also called conduction electrons, (negative
charge).
charge)
•
This vacancy in the valence band is called a hole (positive
charge).
•
For every electron raised to the conduction band
band, there is 1
hole in the valence band creating – electron-hole pair.
•
When a conduction electron loses energy and falls back into a
hole, this is called recombination.
Cont..
Cont
There is an equal
number of holes in the
valence band created
when these electrons
jjump
p into the conduction
band.
Cont..
Cont
•
Free electrons tend to search for p
positive holes,
while holes tends to attract electrons to reform
covalent bonds. (Opposites attract)
•
With the existence of holes and electrons, current
can be
b produced
d
d when
h a voltage
lt
iis applied
li d across
the terminals.
C
Current
t IIn Semiconductor
S i
d t
There are 2 types of current flow:
•
•
Electron current
Hole current
El t
Electron
Current
C
t
•
•
When voltage is applied across a piece of intrinsic
silicon, free electrons are easily attracted towards
the positive end.
This movement caused the electron current.
Hole Current
•
•
•
•
Holes created when valence electrons escaped.
p
Valence electrons remaining at valence band are
still attached to their atoms.
They could only move into a nearby hole with little
change in its energy level, thus leaving another hole
behind.
The hole appears to move from one place to the
nextt in
i the
th crystal
t l structure.
t t
This
Thi ‘‘movement’
t’ off h
hole
l
is called hole current.
Cont...
Cont
When a valence electron moves left to right to fill a hole while leaving another hole behind, the hole has effectively moved from right to left. Gray arrows indicate effective movement of a hole.
FIGURE 1‐13 Hole current in intrinsic silicon.
Cont...
Cont
Electron current
-
+
Hole current
The direction of hole current is normally used as the
conventional current direction.
El t
Electron
and
dH
Hole
l C
Currentt
Electron Current
• Movement of free
electrons in the
conduction band.
• Electron posses the
conduction band.
Hole Current
• Movement of valence
band electron in the
valence band to fill up the
hole left when an electron
moves into the
conduction band.
• Electron posses the
valence band energy.
Review
1. At room temperature, an intrinsic semiconductor
__________
has some holes in it due to __________.
2. The merging
g g of a free electron and a hole is called
__________.
3. __________ electrons are responsible for current in
a material.
4. Hole current occurs at the __________ level.
Semiconductor Material
1.1
Atomic Structure
12
1.2
Materials Classification
1.3
Energy Band
1.4
Covalent Bonds
1.5
Conduction in Semiconductors
1.6
p type and n type semiconductors
- Doping
- majority
j y and minority
y carriers
Doping
• A process of adding impurities to intrinsic (pure)
Sili
Silicon
and
dG
Germanium
i
tto improve
i
th
the
conductivity of the semiconductor material.
• 2 types of semiconductor material that are
subjected to doping process which are:
• N-type
yp
• P-type
C t
Cont..
• 2 types of semiconductor material that are
subjected to doping process which are:
• N-type
• P-type
P t pe
• 2 types of elements used doping are:
• Trivalent element – with 3 valence electrons
• Pentavalent element – with 5 valence electrons
N type Semiconductor
N-type
• Pentavalent impurity
p y atoms are added – Arsenic ((As),
),
phosphorus (P),bismuth (Bi),
• Pentavalent also known as a donor atoms since they
donate electrons. When a pentavalent atom is added to
an intrinsic semiconductor, it’ll readily donate it’s 5th
electron, as a result – becomes n-type extrinsic
semiconductor.
semiconductor
N type Semiconductor
N-type
• Each pentavalent atom forms
covalent bond with 4 adjacent Si atom
• Since only 4 electrons are needed to
form a covalent bond, leaving
g an extra
electron – becomes a free electron
when each pentavalent atom is
added
dd d
•In n-type
type material
ate a e
electrons
ect o s a
are
e
majority carrier, and holes the minority
carrier
P type Semiconductor
P-type
• Trivalent ( with 3 valence electrons) impurity atoms are
added – Aluminium (Al), boron (B), indium (In),gallium (Ga)
• Trivalent also known as a acceptor atom since they accpet
electrons When a trivalent atom is added to an intrinsic
electrons.
semiconductor, it’ll readily accept free electron, as a result –
becomes p
p-type
type extrinsic semiconductor.
Pt
P-type
Semiconductor
S i
d t
• Each trivalent atom forms covalent
bond with 4 adjacent Si atom.
•Since 4 electrons are needed to
form a covalent bond
bond, causes an
existence of hole in the covalent
bonding.
• It also causes a lack of valence
electrons in the B atoms
• In p-type material holes are majority
carrier, and electron the minority
carrier
Review..
Review
1. What’s the difference between a pentavalent atom
and
d a ttrivalent
i l t atom?
t ?
2. By what process are the majority carriers produced?
3. By what process are the minority carriers produced?
4 What’s
4.
What s the difference between intrinsic and extrinsic
semiconductors?