1003. electronics 1 slide
TRANSCRIPT
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INTRODUCTORY ELECTRONICS
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Atomic Structure
Electronic Materials
P-N Junction Diodes Bipolar Junction Transistors (BJTs)
OUTLINE
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ELECTRONICS
Is the study of the behaviour of electronsin vacuum(i.e. absence of air), fluids(i.e.
gases and liquids) and in crystals.
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THE STRUCTURE OF AN ATOM
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ENERGY BAND STRUCTURE
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ENERGY-BAND DIAGRAM
Valence
Band
Conduction
Band
Energy
Gap
Insulator
Valence
Band
Conduction
Band
Conductor
Valence
Band
ConductionBand
Energy Gap
Semiconductor
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ENERGY-BAND DIAGRAM
Valence Band
Conduction Band
Energy Gap
Electron
energy
Generation of electron-hole pairs
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SOLID STATE ELECTRONIC MATERIALS
There are three types
1. Insulators
2. Conductors
3. Semiconductors
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CLASSIFICATION OF THE MATERIALS
1. According to resistivity Resistivity is the primary parameter used to
distinguish between these materials
Insulators: Materials that have very high
resistance and oppose current
Examples of insulators: air, rubber, paper,
teflon,glass,mica etc
Conductors: Materials that have very low
resistance and pass current very easily
Examples of conductors: Iron, silver, copper,
gold, aluminum
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CLASSIFICATION OF THE MATERIALS
Semiconductors: Materials that have
properties which lie between insulators
and conductors
Examples are carbon, silicon, germanium
(elements types), Gallium Arsenide,
Silicon Carbide (compounds types)
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CLASSIFICATION OF THE MATERIALS
Temperature effects on Semiconductor Materials Conductivity of Semiconductor Material is directly
proportional to Temperature
Stated differently, Semiconductor Materials(Devices)
have Negative Temperature Coefficient of Resistance Semiconductors can therefore be controlled either to
Increase their resistance and behave more like insulator
or
Decrease their resistance and behave more like aconductor
This ability to vary semiconductors resistive property
makes it useful in electrical and electronics components
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CLASSIFICATION OF THE MATERIALS
2. According to energy gapLet us use Energy Band Diagram from
Slides 5,6 and 7 to explain.
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CLASSIFICATION OF THE MATERIALS
According to Number of Valence Electrons
Find out
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SEMICONDUCTOR
Semiconductors are a group of solids whose electricalproperties are intermediate between conductors andinsulators .
For example, the resistivity of a conductor is of the orderof 10-8m, that of an insulator is 104m and that of asemiconductor is 10-1m
BASIC SEMICONDUCTOR
CONCEPTS
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Semiconductors are group IV elements i.e.
each has four valence electrons.
They are therefore called Tetravalent
Atoms The valence electrons are shared with four
neighboring atoms in a tetrahedral
arrangement forming covalent bonds,which maintain the crystalline solid
structure.
BASIC SEMICONDUCTOR
CONCEPTS
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BASIC SEMICONDUCTOR CONCEPTS
Silicon crystalline structure with covalent bonds
Si
Si
Si Si
SiSi
Si SiSi
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BASIC SEMICONDUCTOR CONCEPTS
(Semiconductor Atoms)
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BASIC SEMICONDUCTOR
CONCEPTS
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BASIC SEMICONDUCTOR
CONCEPTSINTRINSIC SEMICONDUCTOR
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DOPING
The main reason semiconductor materials
are so useful is that their behaviour can
easily be manipulated by the addition ofimpurities, through a process called doping.
Doping is the process of adding an impurity
atom to an intrinsic semiconductor to alter
its electrical conductivity
What is the purpose of doping?
Doping produces Extrinsic Semiconductor
BASIC SEMICONDUCTOR
CONCEPTS
http://en.wikipedia.org/wiki/Doping_(Semiconductors)http://en.wikipedia.org/wiki/Doping_(Semiconductors) -
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BASIC SEMICONDUCTOR
CONCEPTS Types of Extrinsic Semiconductor
N- type Semiconductor
P-type Semiconductor
N- type Semiconductor is produced by using
pentavalent atom(eg , phosphorus,
antimony, arsenic) P-type Semiconductor is produced by using
trivalent atom(eg boron, aluminium)
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BASIC SEMICONDUCTOR
CONCEPTS (N-TYPE)
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BASIC SEMICONDUCTOR
CONCEPTS(P-TYPE)
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Mobile Charge Carriers And Immobile Ions
Recall the formation of
P-Type material
The number of holes
added is equal to the
number of boron atoms When the hole move away from its parent atom, the
remaining atom becomes a negative ion.
Unlike the mobile and free moving holes, this ion cannot
take part in conduction because it is fixed in the crystallattice.
This immobile ions are shown by circled minus signs
whereas the free and mobile holes are shown by uncircled
plus signs.
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Mobile Charge Carriers And Immobile Ions
Thermally generated electrons (minority carriers in this case) are
shown by un circled minus signs.
Similarly in N-Type material, the number of free and mobile electrons
which are added equals the number of donor atoms
Again, when an electron moves away from its parent atom, it leaves
behind positive ion.
This ion being fixed in the crystal structure cannot take part in
conduction.
These immobile ions are represented by circled plus signs whereas
free and mobile electrons are represented uncircled minus signs.
The thermally generated holes (minority carriers in this case) areshown by uncircled plus signs
In the figure ( with without minority carriers) the minority carriers of both
types have been neglected.
Hence the figure does not show the small number of free electrons in
the P-type material or the small number of free holes in the N-typematerial.
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P-N JUNCTION DIODE
Formed when a pure semiconductor isdoped in such a way that one half is P-Type
and the other half is N-Type
P-n junction
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P-N JUNCTION DIODE
(THEORY)
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BIASING THE DIODE
Two methods of biasing the diodeForward Biasing
Reverse Biasing
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P-N JUNCTION
FORWARD BIAS
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P-N JUNCTION
REVERSE BIAS
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P-N JUNCTION REVERSE BIAS
As shown in the circuit diagram, the barrierwidens as
Free electrons flows towards the positive
terminal of the battery and Holes towards the negative terminal.
Under normal circumstances, no current
should flowBut practically, small amount of current flows
through the circuit
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P-N JUNCTION REVERSE BIAS
For a high applied pd (reverse bias),abreakdown of the barrier occurs leading to
a large reverse current.
The breakdown occurs due to two effects Zener effect
Avalanche effect
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P-N JUNCTION REVERSE BIAS
Zener effect Zener breakdown occurs when the electric
field in the depletion layer increases to thepoint where it can break covalent bonds andgenerate electron hole pairs.
Avalanche effect
This occurs when the minority carriers that
cross the depletion region under the influenceof the electric field, gain sufficient kineticenergy to be able to break covalent bonds in
atoms with which they collide
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I-V CHARACTERISTICS
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Semiconductor devices play an indispensable role inelectronics
Semiconductor devices are electronic componentsthat exploit the electronicproperties of
semiconductormaterials, principally silicon,germanium, and gallium arsenideetc.
SEMICONDUCTOR DEVICES
http://en.wikipedia.org/wiki/Electronic_componenthttp://en.wikipedia.org/wiki/Electronicshttp://en.wikipedia.org/wiki/Semiconductorhttp://en.wikipedia.org/wiki/Siliconhttp://en.wikipedia.org/wiki/Germaniumhttp://en.wikipedia.org/wiki/Gallium_arsenidehttp://en.wikipedia.org/wiki/Gallium_arsenidehttp://en.wikipedia.org/wiki/Germaniumhttp://en.wikipedia.org/wiki/Siliconhttp://en.wikipedia.org/wiki/Semiconductorhttp://en.wikipedia.org/wiki/Electronicshttp://en.wikipedia.org/wiki/Electronic_component -
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In the early days of radio and
television, transmitting and receiving
equipment relied on vacuum tubes, but
these have been completely replaced in
the last three decades by
semiconductor devices, which includetransistors, diodes, relays integrated
circuits and other electronic
components
SEMICONDUCTOR
DEVICES
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SEMICONDUCTOR
DEVICES
Diodes Transistors Integrated circuits
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SUMMARY
*Electronics
*Energy Band Concept*Basic Semiconductor Concepts
*PN junction
*I-V characteristics*Semiconductors Devices
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THANK YOU