Transcript intrinsic semiconductor

BASIC ELECTRONICS
presentation
BY
ARUP CHAKRABORTY
Introduction
 Lattice
 Super conductor & insulator
 Semi conductor : intrinsic & extrinsic
 Band theory of conduction
 Diode
 Rectifier
 Transistor
Lattice
 In mathematics, especially in geometry and group
theory, a lattice in R^n is a discrete subgroup of
R^n which spans the real vector space R^n .
 Every lattice in R^n can be generated from a basis
for the vector space by forming all linear
combinations with integer coefficients.
 A lattice may be viewed as a regular tiling of a space
by a primitive cell.
 Lattices have many significant applications in pure
mathematics, particularly in connection to Lie
algebras, number theory and group theory.
Lattice Energy
 The lattice energy of an ionic solid is a measure of
the strength of bonds in that ionic compound.
 It is usually defined as the enthalpy of formation of
the ionic compound from gaseous ions and as such is
invariably exothermic.
 In the case of NaCl, the lattice energy is the energy
released by the reaction
Na+ (g) + Cl− (g) → NaCl (s) which would amount to
-787 kJ/mol.
Equilateral Triangle Lattice
Concepted in
Euclidean
plane
NaCl Crystal Lattice
Lattice Enthalpy
Superconductor & Insulator
 Superconductivity is a phenomenon of exactly zero
electrical resistance and expulsion of magnetic fields
occurring in certain materials when cooled below a
characteristic critical temperature.
 An electrical insulator is a material whose internal
electric charges do not flow freely, and which therefore
does not conduct an electric current, under the influence
of an electric field.
 A perfect insulator does not exist, but some materials
such as glass, paper and Teflon, which have high
resistivity, are very good electrical insulators.
Semiconductor
 Semiconductors are of two types Intrinsic
 Extrinsic
Intrinsic Semiconductor
 An intrinsic semiconductor, also called an
undoped semiconductor or i-type
semiconductor, is a pure semiconductor without
any significant dopant species present.
 The number of charge carriers is therefore
determined by the properties of the material itself
instead of the amount of impurities.
 In intrinsic semiconductors the number of excited
electrons and the number of holes are equal: n = p.
Band Theory of conduction
Conduction
Band
Conduction
Band
Conduction
Band
Valence
Band
Valence
Band
Valence
Band
insulator
semiconductor
superconductor
Free & Bound Electron
• Free Electron : Electron that can move freely .
 Electron without the coulombian attraction force of
nucleus .
 Bound Electron : Electron that moves round the
nucleus .
 Electron feeling the coulombian attraction force
with the nucleus .
Concept of Hole
A
B
Semiconductor Resistance
resistance
temperature
Extrinsic Semiconductor
 An extrinsic semiconductor is a semiconductor that
has been doped, that is, into which a doping agent has
been introduced, giving it different electrical properties
than the intrinsic (pure) semiconductor.
 Doping involves adding dopant atoms to an intrinsic
semiconductor, which changes the electron and hole
carrier concentrations of the semiconductor at thermal
equilibrium.
 Dominant carrier concentrations in an extrinsic
semiconductor classify it as either an n-type or p-type
semiconductor.
Semiconductor Doping
 Semiconductor doping is the process that changes an
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intrinsic semiconductor to an extrinsic semiconductor.
During doping, impurity atoms are introduced to an
intrinsic semiconductor.
Impurity atoms are atoms of a different element than the
atoms of the intrinsic semiconductor.
Impurity atoms act as either donors or acceptors to the
intrinsic semiconductor, changing the electron and hole
concentrations of the semiconductor.
Impurity atoms are classified as donor or acceptor atoms
based on the effect they have on the intrinsic
semiconductor.
 The two types of extrinsic semiconductor
 N-type semiconductors
 P-type semiconductors
N-type semiconductors
 Extrinsic semiconductors with a larger electron
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concentration than hole concentration are known as ntype semiconductors.
The phrase 'n-type' comes from the negative charge of
the electron.
In n-type semiconductors, electrons are the majority
carriers and holes are the minority carriers.
N-type semiconductors are created by doping an intrinsic
semiconductor with donor impurities.
In an n-type semiconductor, the Fermi energy level is
greater than that of the intrinsic semiconductor and lies
closer to the conduction band than the valence band.
P type Semiconductor
 As opposed to n-type semiconductors, p-type
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semiconductors have a larger hole concentration than
electron concentration.
The phrase 'p-type' refers to the positive charge of the
hole.
In p-type semiconductors, holes are the majority carriers
and electrons are the minority carriers.
P-type semiconductors are created by doping an intrinsic
semiconductor with acceptor impurities.
P-type semiconductors have Fermi energy levels below
the intrinsic Fermi energy level. The Fermi energy level
lies closer to the valence band than the conduction band
in a p-type semiconductor.
N type
P type
Concept of Diode
 What is a diode?: a diode is such a semi conductor
device which does not follow Ohm’s Law.
 In electronics, a diode is a two-terminal electronic
component with an asymmetric transfer
characteristic, with low (ideally zero) resistance to
current flow in one direction, and high (ideally
infinite) resistance in the other.
 A semiconductor diode, the most common type
today, is a crystalline piece of semiconductor
material with a p-n junction connected to two
electrical terminals.
D
I
O
D
E
S
Depletion Region
p
n
Application of Reverse Bias
p
n
Rectifier
 A rectifier is an electrical device that converts alternating
current (AC), which periodically reverses direction, to direct
current (DC), which flows in only one direction. The process is
known as rectification.
 Rectifiers have many uses, but are often found serving as
components of DC power supplies and high-voltage direct
current power transmission systems.
 The simple process of rectification produces a type of DC
characterized by pulsating voltages and currents (although
still unidirectional).
 Depending upon the type of end-use, this type of DC current may
then be further modified into the type of relatively constant
voltage DC characteristically produced by such sources as
batteries and solar cells.
Half Wave Rectification
 In half wave rectification of a single-phase supply, either
the positive or negative half of the AC wave is passed,
while the other half is blocked. Because only one half of
the input waveform reaches the output, mean voltage is
lower.
 Half-wave rectification requires a single diode in a
single-phase supply, or three in a three-phase supply.
 Rectifiers yield a unidirectional but pulsating direct
current; half-wave rectifiers produce far more ripple than
full-wave rectifiers, and much more filtering is needed to
eliminate harmonics of the AC frequency from the
output.
Half Wave Rectifier ckt.(single phase)
Full Wave Rectification
 A full-wave rectifier converts the whole of the input
waveform to one of constant polarity (positive or
negative) at its output.
 Full-wave rectification converts both polarities of the
input waveform to DC (direct current), and yields a
higher mean output voltage.
 Two diodes and a center tapped transformer, or four
diodes in a bridge configuration and any AC source
(including a transformer without center tap), are needed.
Single semiconductor diodes, double diodes with
common cathode or common anode, and four-diode
bridges, are manufactured as single components.
Full Wave Rectifier Ckt.
Full Wave Rectifier(Graphical pattern)
 The no-load output DC voltage of an ideal half wave
rectifier is:
 The average and root-mean-square no-load output
voltages of an ideal single-phase full-wave rectifier
are:
Full Wave Rectifier(with vacuum tube)
3 Phase Rectification(graphically)
Bridge Rectifier
Disassembled Automobile Alternator
six
diodes
that
comprise
a fullwave
threephase
bridge
rectifier.
Transistor
 A transistor is a semiconductor device used to amplify
and switch electronic signals and electrical power.
 It is composed of semiconductor material with at least
three terminals for connection to an external circuit .
 A voltage or current applied to one pair of the transistor's
terminals changes the current through another pair of
terminals.
Because the controlled (output) power can be higher
than the controlling (input) power, a transistor can
amplify a signal.
//Today, some transistors are packaged individually, but
many more are found embedded in integrated circuits.
Bipolar Junction Transistor
n-p-n
p-n-p
About BJT
 Bipolar transistors are so named because they conduct by
using both majority and minority carriers.
 The bipolar junction transistor, the first type of transistor to
be mass-produced, is a combination of two junction diodes,
and is formed of either a thin layer of p-type semiconductor
sandwiched between two n-type semiconductors (an n-p-n
transistor), or a thin layer of n-type semiconductor
sandwiched between two p-type semiconductors (a p-n-p
transistor).
 This construction produces two p-n junctions: a base–
emitter junction and a base–collector junction, separated by
a thin region of semiconductor known as the base region
(two junction diodes wired together without sharing an
intervening semiconducting region will not make a
transistor).
The CE Characteristics of n-p-n Transistor
 Circuit: diagram :
 Characteristic curve :
(set 1)
IC
vCE
(Set 2)
Practical appearance of Transistor
Usage of Transistor
LED Spotlight
Single Transistor Radio