Semiconductor physics electronic devices

SEMICONDUCTOR PHYSICS
PRESENTED BY:- GURKIRAT SINGH

Overview
 Atomic Bonding
 Energy Bands
 Resistivity
 Electronic Materials
 Semiconductors
 Types of Semiconductors
 P-type and N-type semiconductors
 Diodes
Presented By:-Gurkirat Singh (Electrical
Engineering)

Atomic Bonds
 Atomic bonding is chemical bonding. Chemical
bonding is the physical process that is responsible
for the interactions between atoms and molecules.
Bonds vary widely; there are covalent, ionic,
hydrogen, metallic, as well as many other types of
bonds.
Engineering)

Types of Atomic Bonds
 Metallic Bond
Metallic bonds are a metal, and share outer bonds
with atoms in a solid. Each atom gives off a positive
charge by shedding (give off) its outer electrons, and the
negatively charges electrons hold the metal atoms
together.
Engineering)

 Ionic Bond
Atoms are filled with an outer shell of electrons.
Electron shells are filled by transferring electrons
from one atom to the next. Donor atoms will take on
a positive charge, and the acceptors will have a
negative charge. They will attract each other by
being positive and negative, and bonding will then
occur.
 Covalent Bonds
Atoms like to share their electrons and this
causes their outer shell to be complete. A covalent
bond is produced by the sharing of atoms and
electrons. This produces a strong covalent bond.
Engineering)

Engineering)

Energy bands
 The intermixing of atoms in solids,
instead of single energy levels, there will
be bands of energy levels formed.
These set of energy levels, which are
closely packed are called as Energy
bands.
Engineering)

Classification of Energy Bands
 Valance Band : The electrons
that are present in the
outermost shell, containing a
series of energy levels, form
an energy band which is
called as Valence Band.
The valence band is
the band having the highest
occupied energy.
 Conduction Band :
These free electrons are
the ones which conduct
the current in a
conductor and hence
called as Conduction
Electrons. The band
which contains
conduction electrons is
called as Conduction
Band. The conduction
band is the band having
the lowest occupied
energy.
Engineering)

 Forbidden gap : The gap between valence band and
conduction band is called as forbidden energy gap. As the
name implies, this band is the forbidden one without energy.
Hence no electron stays in this band. The valence electrons,
while going to the conduction band, pass through this.
 The following figure shows the structure of energy bands in
solids.
Engineering)

Resistivity
 The electrical Resistance of an electrical or
electronic component or device is generally
defined as being the ratio of the voltage difference
across it to the current flowing through it,
basic Ohm´s Law principals. The quantity that is
used to indicate this specific resistance is
called Resistivity and is given the Greek symbol
of ρ, (Rho). Resistivity is measured in Ohm-
metres, (Ω.m ). Resistivity is the inverse to
conductivity.
Engineering)

Electronic Materials
 The goal of electronic materials is to
generate and control the flow of an
electrical current.
 Electronic materials include:
1. Conductors: have low resistance which
allows electrical current flow
2. Insulators: have high resistance which
suppresses electrical current flow
3. Semiconductors: can allow or suppress
electrical current flow
Engineering)

Semiconductors
 Semiconductors are
materials that essentially
can be conditioned to act
as good conductors, or
good insulators, or any
thing in between.
 Common elements such
as carbon, silicon, and
germanium are
semiconductors.
 Silicon is the best and
most widely used
semiconductor.
 Low resistivity =>
“conductor”
 High resistivity =>
“insulator”
 Intermediate
resistivity =>
“semiconductor”
 conductivity lies
between that of
conductors and
insulators
 generally crystalline
in structure for IC
devices
Engineering)

Semiconductor Materials
Engineering)

Semiconductor Valence Orbit
 The main
characteristic of a
semiconductor
element is that it has
four electrons in its
outer or valence
orbit.
Engineering)

Crystal Lattice Structure
2D Crystal Lattice Structure
 The unique capability of
semiconductor atoms is
their ability to link
together to form a
physical structure called
a crystal lattice.
 The atoms link together
with one another sharing
their outer electrons.
 These links are called
covalent bonds.
Engineering)

3D Crystal Lattice Structure
Engineering)

Types of Semiconductors
Semiconductors are mainly two types
1. Intrinsic (Pure) Semiconductors
2. Extrinsic (Impure) Semiconductors
 Intrinsic Semiconductors: A
Semiconductor which does not
have any kind of impurities,
behaves as an Insulator at 0k
and behaves as a Conductor at
higher temperature is known
as Intrinsic Semiconductor or
Pure Semiconductors.
Example: Germanium and
Silicon.
Engineering)

Extrinsic Semiconductors
 The Extrinsic Semiconductors are those in which
impurities of large quantity are present. Usually, the
impurities can be either 3rd group elements or 5th
group elements.
 Based on the impurities present in the Extrinsic
Semiconductors, they are classified into two
categories.
1. N-type semiconductors
2. P-type semiconductors
Engineering)

 When any pentavalent element such as Phosphorous,
Arsenic or Antimony is added to the intrinsic
Semiconductor , four electrons are involved in covalent
bonding with four neighboring pure Semiconductor atoms.
 The fifth electron is weakly bound to the parent atom. And
even for lesser thermal energy it is released Leaving the
parent atom positively ionized. The Intrinsic
Semiconductors doped with pentavalent impurities are
called N-type Semiconductors.
 The energy level of fifth electron is called donor level. The
donor level is close to the bottom of the conduction band
most of the donor level electrons are excited in to the
conduction band at room temperature and become the
Majority charge carriers.
 Hence in N-type Semiconductors electrons are Majority
carriers and holes are Minority carriers.
N - type Semiconductors
Engineering)

P-type Semiconductors
 When a trivalent elements such as Al, Ga or Indium have
three electrons in their outer most orbits , added to the
intrinsic semiconductor all the three electrons of Indium are
engaged in covalent bonding with the three neighboring Si
atoms.
 Indium needs one more electron to complete its bond. this
electron maybe supplied by Silicon , there by creating a
vacant electron site or hole on the semiconductor atom.
 Indium accepts one extra electron, the energy level of this
impurity atom is called acceptor level and this acceptor
level lies just above the valence band.
 These type of trivalent impurities are called acceptor
impurities and the semiconductors doped the acceptor
impurities are called P-type semiconductors.Presented By:-Gurkirat Singh (Electrical
Engineering)

2D Crystal Lattice Structure of Silicon Doped
with (i) Boron (ii) Phosphorus
Engineering)

Diodes
Electronic devices created by bringing
together a p-type and n-type region
within the same semiconductor lattice.
Used for rectifiers, LED etc
Engineering)

Diodes
It is represented by the following
symbol, where the arrow indicates the
direction of positive current flow.
Engineering)

Forward Bias and Reverse Bias
 Forward Bias : Connect positive of the
Diode to positive of supply…negative of
Diode to negative of supply
 Reverse Bias: Connect positive of the
Diode to negative of supply…negative of
diode to positive of supply.
Engineering)

Characteristics of Diode
 Diode always conducts in one direction.
 Diodes always conduct current when
“Forward Biased” ( Zero resistance)
 Diodes do not conduct when Reverse
Biased
(Infinite resistance)
Engineering)

I-V characteristics of Ideal diode
Engineering)

I-V Characteristics of Practical Diode
Engineering)

Rectification
 Converting ac to dc is accomplished by
the process of rectification.
 Two processes are used:
 Half-wave rectification;
 Full-wave rectification.
Engineering)

Half-wave Rectification
 Simplest process
used to convert ac to
dc.
 A diode is used to
clip the input signal
excursions of one
polarity to zero.
Engineering)

Terminology
donor: impurity atom that increases n
acceptor: impurity atom that increases p
N-type material: contains more electrons than holes
P-type material: contains more holes than electrons
majority carrier: the most abundant carrier
minority carrier: the least abundant carrier
intrinsic semiconductor: n = p = ni
extrinsic semiconductor: doped semiconductor
Engineering)

Summary
 The band gap energy is the energy required to free
an electron from a covalent bond.
 Eg for Si at 300K = 1.12eV
 In a pure Si crystal, conduction electrons and holes
are formed in pairs.
 Holes can be considered as positively charged mobile
particles which exist inside a semiconductor.
 Both holes and electrons can conduct current.
 Substitutional dopants in Si:
 Group-V elements (donors) contribute conduction
electrons
 Group-III elements (acceptors) contribute holes
 Very low ionization energies (<50 meV)
Engineering)

Semiconductor physics electronic devices

More Related Content

What's hot

Similar to Semiconductor physics electronic devices

More from Gurkirat Singh

Recently uploaded

Semiconductor physics electronic devices