This document discusses energy bands in solids and semiconductor devices. It explains how the discrete energy levels in isolated atoms merge and form continuous energy bands as atoms are brought together in a solid. In semiconductors, the valence band is full while the conduction band is empty, with a small band gap between them. Thermally excited electrons can cross this gap, making semiconductors weakly conductive. Doping a semiconductor with impurities introduces donors or acceptors that increase the number of free electrons or holes, making it an n-type or p-type extrinsic semiconductor. The carrier concentrations and conductivity of semiconductors are determined by factors like doping level, temperature, and carrier mobilities.
Electrostatic potential and capacitanceEdigniteNGO
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Electrostatic potential and capacitanceEdigniteNGO
Hello everyone, we are from Edignite NGO and we have come up with chapters of class 11 and 12 (CBSE).
For any queries, please contact
Lekha Periwal : +916290889619
Heer Mehta : +917984844099
Semiconductor.pdf description ki last lin...KALPESH-JNV
Semiconductors (SC) are a class of materials that exhibit intermediate electrical conductivity between conductors (such as metals) & insulators (such as ceramics / plastics). They are used extensively in modern electronics, as the basis for the design & fabrication of transistors, diodes, integrated circuits.
The discovery of the SC properties dates back to the late 19th century, when experiments were carried out on the electrical conductivity of various materials. In 1874, Edwin Hall discovered the phenomenon of Hall effect, which led to the discovery of SC. The Hall effect occurs when a magnetic field is applied perpendicular to the flow of electric current in a conductor, resulting in a voltage difference across the conductor. This effect was found to be more pronounced in certain materials, such as Si & Ge, which led to further investigations into their electrical properties.
SC are characterized by their unique band structure, which determines their electrical conductivity. In an ideal SC crystal, the valence band (the highest occupied energy band) is separated from the conduction band (the lowest unoccupied energy band) by a bandgap. The bandgap is a measure of the energy required to move an electron from the valence band to the conduction band, and determines whether a material is a conductor, an insulator, or a SC.
At absolute zero temperature, all electrons in a SC crystal occupy the valence band, and there are no electrons in the conduction band. However, as the temperature increases, some of the electrons gain enough energy to jump across the bandgap and move to the conduction band, where they are free to move and conduct electricity. This process is called thermal excitation, and it is responsible for the temperature dependence of the electrical conductivity of SC.
SC can be classified into two main types based on their doping properties: intrinsic and extrinsic. Intrinsic SC are pure materials such as Si or Ge, which have no impurities or dopants added to them. Intrinsic SC have a relatively low electrical conductivity at room temperature due to the presence of the bandgap. Extrinsic SC, on the other hand, are doped with impurities to modify their electrical properties.
Doping is the process of intentionally introducing impurities (also called dopants) into a SC crystal to modify its electrical properties. The impurities can either donate or accept electrons, creating excess or deficient electrons, respectively, in the crystal lattice. This alters the band structure and conductivity of the SC, making it more useful for electronic applications.
Extrinsic SC can be further classified into two types: n-type and p-type. N-type SC are doped with impurities that have excess electrons (such as phosphorus)
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Introduction
Formation Of Bond.
Formation Of Band.
Role Of Pauli Exclusion Principle.
Fermi Dirac Distribution Equation
Classification Of Material In Term Of Energy Band Diagram.
Intrinsic Semiconductor.
a)Drive Density Of State
b)Drive Density Of Free Carrier.
c)Determination Of Fermi Level Position
Extrinsic Semiconductor.
a) N Type Extrinsic Semiconductor
b) P Type Extrinsic Semiconductor
Compensated semiconductor.
E Vs. Diagram.
Direct and Indirect Band Gap.
Degenerated and Non-degenerated.
PN Junction.
We all have good and bad thoughts from time to time and situation to situation. We are bombarded daily with spiraling thoughts(both negative and positive) creating all-consuming feel , making us difficult to manage with associated suffering. Good thoughts are like our Mob Signal (Positive thought) amidst noise(negative thought) in the atmosphere. Negative thoughts like noise outweigh positive thoughts. These thoughts often create unwanted confusion, trouble, stress and frustration in our mind as well as chaos in our physical world. Negative thoughts are also known as “distorted thinking”.
Read| The latest issue of The Challenger is here! We are thrilled to announce that our school paper has qualified for the NATIONAL SCHOOLS PRESS CONFERENCE (NSPC) 2024. Thank you for your unwavering support and trust. Dive into the stories that made us stand out!
How to Create Map Views in the Odoo 17 ERPCeline George
The map views are useful for providing a geographical representation of data. They allow users to visualize and analyze the data in a more intuitive manner.
Instructions for Submissions thorugh G- Classroom.pptxJheel Barad
This presentation provides a briefing on how to upload submissions and documents in Google Classroom. It was prepared as part of an orientation for new Sainik School in-service teacher trainees. As a training officer, my goal is to ensure that you are comfortable and proficient with this essential tool for managing assignments and fostering student engagement.
How to Make a Field invisible in Odoo 17Celine George
It is possible to hide or invisible some fields in odoo. Commonly using “invisible” attribute in the field definition to invisible the fields. This slide will show how to make a field invisible in odoo 17.
The Indian economy is classified into different sectors to simplify the analysis and understanding of economic activities. For Class 10, it's essential to grasp the sectors of the Indian economy, understand their characteristics, and recognize their importance. This guide will provide detailed notes on the Sectors of the Indian Economy Class 10, using specific long-tail keywords to enhance comprehension.
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2024.06.01 Introducing a competency framework for languag learning materials ...Sandy Millin
http://sandymillin.wordpress.com/iateflwebinar2024
Published classroom materials form the basis of syllabuses, drive teacher professional development, and have a potentially huge influence on learners, teachers and education systems. All teachers also create their own materials, whether a few sentences on a blackboard, a highly-structured fully-realised online course, or anything in between. Despite this, the knowledge and skills needed to create effective language learning materials are rarely part of teacher training, and are mostly learnt by trial and error.
Knowledge and skills frameworks, generally called competency frameworks, for ELT teachers, trainers and managers have existed for a few years now. However, until I created one for my MA dissertation, there wasn’t one drawing together what we need to know and do to be able to effectively produce language learning materials.
This webinar will introduce you to my framework, highlighting the key competencies I identified from my research. It will also show how anybody involved in language teaching (any language, not just English!), teacher training, managing schools or developing language learning materials can benefit from using the framework.
The Roman Empire A Historical Colossus.pdfkaushalkr1407
The Roman Empire, a vast and enduring power, stands as one of history's most remarkable civilizations, leaving an indelible imprint on the world. It emerged from the Roman Republic, transitioning into an imperial powerhouse under the leadership of Augustus Caesar in 27 BCE. This transformation marked the beginning of an era defined by unprecedented territorial expansion, architectural marvels, and profound cultural influence.
The empire's roots lie in the city of Rome, founded, according to legend, by Romulus in 753 BCE. Over centuries, Rome evolved from a small settlement to a formidable republic, characterized by a complex political system with elected officials and checks on power. However, internal strife, class conflicts, and military ambitions paved the way for the end of the Republic. Julius Caesar’s dictatorship and subsequent assassination in 44 BCE created a power vacuum, leading to a civil war. Octavian, later Augustus, emerged victorious, heralding the Roman Empire’s birth.
Under Augustus, the empire experienced the Pax Romana, a 200-year period of relative peace and stability. Augustus reformed the military, established efficient administrative systems, and initiated grand construction projects. The empire's borders expanded, encompassing territories from Britain to Egypt and from Spain to the Euphrates. Roman legions, renowned for their discipline and engineering prowess, secured and maintained these vast territories, building roads, fortifications, and cities that facilitated control and integration.
The Roman Empire’s society was hierarchical, with a rigid class system. At the top were the patricians, wealthy elites who held significant political power. Below them were the plebeians, free citizens with limited political influence, and the vast numbers of slaves who formed the backbone of the economy. The family unit was central, governed by the paterfamilias, the male head who held absolute authority.
Culturally, the Romans were eclectic, absorbing and adapting elements from the civilizations they encountered, particularly the Greeks. Roman art, literature, and philosophy reflected this synthesis, creating a rich cultural tapestry. Latin, the Roman language, became the lingua franca of the Western world, influencing numerous modern languages.
Roman architecture and engineering achievements were monumental. They perfected the arch, vault, and dome, constructing enduring structures like the Colosseum, Pantheon, and aqueducts. These engineering marvels not only showcased Roman ingenuity but also served practical purposes, from public entertainment to water supply.
1. SOLIDS AND SEMICONDUCTOR DEVICES - I
1. Energy Bands in Solids
2. Energy Band Diagram
3. Metals, Semiconductors and Insulators
4. Intrinsic Semiconductor
5. Electrons and Holes
6. Doping of a Semiconductor
7. Extrinsic Semiconductor
8. N-type and P-type Semiconductor
9. Carrier Concentration in Semiconductors
10.Distinction between Intrinsic and Extrinsic Semiconductors
11.Distinction between Semiconductor and Metal
12.Conductivity of a Semiconductor
2. Energy Bands in Solids:
According to Quantum Mechanical Laws, the energies of electrons in a
free atom can not have arbitrary values but only some definite
(quantized) values.
However, if an atom belongs to a crystal, then the energy levels are
modified.
This modification is not appreciable in the case of energy levels of
electrons in the inner shells (completely filled).
But in the outermost shells, modification is appreciable because the
electrons are shared by many neighbouring atoms.
Due to influence of high electric field between the core of the atoms and
the shared electrons, energy levels are split-up or spread out forming
energy bands.
Consider a single crystal of silicon having N atoms. Each atom can be
associated with a lattice site.
Electronic configuration of Si is 1s2
, 2s2
, 2p6
,3s2
, 3p2
. (Atomic No. is 14)
3. O
• •
• •
• •• •• •
• •
• •
1s2
2s2
2p6
3p2
3s2
Inter atomic spacing (r)
Energy
a b c d
Conduction Band
Valence Band
Forbidden Energy Gap
Ion
core
state
Formation of Energy Bands in Solids:
4. Each of N atoms has its own energy levels. The energy levels are identical,
sharp, discrete and distinct.
The outer two sub-shells (3s and 3p of M shell or n = 3 shell) of silicon atom
contain two s electrons and two p electrons. So, there are 2N electrons
completely filling 2N possible s levels, all of which are at the same energy.
Of the 6N possible p levels, only 2N are filled and all the filled p levels have
the same energy.
(ii) Oc < r < Od:
There is no visible splitting of energy levels but there develops a tendency
for the splitting of energy levels.
(iii) r = Oc:
The interaction between the outermost shell electrons of neighbouring
silicon atoms becomes appreciable and the splitting of the energy levels
commences.
(i) r = Od (>> Oa):
(iv) Ob < r < Oc:
The energy corresponding to the s and p levels of each atom gets slightly
changed. Corresponding to a single s level of an isolated atom, we get 2N
levels. Similarly, there are 6N levels for a single p level of an isolated atom.
5. Since N is a very large number (≈ 1029
atoms / m3
) and the energy of each level
is of a few eV, therefore, the levels due to the spreading are very closely
spaced. The spacing is ≈ 10-23
eV for a 1 cm3
crystal.
The collection of very closely spaced energy levels is called an energy band.
(v) r = Ob:
The energy gap disappears completely. 8N levels are distributed
continuously. We can only say that 4N levels are filled and 4N levels are
empty.
(v) r = Oa:
The band of 4N filled energy levels is separated from the band of 4N unfilled
energy levels by an energy gap called forbidden gap or energy gap or
band gap.
The lower completely filled band (with valence electrons) is called the
valence band and the upper unfilled band is called the conduction band.
Note:
1. The exact energy band picture depends on the relative orientation of
atoms in a crystal.
2. If the bands in a solid are completely filled, the electrons are not permitted
to move about, because there are no vacant energy levels available.
6. Metals:
Conduction Band
• •• •• •
Valence Band
Partially filled
Conduction Band
• •• •• •
The first possible energy band diagram
shows that the conduction band is only
partially filled with electrons.
With a little extra energy the electrons
can easily reach the empty energy
levels above the filled ones and the
conduction is possible.
The second possible energy band
diagram shows that the conduction
band is overlapping with the valence
band.
This is because the lowest levels in the
conduction band needs less energy
than the highest levels in the valence
band.
The electrons in valence band overflow
into conduction band and are free to
move about in the crystal for
conduction.
The highest energy level in the
conduction band occupied by
electrons in a crystal, at absolute 0
temperature, is called Fermi Level.
The energy corresponding to this
energy level is called Fermi energy.
If the electrons get enough energy
to go beyond this level, then
conduction takes place.
7. Conduction Band
Valence Band
Forbidden Energy Gap
• •••
≈1 eV
Semiconductors:
Eg-Si = 1.1 eV EgGe= 0.74 eV
At absolute zero temperature, no
electron has energy to jump from
valence band to conduction band
and hence the crystal is an insulator.
At room temperature, some valence
electrons gain energy more than the
energy gap and move to conduction
band to conduct even under the
influence of a weak electric field.
The fraction is p α e
-
Eg
kB T
Since Eg is small, therefore, the fraction
is sizeable for semiconductors.
As an electron leaves the valence band, it leaves some energy level in band
as unfilled.
Such unfilled regions are termed as ‘holes’ in the valence band. They are
mathematically taken as positive charge carriers.
Any movement of this region is referred to a positive hole moving from one
position to another.
•• ••
8. Conduction Band
Forbidden Energy Gap
Valence Band
• •• •• •
≈6 eV
Insulators:
Eg-Diamond = 7 eV
Electrons, however heated, can not
practically jump to conduction band
from valence band due to a large
energy gap. Therefore, conduction is
not possible in insulators.
Electrons and Holes:
On receiving an additional energy, one of the electrons from a covalent band
breaks and is free to move in the crystal lattice.
While coming out of the covalent bond, it leaves behind a vacancy named
‘hole’.
An electron from the neighbouring atom can break away and can come to the
place of the missing electron (or hole) completing the covalent bond and
creating a hole at another place.
The holes move randomly in a crystal lattice.
The completion of a bond may not be necessarily due to an electron from a
bond of a neighbouring atom. The bond may be completed by a conduction
band electron. i.e., free electron and this is referred to as ‘electron – hole
recombination’.
9. Intrinsic or Pure Semiconductor:
C.B
V.B
Eg 0.74 eV
Heat Energy
+
+
+
Ge Ge
Ge Ge
Ge Ge
Ge Ge
Ge Ge
Ge Ge
Ge Ge
Ge Ge
Broken Covalent Bond
Free electron ( - )
Valence electrons
Covalent Bond
Hole ( + )
10. Intrinsic Semiconductor is a pure semiconductor.
The energy gap in Si is 1.1 eV and in Ge is 0.74 eV.
Ge: 1s2
, 2s2
, 2p6
,3s2
, 3p6
, 3d10
, 4s2
, 4p2
. (Atomic No. is 32)
Si: 1s2
, 2s2
, 2p6
,3s2
, 3p2
. (Atomic No. is 14)
In intrinsic semiconductor, the number of thermally generated electrons
always equals the number of holes.
So, if ni and pi are the concentration of electrons and holes respectively, then
ni = pi.
The quantity ni or pi is referred to as the ‘intrinsic carrier concentration’.
Doping a Semiconductor:
Doping is the process of deliberate addition of a very small amount of
impurity into an intrinsic semiconductor.
The impurity atoms are called ‘dopants’.
The semiconductor containing impurity is known as ‘impure or extrinsic
semiconductor’.
Methods of doping:
i) Heating the crystal in the presence of dopant atoms.
ii) Adding impurity atoms in the molten state of semiconductor.
iii) Bombarding semiconductor by ions of impurity atoms.
11. Extrinsic or Impure Semiconductor:
N - Type Semiconductors:
Ge Ge Ge
Ge
Ge
Ge
Ge Ge
+
+
As
0.045 eV
Eg = 0.74 eV
C.B
V.B
Donor level
-
When a semiconductor of Group IV (tetra valent) such as Si or Ge is doped
with a penta valent impurity (Group V elements such as P, As or Sb), N –
type semiconductor is formed.
When germanium (Ge) is doped with arsenic (As), the four valence
electrons of As form covalent bonds with four Ge atoms and the fifth
electron of As atom is loosely bound.
12. The energy required to detach the fifth loosely bound electron is only of
the order of 0.045 eV for germanium.
A small amount of energy provided due to thermal agitation is sufficient to
detach this electron and it is ready to conduct current.
The force of attraction between this mobile electron and the positively
charged (+ 5) impurity ion is weakened by the dielectric constant of the
medium.
So, such electrons from impurity atoms will have energies slightly less
than the energies of the electrons in the conduction band.
Therefore, the energy state corresponding to the fifth electron is in the
forbidden gap and slightly below the lower level of the conduction band.
This energy level is called ‘donor level’.
The impurity atom is called ‘donor’.
N – type semiconductor is called ‘donor – type semiconductor’.
13. When intrinsic semiconductor is doped with donor impurities, not only does
the number of electrons increase, but also the number of holes decreases
below that which would be available in the intrinsic semiconductor.
The number of holes decreases because the larger number of electrons
present causes the rate of recombination of electrons with holes to increase.
Consequently, in an N-type semiconductor, free electrons are the majority
charge carriers and holes are the minority charge carriers.
Carrier Concentration in N - Type Semiconductors:
If n and p represent the electron and hole concentrations respectively in
N-type semiconductor, then
n p = ni pi = ni
2
where ni and pi are the intrinsic carrier concentrations.
The rate of recombination of electrons and holes is proportional to n and p.
Or, the rate of recombination is proportional to the product np. Since the
rate of recombination is fixed at a given temperature, therefore, the product
np must be a constant.
When the concentration of electrons is increased above the intrinsic value
by the addition of donor impurities, the concentration of holes falls below
its intrinsic value, making the product np a constant, equal to ni
2
.
14. P - Type Semiconductors:
When a semiconductor of Group IV (tetra valent) such as Si or Ge is doped
with a tri valent impurity (Group III elements such as In, B or Ga), P – type
semiconductor is formed.
When germanium (Ge) is doped with indium (In), the three valence
electrons of In form three covalent bonds with three Ge atoms. The
vacancy that exists with the fourth covalent bond with fourth Ge atom
constitutes a hole.
Ge Ge Ge
Ge
Ge
Ge
Ge Ge
+
+
In 0.05 eV
Eg = 0.74 eV
C.B
V.B
Acceptor level
15. The hole which is deliberately created may be filled with an electron from
neighbouring atom, creating a hole in that position from where the electron
jumped.
Therefore, the tri valent impurity atom is called ‘acceptor’.
Since the hole is associated with a positive charge moving from one position
to another, therefore, this type of semiconductor is called
P – type semiconductor.
The acceptor impurity produces an energy level just above the valence band.
This energy level is called ‘acceptor level’.
The energy difference between the acceptor energy level and the top of the
valence band is much smaller than the band gap.
Electrons from the valence band can, therefore, easily move into the acceptor
level by being thermally agitated.
P – type semiconductor is called ‘acceptor – type semiconductor’.
In a P – type semiconductor, holes are the majority charge carriers and the
electrons are the minority charge carriers.
It can be shown that, n p = ni pi = ni
2
16. Distinction between Intrinsic and Extrinsic Semiconductor:
S. No. Intrinsic SC Extrinsic SC
1 Pure Group IV elements. Group III or Group V elements
are introduced in Group IV
elements.
2 Conductivity is only slight. Conductivity is greatly
increased.
3 Conductivity increases with rise
in temperature.
Conductivity depends on the
amount of impurity added.
4 The number of holes is always
equal to the number of free
electrons.
In N-type, the no. of electrons is
greater than that of the holes
and in P-type, the no. holes is
greater than that of the
electrons.
17. Distinction between Semiconductor and Metal:
S. No. Semiconductor Metal
1 Semiconductor behaves like an
insulator at 0 K. Its conductivity
increases with rise in
temperature.
Conductivity decreases with
rise in temperature.
2 Conductivity increases with rise
in potential difference applied.
Conductivity is an intrinsic
property of a metal and is
independent of applied potential
difference.
3 Does not obey Ohm’s law or
only partially obeys.
Obeys Ohm’s law.
4 Doping the semiconductors with
impurities vastly increases the
conductivity.
Making alloy with another metal
decreases the conductivity.
18. σ = e (neμe + nhμh)Or
Electrical Conductivity of Semiconductors:
E
IeIhI = Ie + Ih
Ie = neeAve Ih = nheAvh
So, I = neeAve + nheAvh
If the applied electric field is small,
then semiconductor obeys Ohm’s law.
V
R
= neeAve + nheAvh
= eA (neve + nhvh)
Or
V A
ρl
= eA (neve + nhvh)
since
A
ρl
R =
E
ρ
= e (neve + nhvh) since E =
l
V
Mobility (μ) is defined as the drift
velocity per unit electric field.
1
ρ
= e (neμe + nhμh)
Note:
1. The electron mobility is higher than the hole mobility.
2. The resistivity / conductivity depends not only on the
electron and hole densities but also on their mobilities.
3. The mobility depends relatively weakly on temperature. End of S & SC - I
I