This slide give you idea about the atomic structure, classification of solids based on valance electron, free electron, energy band description, why the silicon is used as semiconductor substance compare to germanium, semiconductor and its types.
Energy bands consisting of a large number of closely spaced energy levels exist in crystalline materials. The bands can be thought of as the collection of the individual energy levels of electrons surrounding each atom. The wavefunctions of the individual electrons, however, overlap with those of electrons confined to neighboring atoms. The Pauli exclusion principle does not allow the electron energy levels to be the same so that one obtains a set of closely spaced energy levels, forming an energy band. The energy band model is crucial to any detailed treatment of semiconductor devices. It provides the framework needed to understand the concept of an energy bandgap and that of conduction in an almost filled band as described by the empty states.
Electrical properties of materialsElectrical properties of materialsElectrical properties of materialsElectrical properties of materialsElectrical properties of materialsElectrical properties of materialsElectrical properties of materialsElectrical properties of materialsElectrical properties of materialsElectrical properties of materialsElectrical properties of materialsElectrical properties of materialsElectrical properties of materialsElectrical properties of materialsElectrical properties of materialsElectrical properties of materialsElectrical properties of materialsElectrical properties of materialsElectrical properties of materialsElectrical properties of materialsElectrical properties of materialsElectrical properties of materialsElectrical properties of materialsElectrical properties of materialsElectrical properties of materialsElectrical properties of materialsElectrical properties of materialsElectrical properties of materialsElectrical properties of materialsElectrical properties of materialsElectrical properties of materialsElectrical properties of materialsElectrical properties of materialsElectrical properties of materialsElectrical properties of materialsElectrical properties of materials
This slide give you idea about the atomic structure, classification of solids based on valance electron, free electron, energy band description, why the silicon is used as semiconductor substance compare to germanium, semiconductor and its types.
Energy bands consisting of a large number of closely spaced energy levels exist in crystalline materials. The bands can be thought of as the collection of the individual energy levels of electrons surrounding each atom. The wavefunctions of the individual electrons, however, overlap with those of electrons confined to neighboring atoms. The Pauli exclusion principle does not allow the electron energy levels to be the same so that one obtains a set of closely spaced energy levels, forming an energy band. The energy band model is crucial to any detailed treatment of semiconductor devices. It provides the framework needed to understand the concept of an energy bandgap and that of conduction in an almost filled band as described by the empty states.
Electrical properties of materialsElectrical properties of materialsElectrical properties of materialsElectrical properties of materialsElectrical properties of materialsElectrical properties of materialsElectrical properties of materialsElectrical properties of materialsElectrical properties of materialsElectrical properties of materialsElectrical properties of materialsElectrical properties of materialsElectrical properties of materialsElectrical properties of materialsElectrical properties of materialsElectrical properties of materialsElectrical properties of materialsElectrical properties of materialsElectrical properties of materialsElectrical properties of materialsElectrical properties of materialsElectrical properties of materialsElectrical properties of materialsElectrical properties of materialsElectrical properties of materialsElectrical properties of materialsElectrical properties of materialsElectrical properties of materialsElectrical properties of materialsElectrical properties of materialsElectrical properties of materialsElectrical properties of materialsElectrical properties of materialsElectrical properties of materialsElectrical properties of materialsElectrical properties of materials
The American Occupation and The Philippine CommonwealthEducation
The American Occupation and the Philippine Commonwealth
Cawagas, Virgina, and Swee-Hin Toh. Our Nation Our World 5. 2nd ed. Quezon City: Sibs Publishing House, 2014. 1-396.
Visit:http://kasaysayan4kids.blogspot.com/
For more resources.
American Colonization Period in the Philippines (1901-1935)Shanish Asuncion
I made this powerpoint presentation all by myself for our Readings in the Philippine History course. Well, I'm just so proud of this ppt which I used for our report in the said course, so I thought of sharing this here, and I hope this'll help a lotta people, especially students, in the future. Don't forget to say thank you if this help/helped you. :)
- Shanish
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.
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”.
Unit 8 - Information and Communication Technology (Paper I).pdfThiyagu K
This slides describes the basic concepts of ICT, basics of Email, Emerging Technology and Digital Initiatives in Education. This presentations aligns with the UGC Paper I syllabus.
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.
For more information, visit-www.vavaclasses.com
Model Attribute Check Company Auto PropertyCeline George
In Odoo, the multi-company feature allows you to manage multiple companies within a single Odoo database instance. Each company can have its own configurations while still sharing common resources such as products, customers, and suppliers.
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!
Operation “Blue Star” is the only event in the history of Independent India where the state went into war with its own people. Even after about 40 years it is not clear if it was culmination of states anger over people of the region, a political game of power or start of dictatorial chapter in the democratic setup.
The people of Punjab felt alienated from main stream due to denial of their just demands during a long democratic struggle since independence. As it happen all over the word, it led to militant struggle with great loss of lives of military, police and civilian personnel. Killing of Indira Gandhi and massacre of innocent Sikhs in Delhi and other India cities was also associated with this movement.
2. Electronic Materials
Conductors Insulators Semiconductors
have low
resistance which
allows electrical
current flow
Ex.:Copper, silver,
gold, aluminum, &
nickel
have high
resistance which
suppresses
electrical current
flow
Ex:Glass,
ceramic, plastics,
& wood
can allow or
suppress electrical
current flow
Ex: carbon, silicon,
and germanium
2
3. Conductors
Copper
Atom
Insulators:
• Insulators have a high resistance so current does not
flow in them.
• Ex:Glass, ceramic, plastics, & wood
3
•The atomic structure of
good conductors usually
includes only one
electron in their outer
shell. It is called a
valence electron.
It is easily striped from
the atom, producing
current flow.
4. Semiconductors
• Semiconductors are materials that essentially can be conditioned to act
as good conductors, or good insulators, or any thing in between.
• Ex.: carbon, silicon, and germanium are semiconductors.
• Silicon is the best and most widely used semiconductor.
• The main characteristic of a semiconductor element is that it has
four electrons in its outer or valence orbit.
Semiconductor
Valence Orbit
4
5. Crystal Lattice Structure
3DCrystal 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.
5
7. Semiconductors
Intrinsic SC Extrinsic SC
1. chemically very pure and
possesses poor conductivity
2. It has equal numbers of negative
charge carriers (electrons) and
positive charge carriers (holes)
3. Small current flow by thermal
agitation
1. small amount of impurities added by
a process, known as doping
2. numbers of negative carriers
(electrons) and positive carriers
(holes) are not equal
3. Doping gives rise to negative charge
conductor(n-type SC). Or positive
charge conductor (P-type SC).
7
8. • The highest energy band completely filled with
electrons (at T = 0 K) is called the Valence Band
• The next band is called the Conduction Band
• The energy difference
between the bottom of
the Conduction and
the top of the Valence
bands is called the
Band Gap
8
9. • Electron Conduction is easy to imagine: electrons (in the
conduction band) move almost like free particles
• Hole Conduction is due to positively charged particles in
the valence band
9
10. Intrinsic Semiconductors
• Consider nominally pure
semiconductor at T = 0 K
• There is no electrons in the
conduction band
• At T > 0 K a small fraction of
electrons is thermally excited
into the conduction band,
“leaving” the same number
of holes in the valence band
10
11. Intrinsic Semiconductors at T >0 K
• Electrons and holes contribute to the current when a voltage is applied
e n
e n
h p
*
2
e n
*
2
h
e
m
m
11
12. Carrier Concentrations at T >0 K
• Let’s take EV = 0, then EC = EG
• The number of electrons equals the number of holes, ne = nh
• The Fermi level lies in the middle of the band gap
1 * * 3/ 4
E
• ne = nh increase rapidly with temperature
kT
m m
kT
n n exp
G
e h 2
e h 2
3/ 2
2
1/ 2
12
13. Carrier Concentrations
• EG of selected semiconductors
– Si: 1.1eV
– Ge: 0.7eV
– GaAs: 1.4eV
– ZnSe: 2.7eV
• Carrier effective masses for
selected semiconductors
– GaAs: me
*= 0.067m0; mh
*= 0.45m0
* = 0.26m0; mh
– Si: me
* = 0.49m0
* = 0.04m0; mh
– Ge: me
* = 0.28m0
* = 0.21m0; mh
– ZnSe: me
* = 0.74m0
Carrier concentration falls with
1/T, i.e. increase with T 13
14. • Semiconductors can be easily doped
• Doping is the incorporation of [substitutional]
impurities into a semiconductor according to our
requirements
• In other words, impurities are introduced in
a controlled manner
• Impurities change the conductivity of the
material so that it can be fabricated into a
device
14
15. Extrinsic Semiconductors
• Electrical Properties of Semiconductors can
be altered drastically by adding minute
amounts of suitable impurities to the pure
crystals
• Impurities: Atoms of the elements different
from those forming solid
– Interstitial: “foreign” atoms “squeezed”
between regular sites crystal sites
– Substitutional: “foreign” atoms occupying the
sites of host atoms
15
16. Donors
• We use Silicon (Si) as an example
– Substitute one Si (Group IV) atom with a
Group V atom (e.g. As or P)
– Si atoms have four valence electrons that
participate in covalent bonding
– When a Group V atom replaces a Si atom, it
will use four of its electrons to form the
covalent bonding
– What happens with the remaining electron?
16
17. Donors
The remaining electron will not
be very tightly bound, and can
be easily ionized at T > 0K
• Ionized electron is free to
conduct
– In term of the band structure,
this electron is now in the
conduction band
• Such Group V impurities are called
Donors, since they “donate”
electrons into the Conduction Band
– Semiconductors doped by
donors are called n-type
semiconductors 17
18. Donors: Energy Levels
• The Band Structure View
– Such impurities “create” an energy
level within the band gap, close to the
conduction band
• A donor is similar to a hydrogen
atom
– A positive charge with a single
electron within its potential
– Such impurities are called hydrogenic
donors
– They create so-called “shallow” levels
- the levels that are very close to the
conduction band, so the energy
required to ionize the atom is small
and a sizable fraction of donor atoms
will be ionized at room temperature 18
21. This crystal has been doped with a pentavalent impurity.
- +
The free electrons in n type silicon support the flow of current.
21
22. Acceptors
• Use Silicon (Si) as an example
– Substitute one Group III atom (e.g. Al or In) with a Si
(Group IV) atom
– Si atoms have four valence electrons that participate in
the covalent bonding
– When a Group III atom replaces a Si atom, it cannot
complete a tetravalent bond scheme
– An “electronic vacancy” – hole – is formed when an
electron from the valence band is grabbed by the atom so
that the core is negatively charged, the hole created is
then attracted t the negative core
– At T = 0 K this hole “stays” with atom – localized hole
– At T > 0 K, electron from the neighboring Si atom can
jump into this hole – the hole can then migrate and
contribute to the current
22
23. Acceptors
• At T > 0 K, electron from the
neighboring Si atom can jump
into this hole – the hole starts to
migrate, contributing to the
current
• We can say that this impurity
atom accepted an electron, so
we call them Acceptors
• Acceptors accept electrons, but
“donate” free holes
23
24. Acceptors
• By “incorporating” the electron into the impurity atom
we can represent this (T = 0 K) as a negative charge in
the core with a positive charge (hole) outside the core
attracted by its [Coulomb] potential
• At T > 0 K this hole can be ionized
• Such semiconductors are called p-type semiconductors
since they contribute positive charge carriers
24
25. Acceptor: Energy Levels
• From the Band Structure View
– Such impurities “create” energy levels within the band gap,
close to the valence band
– They are similar to “negative” hydrogen atoms
– Such impurities are called hydrogenic acceptors
– They create “shallow” levels - levels that are very close to the
valence band, so the energy required to ionize the atom
(accept the electron that fills the hole and creates another hole
further from the substituted atom) is small
25
27. This crystal has been doped with a trivalent impurity.
- +
The holes in p type silicon contribute to the current.
Note that the hole current direction is opposite to electron current
so the electrical current is in the same direction
27
30. Carrier Concentrations in
Extrinsic Semiconductors
• The carrier densities in extrinsic semiconductors can
be very high
• It depends on doping levels ([net] dopant
concentration) and ionization energy of the dopants
• Often both types of impurities are present
– If the total concentration of donors (ND) is larger than the
total concentration of acceptors (NA) have an n-type
semiconductor
– In the opposite case have a p-type semiconductor
30
31. Charge Neutrality Equation
• To calculate the charge concentration, the charge
neutrality condition is used, since the net charge in a
uniformly doped semiconductor is zero
– Otherwise, there will be a net flow of charge from one
point to another resulting in current flow
– p is the concentration of holes in the valence band
– n is the electron concentration
– ND
+ is the ionized donor concentration
- is the ionized acceptor concentration
– NA
D A p N n N
31
32. Resisitivity of Semiconductors
q n
*
2
1
m
n n
• The carrier concentration and thus the conductivity is dominated
by its essentially exponential dependence on temperature
• For intrinsic semiconductors
q n
1
*
2
m
n n
• For impurity semiconductors
]
E
constant exp[- g
2kT
]
1
(E E )
constant exp[- g F
2kT
q n
*
2
m
n n
• EF is first between the impurity level and the band edge and then
approaches Eg/2 after most of the impurities are ionized
32
33. Semiconductors in Summary
• The most widely used material is silicon
• Pure crystals are intrinsic semiconductors
• Doped crystals are extrinsic semiconductors
• Crystals are doped to be n type or p type
• n type semiconductors have few minority
carriers (holes).
• p type semiconductors have few minority
carriers (electrons).
33
34. Optical Properties
• If semiconductor or insulator does not have many impurity
levels in the band gap, photons with energies smaller than
the band gap energy can’t be absorbed
– There are no quantum states with energies in the band gap
• This explains why many insulators or wide band gap
semiconductors are transparent to visible light, whereas
narrow band semiconductors (Si, GaAs) are not
34
35. Optical Properties
• Some applications
– Emission: light emitting diode (LED) and Laser Diode
(LD)
– Absorption: Filtering
• Sunglasses
• Si filters: transmission of infra red light with simultaneous
blocking of visible light
35
36. Optical Properties
• If there are many impurity levels the photons with energies
smaller than the band gap energy can be absorbed, by
exciting electrons or holes from these energy levels into the
conduction or valence band, respectively
– Example: Colored Diamonds 36
37. Photoconductivity
• Charge carriers (electrons or
holes or both) created in the
corresponding bands by
absorbed light can also
participate in current flow, and
thus should increase the current
for a given applied voltage, i.e.,
the conductivity increases
• This effect is called
Photoconductivity
• Want conductivity to be
controlled by light. So want few
carriers in dark → semiconductor
• But want light to be absorbed,
creating photoelectrons
• → Band gap of intrinsic
photoconductors should be
smaller than the energy of the
photons that are absorbed
37
38. Photoconductivity
• Important Applications (Garcia 26.6)
– Night vision systems imaging IR radiation
– Solar cells
– Radiation detectors
– Photoelectric cells (e.g., used for automatic
doors)
– Xerography
– CCD (“Digital Cameras”)
38