Ohm's law relates current, voltage, and resistance. Resistivity is a material property independent of geometry, while conductivity is the inverse of resistivity and indicates how easily a material conducts electricity. Materials are classified as conductors, insulators, or semiconductors based on conductivity. Semiconductors have applications in electronics due to their sensitivity to impurities and ability to be "doped" to control conductivity. Their band structure results in varying conductivity depending on temperature and doping.
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.
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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.
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
4.1 Copper and its alloys - brasses, bronzes Chemical compositions, properties and Applications.
4.2 Aluminium alloys –Y-alloy, Hindalium, duralium with their composition and
Applications.
4.3 Bearing materials like white metals (Sn based), aluminium bronzes. Porous, Self lubricating bearings
ELECTROCHEMICAL MACHINING - NON TRADITIONAL MACHININGSajal Tiwari
Non-conventional machining system in which metal is removed by an electrochemical process. Characterized as ‘Reverse Electroplating’ means it removes metal instead of adding it. Normally used for mass production and for hard materials that are difficult to machine using conventional processes. Both external and internal geometries can be machined.
The following presentation is a part of the level 4 module -- Electrical and Electronic Principles. This resources is a part of the 2009/2010 Engineering (foundation degree, BEng and HN) courses from University of Wales Newport (course codes H101, H691, H620, HH37 and 001H). This resource is a part of the core modules for the full time 1st year undergraduate programme.
The BEng & Foundation Degrees and HNC/D in Engineering are designed to meet the needs of employers by placing the emphasis on the theoretical, practical and vocational aspects of engineering within the workplace and beyond. Engineering is becoming more high profile, and therefore more in demand as a skill set, in today’s high-tech world. This course has been designed to provide you with knowledge, skills and practical experience encountered in everyday engineering environments.
2.1 Concept of phase, pure metal, alloy and solid solutions.
2.2 i Iron Carbon Equilibrium diagram various phases Critical temperatures and significance ii. Reactions on Iron carbon equilibrium diagram
2.3 Broad Classification of steels
i. Plain carbon steels: Definition, Types and Properties, Compositions and applications of low, medium and high carbon steels
ii. Alloy Steels: Definition and Effects of alloying elements on properties of alloy steels.iii. Tool steels: Cold work tool steels, Hot work tool steels, High speed steels(HSS) iv. Stainless Steels: Types and Applications v. Spring Steels: Composition and Applications vi. Specifications of steels and their equivalents
2.4 Steels for following: Shafts, axles, Nuts, bolts, Levers, crank shafts, camshafts, Shear blades, agricultural equipments, house hold utensils, machine tool beds, car bodies, Antifriction bearings and gears
Transformer Construction And Principle | Electronical EngineeringTransweb Global Inc
Construction of Transformer includes two inductive winding and laminated steel core; coils of transformer are coated with insulation to be insulated from each other and the steel core. Copy the link given below and paste it in new browser window to get more information on Transformer Construction And Principle:- http://www.transtutors.com/homework-help/electrical-engineering/transformer/transformer-construction-and-principle.aspx
Cast iron is a group of iron-carbon alloys with a carbon content more than 2%. Its usefulness derives from its relatively low melting temperature. The alloy constituents affect its colour when fractured: white cast iron has carbide impurities.
History:
Cast iron was invented in China in the 5th century BC and poured into molds to make ploughshares and pots as well as weapons and pagodas. Although steel was more desirable, cast iron was cheaper and thus was more commonly used for implements in ancient China, while wrought iron or steel was used for weapons.
The cast-iron is manufactured by re-melting pig-iron with coke and limestone. This re-melting is done in a furnace known as the cupola furnace. It is more or less same as the blast furnace, but it is smaller in size. Its shape is cylindrical with diameter of about 1 m and height of about 5 m.
The working of cupola furnace is also similar to that of blast furnace. The raw materials are fed from top. The cupola furnace is worked intermittently and it is open at top. After the raw materials are placed, the furnace is fired and blast of air is forced through tuyeres. The blast of air is cold as the impurities in pig-iron are removed by the oxidation
#design #architecture #interior #homedesign #house #interiors #construction #deco #interiordesigner #designinspiration #interiorstyling #interiordecor #arquitectura #architecturephotography #kitchendesign #modern #building #architecturelovers #homestyle #bedroom #archilovers #instahome #homestyling #lighting #project #architecturedesign #villa #archdaily #moderndesign #housedesign
4.1 Copper and its alloys - brasses, bronzes Chemical compositions, properties and Applications.
4.2 Aluminium alloys –Y-alloy, Hindalium, duralium with their composition and
Applications.
4.3 Bearing materials like white metals (Sn based), aluminium bronzes. Porous, Self lubricating bearings
ELECTROCHEMICAL MACHINING - NON TRADITIONAL MACHININGSajal Tiwari
Non-conventional machining system in which metal is removed by an electrochemical process. Characterized as ‘Reverse Electroplating’ means it removes metal instead of adding it. Normally used for mass production and for hard materials that are difficult to machine using conventional processes. Both external and internal geometries can be machined.
The following presentation is a part of the level 4 module -- Electrical and Electronic Principles. This resources is a part of the 2009/2010 Engineering (foundation degree, BEng and HN) courses from University of Wales Newport (course codes H101, H691, H620, HH37 and 001H). This resource is a part of the core modules for the full time 1st year undergraduate programme.
The BEng & Foundation Degrees and HNC/D in Engineering are designed to meet the needs of employers by placing the emphasis on the theoretical, practical and vocational aspects of engineering within the workplace and beyond. Engineering is becoming more high profile, and therefore more in demand as a skill set, in today’s high-tech world. This course has been designed to provide you with knowledge, skills and practical experience encountered in everyday engineering environments.
2.1 Concept of phase, pure metal, alloy and solid solutions.
2.2 i Iron Carbon Equilibrium diagram various phases Critical temperatures and significance ii. Reactions on Iron carbon equilibrium diagram
2.3 Broad Classification of steels
i. Plain carbon steels: Definition, Types and Properties, Compositions and applications of low, medium and high carbon steels
ii. Alloy Steels: Definition and Effects of alloying elements on properties of alloy steels.iii. Tool steels: Cold work tool steels, Hot work tool steels, High speed steels(HSS) iv. Stainless Steels: Types and Applications v. Spring Steels: Composition and Applications vi. Specifications of steels and their equivalents
2.4 Steels for following: Shafts, axles, Nuts, bolts, Levers, crank shafts, camshafts, Shear blades, agricultural equipments, house hold utensils, machine tool beds, car bodies, Antifriction bearings and gears
Transformer Construction And Principle | Electronical EngineeringTransweb Global Inc
Construction of Transformer includes two inductive winding and laminated steel core; coils of transformer are coated with insulation to be insulated from each other and the steel core. Copy the link given below and paste it in new browser window to get more information on Transformer Construction And Principle:- http://www.transtutors.com/homework-help/electrical-engineering/transformer/transformer-construction-and-principle.aspx
Cast iron is a group of iron-carbon alloys with a carbon content more than 2%. Its usefulness derives from its relatively low melting temperature. The alloy constituents affect its colour when fractured: white cast iron has carbide impurities.
History:
Cast iron was invented in China in the 5th century BC and poured into molds to make ploughshares and pots as well as weapons and pagodas. Although steel was more desirable, cast iron was cheaper and thus was more commonly used for implements in ancient China, while wrought iron or steel was used for weapons.
The cast-iron is manufactured by re-melting pig-iron with coke and limestone. This re-melting is done in a furnace known as the cupola furnace. It is more or less same as the blast furnace, but it is smaller in size. Its shape is cylindrical with diameter of about 1 m and height of about 5 m.
The working of cupola furnace is also similar to that of blast furnace. The raw materials are fed from top. The cupola furnace is worked intermittently and it is open at top. After the raw materials are placed, the furnace is fired and blast of air is forced through tuyeres. The blast of air is cold as the impurities in pig-iron are removed by the oxidation
#design #architecture #interior #homedesign #house #interiors #construction #deco #interiordesigner #designinspiration #interiorstyling #interiordecor #arquitectura #architecturephotography #kitchendesign #modern #building #architecturelovers #homestyle #bedroom #archilovers #instahome #homestyling #lighting #project #architecturedesign #villa #archdaily #moderndesign #housedesign
A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The term "laser" originated as an acronym for "light amplification by stimulated emission of radiation
Ceramic materials are inorganic , nonmetallic
materials
made from compounds of a metal and a non metal.
Ceramic materials may be crystalline or partly crystalline.
The word ceramic comes from the Greek word keramiko
of pottery" or for pottery from keramos.
Ceramics materials are the phases containing a
compounds of metallic and nonmetallic
elements. In short
ceramics are the inorganic non metallic materials such as
silicates, aluminates, oxides, carbides, borides and
hydroxides. Since there are many possible combinations
of metallic and nonmetallic
atoms and there are many
several structural arrangement of each combination.
Ceramics always composed of more than one element.
Bonds are partially or totally ionic, can have combination
of ionic and covalent bonding (electronegativity)
project report on REMOTE SENSING THERMOMETERdreamervikas
Ever since the invention of thermometer, various techniques have been developed and used to measure temperature of solid, liquid and gaseous matters. But none of these techniques could measure the temperature from a remote place, which sometimes becomes a necessity particularly when the object under testis in a dangerous or inaccessible area. Presented here is a remote sensing thermometer to measure the temperature from a remote place.
The temperature of the object under test is sensed by a temperature sensor convert the sensed voltage into equivalent frequency by using a voltage-to frequency (V-F) converter and send the same to the remote end through a transmitter. At the remote end, a frequency-to-voltage (F-V) converter is used to retrieve the original signal from the received frequency-encoded signal for display or control process.
It can measure from -55°C to 150°C. In a properly calibrated system, meter reading should increase or decrease@ 10mV/°C. Therefore a 0.250V reading on the mV meter indicates 25°C temperature.
undamentals of Crystal Structure: BCC, FCC and HCP Structures, coordination number and atomic packing factors, crystal imperfections -point line and surface imperfections. Atomic Diffusion: Phenomenon, Fick’s laws of diffusion, factors affecting diffusion.
Electrical and Magnetic Properties of MaterialsAbeni9
Properties of a material which determine its response to an electric field.
Materials are classified based on their electrical properties as conductors, semiconductors and insulators and newly super conductors.
the presentation explain about drift velocity ,motion of electrons under the influence of external electric field. resistivity and resistances of mater .how the resistivity varies with temperature
Basics In electricity ( From Unit 1 to Unit 5).
Atoms and atomics structure.
Types of electricity.
Resistance.
Ohm’s law.
Condenser/ capacitor.
Inductors.
Magnetism.
EMI.
Valves.
Transformer.
Sachpazis:Terzaghi Bearing Capacity Estimation in simple terms with Calculati...Dr.Costas Sachpazis
Terzaghi's soil bearing capacity theory, developed by Karl Terzaghi, is a fundamental principle in geotechnical engineering used to determine the bearing capacity of shallow foundations. This theory provides a method to calculate the ultimate bearing capacity of soil, which is the maximum load per unit area that the soil can support without undergoing shear failure. The Calculation HTML Code included.
Final project report on grocery store management system..pdfKamal Acharya
In today’s fast-changing business environment, it’s extremely important to be able to respond to client needs in the most effective and timely manner. If your customers wish to see your business online and have instant access to your products or services.
Online Grocery Store is an e-commerce website, which retails various grocery products. This project allows viewing various products available enables registered users to purchase desired products instantly using Paytm, UPI payment processor (Instant Pay) and also can place order by using Cash on Delivery (Pay Later) option. This project provides an easy access to Administrators and Managers to view orders placed using Pay Later and Instant Pay options.
In order to develop an e-commerce website, a number of Technologies must be studied and understood. These include multi-tiered architecture, server and client-side scripting techniques, implementation technologies, programming language (such as PHP, HTML, CSS, JavaScript) and MySQL relational databases. This is a project with the objective to develop a basic website where a consumer is provided with a shopping cart website and also to know about the technologies used to develop such a website.
This document will discuss each of the underlying technologies to create and implement an e- commerce website.
Welcome to WIPAC Monthly the magazine brought to you by the LinkedIn Group Water Industry Process Automation & Control.
In this month's edition, along with this month's industry news to celebrate the 13 years since the group was created we have articles including
A case study of the used of Advanced Process Control at the Wastewater Treatment works at Lleida in Spain
A look back on an article on smart wastewater networks in order to see how the industry has measured up in the interim around the adoption of Digital Transformation in the Water Industry.
Event Management System Vb Net Project Report.pdfKamal Acharya
In present era, the scopes of information technology growing with a very fast .We do not see any are untouched from this industry. The scope of information technology has become wider includes: Business and industry. Household Business, Communication, Education, Entertainment, Science, Medicine, Engineering, Distance Learning, Weather Forecasting. Carrier Searching and so on.
My project named “Event Management System” is software that store and maintained all events coordinated in college. It also helpful to print related reports. My project will help to record the events coordinated by faculties with their Name, Event subject, date & details in an efficient & effective ways.
In my system we have to make a system by which a user can record all events coordinated by a particular faculty. In our proposed system some more featured are added which differs it from the existing system such as security.
About
Indigenized remote control interface card suitable for MAFI system CCR equipment. Compatible for IDM8000 CCR. Backplane mounted serial and TCP/Ethernet communication module for CCR remote access. IDM 8000 CCR remote control on serial and TCP protocol.
• Remote control: Parallel or serial interface.
• Compatible with MAFI CCR system.
• Compatible with IDM8000 CCR.
• Compatible with Backplane mount serial communication.
• Compatible with commercial and Defence aviation CCR system.
• Remote control system for accessing CCR and allied system over serial or TCP.
• Indigenized local Support/presence in India.
• Easy in configuration using DIP switches.
Technical Specifications
Indigenized remote control interface card suitable for MAFI system CCR equipment. Compatible for IDM8000 CCR. Backplane mounted serial and TCP/Ethernet communication module for CCR remote access. IDM 8000 CCR remote control on serial and TCP protocol.
Key Features
Indigenized remote control interface card suitable for MAFI system CCR equipment. Compatible for IDM8000 CCR. Backplane mounted serial and TCP/Ethernet communication module for CCR remote access. IDM 8000 CCR remote control on serial and TCP protocol.
• Remote control: Parallel or serial interface
• Compatible with MAFI CCR system
• Copatiable with IDM8000 CCR
• Compatible with Backplane mount serial communication.
• Compatible with commercial and Defence aviation CCR system.
• Remote control system for accessing CCR and allied system over serial or TCP.
• Indigenized local Support/presence in India.
Application
• Remote control: Parallel or serial interface.
• Compatible with MAFI CCR system.
• Compatible with IDM8000 CCR.
• Compatible with Backplane mount serial communication.
• Compatible with commercial and Defence aviation CCR system.
• Remote control system for accessing CCR and allied system over serial or TCP.
• Indigenized local Support/presence in India.
• Easy in configuration using DIP switches.
Industrial Training at Shahjalal Fertilizer Company Limited (SFCL)MdTanvirMahtab2
This presentation is about the working procedure of Shahjalal Fertilizer Company Limited (SFCL). A Govt. owned Company of Bangladesh Chemical Industries Corporation under Ministry of Industries.
Water scarcity is the lack of fresh water resources to meet the standard water demand. There are two type of water scarcity. One is physical. The other is economic water scarcity.
Saudi Arabia stands as a titan in the global energy landscape, renowned for its abundant oil and gas resources. It's the largest exporter of petroleum and holds some of the world's most significant reserves. Let's delve into the top 10 oil and gas projects shaping Saudi Arabia's energy future in 2024.
Top 10 Oil and Gas Projects in Saudi Arabia 2024.pdf
Material science metals, bnads etc.,
1. MATERIAL SCIENCE ASSIGNMENT
NIT CALICUT
SUBMITTED BY:
T.VINAYASREE
MOOLA NIHARIKA
NAKA PRIYANKA
HARISH.M
MANOJ MADHAV
MOHAMMED ARSHAK
MOHAMED HARSHID
2. Ohm’s law relates the current I to the applied voltage V as follows:
where R - resistance of the material.
Units: V : volts (j/c)
I : amperes (c/s)
R : ohms (V/A )
The resistivity ‘ρ’ is independent of specimen geometry.
where
l : distance between 2 points at which voltage is measured
A : cross sectional area perpendicular to the direction of
the current.
units : ρ ohm meter (Ω-m)
3. It is defined as the reciprocal of resistivity
It indicates the case with which a material is capable of conducting
an electric current.
units : σ ( ohm meter (1 ̸Ωm ) )
ohm’s law can be expressed as
where J – current density [I/A]
E – Electric field density ( v/l )
solid materials are classified according to ease with whivh they conduct
electric current . They are classified as
1) conductors : conductivity order
2) insulators
3) semi conductors
4. An electric current results from the motion of electrically charged
particles in response to forces that act on them from an externally
applied electric field.
Within most solid materials a current arises from the flow of
electrons, which is termed electronic conduction.
For ionic materials a net motion of charged ions is possible that
produces a current; such is termed ionic conduction.
5. ENERGY BAND STRUCTURES IN SOLIDS:
In all conductors, semiconductors, and many insulating materials,
only electronic.
Conduction exists which is strongly dependent on number of
electros available to participate in the conduction process.
These electrons are related to the arrangement of electron states or
levels.
For each individual atom there exist discrete energy levels that may
be occupied by electrons, arranged into shells and subshells.
Shells are designated by integers (1, 2, 3, etc.), and for each
subshells represented by letters (s, p, d, and f ) there exists one,
three, five, seven states respectively.
Pauli exclusion principle states that the electrons fill in the states
with lower energy with two electrons of opposite spins.
6.
7. A solid may be thought of as consisting of a large number of atoms(say
N) that are brought together and bounded to form the ordered atomic
arrangement.
Each atom has atomic levels that split into a series of closely spaced
electrons in solid to form electron energy band.
The extent of splitting depends on interatomic separation.
Within each band, the energy states are discrete, yet the difference
between adjacent states is exceedingly small.
The number of states within each band will equal the total of all states
contributed by the N atoms.
8. each energy state accommodate two electrons, which must have
oppositely directed spins.
Four different types of band structures are possible at 0 K.
a. In the first one outermost band is only partially filled with
electrons.The energy corresponding to the highest filled state at 0
K is called the Fermi energy Ef.
b. For the second band structure, there is an overlap of an empty
band and a filled band. Eg:Magnesium.
c. The final two band structures are similar; one band (the valence
band) that is completely filled with electrons is separated from an
empty conduction band, and an energy band gap lies between
them.
For the insulators band gap is relatively wide whereas for
semiconductors it is narrow.
9.
10. The energy corresponding to the highest filled state at 0k is
called Fermi energy.
Electrons with energies greater than the Fermi energy acted on
them can be accelerated in the presence of an electric field.
The electrons that participate in the conduction process are
known as free electrons.
Electrical conductivity is a direct function of the numbers of
free electrons and holes.
11. For an electron to become free, it must be excited or
promoted into one of the empty and available energy
states above Fermi energy.
The energy band gap for metals is almost zero for
metals,so they are very good conductors.
12.
13. For insulators and semiconductors, empty states adjacent to the top of the
filled valence band are not available.
To become free, electrons must be promoted across the energy band gap.
The number of electrons excited thermally (by heat energy) into the
conduction band depends on the energy band gap width as well as
temperature.
Larger the band gap, the lower is the electrical conductivity at a given
temperature.
For insulators the width of the band gap is narrow whereas for insulators, it
is relatively wide.
Increasing the temperature of either a semiconductor or an insulator results
in an increase in the thermal energy that is available for electron excitation.
So,conductivity increases.
14. For electrically insulating materials, interatomic
bonding is ionic or strongly covalent.
Thus, the valence electrons are tightly bound to or
shared with the individual atoms.
The bonding in semiconductors is covalent and
relatively weak, which means that the valence
electrons are not as strongly bound to the atoms.
So, these electrons are more easily removed by
thermal excitation than they are for insulators.
15.
16. When an electric field is applied, a force is brought to bear on
the free electrons;so, they all experience an acceleration in a
direction opposite to that of the field, by virtue of their
negative charge.
All the free electrons accelerate as long as the electric field is
applied, which will give rise to an electric current that
continuously increases with time.
Current reaches a constant value the instant that a field is
applied, indicating that there exist “frictional forces,” that
counter this acceleration from the external field.
.
17. These frictional forces result from the scattering of electrons by
imperfections in the crystal lattice, including impurity atoms vacancies,
interstitial atoms, dislocations, and even the thermal vibrations of the atoms
themselves.
Each scattering event causes an electron to lose kinetic energy and to
change it direction of motion.
18. The drift velocity represents the average electron velocity in
the direction of the force imposed by the applied field. It is
directly proportional to the electric field as
The constant of proportionality µe is called the electron
mobility, which is an indication of the frequency of scattering
events.
Units are square meters per volt-second(m2/V-s).
19. The conductivity of most materials is
expressed as
where ,
n is the number of free or conducting electrons per unit
volume (e.g., per cubic meter), and |e| is the absolute
magnitude of the electrical charge on an electron .
Thus, the electrical conductivity is proportional to both
the number of free electrons and the electron mobility.
20. Most metals are extremely good conductors of electricity.
Metals have high conductivities because of the large numbers
of free electrons that have been excited into empty states
above the Fermi energy.
Crystalline defects serve as scattering centers for conduction
electrons in metals, increasing their number raises the
resistivity (or lowers the conductivity).
The concentration of these imperfections depends on
temperature, composition,and the degree of cold work of a
metal specimen.
21. The total resistivity of a metal is the sum of the contributions
from thermal vibrations, Impurities, and plastic deformation.
Where ρt,ρi,ρd represent the individual thermal, impurity, and
deformation resistivity contributions, respectively.
The above is sometimes known as Mat-thiessen’s rule.
22. For the pure metal and all the copper–nickel alloys, the
resistivity rises linearly with temperature:
where ρo and a are constants for each particular metal.This
dependence of the thermal resistivity component on
temperature is due to the increase with temperature in thermal
vibrations and other lattice irregularities (e.g., vacancies),
which serve as electron-scattering centers.
23. For additions of a single impurity that forms a solid
solution, the impurity resistivity ρi is related to the
impurity concentration ci in terms of the atom fraction
(at%100) as follows:
ρi =Aci(1-ci)
A is a composition-independent constant that is a function of
both the impurity and host metals.
24. For a two-phase alloy consisting of and phases, a rule-of-
mixtures expression is used to approximate the resistivity as:
where the V’s and ’s represent volume fractions and individual
resistivities for the respective phases.
27. Copper render it the most widely used metallic conductor.
Oxygen-free high-conductivity (OFHC) copper, having
extremely low oxygen and other impurity contents, is
produced for many electrical applications.
Both solid-solution alloying and cold working improve
strength at the expense of conductivity.
For some applications, such as furnace heating elements
materials must have not only a high resistivity, but also a
resistance to oxidation at elevated temperatures and,a high
melting temperature.
Nichrome, a nickel–chromium alloy, is commonly employed
in heating elements
28. Electrical conductivity of semiconductors less than
that of metals
have unique useful electrical characteristics
sensitive to the presence of even minute
concentrations of impurities
Two types : 1) Intrinsic – pure materials
2) Extrinsic –impurities added
29. band structure
relatively narrow forbidden band
gap (<2 eV)
Eg : Si (1.1eV) and Ge(0.7eV)
Also compounds composed of
Groups IIIA and VA – GaAs, In Sb
Groups IIB and VIA- Cd S, Zn Te
30. In above compounds ,
->dissimiar electronegativities
-> atomic bonding becomes more ionic
-> band gap energy increases—more
insulative
31. a vacant electron state in the VB created because of
e- from VB excited to CB
Treating a missing electron from the valence band
as a positively charged particle called
a hole.
Charge of hole= +1.6x10^-19 C
In the presence of an electric field, excited
electrons and holes move in opposite directions
32.
33. Two types of charge
carrier (free electrons
and holes)
p is the number of
holes per cubic meter
µh is the hole mobility
ni is known as the
intrinsic carrier
concentration
34. impurity concentration determines the
electrical behavior of semiconductors
One atom in 10^12 is sufficient to render
silicon extrinsic at room temperature.
Types : 1) n-type
2) p-type
35. Si has 4 e-s : covalent bonded with other
adjacent atoms
If we add a Grp VA impurity , 4e-s form
bonds , there will be 1 e- free .
It is free e- / conducting e-
For these free e-s , energy state is in
forbidden band gap just below CB
If energy is given,e- get excited to CB
Hence this type impurity is termed a ‘donor’
No hole in VB
36. At room temp, we can easily excite
large no. of e-s from donor states
No.of e-s in CB >>no.of holes in
VB
This type material is n-type
extrinsic semiconductors
e- are majority carriers
Holes are minority charge carriers
n-type : Fermi level shifted
upward in band gap
37.
38.
39. If we add a Group IIIA such as Al, Ga, B three electrons form bonds.
One covalent bond is deficient in electrons. This is called Hole. It
participates in conduction process.
Impurity atom introduces energy close to the top of valence band in
band gap.
No free electrons are created either in valence band or conduction band.
This type of impurity is called acceptor.
40.
41. For p>>n material is called P type(positively charged)
Holes are majority carries ,electronns are minority.
For P type, fermi level with bond gap near to the acceptor level.
Extrinsic semiconductors (both n- and p-type) Controlled
concentrations of specific donors or acceptors are then intentionally
added.
This alloying process in
semiconducting materials is termed doping.
At relatively high room-temperature electrical conductivities are
obtained in extrinsic semiconductors
42.
43. Figure,plots the logarithm of the intrinsic carrier
concentration versus temperature
for both silicon and germanium.
The concentrations of electrons and holes increase
with temperature because, with rising temperature
At all temperatures, carrier concentration in Ge is
greater than for Si . This effect is due to germanium’s
smaller band gap thus, for Ge, at any given
temperature more electrons will be excited across its
band gap.
44.
45. The conductivity (or resistivity) of a semiconducting material, in addition
to being dependent on electron and/or hole concentrations, is also a
function of the charge carriers’ mobilities.
Influence of Dopant Content:
46. At dopant concentrations less than about both
carrier mobilities are at their maximum levels
and independent of the doping concentration.
Influence of Temperature:
47. The temperature dependences of electron and
hole mobilities for silicon are presented in
above figures.
These plots, note that, for dopant
concentrations of 10−24
𝑚−3
and below, both
electron and hole mobilities decrease in
magnitude with rising temperature.