Electrical Properities (1)

Chapter 18 - 1

ISSUES TO ADDRESS...

• How are electrical conductance and resistance characterized?

• What are the physical phenomena that distinguish conductors, semiconductors, and insulators?

• For metals, how is conductivity affected by imperfections, temperature, and deformation?

• For semiconductors, how is conductivity affected by impurities (doping) and temperature?

Chapter 18: Electrical Properties

Chapter 18 - 2

Electrical Conduction• Ohm's Law: V = I R

voltage drop (volts = J/C) C = Coulomb

resistance (Ohms)current (amps = C/s)

1

• Conductivity, s

• Resistivity, r: -- a material property that is independent of sample size and geometry

RA

l

surface area of current flow

current flow path length

Chapter 18 - 3

Electrical Properties

• Which will have the greater resistance?

• Analogous to flow of water in a pipe• Resistance depends on sample geometry and

size.

D

2D

R1 2

D

2

2

8D2

2

R2

2D2

2

D2

R1

8

Chapter 18 - 4

Measurement of R

Chapter 18 - 5

Definitions

Further definitions

J = <= another way to state Ohm’s law

J current density

electric field potential = V/

flux a like area surface

current

A

I

Electron flux conductivity voltage gradient

J = (V/ )

Chapter 18 - 6

DefinitionsElectric field is defined as the electric force per unit charge. The direction of the field is taken to be the direction of the force it would exert on a positive test charge. The electric field is radially outward from a positive charge and radially in toward a negative point charge.

http://www.mysearch.org.uk/website1/html/479.Fieldlines.html

Chapter 18 - 7

• Room temperature values (Ohm-m)-1 = ( - m)-1

Selected values from Tables 18.1, 18.3, and 18.4, Callister & Rethwisch 8e.

Conductivity: Comparison

Silver 6.8 x 10 7

Copper 6.0 x 10 7

Iron 1.0 x 10 7

METALS conductors

Silicon 4 x 10-4

Germanium 2 x 10 0

GaAs 10 -6

SEMICONDUCTORS

semiconductors

Polystyrene <10-14

Polyethylene 10-15-10-17

Soda-lime glass 10

Concrete 10-9

Aluminum oxide <10-13

CERAMICS

POLYMERS

insulators

-10-10-11

Chapter 18 - 8

What is the minimum diameter (D) of the wire so that V < 1.5 V?

Example: Conductivity Problem

Cu wire I = 2.5 A- +

V

Solve to get D > 1.87 mm

< 1.5 V

2.5 A

6.07 x 107 (Ohm-m)-1

100 m

I

V

AR

4

2D

100 m

Chapter 18 - 9

Electron Conductivity

• The magnitude of the conductivity depends on the number of electrons available to participate in the conduction process

• Not all electrons in every atom will accelerate in the presence of an electric field

• It depends on the arrangement of electron states or levels w.r.t energy and the manners in which these states are occupied by electrons.

Chapter 18 -10

Electron Energy Band Structures

Adapted from Fig. 18.2, Callister & Rethwisch 8e.

Chapter 18 -11

Band Structure Representation


Chapter 18 -12

Band Structures in Solids at 0K

Outermost band is partially filled Ex. Copper has one electron in 4s

Overlap between an empty and filled band Ex. Magnesium has one two 3s electrons. Then 3s and 3p bands overlap

Valence band i.e. completely filled is separated from an empty band and an energy band gap lies between them. Difference depends on the magnitude of the energy gap. Insulators: gap is relatively wide. Semiconductors: gap is narrow

Femi Energy

Chapter 18 -13

Conduction & Electron Transport• Metals (Conductors):-- for metals empty energy states are adjacent to filled states.

-- two types of band structures for metals

-- thermal energy excites electrons into empty higher energy states.

- partially filled band - empty band that overlaps filled band

filled band

Energy

partly filled band

empty band

GAP

fille

d st

ates

Partially filled band

Energy

filled band

filled band

empty band

fille

d st

ates

Overlapping bands

Chapter 18 -14

Energy Band Structures: Insulators & Semiconductors

• Insulators: -- wide band gap (> 2 eV) -- few electrons excited across band gap

Energy

filled band

filled valence band

fille

d st

ates

GAP

empty

bandconduction

• Semiconductors: -- narrow band gap (< 2 eV) -- more electrons excited across band gap

Energy

filled band

filled valence band

fille

d st

ates

GAP?

empty

bandconduction

Chapter 18 -15

Conduction In Metals• For an electron to become free, it must be excited or promoted

into one of the empty and available energy states above Ef

Chapter 18 -16

Charge Carriers in Insulators and Semiconductors

Two types of electronic charge carriers:

Free Electron – negative charge – in conduction band

Hole – positive charge

– vacant electron state in the valence band

Adapted from Fig. 18.6(b), Callister & Rethwisch 8e.

Move at different speeds - drift velocities

Chapter 18 -17

Electron Mobility• Free Electrons accelerates when

electric field is applied. • The acceleration direction is

opposite to the applied field.• Free electrons should accelerate

as long as the field is applied!! • But! We know that the current

reaches a constant value the instant that field applied.

• Thus frictional forces exists, which counter this acceleration from the field.

Why?

Scattering of electrons by imperfections in the crystal lattice

It is the resistance to the passage of an electric current Parameters

mobilityDrift velocity

v

Chapter 18 -18

EXAMPLE

At room temperature the electrical conductivity and the electron mobility for copper are 6.0 107 (W-m)-1 and 0.0030 m2/V-s, respectively. (a) Compute the number of free electrons per cubic meter for copper at room temperature. (b) What is the number of free electrons per copper atom? Assume a density of 8.9 g/cm3.

Chapter 18 -19

Metals: Influence of Temperature and Impurities on Resistivity

• Presence of imperfections increases resistivity -- grain boundaries -- dislocations -- impurity atoms -- vacancies

These act to scatterelectrons so that theytake a less direct path.

• Resistivity increases with:

=

deformed Cu + 1.12 at%Ni

Adapted from Fig. 18.8, Callister & Rethwisch 8e. (Fig. 18.8 adapted from J.O. Linde, Ann. Physik 5, p. 219 (1932); and C.A. Wert and R.M. Thomson, Physics of Solids, 2nd ed., McGraw-Hill Book Company, New York, 1970.)

T (ºC)-200 -100 0

1

2

3

4

5

6

Res

istiv

ity,

r

(10

-8 O

hm

-m)

0

Cu + 1.12 at%Ni

“Pure” Cu

d -- %CW

+ deformation

i

-- wt% impurity

+ impurity

t

-- temperature

thermal

Cu + 3.32 at%Ni

Chapter 18 -20

Estimating Conductivity

Adapted from Fig. 7.16(b), Callister & Rethwisch 8e.

• Question:-- Estimate the electrical conductivity of a Cu-Ni alloy that has a yield strength of 125 MPa.

mOhm10 x 30 8

16 )mOhm(10 x 3.31

Yie

ld s

tre

ngt

h (

MP

a)

wt% Ni, (Concentration C)0 10 20 30 40 50

6080

100120140160180

21 wt% Ni


wt% Ni, (Concentration C)R

esi

stiv

ity,

r

(10

-8 O

hm

-m)

10 20 30 40 500

10203040

50

0

125

CNi = 21 wt% Ni

From step 1:

30

Chapter 18 -21

What is a 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• In recent years, however, non-crystalline

semiconductors have become commercially very important

polycrystalline amorphous crystalline

Chapter 18 -22

Semiconductor Materials

Chapter 18 -23

Intrinsic Semiconductors

• Pure material semiconductors: e.g., silicon & germanium– Group IVA materials

• Compound semiconductors – III-V compounds

• Ex: GaAs & InSb

– II-VI compounds• Ex: CdS & ZnTe

– The wider the electronegativity difference between the elements the wider the energy gap.

Chapter 18 -24

Band Gap of SemiconductorsMaterial Band Gap

Si 1.11

Ge 0.67

GaP 2.25

GaAs 1.42

InSb 0.17

CdS 2.4

ZnTe 2.26

Chapter 18 -25

Silicon

• Atomic density: 5 x 1022 atoms/cm3

• Si has four valence electrons. Therefore, it can form covalent bonds with four of its nearest neighbors.

• When temperature goes up, electrons can become free to move about the Si lattice.

Chapter 18 -26

Intrinsic Semiconduction in Terms of Electron and Hole Migration


electric field electric field electric field

• Electrical Conductivity given by:

# electrons/m3 electron mobility

# holes/m3

hole mobilityhe epen

• Concept of electrons and holes:

+-

electron hole pair creation

+-

no applied applied

valence electron Si atom

applied

electron hole pair migration

Chapter 18 -27

Number of Charge Carriers

Intrinsic Conductivity

)s/Vm 45.085.0)(C10x6.1(

m)(10219

16

hei e

n

For GaAs ni = 4.8 x 1024 m-3

For Si ni = 1.3 x 1016 m-3

• Ex: GaAs

he epen

• for intrinsic semiconductor n = p = ni = ni|e|(e + h)

Chapter 18 -28

Intrinsic Semiconductors: Conductivity vs T

• Data for Pure Silicon: -- s increases with T -- opposite to metals


material Si Ge GaP CdS

band gap (eV) 1.11 0.67 2.25 2.40

Selected values from Table 18.3, Callister & Rethwisch 8e.

ni e Egap / kT

ni e e h

Chapter 18 -29

Intrinsic Semiconductors: Conductivity vs T

material Si Ge GaP CdS

band gap (eV) 1.11 0.67 2.25 2.40

Selected values from Table 18.3, Callister & Rethwisch 8e.

ni e Egap / kT

ni e e h

Chapter 18 -30

Example• At room temperature the electrical conductivity of PbTe is

500 (Ω-m)–1, whereas the electron and hole mobilities are 0.16 and 0.075 m2/V-s, respectively. Compute the intrinsic carrier concentration for PbTe at room temperature.

Chapter 18 -31

• Intrinsic: -- case for pure Si -- # electrons = # holes (n = p)

• Extrinsic: -- electrical behavior is determined by presence of impurities that introduce excess electrons or holes -- n ≠ p

Intrinsic vs Extrinsic Conduction

3+

• p-type Extrinsic: (p >> n)

no applied electric field

Boron atom

4+ 4+ 4+ 4+

4+

4+4+4+4+

4+ 4+ hep

hole

• n-type Extrinsic: (n >> p)

no applied electric field

5+

4+ 4+ 4+ 4+

4+

4+4+4+4+

4+ 4+

Phosphorus atom

valence electron

Si atom

conductionelectron

een

Adapted from Figs. 18.12(a) & 18.14(a), Callister & Rethwisch 8e.

Chapter 18 -32

Extrinsic Semiconductors

N-type(a) Without field(b) With field

P-type(a) Without field(b) With field

Chapter 18 -33

Extrinsic Semiconductors: Conductivity vs. Temperature

• Data for Doped Silicon: -- s increases doping -- reason: imperfection sites lower the activation energy to produce mobile electrons.

• Comparison: intrinsic vs extrinsic conduction... -- extrinsic doping level: 1021/m3 of a n-type donor impurity (such as P). -- for T < 100 K: "freeze-out“, thermal energy insufficient to excite electrons. -- for 150 K < T < 450 K: "extrinsic" -- for T >> 450 K: "intrinsic"

Adapted from Fig. 18.17, Callister & Rethwisch 8e. (Fig. 18.17 from S.M. Sze, Semiconductor Devices, Physics, and Technology, Bell Telephone Laboratories, Inc., 1985.)

Co

nd

uct

ion

ele

ctro

n

con

cen

tra

tion

(1

021/m

3 )T (K)6004002000

0

1

2

3

fre

eze

-ou

t

ext

rin

sic

intr

insi

c

doped

undoped

Chapter 18 -34

Numerical Example• An extrinsic p-type silicon material is desired having a

room-temperature conductivity of 50 (ohm.m)-1. Specify an acceptor impurity type that may be used as well as its concentration in atom percent to yield these electrical characteristics.

Chapter 18 -35

Summary of Charge Carriers

Chapter 18 -36

• Allows flow of electrons in one direction only (e.g., useful to convert alternating current to direct current).• Processing: diffuse P into one side of a B-doped crystal.

-- No applied potential: no net current flow.

-- Forward bias: carriers flow through p-type and n-type regions; holes and electrons recombine at p-n junction; current flows.

-- Reverse bias: carriers flow away from p-n junction; junction region depleted of carriers; little current flow.

p-n Rectifying Junction

++

++

+- ---

-p-type n-type

+ -

++ +

++

--

--

-

p-type n-typeAdapted from Fig. 18.21 Callister & Rethwisch 8e.

+++

+

+

---

--

p-type n-type- +

Chapter 18 -37

Properties of Rectifying Junction

Fig. 18.22, Callister & Rethwisch 8e. Fig. 18.23, Callister & Rethwisch 8e.

Chapter 18 -38

Properties of Diodes• The transconductance curve on the previous slide is characterized by the following

equation:

ID = IS(eVD/VT – 1)• As described in the last slide, ID is the current through the diode, IS is the saturation

current and VD is the applied biasing voltage.

• VT is the thermal equivalent voltage and is approximately 26 mV at room temperature. The equation to find VT at various temperatures is:

VT = kT q

k = 1.38 x 10-23 J/K T = temperature in Kelvin q = 1.6 x 10-19 C

• is the emission coefficient for the diode. It is determined by the way the diode is constructed. It somewhat varies with diode current. For a silicon diode is around 2 for low currents and goes down to about 1 at higher currents

Chapter 18 -39

Diode Circuit ModelThe Ideal Diode Model The diode is designed to allow current to flow in only one

direction. The perfect diode would be a perfect conductor in one direction (forward bias) and a perfect insulator in the other direction (reverse bias). In many situations, using the ideal diode approximation is acceptable.

Example: Assume the diode in the circuit below is ideal. Determine the value of ID if a) VA = 5 volts (forward bias) and b) VA = -5 volts (reverse bias)

+

_VA

ID

RS = 50 a) With VA > 0 the diode is in forward bias and is acting like a perfect conductor so:

ID = VA/RS = 5 V / 50 = 100 mA

b) With VA < 0 the diode is in reverse bias and is acting like a perfect insulator, therefore no current can flow and ID = 0.

Chapter 18 -40

Diode Circuit ModelsThe Ideal Diode with Barrier Potential This model is more accurate than the simple ideal

diode model because it includes the approximate barrier potential voltage. Remember the barrier potential voltage is the voltage at which appreciable current starts to flow.

Example: To be more accurate than just using the ideal diode model include the barrier potential. Assume V = 0.3 volts (typical for a germanium diode) Determine the value of ID if VA = 5 volts (forward bias).

+

_VA

ID

RS = 50 With VA > 0 the diode is in forward bias and is acting like a perfect conductor so write a KVL equation to find ID:

0 = VA – IDRS - V

ID = VA - V = 4.7 V = 94 mA RS 50

V

+

V

+

Chapter 18 -41

Types of DiodesPN Junction Diodes:

Are used to allow current to flow in one direction while blocking current flow in the opposite direction. The pn junction diode is the typical diode that has been used in the previous circuits.

A K

Schematic Symbol for a PN Junction Diode

P n

Representative Structure for a PN Junction Diode

Zener Diodes: Are specifically designed to operate under reverse breakdown conditions. These diodes have a very accurate and specific reverse breakdown voltage.

A K

Schematic Symbol for a Zener Diode

Chapter 18 -42

Types of DiodesLight-Emitting Diodes (LED):

Light-emitting diodes are designed with a very large bandgap so movement of carriers across their depletion region emits photons of light energy. Lower band gap LEDs (Light-Emitting Diodes) emit infrared radiation, while LEDs with higher band gap energy emit visible light. Many stop lights are now starting to use LEDs because they are extremely bright and last longer than regular bulbs for a relatively low cost.

A K

Schematic Symbol for a Light-Emitting Diode

The arrows in the LED representation indicate emitted light.

Chapter 18 -43

Types of DiodesPhotodiodes:

While LEDs emit light, Photodiodes are sensitive to received light. They are constructed so their pn junction can be exposed to the outside through a clear window or lens.In Photoconductive mode the saturation current increases in proportion to the intensity of the received light. This type of diode is used in CD players.In Photovoltaic mode, when the pn junction is exposed to a certain wavelength of light, the diode generates voltage and can be used as an energy source. This type of diode is used in the production of solar power.

A K

A K

Schematic Symbols for Photodiodes

Chapter 18 -44

PhotoVoltaic

+

+

++-

--

-

Photo Voltaic cell

Electrode

P-Type Semiconductor

N-Type Semiconductor

Reflect-Proof Film

Electrode

Solar Energy

Load

Ele

ctri

c C

urre

nt

The solar cell is composed of a P-type semiconductor and an N-type semiconductor. Solar light hitting the cell produces two types of electrons, negatively and positively charged electrons in the semiconductors.Negatively charged (-) electrons gather around the N-type semiconductor while positively charged (+) electrons gather around the P-type semiconductor. When you connect loads such as a light bulb, electric current flows between the two electrodes.

Chapter 18 -45

PhotoVoltaic• Direction of current inside PV cell

P

N

Current appears to be in the

reverse direction ?

• Inside current of PV cell looks like “Reverse direction.” Why?

?

• By Solar Energy, current is pumped up from N-pole to P-pole.

• In generation, current appears reverse. It is the same as for battery.

P

N

Looks like

reverse

Chapter 18 -46

Photovoltaic• Voltage and Current of PV cell ( I-V Curve )

(V)

(A)

Voltage(V)

Cur

rent

(I)

P

N

A

Short Circuit

Open Circuit

P

N

V

about 0.5V (Silicon)

High insolation

•Voltage on normal operation point0.5V (in case of Silicon PV)

•Current depend on- Intensity of insolation- Size of cell

•Voltage on normal operation point0.5V (in case of Silicon PV)

•Current depend on- Intensity of insolation- Size of cell

Low insolation

Normal operation point(Maximum Power point)

I x V = W

Chapter 18 -47

PhotoVoltaic• I / V curve and P-Max control

P

N

A

V

• To obtain maximum power, current control (or voltage control) is very important.

(V)

(A)

Voltage(V)

Cur

rent

(I)

I x V = W

P2

PMAX

P1

Vpmax

IpmaxI/V curve

P- Max controlP- Max control

• “Power conditioner” (mentioned later) will adjusts to be most suitable voltage and current automatically.

Power curve

Chapter 18 -48

PhotoVoltaic• Estimate obtained power by I / V curve

(V)

(A)

Voltage(V)

Cur

rent

(I)

12

10

8

6

4

2

0

0 0.1 0.2 0.3 0.4 0.5 0.6

P

N

A

)(05.0 R

PV character( I/V curve )

If the load has 0.05 ohm resistance, cross point of resistance character and PV-Character will be following point.Then power is 10x0.5=5 W

)(05.0 R

Resista

nce chara

cter

05.0/VI R

VI

Ohm’s law

Chapter 18 -49

PhotoVoltaic• Temperature and efficiency

4

6

8

10

12

14

0 10 20 30 40 50 60 70 80 90 100Module Temperature (deg.C)

Eff

icie

ncy

(%)

Crystalline cell

Amorphous cell

0.25 (%/deg)

Typical(25C)

Summer timeon roof top

(65C)

2%down 0.4 – 0.5 (%/deg)

• When module temperature rises up, efficiency decreases.• The module must be cooled by natural ventilation, etc.

Chapter 18 -50

PhotoVoltaic

CrystallineCrystalline

Non-crystallineNon-crystalline

Single crystalSingle crystal

Poly crystallinePoly crystalline

AmorphousAmorphous

Gallium Arsenide (GaAs)Gallium Arsenide (GaAs)

Conversion Efficiency of ModuleConversion Efficiency of Module

10 - 17%10 - 17%

10 - 13%10 - 13%

7 - 10%7 - 10%

18 - 30%18 - 30%

Conversion Efficiency =Electric Energy Output

Energy of Insolation on cellx 100%

Dye-sensitized TypeDye-sensitized Type

Organic Thin Layer TypeOrganic Thin Layer Type

7 - 8%7 - 8%

2 - 3%2 - 3%

• Types and Conversion Efficiency of Solar Cell

Silicon SemiconductorSilicon Semiconductor

CompoundSemiconductorCompoundSemiconductor

Solar CellSolar Cell

OrganicSemiconductorOrganicSemiconductor

Chapter 18 -

PhotoVoltaic

51

• Crystal cell (Single crystal and Poly crystalline Silicon)

Formed by melting high purity silicon like as Integrated Circuit

For mass production, cell is sliced from roughly crystallized ingot.

Single crystal Poly crystalline

Chapter 18 -52

PhotoVoltaic• Surface of PV cell

Front Surface(N-Type side)

• Aluminum Electrode (Silver colored wire)

• To avoid shading, electrode is very fine.

Anti reflection film(Blue colored film)

• Back surface is P-type.

• All back surface is aluminum electrode with full reflection.

Example of Poly Crystalline PV

Chapter 18 -53

PhotoVoltaic

Single crystal Poly crystalline

120W(25.7V , 4.7A)

1200mm

800mm800mm

1200mm

• PV Module (Single crystal, Poly crystalline Silicon)

(3.93ft)

（ 2.62ft ）

（ 3.93ft）

(2.62ft)

128W(26.5V , 4.8A)

Efficiency is higher Efficiency is lower

Same size

Chapter 18 -54

PhotoVoltaic• Hierarchy of PV

2 – 3 W

100 - 200 W

10 - 50 kW

Cell

Array

Module,Panel

Volt Ampere Watt SizeCell 0.5V 5-6A 2-3W about 10cmModule 20-30V 5-6A 100-200W about 1mArray 200-300V 50A-200A 10-50kW about 30m

6x9=54 (cells) 100-300 (modules)

Chapter 18 -55

PhotoVoltaic• Roughly size of PV Power Station.

How much PV can we install in this conference room?

1 kw PV need 10 m21 kw PV need 10 m2 Please remember

10m(33feet)

20m

(66f

eet)

ConferenceRoom

(We are now)

Our room has about 200 m2

We can install about20 kW PV in this room

(108 feet2)

(2,178 feet2)

Chapter 18 -56

PhotoVoltaic• Roof top of residence ( Grid connected )

Most popular installation style in Japan.(Almost 85% PV in Japan )

Owner can sell excess power to power utility.

Chapter 18 -57

PhotoVoltaic• Distant and independent power supply ( Off grid )

Relay station on top of mountain

Advertising sign beside highway

Chapter 18 -58

Junction Transistor

Fig. 18.24, Callister & Rethwisch 8e.

Chapter 18 -59

MOSFET Transistor Integrated Circuit Device

• Integrated circuits - state of the art ca. 50 nm line width– ~ 1,000,000,000 components on chip– chips formed one layer at a time


• MOSFET (metal oxide semiconductor field effect transistor)

Chapter 18 -60

Dielectric Behavior• Dielectric material is non-

conducting and it exhibit an electric dipole. i.e. separation between a positive and negative electric charge

• Electric dipole moment: a vector directed from –q to +q, p=qd

• When a field is applied (vector), a force or torque will come to bear on an electric dipole to orient it with the field. Known as Polarization

Chapter 18 -61

Capacitance• When a voltage is applied across a

capacitor, one plate becomes positively charged, the other negatively charged. The capacitance C is related to the quantity of charge stored on either plate Q by:

• C=Q/V

• If a vacuum exists between the two plates; C can be computed from

• • If a dielectric material is inserted into the

region within the plates then:

• ,

Chapter 18 -62

Dielectric Displacement• The surface charge density D in case of

vacuum is:

• If a dielectric material is inserted into the region within the plates then:

• =+P

(-1)

Chapter 18 -63

Numerical Problems

• Consider a parallel-plate capacitor having an area of 6.45x10-3 m (0.08 in) across which a potential of 10 V is applied. If a material having a dielectric constant of 6.0 is positioned within the region between the plates, compute the following:

• (a) The capacitance• (b) The magnitude of the charge stored on each

plate• The dielectric displacement D• The polarization.

Chapter 18 -64

Ferroelectric Ceramics

• Experience spontaneous polarization


BaTiO3 -- ferroelectric below its Curie temperature (120ºC)

Chapter 18 -65

Piezoelectric Materials

stress-free with applied stress

Adapted from Fig. 18.36, Callister & Rethwisch 8e. (Fig. 18.36 from Van Vlack, Lawrence H., Elements of Materials Science and Engineering, 1989, p.482, Adapted by permission of Pearson Education, Inc., Upper Saddle River, New Jersey.)

Piezoelectricity – application of stress induces voltage – application of voltage induces dimensional change

Chapter 18 -66

• Electrical conductivity and resistivity are: -- material parameters -- geometry independent• Conductors, semiconductors, and insulators... -- differ in range of conductivity values -- differ in availability of electron excitation states• For metals, resistivity is increased by -- increasing temperature -- addition of imperfections -- plastic deformation• For pure semiconductors, conductivity is increased by -- increasing temperature -- doping [e.g., adding B to Si (p-type) or P to Si (n-type)]• Other electrical characteristics -- ferroelectricity -- piezoelectricity

Summary

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Electrical Properities (1)