conduction

Question 1

metals

Answer 1

Metals

Question 2

semiconductors

Answer 2

Silicon
Germanium
GaAs

Question 3

Insulators

Answer 3

Ceramics
Polymers

Question 4

band of insulators

Answer 4

Insulators: the
filled valence band
is separated from
the empty
conduction band
by a relatively large
band gap (2 eV

Question 5

Semiconductors band gap

Answer 5

Semiconductors:
same as for
insulators except
that the band gap
is relatively narrow
(2 eV).

Question 6

• Imperfections increase

Answer 6

resistivity
* Grain boundaries
* Dislocations
* Impurity atoms
* Vacancies

Question 7

Resistivity increases with:

Answer 7

• Temperature
• Impurity concentration
• % Cold Work (which increases the number of dislocations)

Question 8

As T ↑
As %CW ↑

Answer 8

As T ↑ à vibrations and lattice
defects ↑ à electron scattering ↑
As %CW ↑ à dislocation
concentration ↑ à resistivity ↑

Question 9

in semiconductors conductivity given by

Question 10

what is intrinsic semiconductor

Answer 10

number of elec equal to number of holes p

Question 10

what can intrinsic semiconductors have

Answer 10

si or ge

Question 10

what happens in extrinsic semicond

Answer 10

• n≠p
• Occurs when impurities with different
  # of valance electrons are present
• e.g. doping Si with P or B

Question 10

what are the types of extrinsic semi conductors

Answer 10

n type (n greater than p) donates e
p type (p greater n) accepts e

Question 10

in intrinsic conductors electrons have to overcome what

Answer 10

Electron has to overcome the energy gap Eg
*

Question 10

Intrinsic conductivity strongly depends

Answer 10

Intrinsic conductivity strongly depends on
temperature and as-present impurities

Question 10

doping does whta to conductivity and why

Answer 10

Doping increases σ
* Reason: imperfection sites lower
the activation energy to produce
mobile electrons

Question 10

P-N Rectifying Junction

Answer 10

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

Question 11

Piezoelectricity

Answer 11

• Literally “pressure electricity”