Solid-state physics: conductionPHY 3305 (Modern Physics) Harris, Ch. 10.6-10.8 table of contents Review Bands (T=0, T>0) Lithium vs. Beryllium Band Pictures Holes Semiconductors intrinsic

Solid-state physics: conduction

Prof. Stephen Sekula(3/30/2010)

Supplementary Material for PHY 3305 (Modern Physics)

Harris, Ch. 10.6-10.8

table of contents

● Review

● Bands (T=0, T>0)

● Lithium vs. Beryllium

● Band Pictures

● Holes

● Semiconductors● intrinsic and extrinsic

● Example: Diode

● Example: Transistor

solid, no Electric field applied

Equal populations of -k and +k electrons

solid, WITH Electric field applied

A picture: bands/Gaps

N s

tate

s pe

r ba

n dN s

tate

s pe

r ba

n d

Gap

A picture: bands/Gaps

N s

tate

s pe

r ba

n dN s

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s pe

r ba

n d

Gap

Energy levels so close as to resemble a continuum

Energy levels so close as to resemble a continuum

Questions

● How many conduction electrons can each band hold?

● Which is a better conductor: Lithium or Beryllium?● Lithium has 3 electrons● Beryllium has 4 electrons

Insulator (T=0)N s

tate

s pe

r ba

n dN s

tate

s pe

r ba

n d

Empty(Conduction Band)

Full(Valence Band)

conductor (T=0)N s

tate

s pe

r ba

n dN s

tate

s pe

r ba

n d

Partially Full

Full

Semi-Conductor (T=0)N s

tate

s pe

r ba

n dN s

tate

s pe

r ba

n d

Empty

Full

conductor (T>0)N s

tate

s pe

r ba

n dN s

tate

s pe

r ba

n d

Partially Full

Full

Semi-Conductor (T>0)N s

tate

s pe

r ba

n dN s

tate

s pe

r ba

n d

Mostly Empty

Mostly Full

HOLES (T>0)N s

tate

s pe

r ba

n dN s

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s pe

r ba

n d

Conduction Band

Valence Band

Temperature causes an

electron to jump the gap, leaving a

“hole” in the valence band.

Holes floatN s

tate

s pe

r ba

n d

Valence Band

Total Energy E1

N s

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s pe

r ba

n d

Valence Band

Total Energy E2

E2 < E1

n-type extrinsic semiconductor (T=0)

N s

tate

s pe

r ba

n d

Conduction Band

Valence Band

Donor States

0.05 eV

N s

tate

s pe

r ba

n d

n-type extrinsic semiconductor (T>0)

N s

tate

s pe

r ba

n d

Conduction Band

Valence Band

N s

tate

s pe

r ba

n d

Donor States

0.05 eV

N s

tate

s pe

r ba

n d

P-type extrinsic semiconductor (T=0)

N s

tate

s pe

r ba

n d

Conduction Band

Valence Band

Acceptor States 0.05 eV

N s

tate

s pe

r ba

n d

P-type extrinsic semiconductor (T>0)

N s

tate

s pe

r ba

n d

Conduction Band

Valence Band

N s

tate

s pe

r ba

n d

Acceptor States 0.05 eV

N s

tate

s pe

r ba

n d

the diode

energy band picture

Transistor

Next time

● Superconductivity● Nuclear Physics● Good presentation style● Reading for next time: Harris Ch. 10.9, 11.1-11.2