Lectures 5-7

Question 1

Equilibrium

Answer 1

Temperature is constant, no external voltage, no charge carriers (electrons/holes), no electrical current

Question 2

No

Answer 2

Concentration of conduction electrons (cm^-3)

Question 3

Po

Answer 3

Concentration of holes in valence band (cm^-3)

Question 4

Pure Si is also called ____

Answer 4

Intrinsic Si

Question 5

No for intrinsic semiconductor is labeled as ___

Answer 5

Ni

Concentration of electrons in conduction band

Question 6

Po for intrinsic semiconductor is labeled as ___

Answer 6

Pi

Concentration of holes in valence band

Question 7

Eg =

Answer 7

Ec-Ev

Question 8

Doping Si will make Si…

Answer 8

Less sensitive to temperature

Question 9

Substitutional Impurity

Answer 9

Add dopants (B, P)

Tiny amount, less than 1%

Need high temp - diffusion, ion implantation

Question 10

P-type Si

Answer 10

Si with B dopant — intentionally making more holes in valence band

Higher conductivity than pure Si

Conducts electricity mostly through holes as charge carriers

Po - concentration of holes in valence band in equilibrium

Po > Ni
Po > No
No < Ni
Ef < Efi

Hole concentration (majority carrier) > electron concentration (minority carrier)

Acceptor impurity atoms added

Question 11

Ea

Answer 11

Acceptance band (accepts electrons from valence band leaving behind hole)

Question 12

Adding Group III element

Answer 12

B

3 valence electrons

• all taken up in covalent bonding
• one covalent bonding position empty
• empty position becomes occupied, leaving valence electron positions to be vacated (holes)

Acceptor impurity atom (p-type)

Question 13

Acceptor impurity atom

Answer 13

Hole can move through the crystal generation a current, while the negatively charged B atom remains fixed

Group III atom accepts an electron from the valence band

Can generate holes in valence band without generation electrons in the conduction band

Question 14

N-type Si

Answer 14

Si doped with Phosphorus (P) - extrinsic

Conductivity of n-type Si is higher than conductivity of pure intrinsic Si

No > Ni
Ef > Efi
No > Po
Po < Ni

Electron concentration (majority carrier) > hole concentration (minority carrier)

Donor impurity atoms added

Question 15

Donor electron

Answer 15

N-type

Heat added, electron elevated into conduction band, leaving behind a positively charged P ion (fixed)

Electron in conduction band can now move through the crystal generating a current

Question 16

Adding Group V/VI element

Answer 16

P

5 valence electrons

• 4 will contribute to covalent bonding with Si atoms
• 5th loosely bound to P atom (donor electron)

Question 17

P atom without donor electron

Answer 17

Positively charged

At very low temperature, the donor electron is bound to the P atom

Question 18

Donor impurity atom

Answer 18

P atom

Donates an electron to the conduction band without creating holes in the valence band

Question 19

Intrinsic semiconductor

Answer 19

Pure single-crystal semiconductor material

Question 20

Nd

Answer 20

Concentration of donor atoms

Question 21

Na

Answer 21

Concentration of acceptor atoms

Question 22

Compensated semiconductor

Answer 22

Doped with both donors and acceptors

Question 23

N-type compensated semiconductor

Answer 23

Nd > Na

Question 24

P-type compensated semiconductor

Answer 24

Na > Nd

Question 25

If Na = Nd

Answer 25

Completely compensated semiconductor that has the characteristics of an intrinsic material