Lectures 5-7 Flashcards
Equilibrium
Temperature is constant, no external voltage, no charge carriers (electrons/holes), no electrical current
No
Concentration of conduction electrons (cm^-3)
Po
Concentration of holes in valence band (cm^-3)
Pure Si is also called ____
Intrinsic Si
No for intrinsic semiconductor is labeled as ___
Ni
Concentration of electrons in conduction band
Po for intrinsic semiconductor is labeled as ___
Pi
Concentration of holes in valence band
Eg =
Ec-Ev
Doping Si will make Si…
Less sensitive to temperature
Substitutional Impurity
Add dopants (B, P)
Tiny amount, less than 1%
Need high temp - diffusion, ion implantation
P-type Si
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
Ea
Acceptance band (accepts electrons from valence band leaving behind hole)
Adding Group III element
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)
Acceptor impurity atom
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
N-type Si
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
Donor electron
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
Adding Group V/VI element
P
5 valence electrons
- 4 will contribute to covalent bonding with Si atoms
- 5th loosely bound to P atom (donor electron)
P atom without donor electron
Positively charged
At very low temperature, the donor electron is bound to the P atom
Donor impurity atom
P atom
Donates an electron to the conduction band without creating holes in the valence band
Intrinsic semiconductor
Pure single-crystal semiconductor material
Nd
Concentration of donor atoms
Na
Concentration of acceptor atoms
Compensated semiconductor
Doped with both donors and acceptors
N-type compensated semiconductor
Nd > Na
P-type compensated semiconductor
Na > Nd
If Na = Nd
Completely compensated semiconductor that has the characteristics of an intrinsic material
