Lecture 13 (Ionic and Metallic Lattices) Flashcards
What is a band?
A group of MOs
What is the band theory?
Electrons can move into vacant MOs within the band under the influence of small energetic contributions. The electron will be delocalized over the entire metallic crystal resulting in electrical conductivity
What does electrical conductivity mean?
the characteristic property of partially filled bands of MOs
What does thermal vibrations of the nuclei produce?
Electrical resistance
How is electrical resistance enhanced?
higher temperatures
What is a band gap?
Bands can overlap or can be separated by a difference in energy
How does the band gap work for an insulator?
A fully occupied band separated by the next empty band by a large band gap
How does the band gap work for a metallic conductor?
A partially occupied band or an overlap between a fully occupied band and a vacant band
What is the Fermi level?
the energy level of the highest occupied orbital in a metal at absolute zero
How does the band gap work for a semiconductor?
A fully occupied band separated from an unoccupied band by a small band gap
What does electric conductivity in semiconductors depend on?
the availability of sufficient energy for the thermal population of upper, vacant band.
As conductivity increases, the temperature increases. True or false?
True
C (diamond) is an insulator. True and False?
True
α-Sn is a metallic conductor. True or false?
True
What elements are intrinsic semiconductors?
Si and Ge
What do Si and Ge act as?
charge carriers
How are positive holes create?
The removal of electrons from the lower valence band. Where electrons can move, leading to the ability to conduct electricity
What is a charge carrier in a semiconductor?
A positive hole or an electron that is able to conduct electricity
Extrinsic (n and p type) semiconductors are used for?
Are tuned by doping with Group 13 or Group 15 elements
What does an extrinsic semiconductor contain?
it contains a dopant, which is a controlled impurity
What does doping of Si with B, Al, or Ga create?
An acceptor level, populated and the positive holes act as charge carriers (p-type (positive) semiconductor)
What does doping of Si with P or As create?
A donor level, populated on the conduction band, acting as carge carriers (n-type (negative) semiconductor)
What does ionic radii depend on?
The estimation method
what is lattice energy?
It is the change in the internal energy that accompanies the formation of one mole of the solid from its constituent gas-phase ions
What is the Coulombic (electrostatic) force?
The main force acting between charged particles
What are born forces?
Non-coulombic, repulsive electron-electron and nucleus-nucleus interactions also arise
