Lecture 9 - Electrical, Thermal And Optical Properties Flashcards
For a metal how is the conductivity determined
By the concentration of electrons in the conduction band and the mobility of the electrons
For a metal how is the mobility determined
By the N.O of scattering centres and the effectiveness mass of the electron in the conduction band
What happens when temperature increases in a metal
Scattering goes up and mobility drops
What are the charge carriers in a semiconductor. Explain
Both electrons in the conduction band the holes in the valance band
The mobility in the electrons and hole are usually different in a given semiconductor and also vary between semiconductors- different effective masses
Why does the conductivity of semiconductors increase with temperature
Bc although there mobility is reduced the concentration of electrons and holes increases and that dominates
What does it mean when there is a wider electronegativity difference between the elements
The wider the energy gap
What is the difference between an intrinsic and extrinsic semiconductor
Intrinsic - pure form of a semi conductor
Extrinsic - impurities are intentionally added to make it conductive (known as doping)
What do dielectrics (insulators) not do
Don’t conduct electricity - not DC
When do electric dipoles form
When voltage is applied
What does refractive index and the relative permittivity relate to
Dipoles - that form in a material when the electric field is applied
What is the change in reflective index with photon energy called
Dispersion - gives rise to the colour dispersion of a prism
What does dispersion relate to
How quickly the dipoles form, when the electric field is applied
