ECE3030 Physical Foundations of Computer Engineering, Fall 2016 Assigned Aug. 31; Rev. 9/3
Homework 3 Solution to Problem 7
7.
(25) Short answer questions. Use your own words to answer the following questions. Please
limit your answer to 50 words or less per answer (a total of 250 words for parts a through e).
a. (5 pts.) What does the Fermi energy level EF represent?
b. (5 pts.) What does the intrinsic energy level Ei represent?
c. (5 pts.) What does the conduction band energy level Ec represent?
d. (5 pts.) What does the valence band energy level Ev represent?
e. (5 pts.) Describe the location of electrons at zero Kelvin in terms of the energy bands
Ec, Ev, Ei and EF.
Answers:
a. EF represents the energy level at which the probability of an electron
orbital having an energy level EF being filled is ½.
b. Ei represents the Fermi energy level of an intrinsic material. Note that
Ei is not exactly halfway between EC and EV, due in part to the different
effective masses of electrons and holes.
c. EC represents the lowest energy level of the electron orbitals available
within the conduction band.
d. EV represents the highest energy level of the electron orbitals available
within the valence band.
e. At zero Kelvin, all electrons occupy orbitals at or below EV. No
electrons are in the conduction band. Since all electrons are within the
valence band, all electrons occupy orbitals with energy levels below Ei
and EF.