FACULTY OF ENGINEERING
DEPARTMENT OF ELECTRICAL AND ELECTRONIC ENGINEERING
MIDTERM EXAMINATION I
Spring 2001-02
EEE 245 – PHYSICAL ELECTRONICS
Instructors:
E.Erdil
Date: April 26, 2002
Duration : 100 minutes
Number of Questions: 4
Answer all questions
Good Luck
STUDENT NO
NAME
SURNAME
Question
Points
1
25
2
25
3
25
4
25
TOTAL
100
Points earned
1-
a) Draw the (012) and (040) planes of a cubic lattice structure.
b) Calculate the planar atomic density (surface density of atoms) on the
(220) plane of a silicone lattice in atoms per square centimeter. The lattice
constant of silicone is 5.43 Angstrom. (Reminder:
planar atomic density=equivalent number of atoms whose centers are
intersected by the selected area divided by the selected area.)
c) Calculate the linear atomic density in the [111] direction in the -iron
BCC lattice. The lattice constant of -iron is 2.87 Angstrom.. (Reminder:
Linear atomic density=equivalent number of atomic diameters intersected by
the selected length of line in the direction of interest divided by the selected
length of line.
Note also that the direction [x0 y0 z0] gives the direction of the vector starting
from the origin (0 0 0) and pointing to the point (x0 y0 z0))
2- A direct- conduction band electron initially has energy Ec . It gains
kinetic energy and the “k’ value increase to 0.25 10 10 m-1 . Show all
the energy levels involved, on a diagram, and clearly identify them. If
the total energy of the electron, relative to the vacuum energy level, is
“–4 eV” after it gains the kinetic energy, find the electron affinity of the
material in eV. ( h/2 = 1.05 10 –34 Js , m* = 0.09 10 –30 kg , and eV =
1.6 10 –19 J )
3- Explain in detail (use diagrams if necessary) what is meant by the
following:
i) Conduction Band
ii) Electron Affinity
iii) Fermi Energy
iv) Work Function
v) Doping
vi) Intrinsic concentration
vii) Fermi Half Integral
viii)Density of states
ix) p-type semiconductor
x) Semiconductor Band-gap
4Silicon n-type sample with band-gap 1.1 eV at 300 Kelvin, has
EC – EF = 0.21 eV. Assuming 100% solubility of dopant;
a) calculate the density of dopant in cubic centimeters
b) what is the valency of the dopant used in silicone
c) what is the hole concentration.
Some useful information:
Effective density of states in the conduction band at 300 K, Nc (cm-3)=
2.82x1019
Boltzman constant , kB=8.62x10-5 eV/K.