Callister - An introduction - 8th edition

746 • Chapter 18 / Electrical Properties
The concentration of acceptor impurities in atom percent 1C¿ a 2
ratio of N a and N a N Si multiplied by 100 as
is just the
N a
C¿ a 100
N a N Si
8 10 21 m 3
100 1.60
18 10 21 m 3 2 15 10 28 m 3 105
2
Thus, a silicon material having a room-temperature p-type electrical conductivity
of 50 (#
m) 1 must contain 1.60 10 5 at% boron, aluminum, gallium,
or indium.
18.14 THE HALL EFFECT
For some materials, it is on occasion desired to determine the material’s majority
Hall effect
charge carrier type, concentration, and mobility. Such determinations are not possible
from a simple electrical conductivity measurement; a Hall effect experiment
must also be conducted. This Hall effect is a result of the phenomenon whereby a
magnetic field applied perpendicular to the direction of motion of a charged particle
exerts a force on the particle perpendicular to both the magnetic field and the
particle motion directions.
In demonstrating the Hall effect, consider the specimen geometry shown in
Figure 18.20, a parallelepiped specimen having one corner situated at the origin of
a Cartesian coordinate system. In response to an externally applied electric field, the
electrons and/or holes move in the x direction and give rise to a current I x . When a
magnetic field is imposed in the positive z direction (denoted as B z ), the resulting
force brought to bear on the charge carriers will cause them to be deflected in the
y direction—holes (positively charged carriers) to the right specimen face and electrons
(negatively charged carriers) to the left face, as indicated in the figure. Thus, a
x
I x
Figure 18.20 Schematic demonstration
of the Hall effect. Positive and/or
negative charge carriers that are part
of the I x current are deflected by the
magnetic field B z and give rise to the
Hall voltage, V H .
B z
− +
z
V H
c
d
y