Fundamentals of Materials Science and Engineering: An Integrated Approach, 3e

GTBL042-12 GTBL042-Callister-v2 August 13, 2007 18:22

12.15 Semiconductor Devices • 489

Furthermore, from Equation 12.8, the electron mobilityμeis just

μe=

σ

n|e|

(12.20a)

or, using Equation 12.19,

μe=|RH|σ (12.20b)

For metals, electron

mobility in terms of

the Hall coefficient

and conductivity

Thus, the magnitude ofμemay also be determined if the conductivityσhas also been

measured.

For semiconducting materials, the determination of majority carrier type and

computation of carrier concentration and mobility are more complicated and will

not be discussed here.

EXAMPLE PROBLEM 12.4

Hall Voltage Computation

The electrical conductivity and electron mobility for aluminum are 3.8× 107

(-m)−^1 and 0.0012 m^2 /V-s, respectively. Calculate the Hall voltage for an alu-

minum specimen that is 15 mm thick for a current of 25 A and a magnetic field

of 0.6 tesla (imposed in a direction perpendicular to the current).

Solution

The Hall voltageVHmay be determined using Equation 12.18. However, it first

becomes necessary to compute the Hall coefficient (RH) from Equation 12.20b

as

RH=−

μe

σ

=−

0 .0012 m^2 /V-s

3. 8 × 107 (-m)−^1

=− 3. 16 × 10 −^11 V-m/A-tesla

Now, employment of Equation 12.18 leads to

VH=

RHIxBz

d

=

(− 3. 16 × 10 −^11 V-m/A-tesla)(25 A)(0.6 tesla)

15 × 10 −^3 m

=− 3. 16 × 10 −^8 V

12.15 SEMICONDUCTOR DEVICES

The unique electrical properties of semiconductors permit their use in devices to

perform specific electronic functions. Diodes and transistors, which have replaced

old-fashioned vacuum tubes, are two familiar examples. Advantages of semiconduc-

tor devices (sometimes termed solid-state devices) include small size, low power

consumption, and no warmup time. Vast numbers of extremely small circuits, each

consisting of numerous electronic devices, may be incorporated onto a small silicon

chip. The invention of semiconductor devices, which has given rise to miniaturized