GTBL042-12 GTBL042-Callister-v2 August 13, 2007 18:22
492 • Chapter 12 / Electrical PropertiesTimeVoltage,VReverse Forward0- V 0
+V 0(a)TimeCurrent,IReverse Forward0
IRIF(b)Figure 12.23 (a) Voltage versus time for
the input to ap–nrectifying junction.
(b) Current versus time, showing
rectification of voltage in (a)byap–n
rectifying junction having the
voltage–current characteristics shown in
Figure 12.22.Junction Transistors
The junction transistor is composed of twop–njunctions arranged back to back
in either then–p–nor thep–n–pconfiguration; the latter variety is discussed here.
Figure 12.24 is a schematic representation of ap–n–pjunction transistor along with
its attendant circuitry. A very thinn-typebaseregion is sandwiched in between
p-typeemitterandcollectorregions. The circuit that includes the emitter–base junc-
tion (junction 1) is forward biased, whereas a reverse bias voltage is applied across
the base–collector junction (junction 2).
Figure 12.25 illustrates the mechanics of operation in terms of the motion of
charge carriers. Since the emitter isp-type and junction 1 is forward biased, large
numbers of holes enter the base region. These injected holes are minority carriers
in then-type base, and some will combine with the majority electrons. However, if
the base is extremely narrow and the semiconducting materials have been properly
prepared, most of these holes will be swept through the base without recombination,Time Time0.1Emitter
pJunction 1 Junction 2Base
nCollector
p10Inputvoltage(mV) Outputvoltage(mV)++Output
voltageLoadInput
voltageForward-biasing voltage Reverse-biasing voltageFigure 12.24
Schematic diagram of
ap–n–pjunction
transistor and its
associated circuitry,
including input and
output voltage–time
characteristics showing
voltage amplification.
(Adapted from A. G.
Guy,Essentials of
Materials Science,
McGraw-Hill Book
Company, New York,
1976.)