GTBL042-12 GTBL042-Callister-v2 August 13, 2007 18:22
490 • Chapter 12 / Electrical Properties+ +++ –+–+ +
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(a)p-side n-sideRecombination zone
Electron flowHole flow Electron flowBatteryHole flow++ +++
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+ ++
(b)+
+++++
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+ ++
(c)–+BatteryFigure 12.21 For ap–nrectifying junction,
representations of electron and hole
distributions for (a) no electrical potential,
(b) forward bias, and (c) reverse bias.circuitry, is responsible for the advent and extremely rapid growth of a host of new
industries in the past few years.Thep–nRectifying Junction
diode A rectifier, ordiode,is an electronic device that allows the current to flow in one
direction only; for example, a rectifier transforms an alternating current into direct
current. Before the advent of thep–njunction semiconductor rectifier, this oper-
rectifying junction ation was carried out using the vacuum tube diode. Thep–nrectifying junctionis
constructed from a single piece of semiconductor that is doped so as to ben-type on
one side andp-type on the other (Figure 12.21a). If pieces ofn- andp-type materials
are joined together, a poor rectifier results, since the presence of a surface between
the two sections renders the device very inefficient. Also, single crystals of semicon-
ducting materials must be used in all devices because electronic phenomena that are
deleterious to operation occur at grain boundaries.
Before the application of any potential across thep–nspecimen, holes will be the
dominant carriers on thep-side, and electrons will predominate in then-region, as
illustrated in Figure 12.21a. An external electric potential may be established across
ap–njunction with two different polarities. When a battery is used, the positive
terminal may be connected to thep-side and the negative terminal to then-side; this
forward bias is referred to as aforward bias.The opposite polarity (minus topand plus ton)is
reverse bias termedreverse bias.
The response of the charge carriers to the application of a forward-biased po-
tential is demonstrated in Figure 12.21b. The holes on thep-side and the elec-
trons on then-side are attracted to the junction. As electrons and holes encounter
one another near the junction, they continuously recombine and annihilate one