TABLE OF CONTENTS As mentioned on page 141, a diode is an electronic device having two terminals. There are many types, but the most common one is the PN diode. This can "rectify" ac, by only allowing current to flow in one direction, thus converting the ac into dc.
The P-type semiconductor (usually single crystal silicon, doped with B or Al) is contacting N-type material (usually Si doped with P or As). This can be made from a piece of intrinsic (very pure) silicon, with acceptors diffused into half of it and donors into the other half, ending up with P-type making contact to N-type along a plane inside the crystal. The contact plane is called a "junction."
Alternatively the PN junction can be made by growing the whole crystal with a moderate amount of acceptor material already mixed into it, and then diffusing a relatively larger amount of donor atoms into half of it, overwhelming the effect of the acceptors in that half. Again, where the two types meet there is a planar junction.
If an external voltage, from a battery for example, is put across a PN diode so the P type material is made positive and the N-type negative, then current will flow, as shown in Fig. 14.1. The electrons "fall into" the holes, becoming lower energy electrons. The energy they lose can be emitted as light ("photons") and heat (random vibrations of the silicon's atoms). A silicon diode does not produce...
