Page 46 - Bebop to The Boolean Boogie An Unconventional Guide to Electronics Fundamentals, Components, and Processes

Semiconductors: Diodes and Transistors 2 7

If a pure piece of silicon is surrounded by a gas containing boron or
phosphorus and heated in a high-temperature oven, the boron or phosphorus
atoms will permeate the crystal lattice and displace some silicon atoms without
disturbing other atoms in the vicinity. This process is known as diffusion.
Boron-doped silicon is called P-type silicon and phosphorus-doped silicon is
called N-type (Figure 4-3).2

Boron gas

Figure 4-3. Creating P-type and N-type silicon

Because boron atoms have only three electrons in their outermost electron
shells, they can only make bonds with three of the silicon atoms surrounding
them. Thus, the site (location) occupied by a boron atom in the silicon crystal
will accept a free electron with relative ease and is therefore known as an
acceptor. Similarly, because phosphorous atoms have five electrons in their
outermost electron shells, the site of a phosphorous atom in the silicon crystal
will donate an electron with relative ease and is therefore known as a donor.

2 If you ever see an illustration of an integrated circuit, you may see symbols like n, n+, n++, p,
p+, and p++. In this case, the n and p stand for standard N-Type and P-type material (which
we might compare to an average guy), the n+ and p+ indicate a heavier level of doping (say a
bodybuilder or the author flexing his rippling muscles on the beach), and the n++ and p++
indicate a really high level of doping (like a weightlifter on steroids).