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Semiconductors A class of materials called semiconductors can change from being an insulator to being a conductor and back to an insulator again. Engineers produce extrinsic semiconductors by doping, which is the addition of minute amounts (typically 1 part in 106 ) of other materials that can act as electron donors or electron receptors.If the doping substance acts as an electron receptor, the hole left behind by an electron that attaches to a receptor can also travel through the semiconductor and acts as an effective positive charge carrier.Gordon Moore, cofounder of Intel, famously stated that due to advancing technology, the power of the average computer's CPU (central processing unit) doubles every 18 months, which is an empirical average over the last 5 decades.Examples of intrinsic semiconductors are chemically pure crystals of gallium arsenide, germanium, or, especially, silicon.This doubling phenomenon is known as Moore's Law.

Semiconductors
A class of materials called semiconductors can change from being an insulator to
being a conductor and back to an insulator again. Semiconductors were discovered
only a little more than 50 years ago but are the backbone of the entire computer and
consumer electronics industries. The first widespread use of semiconductors was in
transistors (Figure 1.7a); modern computer chips (Figure 1.7b) perform the functions
of millions of transistors. Computers and basically all modern consumer electronics
products and devices (televisions, cameras, video game players, cell phones, etc.)
would be impossible without semiconductors. Gordon Moore, cofounder of Intel,
famously stated that due to advancing technology, the power of the average computer’s CPU (central processing unit) doubles every 18 months, which is an empirical
average over the last 5 decades. This doubling phenomenon is known as Moore’s Law.
Physicists have been and will undoubtedly continue to be the driving force behind
this process of scientific discovery, invention, and improvement.
Semiconductors are of two kinds: intrinsic and extrinsic. Examples of intrinsic semiconductors are chemically pure crystals of gallium arsenide, germanium, or, especially, silicon. Engineers produce extrinsic semiconductors by doping, which is the addition of minute
amounts (typically 1 part in 106
) of other materials that can act as electron donors or electron receptors. Semiconductors doped with electron donors are called n-type (n stands for
“negative charge”). If the doping substance acts as an electron receptor, the hole left behind
by an electron that attaches to a receptor can also travel through the semiconductor and
acts as an effective positive charge carrier. These semiconductors are consequently called
p-type (p stand for “positive charge”). Thus, unlike normal solid conductors in which only
negative charges move, semiconductors have movement of negative or positive charges
(which are really electron holes, that is, missing electrons).