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T
homas Edison struggled with invention, trying
through a process of elimination to “invent”
the carbon filament for incandescent light
bulbs.
“I speak without exaggeration when I say that
I have constructed 3000 different theories in con-
nection with the electric light, each one of them
reasonable and apparently likely to be true. Yet only
in two cases did my experiments prove the truth of
my theory. My chief difficulty was in constructing the
carbon filament. … Every quarter of the globe was
ransacked by my agents, and all sorts of the queer-
est materials used, until finally the shred of bamboo,
now utilized by us, was settled upon,” he declared.
He has nothing on Isamu Akasaki, Hiroshi Amano
and Shuji Nakamura who have just won the 2014
Nobel Prize for Physics “for the invention of efficient
The
dedicated
pursuit of
white light
by Gavin Chait
Images: www.nobelprize.org
blue light-emitting diodes, which has enabled bright
and energy-saving white light sources”.
Diodes are electrical components with asym-
metrical conductance to current; low resistance
in one direction and high resistance in the other.
Transistors, the essential components of all logic
circuits and microprocessors, are a type of diode.
Semiconductors, like silicon, can be doped so
that they have different electrical properties. Dop-
ing introduces into the material impurity atoms,
which then either act as donors or receptors for
valence (or outer band) electrons. Such extrinsic
semiconductors can have either a higher electron
concentration (more valence electrons) or more
holes (spaces to accept valence electrons). These
are, respectively, n- or p-type semiconductors.
Each of these n- or p-type semiconductors is
LiD
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