by Vaughn D. Martin
Parts 1 and 2 covered
These last two parts
examine active components.
This part begins by
investigating basic solid-state
theory, diodes, rectifiers,
transistor amplifiers, and
Part 4 concludes the series
with JFET and MOSFET
transistors, and thyristors
(to be explained).
Semiconductors are not truly conductors nor are they
pure insulators. They are somewhere in between, residing
in the Periodic Table’s middle columns. Compared with
metals, semiconductors are moderately good insulators,
but nothing resembling true insulators like glass. A useful
intrinsic semiconductor must have no more than one
impurity atom in 10 billion. This is like a grain of salt
An intrinsic semiconductor — or I-type semiconductor
— is a pure semiconductor without any significant dopant
in a boxcar of sugar. Impure semiconductors are
considerably more conductive. That is why semiconductor
manufacturers intentionally add dopants.
Doping is the process of adding controlled impurities
to a semiconductor.
Dopants depend on the atomic properties of both
the dopant and the material it affects. Generally, dopants
producing the desired effects are either electron acceptors
In 1869, the Russian chemist Dmitri Mendeleev
conceived of the Periodic Table of elements. His design
successfully accomplished its intent: to illustrate the recurring
“periodic” trends of the elements. Elements occur by
increasing atomic numbers, i.e., the number of protons in the
atomic nucleus. Rows are arranged so that elements with
similar properties fall into the same vertical columns. As
stated, semiconductors occupy the middle three columns
and have an equal number of valence or outer shell
electrons to either dispense or capture.
September 2009 47