As the applications of solid-state devices mount, the need for knowledge of these devices becomes
increasingly important. Personnel in the Navy today will have to understand solid-state devices if they are
to become proficient in the repair and maintenance of electronic equipment. Therefore, our objective in
this module is to provide a broad coverage of solid-state devices and, as a broad application, power
supplies. We will begin our discussion with some background information on the development of the
semiconductor. We will then proceed to the semiconductor diode, the transistor, special devices and,
finally, solid-state power supplies.
Although the semiconductor was late in reaching its present development, its story began long before
the electron tube. Historically, we can go as far back as 1883 when Michael Faraday discovered that
silver sulfide, a semiconductor, has a negative temperature coefficient. The term negative temperature
coefficient is just another way of saying its resistance to electrical current flow decreases as temperature
increases. The opposite is true of the conductor. It has a positive temperature coefficient. Because of this
particular characteristic, semiconductors are used extensively in power-measuring equipment.
Only 2 years later, another valuable characteristic was reported by Munk A. Rosenshold. He found
that certain materials have rectifying properties. Strange as it may seem, his finding was given such little
notice that it had to be rediscovered 39 years later by F. Braun.
Toward the close of the 19th century, experimenters began to notice the peculiar characteristics of
the chemical element SELENIUM. They discovered that in addition to its rectifying properties (the ability
to convert ac into dc), selenium was also light sensitive-its resistance decreased with an increase in light
intensity. This discovery eventually led to the invention of the photophone by Alexander Graham Bell.
The photophone, which converted variations of light into sound, was a predecessor of the radio receiver;
however, it wasnt until the actual birth of radio that selenium was used to any extent. Today, selenium is
an important and widely used semiconductor.
Many other materials were tried and tested for use in communications. SILICON was found to be the
most stable of the materials tested while GALENA, a crystalline form of lead sulfide, was found the most
sensitive for use in early radio receivers. By 1915, Carl Beredicks discovered that GERMANIUM,
another metallic element, also had rectifying capabilities. Later, it became widely used in electronics for
low-power, low-frequency applications.
Although the semiconductor was known long before the electron tube was invented, the
semiconductor devices of that time could not match the performance of the tube. Radio needed a device
that could not only handle power and amplify but rectify and detect a signal as well. Since tubes could do
all these things, whereas semiconductor devices of that day could not, the semiconductor soon lost out.
It wasnt until the beginning of World War II that interest was renewed in the semiconductor. There
was a dire need for a device that could work within the ultra-high frequencies of radar. Electron tubes had
interelectrode capacitances that were too high to do the job. The point-contact semiconductor diode, on
the other hand, had a very low internal capacitance. Consequently, it filled the bill; it could be designed to
work within the ultra-high frequencies used in radar, whereas the electron tube could not.
As radar took on greater importance and communication-electronic equipment became more
sophisticated, the demands for better solid-state devices mounted. The limitations of the electron tube
made necessary a quest for something new and different. An amplifying device was needed that was
smaller, lighter, more efficient, and capable of handling extremely high frequencies. This was asking a