As the applications of solid state devices increase, the need for knowledge of these
devices becomes greater in importance. Army personnel will have to understand solid state
devices if they are to become proficient in the repair and maintenance of electronic
In l883, Michael Faraday discovered that silver sulfide, a semiconductor, had 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 (see TC 9-60).
Two years later, Munk A. Rosenshold discovered that certain materials have
rectifying properties (the ability to convert AC into DC). 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 strange
characteristics of the chemical element SELENIUM. They discovered that in addition to its
rectifying properties, selenium was also light sensitive (its resistance decreased with an
increase in light intensity). This discovery 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. It was not until the actual birth of radio that
selenium was largely used. Today, selenium is an important and widely used
Many other materials were tried and tested for use in communications. SILICON, a
metallic element, was found to be the most stable of the materials tested while GALENA, a
crystallized form of lead sulfide, was found the most sensitive for use in early radio
receivers. Carl Beredicks discovered that GERMANIUM, another metallic element, also
had rectifying capabilities. It later became widely used in electronics for low-power, low
Although the semiconductor existed 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 also rectify and detect a
signal as well. Since tubes could do all these things and semiconductor devices of that day
could not, the semiconductor was replaced.
Interest was renewed in the semiconductor at the beginning of World War II. There
was an urgent 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. However,
the point-contact semiconductor diode had a very low internal capacitance. Therefore, it
could be designed to work within the ultra-high frequencies used in radar, while the
electron tube could not.
23 June 2005