Semiconductor device An electronic device whose essential characteristics are governed by the flow of charge carriers within a semiconductor. History The oldest ancestor of semiconductor devices was the crystal detector, used in early wireless radios. This device (patented by a German scientist, Ferdinand Braun, in 1899) was made of a single metal wire (fondly called a "cat's whisker") touching against a semiconductor crystal. The result was a "rectifying diode" (so called because it has two terminals), which lets current through easily one way, but hinders flow the other way. By 1930, though, vacuum-tube diodes had all but replaced the smaller but much quirkier crystal detector. The crystal and "cat's whisker" were left to languish as a kids' toy in the form of "crystal radios." The development of radar during World War II did much to revive the fortunes of crystal detectors (and, as a result, that of semiconductor devices) -- although temperamental, crystals were better than vacuum-tube diodes at rectifying the high frequencies used by radar. So, during the war, much effort was put into improving the semiconductors, mostly silicon and germanium, used in crystal detectors. At about the same time, Russell Ohl at Bell Laboratories discovered that these materials could be "doped" with small amounts of foreign atoms to create interesting new properties. Depending on the selection of impurities (often called dopants) added, semiconductor material of two electrically-different types can be created -- one that is electron-rich (called N-type, where N stands for Negative), or one that is electron-poor (called P-type, where P stands for Positive). Most of the "magic" of semiconductor devices occurs at the boundary between P-type and N-type semiconductor material -- such a boundary is called a P-N junction. Ohl and his colleagues found that such a P-N junction made an effective diode. For BEAMbots, we'll be concerned with two broad types of semiconductor devices: Single-junction devices -- semiconductor devices with just one P-N junction. This includes diodes and all their variants (Zener diodes, Light Emitting Diodes, Photodiodes, solar cells, etc.). BEAM From the Ground Up has a writeup on these devices here. Multi-junction devices -- semiconductor devices with two or more P-N junctions; namely, transistors (bipolar, field-effect, phototransistors, and the like). BEAM From the Ground Up has a writeup on these devices here.

Legalities    Page author: Eric Seale   This page was last updated on This work is licensed under a Creative Commons License.