A Few Words from Sara Shepherd, Screaming Circuits Contributing Blogger…
We return to our series celebrating the periodic table’s 150th birthday. As we learned in our first post on the subject, there were several chemists working to arrange the elements, but it was Dmitri Mendeleev’s ability to predict undiscovered elements that set him apart. We explored one of these elements in our first post: gallium, the discovery of which caused Mendeleev’s table to become universal accepted.
Another of Mendeleev’s predicted but not-yet-discovered elements had a space reserved on his table in group 14 between silicon and tin. Mendeleev called the missing element “eka-silicon,” meaning “beyond silicon.” While Mendeleev could predict that the element existed, he had no way of knowing how great the impact it would have on the world of electronics.
Fifteen years after Mendeleev predicted the element existed, a new mineral named argyrodite was found deep in a mine in Germany. The hunk of rock contained silver, sulfur, and… something else. Chemist Clemens Alexander Winkler was able to isolate the new element in 1886. He named it “Germanium” after his homeland of Germany.
The physical properties of Germanium were similar to antimony and arsenic, but it was not at all similar from a reactivity standpoint. Winkler was not sure where to place the new element on the table until he realized the atomic mass matched Mendeleev’s prediction for eka-silicon, and so Germanium was placed in group 14.
Hooray! Another gap in Mendeleev’s table was filled, and both chemists moved on with their lives. Poor, brittle Germanium was dismissed as a weakly conducting metal without much use. In fact, the worth of germanium did not become recognized until World War II.
During the war, there was a need for high frequency rectifiers to achieve high resolution from radar receivers. American physicist Karl Lark-Horovitz — through his pioneering work in solid-state physics — was the first to realize and tabulate the valuable properties of germanium, including its low melting point and relatively high stability. As a result of his findings, point contact rectifiers used for radar receivers during the war were made of germanium.
Further experiments after the war demonstrated germanium’s usefulness as a semiconductor. In 1947, Walter Brattain, John Bardeen, and William Shockley of Bell Labs found that — by applying a small amount of electricity to a piece of germanium — the element could increase the flow of electricity through a second circuit which was also connected to it. In other words, germanium worked as an amplifier. After this discovery, the researchers added gold contacts to the setup and the first germanium transistor was created.
The transistor overcame many of the limitations of the vacuum tubes previously used for electronics: transistors had very long lives, were much smaller yet mechanically rugged, and required no filament current. They also allowed for devices to operate at a higher frequency.
The creation of the germanium transistor forever changed the world of electronics. Yet only a decade later, germanium was all but abandoned in favor of a different element: silicon, due to its larger band gap and the existence of stable silicon oxides. But don’t shed a tear for germanium, just as its use in transistors was becoming obsolete, a new application was developed: gamma ray and infrared detectors.
Today, germanium continues to be a critical element for electronics and technology, and is now being used in fiberoptic systems and solar cell applications. And — because apparently even elements go in and out of style — there is renewed interest in using germanium in transistors!