What began as research to improve telephone service became one of the most important inventions in electronics history.
In 1945, AT&T’s research division, Bell Labs, began working on technology to replace vacuum tubes and make long-distance telephone service more reliable. William Shockley organized a solid-state physics group to research semiconductor replacements for vacuum tubes and electromechanical switches.
Possibly influenced by JE Lilienfled’s idea for the field-effect transistor patented in 1926, Shockley conceived of a “field-effect” amplifier and switch based on recent germanium and silicon technology. He built a small cylinder coated thinly with silicon, mounted close to a small, metal plate, but was unable to get it to work.
A member of the research team, John Bardeen, suggested electrons on the semiconductor surface could be blocking the penetration of electric fields in Shockley’s experiments. Bardeen and Walter Brattain began using a silicon contraption built to help study how electrons acted on the surface of a semiconductor to test the theory.
It wasn’t until December 16, 1947 that the first successful test of their semiconductor amplifier occurred. They applied two closely-spaced gold contacts held in place by a plastic wedge to the surface of a small slab of high-purity germanium. The voltage on one contact modulated the current flowing through the other, amplifying the input signal up to 100 times.
The team demonstrated the discovery a week later on December 23, often considered the date the transistor was invented.
For more detail: 1st successful test of the transistor, December 16, 1947