- 1940s
- 1940 - PN junction
- Russel Ohl at Bell Labs develops the PN junction that produces 0.5 volts when exposed to light.
- 1945 - Transistor invented [1],[2],[3],[4]
- In 1945, Bell Labs established a group to develop a semiconductor replacement for the vacuum tube. The group led by William Shockley, included, John Bardeen, Walter Brattain and others. In 1947 Bardeen and Brattain succeeded in creating an amplifying circuit utilizing a point-contact "transfer resistance" device that later became known as a transistor. Bardeen and Brattain's device was the Point Contact Transistor the first transistor. In 1948, Bardeen and Brattain filed for a patent, that in 1950 was issued to Bell Labs - U.S. patent # 2,524,035, "Three Electrode Circuit Element Utilizing Semiconductive Materials".
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