When Russell Ohl began working at Bell Laboratories in 1927, vacuum tubes were seen as the future of electronics. It was his chance discovery, however, that led to the creation of both the transistor and the solar cell and helped spark the “silicon revolution.”In the late 1930s Ohl was a radio researcher trying to create a receiver that would be more effective than vacuum tubes. The tubes easily picked up low-frequency radio signals, but had trouble with higher frequencies such as those being tested in radar-a technology that was gaining importance as war brewed overseas. Ohl thought an alternative might lie in the crystal receiver, an antiquated radio device from the 1920s. He devoted himself completely to his research: when his workweek was shortened during the Depression, Ohl used his extra time to study crystal structure.
Crystal receivers were tricky, poorly understood devices. To get a signal, an operator would search the surface of a crystal with a metal strand for the “hot spot,” which caused current flow in only one direction. After exhaustive experimentation, Ohl concluded that the best receivers were the elements now known as semiconductors. He theorized that purer materials would make better receivers and had special samples prepared for his tests.