Russell Ohl (1898-1987) was a precocious talent who by the age of sixteen had already entered Pennsylvania State University After a period in the Army Signal Corps and a brief career as a teacher, OhI finally took a research position in U.S. industry.
Early radios were only able to receive low- frequency transmissions. At Bell Labs in Holmdel, New Jersey, Ohl worked to create an improved radio receiver for high frequencies. Here he experimented with semiconductor materials that he thought would outperform the electron tubes used in existing receivers. An expert in the behavior of crystals, Ohl investigated different materials for semiconductors, such as germanium and silicon. The crystals were heated, and when cool would be sliced for use.
In 1939 Ohl was working with a silicon sample that he noticed had a crack down the middle. When he tested the electrical resistance of the sample he noted that when it was exposed to light, the current flowing between the two sides of the crack jumped significantly. As a result of this accidental impurity in the silicon, atoms on one side of the crack were shown to have extra electrons; the crystallized silicon on the other side had a deficit. Ohl deduced that it was these impurities that made different areas of the silicon more or less resistant to electrical flow, and thus it was the "barrier" between these areas of differing purities that made the semiconductor work. Ohl named the two areas "p" (positive) and "n" (negative); the barrier between was called the "p-n junction." In the research that followed, OhI was able to show that by super- purifying germanium crystals he was able to create semiconductor diodes that could behave in predictable and measurable ways.
