During the 1920s, the French physicist Louis de Broglie introduced the notion that particles can have wave properties. The equations that he, Erwin Schrödinger, and other physicists developed to describe these properties led to some startling new interpretations of particle behavior. One of these properties has come to be known as tunneling.

In classical physics, a charged particle is not allowed to pass through certain regions where the energy is too high for it to overcome. Quantum mechanical wave theory offers a somewhat different perspective on this phenomenon. It says that the particle has some small, but non-zero, chance of passing through that energy barrier provided that the barrier is thin enough. The name given to the phenomenon suggests that the particle may " tunnel under" the apparently insurmountable energy barrier.

No opportunity to test this prediction was available before the 1950s. Then, research on semiconductors resulted...