Electron tunneling in solids

Quantum tunneling of a particle through a barrier was introduced in the theory of field ionization of atoms (1927), and to account for field emission of electrons from surfaces and for alpha emission by nuclei (1928). Electron tunneling within a solid, though more complicated than tunneling of a free particle, arises in essentially the same way from a mode of wave propagation. It has recently become the basis of a new area of research. The figures below depict these varieties of tunneling process. In Fig. 1, according to classical mechanics, the particle coming from the left would be reflected at the “classical turning point”, A, where the potential energy equals its original kinetic energy. The Schrödinger wave governing its quantum behavior penetrates into the “forbidden” region, however, and in consequence the particle may travel onward from the second turning point, B. The probability of transmission, instead of reflection, decreases exponentially with increasing forbidden path length, AB.