Charles H. Henry - Quantum Wells

Quantum Wells

The idea of the quantum well occurred to Henry in late 1972. While thinking about optical waveguides, Henry suddenly realized that a double heterostructure is a waveguide for electrons, and that a heterostructure with a thin central active layer would have discrete electron modes. Such a heterostructure was later named a quantum well, and the modes are the electron states of the quantum well.

Henry further realized that these discrete electron states would greatly alter the optical absorption edge of the semiconductor. Instead of the absorption being a smooth curve steeply rising with optical energy, it would consist of a series of steps.

In early 1973, he proposed to R. Dingle that he look for these steps, and they were observed and reported in 1974 in a paper the pair wrote with W. Wiegmann.

After Dingle’s experiment showed the reality of Henry's predicted quantum effects, Henry realized that the quantum well structure would alter the density of states of the semiconductor and result in an improved semiconductor laser. He also realized that the laser wavelength could be changed merely by changing the thickness of the thin quantum well layers, whereas in a conventional laser, a change in wavelength requires a change in layer composition.

On March 7, 1975, Henry and Dingle filed a patent entitled "Quantum Effects in Heterostructure Lasers," which was issued on Sept. 21, 1976. The story of the origin of the quantum well laser is told by Henry in the foreword to Quantum Well Lasers, edited by Peter S. Zory, Jr. (1993).