1. F. Capasso (ed.), Physics of Quantum Electron Devices, Springer-Verlag, Berlin (1990).
2. R. K. Willardson and A. C. Beers (eds.), Semiconductors and Semimetals, Vol. 24, Academic, New York (1987).
3. F. Capasso, in: Semiconductors and Semimetals (R. K. Willardson and A-. C. Beers, eds.), Vol. 24, p. 319, Academic, New York (1987).
4. J. A. Morton, IEEE Spectrum, p. 62 (September 1965).
5. D. A. B. Miller, D. S. Chemla, T. C. Damen, A. C. Gossard, W. Wiegmann, T. H. Wood, and C. A. Burrus, Appl. Phys. Lett.
45, 13 (1984).