1. C. Weisbuch and B. Vinter,Quantum Semiconductor Struc- tures (San Diego: Academic Press, 1991).
2. R.L. Anderson,Sol. State Electron. 5, 341 (1962).
3. F. Capasso and G. Margaritondo, eds.,Heterojunction Band Discontinuities (Amsterdam: North-Holland, 1987), and ref- erences therein.
4. For a recent overview on the state of the art in this field, see theProc. 20th Annual Conf. Physics and Chemistry of Semi- conductor Interfaces, Williamsburg (1993) (and references therein), inJ. Vac. Sci. Techn. B11 (4) (1993), and especially the reviews of G. Margaritondo and H. Kroemer therein.
5. G. Margaritondo,J. Vac. Sci. B11, 1362 (1993).