1. R. C. Curby and D. K. Ferry, Proc. 11th Int. Conf. Phys. Semicond. Warsaw, 1972, p.312. Pol. Scientific Publ. Warsaw, (1972).
2. K. Kasai and C. Hamaguchi, J. Phys. Soc. Jpn. 44, 1749 (1978).
3. H. Kahlert, D.G. Seiler and J.R. Barker, Solid-St. Electron. 21, 229 (1978).
4. R. A. Stradling, L. Eaves, R.A. Hoult, A.L. Mears and R.A. Wood, Proc. 10th Int. Conf. Phys. Semicond. Cambridge, 1970, p.369. USAEC (1970).
5. R. A. Stradling and R. A. Wood, J. Phys. C: Solid State Phys. 3, 2425 (1970).