1. Street, R.A., Senske, W.: Phys. Rev. Lett.37, 1292 (1976)
2. Nakashima, S., Hattori, T., Yamaguchi, Y.: Solid State Commun.25, 137 (1978)
3. Hattori, T., Nakashima, S., Mitsuishi, A.: In: Proceedings of the 13th International Conference on the Physics of Semiconductors, Rome, Italy, 1976, (edited by Fumi, F.G.) p. 635 Amsterdam: North-Holland 1976
4. Dean, P.J., Venghaus, H., Pfister, J.C., Schaub, B., Marine, J.: J. Luminescence: in press
5. Venghaus, H., Dean, P.J., Pfister, J.C.: to be published