1. Nato Advanced Study Institute Series B,1980
2. D.Kranzer, H.Hillbrand, H.Pötzl, O.Zimmerl: Acta Phys. Austriaca35, 110 (1972)
3. R.G. van Welzenis, W.C. de Zeeuw: To be published
4. A.G.Chynoweth: ?Charge Multiplication Phenomena? inSemiconductors and Semimetals 4, ed. by R.C.Willardson and A.C.Beer (Academic Press, New York 1968) Chap. 4
5. A.H.Thompson, G.S.Kino: IBM J. Res. Dev.13, 616 (1969)