Epitaxial CaGe2 films on germanium

The epitaxial growth of thin CaGe2 films with reactive deposition epitaxy ( RDE) on Ge(1 1 1) substrates is described. The films consist in general of a mixture of the known trigonal rhombohedral tr6 modification and a hexagon al h2 modification of CaGe2 containing two Ca and two buckled Ge layers per unit cell in a twofold stacking sequence whose formation appears to be fav ored by strain. Epitaxial layers of both polytypes show remarkably higher c rystalline quality compared to epitaxial CaSi2 films grown on silicon subst rates. The tr6 modification is found to be unstable in air in contrast to t he h2 modification. (C) 2000 Elsevier Science B.V. All rights reserved.