MBE Growth of Ca sub (.5) Sr sub (.5) F sub 2 on (100), (111), (511), and (711) GaAs Surfaces.

We have used molecular beam epitaxy to grow Ca sub x Sr sub (1-x) F sub 2 films of various thicknesses on GaAs substrates with different orientations, i.e., (100), (111)A, (511)A, (511)B, (711)A and (711)B. On all orientations, the same crystallographic direction is normal to the surface in both the substrate and fluoride film. For all orientations except (111), the fluoride surface is reconstructed with (111) facets. Without annealing, the best crystallinity is obtained for the (100), (111) and (511)B orientations.