Epitaxial Growth of Gallium Phosphide on Cleaved and Polished (111) Calcium Fluoride

The mechanism of growth of GaP on a cleaved CaF2 (111) surface was studied in situ in a high-energy reflection electron diffraction system. It was found that in the early stages of growth, GaP forms tetrahedral nuclei with {111} faces. The three edges of the tetrahedron are parallel to the three 〈110〉 directions. These microcrystals coalesce and form a smooth film after a mean thickness of more than 300 monolayers of GaP is deposited on the surface. Temperatures for epitaxial growth of a single crystal without twinning as a function of the atom arrival rate were studied for GaP on a clean CaF2 surface and on a GaP-covered CaF2 surface. It was found that growing GaP without twinning on a bare cleaved CaF2 surface requires a temperature ∼65°C higher than on a surface that is covered with GaP. The structural characteristics of the GaP film as a function of the substrate temperature are also discussed.