Orientation epitaxy of Ge1−xSnx films grown on single crystal CaF2 substrates

Ge1-xSnx films were grown via physical vapor deposition below the crystallization temperature of Ge on single crystal (111) and (100) CaF2 substrates to assess the role of Sn alloying in Ge crystallization. By studying samples grown at several growth temperatures ranging from 250 degrees C to 400 degrees C we report temperature-dependent trends in several of the films' properties. X-ray diffraction theta vs. two-theta (theta/2 theta) scans indicate single orientation Ge1-xSnx(111) films are grown on CaF2(111) substrates at each temperature, while a temperature-dependent superposition of (111) and (100) orientations are exhibited in films grown on CaF2(100) above 250 degrees C. This is the first report of (111) oriented Ge1-xSnx grown on a (100) oriented CaF2 substrate, which is successfully predicted by a superlattice area matching model. These results are confirmed by X-ray diffraction pole figure analysis. theta/2 theta results indicate substitutional Sn alloying in each film of about 5%, corroborated by energy dispersive spectroscopy. Additionally, morphological and electrical properties are measured by scanning electron microscopy, atomic force microscopy and Hall mobility measurements and are also shown to be dependent upon growth temperature.