Orientation epitaxy of Ge_1−xSn_xfilms grown on single crystal CaF₂substrates

Abstract

Ge 1−x Sn x films were grown via physical vapor deposition below the crystallization temperature of Ge on single crystal ( 111) and ( 100) CaF 2 substrates to assess the role of Sn alloying in Ge crystallization. By studying samples grown at several growth temperatures ranging from 250 °C to 400 °C we report temperaturedependent trends in several of the films' properties. X-ray diffraction theta vs. two-theta (θ/2θ) scans indicate single orientation Ge 1−x Sn x (111) films are grown on CaF 2 (111) substrates at each temperature, while a temperature-dependent superposition of ( 111) and ( 100) orientations are exhibited in films grown on CaF 2 (100) above 250 °C. This is the first report of (111) oriented Ge 1−x Sn x grown on a (100) oriented CaF 2 substrate, which is successfully predicted by a superlattice area matching model. These results are confirmed by X-ray diffraction pole figure analysis. θ/2θ 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.