Simple chemical routes to diamond-cubic germanium-tin alloys

We report the development of a simple chemical route to growing Ge_1-xSn_x semiconductors using ultrahigh-vacuum chemical vapor deposition and the molecular precursor (Ph)SnD₃ as the source of Sn atoms. Thin films were deposited on oxidized and oxide-free Si by reactions of (Ph)SnD₃ with Ge₂H₆ at 350°C. The composition, microstructure, and bonding properties of the films were characterized by Rutherford backscattering, high-resolution analytical electron microscopy, and Raman spectroscopy. As-deposited Ge_1-xSn_x on oxidized Si displayed good crystallinity which improved significantly by annealing at 400°C. High-resolution electron microscopy and diffraction indicated a diamond-cubic structure with lattice constants intermediate to those of Ge and α-Sn. As-deposited Ge_1-xSn_x on pure Si was monocrystalline and epitaxial. Nanoprobe analysis in plan view and cross section revealed that the as-deposited and annealed materials were homogeneous with good chemical purity. The Raman spectra showed bands corresponding to Ge-Ge and Sn-Ge vibrations with frequencies consistent with a random tetrahedral alloy.