Simple chemical routes to diamond-cubic germanium–tin alloys

We report the development of a simple chemical route to growing Ge1−xSnx 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 Ge1−xSnx 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 Ge1−xSnx 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.