A novel method for synthesizing device-quality alloys and ordered phases in a Si--Ge--Sn system uses a UHV-CVD process and reactions of SnD.sub.4 with SiH.sub.3GeH.sub.3. Using the method, single-phase Si.sub.xSn.sub.yGe.sub.1-x-y semiconductors (x.ltoreq.0.25, y.ltoreq.0.11) are grown on Si via Ge.sub.1-xSn.sub.x buffer layers The Ge.sub.1-xSn.sub.x buffer layers facilitate heteroepitaxial growth of the Si.sub.xSn.sub.yGe.sub.1-x-y films and act as compliant templates that can conform structurally and absorb the differential strain imposed by the more rigid Si and Si--Ge--Sn materials. The SiH.sub.3GeH.sub.3 species was prepared using a new and high yield method that provided high purity semiconductor grade material.