Abstract: The development of a new class of semiconductors in the silicon-germanium-tin system, based on novel deuterium-stabilized tin hydrides epitaxially grown on silicon substrates, provides a new low-temperature chemical vapor deposition route to a broad range of highly metastable compositions and structures that cannot be obtained by other methods. This research focuses on the continued synthesis, characterization, and performance evaluation of Ge_1-xSn _x binary and Ge_1-x-ySi_xSn_y ternary semiconductors. The Ge_1-xSn_x alloys are grown as thin films directly on Si(100) via ultrahigh vacuum chemical vapor deposition (UHV-CVD) reactions of gaseous SnD₄ and Ge₂H₆. The alloys display random diamond-cubic monocrystalline structures and unique morphological and optical properties such as atomically flat surfaces and tunable bandgaps. The large lattice mismatch of the layers and the Si substrates is accommodated by Lomer edge dislocations located at the interface. In this study a detailed determination of the Ge_{1- x}Sn_x alloys optical properties is conducted via spectroscopic ellipsometry. The materials display a Ge like band gap structure with critical point energies (E ₁, E_1+Δ, E₀, E₂) that decrease monotonically with increasing Sn content from 1-20 at.%. Another aspect of this research is the use of the Ge_1-xSn_x alloys as buffer layers to grow Ge_1-x-ySi_xSn_y ternaries. The ternaries demonstrate good crystallinity with low defect densities. Deep ultraviolet spectroscopic ellipsometry analysis of the materials yields dielectric functions consistent with crystalline alloys of cubic symmetry. The primary focus of this study is the growth of n-type doped Ge 1-xSn_x alloys via in situ reactions of SnD₄/Ge ₂H₆ with appropriate concentrations of the newly prepared As(GeH₃)₃ single source hydride. The thin films demonstrate excellent microstructural quality and high doping concentrations (10 19). The levels of activated As atoms incorporated in the Ge-Sn lattice are determined by infrared spectroscopic ellipsometry (IR-SE) and found to be close to the doping concentrations measured by secondary ion mass spectrometry (SIMS) analysis. Other important electrical properties such as electron mobilities and resistivities are also derived from the IR ellipsometric characterizations and are comparable to those in germanium.