Group-IV semiconductors, including alloys incorporating Sn, have been grown on dimensionally dissimilar Si substrates using novel molecular hydride chemistries with tunable reactivities that enable low temperature, CMOS compatible integration via engineering of the interface microstructure. Here we focus on properties of three such Ge-based systems including: (1) device quality Ge layers with thicknesses >5m possessing dislocation densities <105/cm2 are formed using molecular mixtures of Ge2H6 and highly reactive (GeH3)2CH2 organometallic additives circumventing the classical Stranski-Krastanov growth mechanism, (2) metastable GeSn alloys are grown on Si via reactions of Ge2H6 and SnD4, and (3) ternary SiGeSn analogs are produced lattice-matched to Ge-buffered Si using admixtures of SiGeH6, SiGe2H8, SnD4, Ge2H6, and Si3H8. Optical experiments and prototype device fabrication demonstrate that the ternary SiGeSn system represents the first group-IV alloy with a tunable electronic structure at fixed lattice constant, effectively decoupling band gap and strain and eliminating the most important limitation in device designs based on group-IV materials. Doping at levels higher than 1019 cm-3 (both p and n-type) is achieved for all the above semiconductor systems using a similar precursor chemistry approach. Electrical and infrared optical experiments demonstrate that doped GeSn and SiGeSn have mobilities that compare or exceed that of bulk Ge. The potential applications of these materials, including micro- and optoelectronics as well as photovoltaics and thermoelectricity, are discussed.