Si1-x-yGexCy thin films grown by low temperature chemical vapor deposition containing up to 1.2% substitutional C were incorporated into microelectronic devices. The chief aims are to demonstrate that the material is of suitable quality for device applications and to use the electrical and optical characteristics of the devices to study the material. Three sets of devices containing epitaxial Si1-x-yGexCy layers were fabricated and characterized. The temperature dependence of the collector current in Si1-x-yGexCy base heterojunction bipolar transistors indicated that the band gap of Si1-x-yGexCy increases + 26 meV %C-1. Capacitance measurements on p(+)-Si1-x-yGexCy/p(-)-Si heterojunction internal photoemission structures indicated that the increase in band gap in the Si1-x-yGexCy is due primarily to downward movement of the valence band. Finally, Si1-x-yGexCy p-i-n diodes showed no degradation in reverse bias leakage compared with C-free devices for y < 0.01. However, the diodes did exhibit excess sub-band gap absorption which increased with [C].