Metal–oxide–semiconductor (MOS) capacitors were fabricated onin situdopedn- andp-typeSi1−yCy/Siheterostructures grown on Si substrates by chemical vapor deposition. StrainedSi1−yCyepitaxial layers with substitutional carbon contents up to 1.6&percent; were studied. High frequency and quasistatic capacitance–voltage(C–V)measurements exhibit well-behaved MOS characteristics, indicating high electronic material quality. Band alignments were extracted from MOSC–Vmeasurements and one-dimensional device simulations performed over a range of temperatures. The conduction band energy of strainedSi1−yCyis lower than that of Si by approximately 65 meV for 1 at. &percent; carbon, while the valence band shows negligible offset to Si valence band. ©1998 American Institute of Physics.