A polycrystalline Si1-x-yGexCy layer grown by rapid thermal chemical vapor deposition has been used as a thin intermediate layer on top of the thin gate oxide in a metal–oxide–semiconductor structure with boron-doped polycrystalline silicon as the gate electrode. Although boron readily penetrated through the Si1-x-yGexCy and accumulated in it, boron penetration across the gate oxide into the substrate was greatly suppressed compared to that in structures without Si1-x-yGexCy layer. Our work suggests that the addition of carbon reduced the chemical potential of boron in polycrystalline Si1-x-yGexCy, compared to that in polycrystalline silicon or polycrystalline Si1-xGex. We have also observed no gate depletion effects with the use of poly-Si1-x-yGexCy layers in both p+ and n+ gate doping. © 1999 American Institute of Physics.