By introducing Si1-x-yGexCy layers in vertical p-channel MOSFETs, boron diffusion from the source/drain regions into the channel region has been suppressed to enable sub-100 nm scaling. The trade-off of doped and undoped Si1-x-yGexCy layers has been studied. Due to detrimental effects from oxide grown on Si1-x-yGexCy layers, doped Si1-x-yGexCy diffusion barriers are preferable, and have allowed vertical p-channel MOSFETs with channel lengths down to 25 nm to be demonstrated. No excess leakage current due to the Si1-x-yGexCy layers is observed.