A semiconductor device includes a doped Si base substrate, one or more device epitaxial layers formed over a main surface of the doped Si base substrate, a diffusion barrier structure, and a gate formed above the diffusion barrier structure. The diffusion barrier structure includes alternating layers of Si and oxygen-doped Si formed in an upper part of the doped Si base substrate adjacent the main surface of the doped Si base substrate, in a lower part of the one or more device epitaxial layers adjacent the main surface of the doped Si base substrate, or in one or more additional epitaxial layers disposed between the main surface of the doped Si base substrate and the one or more device epitaxial layers.