A wafer structure for an image sensor includes a substrate that has a given conductivity type, a given dopant concentration, and a given concentration of oxygen. An intermediate epitaxial layer is formed over the substrate. The intermediate epitaxial layer has the same conductivity type and the same, or substantially the same, dopant concentration as the substrate but a lower oxygen concentration than the substrate. A thickness of the intermediate epitaxial layer is greater than the diffusion length of a minority carrier in the intermediate layer. A device epitaxial layer is formed over the intermediate epitaxial layer. The device epitaxial layer has the same conductivity type but lower dopant and oxygen concentrations than the substrate.