A CMOS sensor includes a silicon material having a surface periodic structure of silicon portions and non-silicon portions, formed by multiple supercells repeated in a 2-dimensional lattice pattern. Each image pixel of the sensor has at least 2×2 supercells. The lattice constants in both lateral directions are within a range defined by a wavelength of the light to be sensed. Within each supercell, the non-silicon portions create an effective refractive index for the light that changes gradually with depth. The non-silicon portions within the supercell have lateral feature sizes smaller the wavelength of the light to be sensed, and vertical feature sizes larger than the wavelength of the light to be sensed. In some examples, each supercell includes at least two inverted pyramids having different base sizes and/or different heights. A dielectric material fills the non-silicon portions of the periodic structure and covers the silicon material.