An apparatus comprising an electronic-photonic device. The device includes a planar substrate having a top layer on a middle layer, active electronic components and active photonic waveguide components. The active electronic components are located on first lateral regions of the top layer, and the active photonic waveguide components are located on second lateral regions of the top layer. The second-region thickness is greater than the first-region thickness. The top layer has a higher refractive index than the middle layer.