The disclosed invention relates to masked silicon structures and methods for making porous silicon in selected areas of a silicon substrate via anodic etching. The masked silicon structures comprise: (1) a frontside barrier layer; and (2) a backside opaque ohmic contact layer. The frontside barrier layer includes a plurality of discrete barrier openings bounded by a contiguous frontside portion of the barrier layer, thereby defining a first aperture having a first shape and a first center point. The backside opaque ohmic contact layer includes a second aperture bounded by a contiguous backside portion of the ohmic contact layer, thereby defining a second aperture having a second shape and a second center point. The first and second center points share a perpendicular axis. The first shape is substantially the same as the second shape but slightly larger, and is trans-concentrically positioned relative to the second shape about the shared axis.