In a general aspect, a device includes a substrate, a light transmission formed on a top surface of the substrate, a first contact, and a second contact. The light transmission structure includes a first doped region; a second doped region doped oppositely to the first region; a lateral junction between a part of the first doped region and a part of the second doped region, the lateral junction oriented substantially perpendicular to the top surface of the substrate; and a vertical junction between a part of the first doped region and a part of the second doped region, the vertical junction oriented substantially parallel to the top surface of the substrate. The first contact is in electrical contact with the first region and the second contact is in electrical contact with the second region.