Photograph of an L0 detector viewed from the junction surface (a) and from the ohmic surface (b). The junction surface is segmented into five active regions, consisting of a central bull’s eye surrounded by four quadrants, each with an active area of 0.2 cm². This 5-segment structure is located at the center of a silicon membrane of 12 μm thickness, the remainder of which is not active. On the ohmic surface, the thin membrane is supported by an approximately octagonal, thick frame, the inner edge of which is visible in the photo. The shape of this edge is due to the different rates at which TMAH etches into different crystal planes. The ohmic surface, including the thin and the thick parts and the transition between them, is metallized with a single aluminum contact.