The only problem with the photodiode is that it is not really compatible with the Google-sponored open-MPW, as that MPW run gets post-processed with bump bonds, and the chip is expected to be mounted upside down on a board. It would be appropriate for the ChipIgnite run. If you (or anyone) has a design that makes use of photodiodes, we can probably get it put on a ChipIgnite run. You would want to make sure you get bare die back, because even the ChipIgnite projects by default are wirebonded into (opaque) QFN packages, and you would want to have it wirebonded into an open frame package with a removable lid.