This work was supported through the Center for Excitonics, an Energy Frontier Research Center, by the US Department of Energy, Office of Science, Office of Basic Energy Sciences under award number DE-SC0001088 (MIT). Surface characterization work at Princeton was supported in part by the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering under award DE-SC0012458 (A.K.) and the National Science Foundation Graduate Research Fellowship grant DGE-1656466 (H.L.S.). We thank T. Buonassisi for access to the silicon lifetime and wafer metrology system. We thank D.-G. Ha for help with the atomic force microscopy measurements.

Peer review information

Nature thanks Akshay Rao and the other anonymous reviewer(s) for their contribution to the peer review of this work.