ZnO: Ultrafast generation and decay of a surface metal
Band bending at semiconductor surfaces induced by e.g. chemical doping can create metallic surfaces with properties not found in the bulk, such as high electron mobility, magnetism or superconductivity. Optical generation of such metallic surfaces on ultrafast timescales would be appealing for high-speed electronics. We demonstrate the ultrafast generation of a metal at the surface of ZnO upon photoexcitation. Compared to known ultrafast photoinduced semiconductor-to-metal transitions that occur in the bulk of inorganic semiconductors, the metallization of the ZnO surface is launched by 3–4 orders of magnitude lower photon fluxes. Using time- and angle-resolved photoelectron spectroscopy, we show that the phase transition is caused by photoinduced downward surface band bending due to photodepletion of donor-type deep surface defects. These findings present a general route for controlling surface-confined metallicity on ultrafast timescales.
Humboldt-Univ. zu Berlin (Germany), Fritz-Haber-Institut der Max-Planck-Gesellschaft (Germany)
Prof. Stähler studied physics at the Freie Universität in Berlin and received her PhD in the group of Prof. Martin Wolf in 2007 and received the Klaus-Tschira-Prize for "Understandable Science". After that, she did a postdoc at the University of Oxford and visited at the University of Pittsburgh and Columbia University for research stays. As an Independent Max Planck Research Group Leader, Prof. Stähler received the Gaede Prize of the German Vacuum Society and the Edith Flanigan Award in 2016. Since 2020, she is full professor in the Chemistry Department of the Humboldt-Universität zu Berlin and chair for Ultrafast Spectroscopy.