Harvesting Sub-Bandgap IR Photons by Photothermionic Hot Electron Transfer in a Plasmonic p–n Junction
Wenxing Yang, Yawei Liu, David A. Cullen, James R. McBride, Tianquan Lian
Abstract
Plasmonic semiconductors are an emerging class of low-cost plasmonic materials, and the presence of a bandgap and band-bending in these materials offer new opportunities to overcome some of the limitations of plasmonic metals. Here, we demonstrate that in a plasmonic p–n heterojunction (Cu2-xSe-CdSe) the near-IR excitation (1.1 eV) of the hole plasmon in the p-Cu2–xSe phase results in rapid hot electron transfer to n-CdSe, with an energy 2.2 eV above the Fermi level. This hot electron generation and energy upconversion process can be well-described by a photothermionic mechanism, where the presence of a bandgap in p-Cu2–xSe facilitates the generation of energetic photothermal electrons. The lifetime of the transferred electrons in Cu2–xSe-CdSe can reach ∼130 ps, which is nearly 100× longer than that of its metal–semiconductor counterpart. This result demonstrates a novel approach for harvesting the sub-bandgap near IR photons using plasmonic p–n junctions and the potential advantages of plasmonic semiconductors for hot carrier-based devices.