5, Joint Center for Artificial Photosynthesis, California Institute of Technology, Pasadena, California, United States
2, Department of Chemistry-Ångström Laboratory, Uppsala University, Uppsala, , Sweden
3, Center for Nanoscale Materials, Argonne National Laboratory, Argonne, Illinois, United States
4, Institute of Physical Chemistry, Polish Academy of Sciences, Warsaw, , Poland
Harvesting hot carriers from photo-excited metal nanoparticles on ultrafast (~fs) timescales holds great promise for the operation of non-equilibrium optoelectronics. While the ultrafast dynamics of hot electrons in metal nanostructures have been extensively studied, the temporal evolution of plasmon-induced hot holes remains unexplored. Here, we monitor ultrafast hot-hole injection from gold (Au) nanoparticles into the valence band of p-type gallium nitride (p-GaN) via ultrafast transient absorption spectroscopy. By spatially separating hot electron-hole pairs across the metal-semiconductor interface via plasmon excitation, Au/p-GaN heterostructures offer an ideal platform for spectrally distinguishing the dynamics of the hot holes, which can be probed in the infrared regime via free-carrier absorption within the p-GaN valence band, from the hot electron dynamics occurring on the metal, which are monitored across the visible spectrum with a white-light supercontinuum probe. We observe plasmon-induced hot-hole injection from Au to p-GaN within the 200 fs instrument response of our experimental setup, placing hot-hole transfer from a plasmonic metal to a p-type semiconductor on similar timescales as hot-electron injection into an n-type semiconductor. Moreover, hot holes persist within the p-GaN valence band for several nanoseconds before recombination of the charge-separated state occurs across the Au/p-GaN heterojunction. We further evaluated the influence of hot-hole injection on the temporal dynamics of hot electrons left behind on Au by comparison with Au/SiO2 heterostructures for which hot-hole injection is prohibited. Interestingly, we found that the ultrafast (t < 200 fs) injection of hot-holes into p-GaN on timescales commensurate with electron-electron scattering exerts a profound influence on the spectral and temporal dynamics of hot electrons on the Au nanoparticles. Taken together, these ultrafast studies offer a comprehensive picture of hot-carrier dynamics across the Au/p-GaN heterojunction and suggest the potential for manipulating the energy distributions and subsequent thermalization dynamics of hot electrons above the metal Fermi level by controlling the collection of hot holes on ultrafast timescales.