Ultrafast hot-hole injection modifies hot-electron dynamics in Au/p-GaN heterostructures

Abstract

Harvesting non-equilibrium "hot" carriers from photo-excited metal nanoparticles has enabled plasmon-driven photochemical transformations and tunable photodetection with resonant nanoantennas 1-13. Despite numerous studies on the ultrafast dynamics of hot electrons 14-26 , to date, the temporal evolution of hot holes in metal-semiconductor heterostructures remains unknown. An improved understanding of the carrier dynamics in hot-hole-driven systems is needed to help expand the scope of hot-carrier optoelectronics beyond hot-electron-based devices. Here, using ultrafast transient absorption spectroscopy, we show that plasmon-induced hot-hole injection from gold (Au) nanoparticles into the valence band of p-type gallium nitride (p-GaN) occurs within 200 fs, placing hot-hole transfer on a similar timescale as hot-electron transfer 22,25. We further observed that the removal of hot holes from below the Au Fermi level exerts a discernible influence on the thermalization of hot electrons above it, reducing the peak electronic temperature and decreasing the electron-phonon coupling time relative to Au samples without a pathway for hot-hole collection. First principles calculations 27-29 corroborate these experimental observations, suggesting that hot-hole injection modifies the relaxation dynamics of hot electrons in Au nanoparticles through ultrafast modulation of the d-band electronic structure. Taken together, these ultrafast studies substantially advance our understanding of the temporal evolution of hot holes in metal-semiconductor heterostructures and suggest new strategies for manipulating and controlling the energy distributions of hot carriers on ultrafast timescales.

Challenges in Plasmonic Catalysis

“…Furthermore, advanced ultrafast experimental techniques are needed to probe these electronic processes at different time scales. 113,114 Remarkably, a major discrepancy remains between the hot-carrier-collection efficiencies estimated by ultrafast spectroscopy experiments (> 40%; as shown in refs 32,44,46 ) and those measured in solidstate or photoelectrochemical devices (<1%) under steady-state conditions. Although interfacial excitation can enhance charge separation in metallic nanocrystals (Figure 3f), 32,113 such discrepancy persists for metal/semiconductor interfaces employed in larger scale devices that are accurately described by a three-step generation and collection model (e.g., Au/p-GaN).…”

“…16 Going beyond solid-state photodetectors, efficient collection of hot carriers across a metal semiconductor/interface plays an important role in plasmonic catalysis (Figure 3a): the long-lived charge-separated state that is established counteracts the ultrafast recombination of hot electrons and hot holes in the metal. 46,108 Efficient hot-carrier collection also permits the realization of photoelectrodes, preventing charge build-up in the metal and avoiding the use of electron/hole scavengers in solution. Therefore, quantifying the energy distribution of the collected charge carriers as well as their collection efficiency is critical for understanding and engineering hot-carrier catalysis.…”

Recent Progress on Metal-Enhanced Photocatalysis: A Review on the Mechanism

“…However, to comprehensively understand the carriers' relaxation dynamics and the utilization of light energy, the investigation on the hot hole injection to the valence band of a p-type semiconductor is needed. Therefore, Tagliabue et al hybridized Au nanoparticles (7.3 ± 2.4 nm) onto a p-GaN substrate [ 45 ]. The size of the Schottky barrier is 1.1 eV to ensure the successful injection of near 90% hot holes to the valence band of GaN.…”

Ultrafast Photoinduced Heat Generation by Plasmonic HfN Nanoparticles

“…The same likely applies to ballistic hot holes, although these have not yet been explored. [69] On the other hand, thermal ized electrons can be harvested as well, albeit with lower energy than ballistic ones. [4] However, when transforming the simu lated electronic temperature from Figure 3d to a thermalized…”