Auger scattering dynamic of photo-excited hot carriers in nano-graphite film

Abstract

Charge carrier scattering channels in graphite bridging its valence and conduction band offer an efficient Auger recombination dynamic to promote low energy charge carriers to higher energy states. It is of importance to answer the question whether a large number of charge carriers can be promoted to higher energy states to enhance the quantum efficiency of photodetectors. Here, we present an experimental demonstration of an effective Auger recombination process in the photo-excited nano-graphite film. The time-resolved hot carrier thermalization was analyzed based on the energy dissipation via the Auger scattering channels. We split the Auger recombination occurrence centered at 0.40 eV energy state into scattering and recombination parts, for characterizing the scattering rate in the conduction band and the recombination rate toward the valence band. The scattering time with respect to the energy state was extracted as 8 ps · eV−1, while the recombination time with respect to the energy state was extracted as 24 ps · eV−1. Our study indicates a 300 fs delay between the hot carrier recombination and generation, leading to a 105 ps−1 · cm−3 Auger scattering efficiency. The observed duration for the Auger recombination to generate hot carriers is prolonged for 1 ps, due to the hot carriers energy relaxation bottleneck with optical-phonons in the nano-graphite. The presented analytic expression gives valuable insights into the Auger recombination dynamic to estimate its most efficient energy regime for mid-infrared photodetection.

Competition Pathways of Energy Relaxation of Hot Electrons through Coupling with Optical, Surface, and Acoustic Phonons

“…Then, the τ 0 shortens as the energy state increases from 0.47 to 0.51 eV. This could be attributed to the fact that Auger recombination scattering is stronger at 0.47 eV, which is confirmed by our previous studies . The τ 1 and τ 2 shorten as the energy state increases from 0.43 to 0.51 eV.…”

“…This could be attributed to the fact that Auger recombination scattering is stronger at 0.47 eV, which is confirmed by our previous studies. 26 The τ 1 and τ 2 shorten as the energy state increases from 0.43 to 0.51 eV. The difference in the τ 2 values indicates that thickness plays an important role in the population and decay of the optical phonons.…”

“…Previous work done by us confirmed that this is attributed to the increase of the Auger recombination scattering, as sufficient photoexcitation energy is offered. 26 In addition, under a 1 μJ•cm −2 pump fluence, the ΔR/R 0 signals are relatively too weak to be detected, suggesting that the photoexcited electrons are difficult to scatter up from the initial photoexcitation energy state (0.175 eV) to the probe energy range (0.42−0.52 eV).…”

“…The differential reflectivity was collected to analyze the optical, surface, and acoustic phonon interactions with the hot electrons during their cooling period. Previous work from us reported that hot electron thermalization is dominated by Auger-type scattering in similar experimental conditions . Therefore, this work is focused on the cooling period of these hot electrons after their thermalization, where the hot optical phonon effect encounters competing processes, as illustrated in Figure b.…”

“…Previous work from us reported that hot electron thermalization is dominated by Auger-type scattering in similar experimental conditions. 26 Therefore, this work is focused on the cooling period of these hot electrons after their thermalization, where the hot optical phonon effect encounters competing processes, as illustrated in Figure 1b.…”