Disorder-assisted Robustness of Ultrafast Cooling in High Doped CVD-Graphene

TL;DR

This study reveals that in highly doped CVD-graphene, disorder-assisted lattice-phonon interactions dominate ultrafast cooling, offering a robust and efficient channel for hot electron relaxation, which could enhance graphene-based photoconversion devices.

Contribution

It experimentally demonstrates that disorder-assisted lattice-phonon interactions, not electron-phonon coupling, dominate ultrafast cooling in highly doped graphene.

Findings

Disorder-assisted phonon interactions are key in ultrafast cooling.

Cooling process is robust across different pump wavelengths and temperatures.

Provides a new cooling channel for improved device efficiency.

Abstract

Dirac Fermion, which is the low energy collective excitation near the Dirac cone in monolayer graphene, have gained great attention by low energy Terahertz probe. In the case of undoped graphene, it has been generally understood that the ultrafast terahertz thermal relaxation is mostly driven by the electron-phonon coupling (EOP), which can be prolonged to tens and hundreds of picoseconds. However, for the high doped graphene, which manifests the negative photoinduced terahertz conductivity, there is still no consensus on the dominant aspects of the cooling process on a time scale of a few picoseconds. Here, the competition between the disorders assisted defect scattering and the electron-phonon coupling process in the cooling process of the graphene terahertz dynamics is systematically studied and disentangled. We verify experimentally that the ultrafast disorder assisted lattice-phonon interaction, rather than the electron-phonon coupling process, would play the key role in the ultrafast thermal relaxation of the terahertz dynamics. Furthermore, the cooling process features robustness which is independent on the pump wavelength and external temperature. Our finding is expected to propose a considerable possible cooling channel in CVD-graphene and to increase the hot electron extracting efficiency for the design of graphene-based photoconversion devices.