Thermalization of photoexcited carriers in two-dimensional transition metal dichalcogenides and internal quantum efficiency of van der Waals heterostructures

TL;DR

This study uses ab-initio methods to analyze how phonon spectrum and spin-orbit coupling influence hot-carrier thermalization in 2D transition metal dichalcogenides, impacting the efficiency of van der Waals heterostructure devices.

Contribution

It reveals the dependence of carrier thermalization times on phonon spectrum and spin-orbit effects, highlighting material-specific differences in MoS₂ and WSe₂.

Findings

Hole thermalization is slower than electron thermalization by an order of magnitude.

Spin-orbit coupling suppresses hole scattering on acoustic phonons.

Quantum efficiency varies depending on whether MoS₂ or WSe₂ is used.

Abstract

Van der Waals semiconductor heterostructures could be a platform to harness hot photoexcited carriers in the next generation of optoelectronic and photovoltaic devices. The internal quantum efficiency of hot-carrier devices is determined by the relation between photocarrier extraction and thermalization rates. Using \textit{ab-initio} methods we show that the photocarrier thermalization time in single-layer transition metal dichalcogenides strongly depends on the peculiarities of the phonon spectrum and the electronic spin-orbit coupling. In detail, the lifted spin degeneracy in the valence band suppresses the hole scattering on acoustic phonons, slowing down the thermalization of holes by one order of magnitude as compared to electrons. Moreover, the hole thermalization time behaves differently in MoS$_2$ and WSe$_2$ because spin-orbit interactions differ in these seemingly similar materials. We predict that the internal quantum efficiency of a tunneling van der Waals semiconductor heterostructure depends qualitatively on whether MoS$_2$ or WSe$_2$ is used.