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

Dinesh Yadav,Fabian Pauly,Maxim Trushin

doi:10.1103/physrevresearch.2.043051

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.

Highlights

Utilizing high-energy carriers in photovoltaic devices could improve light-to-energy conversion efficiencies [1]
Using 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 the present work we study the influence of spin-orbit coupling (SOC) on photocarrier thermalization in single-layer transition metal dichalcogenide (TMDC) and relate intralayer thermalization rates to interlayer tunneling rates in Van der Waals (vdW) heterostructures, important for future optoelectronic devices with improved internal quantum efficiency (IQE)

Summary

Introduction

Utilizing high-energy carriers in photovoltaic devices could improve light-to-energy conversion efficiencies [1]. Despite recent progress with hot-carrier generation and injection in plasmonic nanostructures [2], the conventional semiconductor solar cells still demonstrate a superior efficiency without need for nanoscale fabrication. Alternative approaches to the problem either facilitate hot-electron transfer, e.g., from a chemically modified surface of lead selenide to titanium oxide [3], or extend photocarrier lifetimes, e.g., in some perovskites [4,5]. The possibility to assemble vdW heterostructures layer by layer enables to tune electron transfer across interfaces in the out-of-plane dimension. This interlayer charge transfer directly competes with intralayer photocarrier thermalization.

Methods

Results

Conclusion