Ultrafast Thermionic Electron Injection Effects on Exciton Formation Dynamics at a van der Waals Semiconductor/Metal Interface

Abstract

Inorganic van der Waals bonded semiconductors such as transition metal dichalcogenides are the subject of intense research due to their electronic and optical properties which are promising for next-generation optoelectronic devices. In this context, understanding the carrier dynamics, as well as charge and energy transfer at the interface between metallic contacts and semiconductors, is crucial and yet quite unexplored. Here, we present an experimental study to measure the effect of mutual interaction between thermionically injected and directly excited carriers on the exciton formation dynamics in bulk WS2. By employing a pump–push–probe scheme, where a pump pulse induces thermionic injection of electrons from a gold substrate into the conduction band of the semiconductor, and another delayed push pulse that excites direct transitions in the WS2, we can isolate the two processes experimentally and thus correlate the mutual interaction with its effect on the ultrafast dynamics in WS2. The fast decay time constants extracted from the experiments show a decrease with an increasing ratio between the injected and directly excited charge carriers, thus disclosing the impact of thermionic electron injection on the exciton formation dynamics. Our findings might offer a new vibrant direction for the integration of photonics and electronics, especially in active and photodetection devices, and, more in general, in upcoming all-optical nanotechnologies.

Enhanced Optical Response in Au Nanopillar/La0.67Sr0.33MnO3 Film Composites: Implications for Magnetooptical Devices

“…When the Au/LSMO interface is photoexcited, the photogenerated carriers in Au with sufficient energy can overcome the barrier and be injected into LSMO. This model is in good agreement with similar systems. , …”

Ultra-confined Propagating Exciton–Plasmon Polaritons Enabled by Cavity-Free Strong Coupling: Beating Plasmonic Trade-Offs

“…In some applications, the direct contact of metal and TMD materials may induce weak electronic coupling that affects the exciton formation in the WS 2 and the electron dynamics in the metal [ 63 , 64 ]. To minimize the influence, one may use the structure of a core/shell MNW with a TMD layer.…”

Ultrafast control of exciton dynamics by optically-induced thermionic carrier injection in a metal-semiconductor heterojunction

“…The pulse duration of the fundamental (pump pulse) at 1030 nm (1.2 eV) was 220 fs. In contrast to our previous study, where we were mainly interested in understanding the thermionic carriers injection effect on the exciton formation 19 , in the present work this pulse is coming after the push pulse, since here we aim to understand effects of thermionic carriers injections on a system where the excitons are already formed. The first pulse arriving at the interface is the "push" pulse, and it is the previously mentioned second harmonic at 515 nm (2.4 eV) with a fluence of 200 mJ/cm 2 .…”

“…Examples on how photonics, the science of light, can enable real life applications based on advanced materials and interfaces, has been reported in the past years, for instance for sensing [1][2][3][4][5][6] , photocatalysis and spectroscopy [7][8][9][10][11][12][13][14][15] , as well as data storage and processing 16 and quantum technologies 17 . In this context, it is fundamental to unveil and understand light-matter interactions in novel materials able to combine both electronic and optical properties and, consequently, to work at significantly higher speeds than electronics 18,19 . After the development of femtosecond lasers for the generation of ultrashort light pulses 20,21 , it became clear that we can use such technology to drive ultrafast electronic processes at the nanoscale, including plasmonic excitations [22][23][24][25][26][27][28] .…”