Contact morphology and revisited photocurrent dynamics in monolayer MoS2

TL;DR

This study investigates ultrafast photo-conductance in monolayer MoS2, revealing a dominant bolometric effect and contact morphology changes under focused laser illumination, with implications for high-frequency optoelectronic devices.

Contribution

It uncovers the ultrafast photoconductance dynamics and contact morphology modifications in monolayer MoS2, emphasizing the importance of bolometric effects and laser-induced contact annealing.

Findings

Bolometric contribution dominates photoconductance.

Focused laser modifies and anneals metal contacts.

Lateral built-in electric fields develop without phase change.

Abstract

Two-dimensional (2D) layered transition metal dichalcogenides (TMDs) have emerged as promising materials for electronic, optoelectronic, and valleytronic applications. Recent work suggests drastic changes of the band gap and exciton binding energies of photo-excited TMDs with ultrafast non-radiative relaxation processes effectively heating the crystal lattice. Such phenomena have not been considered in the context of optoelectronic devices yet. We resolve corresponding ultrafast photo-conductance dynamics within monolayer MoS2 and demonstrate that a bolometric contribution dominates the overall photoconductance. We further reveal that a focused laser illumination, as is used in many standard optoelectronic measurements of MoS2, modifies and anneals the morphology of metal contacts. We show that a junction evolves with lateral built-in electric fields, although Raman- and photoluminescence spectra indicate no significant changes such as a crystal phase transition. We highlight how such optimized devices can drive ultrafast electromagnetic signals in on-chip high-frequency and THz circuits.