Vacancy-Regulated Charge Carrier Dynamics and Suppressed Nonradiative Recombination in Two-Dimensional ReX₂ (X = S, Se)

Abstract

Point defects in semiconductors usually act as nonradiative charge carrier recombination centers, which severely limit the performance of optoelectronic devices. In this work, by combining time-domain density functional theory with nonadiabatic molecular dynamics simulations, we demonstrate suppressed nonradiative charge carrier recombination and prolonged carrier lifetime in two-dimensional (2D) ReX 2 (X = S, Se) with S/Se vacancies. In particular, a S vacancy introduces a shallow hole trap state in ReS 2 , while a Se vacancy introduces both hole and electron trap states in ReSe 2 . Photoexcited electrons and holes can be rapidly captured by these defect states, while the release process is slow, which contributes to an elongated photocarrier lifetime. The suppressed charge carrier recombination lies in the vacancy-induced lowfrequency phonon modes that weaken electron−phonon coupling, as well as the reduced overlap between electron and hole wave functions that decreases nonadiabatic coupling. This work provides physical insights into the charge carrier dynamics of 2D ReX 2 , which may stimulate considerable interest in using defect engineering for future optoelectronic nanodevices.

2D Rhenium Dichalcogenides: From Fundamental Properties to Recent Advances in Photodetector Technology

“…While intrinsic defects can be manifold, [285] chalcogen vacancies in ReX 2 remain as the most common and prevailing defects, similar to the well-established case of MoS 2 . [228,268,286,287] Moreover, due to their low forming energy, sulfur vacancy defects can be highly mobile in ReS 2 , and hence under the application of an electric field, their motion can be used to modulate the Schottky barrier height at the metal contact region. [288] The presence of trap states within the bandgap provides ReS 2 photodetectors with significant photoconductive gain enhancement and much faster temporal response.…”

“…[223] But for AB stacking, the exciton dynamics can be anisotropic due to missing of indirect state of exciton II perpendicular to b-axis. [164,223] Chalcogen vacancyinduced localized mid-gap states significantly extends the exciton or photocarrier lifetime in both ReS 2 and ReSe 2 [227,228] In ReX 2 , sulfur vacancies can introduce shallow hole trap states, while selenium vacancies introduce both electron and hole trap states. Under photoexcitation, carriers halt selectively in these trap states and since the carrier release process is a slow event, the photocarrier lifetime is enhanced.…”

How the Stacking Pattern Influences the Charge Transfer Dynamics of van der Waals Heterostructures: An Answer from a Time-Domain Ab Initio Study

“…To achieve this target, researchers have put continuous efforts into searching for unique routes to control the charge carrier relaxation dynamics. Application of stress and strain along different directions over the monolayers, introduction of defects of different natures (vacancy, divacancy, Stone–Wales defect, and doping of similar or heteroatoms), creation of van der Waals heterostructures, atom substitution defects, temperature-dependent phase transfer, twisting of angles, and hot hole injection were found to be promising tools in this aspect of tuning the electron–hole recombination process. − In one of our previous studies, the effect of the heterostructure formation on charge carrier dynamics was studied in detail, where the pristine monolayers (2D g-CN and WTe 2 ) promisingly generated a much more efficient heterostructure (heterobilayer g-CN/WTe 2 ) for photovoltaic and optoelectronic application. , Herein, we have selected SnS 2 and SnSe 2 monolayers as the matrices to hold ZrS 2 , ZrSe 2 , and ZrSSe monolayers in two different stacking patterns, such as AA and AB stacking, and would like to unravel the role of the stacking pattern on the time scale of charge carrier dynamics.…”

“…To obtain the best results in these areas, we must find out the ways to deal with the major obstacles, which are charge and energy losses, as a result of faster nonradiative electron−hole recombination. 11,12 Therefore, to achieve a high-quality photovoltaic and optoelectronic performance, the electron−hole recombination should be slow or delayed. 3 In contrast, the non-radiative electron and hole transfers toward the conduction band minimum (CBM) and valence band maximum (VBM) states, respectively, are highly desirable in an ultrafast time scale for optimum results.…”

“…A high surface area, large carrier mobility, and exceptionally high mechanical strength establish the wide-range applicability of these monolayers in the fields of photovoltaics, photocatalysis, electrocatalysis, efficient electrode materials, spintronics, supercapacitors, etc. − Among these materials, TMDs are emerging with sufficiently high carrier mobility (10 3 cm 2 V –1 s –1 ), making a promise to be used in solar cells, photocatalysis, and photodetectors. To obtain the best results in these areas, we must find out the ways to deal with the major obstacles, which are charge and energy losses, as a result of faster non-radiative electron–hole recombination. , Therefore, to achieve a high-quality photovoltaic and optoelectronic performance, the electron–hole recombination should be slow or delayed . In contrast, the non-radiative electron and hole transfers toward the conduction band minimum (CBM) and valence band maximum (VBM) states, respectively, are highly desirable in an ultrafast time scale for optimum results.…”