Excitons in Two-Dimensional Materials

Abstract

Because of the reduced dielectric screening and enhanced Coulomb interactions, two-dimensional (2D) materials like phosphorene and transition metal dichalcogenides (TMDs) exhibit strong excitonic effects, resulting in fascinating many-particle phenomena covering both intralayer and interlayer excitons. Their intrinsic bandgaps and strong excitonic emissions allow the possibility to tune the inherent optical, electrical, and optoelectronic properties of 2D materials via a variety of external stimuli, making them potential candidates for novel optoelectronic applications. In this review, we summarize exciton physics and devices in 2D semiconductors and insulators, especially in phosphorene, TMDs, and their van der Waals heterostructures (vdWHs). In the first part, we discuss the remarkably versatile excitonic landscape, including bright and dark excitons, trions, biexcitons, and interlayer excitons. In the second part, we examine common control methods to tune excitonic effects via electrical, magnetic, optical, and mechanical means. In the next stage, we provide recent advances on the optoelectronic device applications, such as electroluminescent devices, photovoltaic solar cells, and photodetectors. We conclude with a brief discussion on their potential to exploit vdWHs towards unique exciton physics and devices.

Emergent Midgap Excitons in Large‐Size Freestanding 2D Strongly Correlated Perovskite Oxide Films

“…The Ti ions attracted around the oxygen vacancies in TiO 6 octahedral forms potential minima which localize electrons and holes to form self-trapped excitons (STE). [29][30][31] We found that the time-resolved PL at 530 nm (2.34 eV) peak is best fitted by the stretched biexponential decay model while time-resolved PL at 690 nm (1.8 eV) peak could be fitted well by simple biexponential decay model as shown in Figure S6 in the Supporting Information. This indicates that the 2.34 eV luminescence is excited from electron-hole pair excitonic state while 1.8 eV luminescence could possibly be due to the Ti vacancy defect states.…”

Електронно-Дірковий Упорядкований Конденсат Як Пер-Спективне Лазерне 2D Середовище Для Кімнатних Температур

“…It should be noted that the role of various indicated factors remains unclear at length and is a subject of intense researches (see, e.g., works [16][17][18] and references therein). In any case, a reduction of the dielectric screening and an enhancement of the Coulomb interaction lead to intense exciton and multiparticle effects in 2D systems.…”

Electronic structure of $\boldsymbolα$-RuCl$_3$ by fixed-node and fixed-phase diffusion Monte Carlo methods

“…Our results also indicate that the sharp α peak at around 1 eV observed in optical experiments [2,3,11] has either an excitonic nature, or it is related to defects/impurities, or a combination thereof. Because α−RuCl 3 is a quasi-2D material, this is not surprising since very large excitonic binding energies of that order are observed in other 2D materials [56,57]. Indeed, recent time-resolved two-photon PE spectroscopy experiments indicate that abovementioned ∼ 1 eV gap is excitonic [54].…”