Complete-series excitonic dipole emissions in few layer ReS2 and ReSe2 observed by polarized photoluminescence spectroscopy

• Published in: Nano energy 2019-02, Vol.56, p.641-650
• Main Authors: Ho, Ching-Hwa, Liu, Zhan-Zhi
• Format: Article
• Language: English
• Subjects: 2D semiconductor; Dipole emitter; Excitons; In-plane anisotropy; Polarized photoluminescence
• ISSN: 2211-2855
• DOI: 10.1016/j.nanoen.2018.12.014

Excitonic emission is a key factor for a two-dimensional (2D) semiconductor to be fabricated in light-emitting device for optoelectronics application. Especially when the 2D material has a specific in-plane optical anisotropy, its excitons would become polarized dipole emitters. In this study, the whole series excitonic emissions of few-layer ReS2 and ReSe2 have been detailed characterized using polarized micro-photoluminescence (μPL) measurement. There are totally five excitonic emissions denoted as E1ex, E2ex, E3ex, ES1ex and ES2ex can be detected by the μPL experiment for both the few-layer ReS2 and ReSe2. The angular dependencies of the polarized excitonic emissions with respect to b axis (Re4 diamond-chain direction) are determined. The emission feature E1ex is the band-edge exciton while it shows orthogonal polarization with respect to both E2ex and E3ex in layered ReX2 (X = S, Se). The formation of Re4 diamond chains (DCs) in the 1 T′-phase ReS2 and ReSe2 will also assist the development of in-plane built-in electric field and forming dipoles around the DC regions. The built-in electric field effect greatly enhances the higher ES1ex and ES2ex excitonic features as evident in the photo-modulated reflectance spectra of the layered ReX2 with in-plane electrical field modulation. The binding energy and transition origin of all the excitons are also analyzed and discussed. [Display omitted] •Complete-series of five excitonic dipole emissions are demonstrated for few-layer ReS2 and ReSe2.•With specific in-plane anisotropy of Re4 diamond chain (b axis), the polarized dipole emitters show largely E || b and E ⊥ b polarizations.•Angular dependences of five polarized excitonic emissions are demonstrated.•Donor-bound excitonic emission with largely E || b and largely E ⊥ b polarization is detected by ReS2.