Atomically thin semiconducting transition-metal dichalcogenides provide novel insights into the physics of many-body effects mediated by Coulomb interactions. Here, we report on temperature-dependent (T = 7-295 K) reflectance contrast and photoluminescence studies of three-particle complexes in n-doped WS2 monolayers. In low-temperature reflectance contrast spectra we observe distinct resonances of the neutral exciton, negative trion and exciton bound to a donor (X, X− and XD). For temperatures above 80 K, reflectance contrast signatures of the XD disappear, whereas the X− remains detectable up to 240 K, despite the fact that the XD signal is more red-shifted from the neutral exciton than that of the X−. This experimental observation underlines that in WS2 the dissociation energy of X− considerably exceeds (factor of 2.5) that of XD. In the laser-power dependent photoluminescence experiments, performed at room temperature, we demonstrate the control of the intensity ratio and energy position of the X and X− lines, which allows us to evaluate the trion binding energy. Moreover, we demonstrate that the room-temperature PL is sensitive to the environmental gas (ambient, N2, He).
@article{arxiv.1612.04122,
title = {Observation of three-particle complexes in WS$_2$ monolayers},
author = {J. Jadczak and J. Kutrowska-Girzycka and P. Kapuscinski and J. Debus and D. Kudlacik and D. Schmidt and Y. S. Huang and M. Bayer and L. Bryja},
journal= {arXiv preprint arXiv:1612.04122},
year = {2016}
}