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We report on studies of photoluminescence spectra from suspended monolayer MoS₂ as a function of incident excitation power, temperature, and applied gate voltage. The samples are synthesized via ambient-pressure chemical vapor deposition (APCVD). Prior work [1, 2] showed that power densities above a threshold value of about 3 kW/cm² yielded a substantial red shift and broadening of the free exciton photoluminescence peak, indicative of electron-hole liquid formation at room temperature. However, our research demonstrates that the emission characteristics and dynamics of excitons in 2D systems are complex and depend on several external and internal factors.  One parameter that seems to mask or convolute the picture is the varied and inhomogeneous doping levels in the materials made and transferred through different processes. In this work we will systematically examine the effect of doping in the emission and the possible exciton condensation through electrostatic doping and photoluminescence mapping.

 

[1] Y. Yu, A. W. Bataller, R. Younts, Y. Yu, G. Li, A. A. Puretzky, D. B. Geohegan, K. Gundogdu, and L. Cao, Room-Temperature Electron–Hole Liquid in Monolayer MoS₂, ACS Nano 13, 10351 (2019).

[2] A. Rustagi and A. F. Kemper, Theoretical Phase Diagram for the Room-Temperature Electron–Hole Liquid in Photoexcited Quasi-Two-Dimensional Monolayer MoS₂, Nano Lett. 18, 455 (2018).