Exciton-dominant photoluminescence of MoS by a functionalized substrate.

Transition metal dichalcogenides (TMDs) have been considered as promising candidates for transparent and flexible optoelectronic devices owing to their large exciton binding energy and strong light-matter interaction. However, monolayer (1L) TMDs exhibited different intensities and spectra of photoluminescence (PL), and the characteristics of their electronic devices also differed in each study. This has been explained in terms of various defects in TMDs, such as vacancies and grain boundaries, and their surroundings, such as dielectric screening and charged impurities, which lead to non-radiative recombination of trions, low quantum yield (QY), and unexpected doping. However, it should be noted that the surface conditions of the substrate are also a critical factor in determining the properties of TMDs located on the substrate. Here, we demonstrate that the optical and electrical properties of 1L MoS are strongly influenced by the functionalized substrate. The PL of 1L MoS placed on the oxygen plasma-treated SiO substrate was highly p-doped owing to the functional groups of -OH on SiO, resulting in a strong enhancement of PL by approximately 20 times. The PL QY of 1L MoS on plasma-treated SiO substrate increased by one order of magnitude. Surprisingly, the observed PL spectra show the suppression of non-radiative recombination by trions, thus the exciton-dominant PL led to a prolonged lifetime of MoS on the plasma-treated substrate. The MoS field-effect transistors fabricated on plasma-treated SiO also exhibited a large hysteresis in the transfer curve owing to charge trapping of the functional groups. Our study demonstrates that the functional groups on the substrate strongly affect the characteristics of 1L MoS, which provides clues as to why MoS exfoliated on various substrates always exhibited different properties in previous studies.