Recently, a research team led by Prof. LIU Xinfeng from the National Center for Nanoscience and Technology (NCNST) of the Chinese Academy of Sciences reported the exciton emission enhancement in monolayer WS₂ on a silicon substrate via a Fabry–Pérot microcavity with 438 of enhancement factor. The study was published in Nano Letters.

Two-dimensional monolayer transition-metal dichalcogenides (TMDs) are direct band gap semiconductor materials. The nonbonding surface of monolayer TMDs facilitates their transfer or direct growth onto diverse substrates. However, low quantum yield and short photoluminescence (PL) lifetime are the main factors restricting the practical application of monolayer TMDs materials, and the substrate on which monolayer TMDs grows and transfers has significant influence on its exciton PL yield.

It is difficult to realize the ideal monolayer TMDs exciton emitter at room temperature. The PL enhancement of existing monolayer TMDs materials in silicon-based microhole systems is only one order of magnitude, and there is a lack of comprehensive and detailed explanation of the mechanism of PL enhancement, which is important for the development and application of silicon-based monolayer TMDs materials in miniaturized optoelectronic devices.

In this study, researchers used inductively coupled plasma etching method to prepare SiO₂/Si substrate microhole array, and obtained monolayer WS₂ by mechanical exfoliation. The monolayer WS₂ was transferred onto microholes on SiO₂/Si substrate to construct Fabry–Pérot microcavity. Optical imaging, scanning electron microscopy, and atomic force microscopy were used to characterize the sample structure. The PL enhancement of monolayer WS₂ in the Fabry–Pérot cavity was demonstrated by steady-state PL spectra and PL imaging.

The largest exciton PL enhancement factor ~438 in monolayer WS₂ was obtained by regulating the detuning between the excitation wavelength and the Fabry-Perot cavity mode. Temperature-dependent PL spectra showed that the collected signal is mainly from the exciton emission at room temperature, and is due to the weakening of the substrate effect. At low temperature, the monolayer WS₂ on cavity exhibits multiple exciton emissions, which reflects superior sample quality.

By using time-resolved PL spectra and transient absorption spectra, researchers demonstrated that suspended monolayer WS₂ weakens the substrate effect, reduces the generation of trions, and causes more excitons to decay in the form of radiation recombination, resulting in a longer exciton radiation lifetime.

This study proves that the coupling system of monolayer TMDs and silicon-based microholes is a practical platform for enhancing exciton emission and weakening substrate effect, which opens a way for the development of monolayer TMDs materials in the field of integrated optoelectronics.