Tensile strain creates trion: Excitonic photoluminescence distribution over bilayer MoS2 grown by CVD

Raman and photoluminescence (PL) hyperspectral mapping of a bilayer MoS2 flake grown on SiO2/Si substrate by chemical vapor deposition is studied focusing on the surface variation of the exciton and trion PL charac-teristics. The Raman modes and the excitonic PL in the flake interior are redshifted compared to those at the perimeter. This is attributed to tensile strain present after the post-growth cooling so that the flake perimeter is less strained. At the perimeter, the PL blueshift is also enhanced due to a reduction of the trion (a negatively charged exciton) peak, being attributed to an outflow of electrons (p-doping) induced by a weakening of tensile strain towards the flake edge. This occurs because tensile strain bends down the conduction band of MoS2, causing a drift of electrons towards the strained interior region and, in turn, creating there an increased electron density which fosters the creation of trion.

Automated summary

The surface variation of the exciton and trion PL characteristics in a bilayer MoS2 flake grown on a SiO2/Si substrate by chemical vapor deposition was studied using Raman and photoluminescence hyperspectral mapping. The Raman modes and excitonic PL in the flake interior were found to be redshifted compared to those at the perimeter, which was attributed to the presence of tensile strain. The PL at the perimeter also experienced a blueshift, potentially due to a reduction in trion peak caused by electron outflow induced by weakening of tensile strain.