Substrate engineering for high-quality emission of free and localized excitons from atomic monolayers in hybrid architectures

Abstract

Atomic monolayers represent a novel class of materials to study localized and\nfree excitons in two dimensions and to engineer optoelectronic devices based on\ntheir significant optical response. Here, we investigate the role of the\nsubstrate on the photoluminescense response of MoSe$_2$ and WSe$_2$ monolayers\nexfoliated either on SiO$_2$ or epitaxially grown InGaP substrates. In the case\nof MoSe$_2$, we observe a significant qualitative modification of the emission\nspectrum, which is widely dominated by the trion resonance on InGaP substrates.\nHowever, the effects of inhomogeneous broadening of the emission features are\nstrongly reduced. Even more strikingly, in sheets of WSe$_2$, we could\nroutinely observe emission lines from localized excitons with linewidths down\nto the resolution limit of 70\\,$\\mu$ eV. This is in stark contrast to reference\nsamples featuring WSe$_2$ monolayers on SiO$_2$ surfaces, where the emission\nspectra from localized defects are widely dominated by spectral diffusion and\nblinking behaviour. Our experiment outlines the enormous potential of\nIII-V-monolayer hybrid architectures to obtain high quality emission signals\nfrom atomic monolayers, which are straight forward to integrate into\nnanophotonic and integrated optoelectronic devices.\n