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

Atomic monolayers represent a novel class of materials for studying localized and free excitons in two dimensions and for engineering optoelectronic devices based on their significant optical response. Here, we investigate the role of the substrate in the photoluminescence response of MoSe2 and WSe2 monolayers exfoliated either on SiO2 or epitaxially grown InGaP substrates. In the case of MoSe2, we observe a significant qualitative modification of the emission spectrum, which is widely dominated by the trion resonance on InGaP substrates. However, the effects of inhomogeneous broadening of the emission features are strongly reduced. Even more striking, in sheets of WSe2, we could routinely observe emission lines from localized excitons with linewidths down to the resolution limit of 70 μeV. This is in stark contrast to reference samples featuring WSe2 monolayers on SiO2 surfaces, where the emission spectra from localized defects are widely dominated by spectral diffusion and blinking behavior. Our experiment outlines the enormous potential of III–V monolayer hybrid architectures to obtain high quality emission signals from atomic monolayers, which are simple to integrate into nanophotonic and integrated optoelectronic devices.