Excitonic Rydberg series in gate-tunable hBN-encapsulated monolayer MoTe₂

Two-dimensional semiconducting TMDs have been studied extensively in the past few years due to their outstanding optical properties which are dominated by excitons. In particular, monolayer MoTe₂ has a bandgap in the near-infrared (NIR) region which makes it a good candidate to be incorporated in electro-optical NIR devices. In this work, we performed optical measurements at low temperature (4K) on hBN-encapsulated monolayer MoTe₂. First, we confirmed that our MoTe₂ sample was a single layer by optical contrast and Raman spectroscopy. We then measured the photoluminescence (PL) spectra and observed the first three excitonic states of the Rydberg series, with the linewidth of the lowest excitonic state (1s) being around 2 meV. The energy differences between these excitonic states were used to calculate an electronic bandgap of 1.337 eV. In addition, we were able to effectively inject carriers in monolayer MoTe₂ by applying a gate voltage from a bottom graphite electrode which allowed us to tune the chemical potential and measure trion emissions from the 1s state. The identification of these excitations as excitons and trions was confirmed by a linear relationship between PL intensity and laser power. Our work contributes to identifying MoTe₂ as a new platform to study excitonic physics in the NIR range.