Unraveling biexciton and excitonic excited states from defect bound states in monolayer MoS2

Abstract Being direct band gap semiconductor, two-dimensional monolayer (ML) MoS 2 has remarkable optical transitions arising from excitons, trions, biexciton and defects mediated bound states. However, experimental realization of biexciton in ML MoS 2 has been challenging due to broad spectral feature of exciton. Here, we report on systematic observation of biexciton (A XX ∼ 1.90 eV) along with A- trion ∼ 1.92 eV and ground state exciton A 1s ∼ 1.96 eV in ML MoS 2 at 4 K, by laser-power and temperature-dependent non-resonant photoluminescence (PL) spectroscopy. At low temperatures the excited state of A exciton has also been observed, A 2s ∼ 2.13 eV, which consequently merges in thermal broadening of B excitons, with rise in temperature. With excitation energy and power dependent PL, emission arising from exciton bound to sulfur vacancy (∼1.82 eV) have been distinguished from biexciton. Thus understanding of such excitonic states and biexcitons is useful for future quantum information processing, optoelectronic, photonics and THz applications.