Phonon induced luminescence decay in monolayer MoS_2 on SiO_2/Si substrates

摘要

Exfoliated monolayer MoS_2 films on SiO_2/Si substrates have been studied using photoluminescence (PL), Raman and reflectance contrast (RC) spectroscopies. With increase in temperature, the intensity of the two dominant PL spectral features A and D, attributed to A exciton/trion and to defects, seemingly decay in an activated fashion with an energy ～50meV, which is close to the energies of E__(2g)~1 and A_(1g) phonons. Comparison of absorption spectrum derived from RC with circular polarization resolved PL spectrum suggests that both D and A emissions are associated with bound excitons, the A emission involving relatively weakly localized ones. The PL decay behaviour is explained using a phenomenological model where non-radiative loss of excitons is determined by the number of excited phonon modes. This corroborates the recent finding of strong A exciton and A_(1g) phonon coupling in monolayer MoS_2.