Hot Exciton Effect in Photoluminescence of Monolayer Transition Metal
Dichalcogenide
Abstract
Hot excitons are usually neglected in optical spectroscopy in 2D
semiconductors for the sake of momentum conservation, as the majority of
hot excitons are out of light cones. In this letter, we elaborate the
contribution of hot excitons to optical properties of monolayer MoSe2
with photoluminescence (PL) and photoluminescence excitation (PLE)
spectroscopy. With the excitation-intensity-dependent PL,
temperature-dependent PL and PLE experiments combined with the
simulations, we experimentally distinguish the influences of the exciton
temperature and the lattice temperature in the PL spectrum. It is
concluded that the acoustic phonon assisted photoluminescence accounts
for the non-Lorentzian high energy tail in the PL spectrum and the hot
exciton effect is significant to linear optical properties of TMDs.
Besides, the effective exciton temperature is found to be several tens
of Kelvin higher than the lattice temperature at non-resonant optical
excitation. It indicates that the exciton temperature needs to be
carefully taken into account when considering the exciton related
quantum phase phenomena such as exciton condensation. It is
experimentally demonstrated that the effective exciton temperature can
be tuned by excitation energy.