Long lived localized defect states in monolayer WSe$_2$: Optical Lifetime distribution and thermal evolution

Abstract

We carefully investigate the recombination dynamics of localized defect emission in monolayer WSe$_2$ on SiO$_2$/Si substrate using time-resolved photoluminescence over the temperature range of 4 K to 120 K. We observe two long-lived optical lifetimes, one few nanosecond and one hundreds of nanoseconds. PL decay profile of these long lived states is fit well by a power-law, and based on laser fluence studies, the likely origin of the power-law is due to a distribution of life-times rather than many body interactions. Temperature-dependence of these rates shows that thermal detrapping governs these long-lived channels and we obtained a value of 60 meV for the characteristics energy in a Bose-Einstein model. We performed spin-resolved density functional calculations for selenium vacancies, the most likely source of native defects, to elucidate on spin- and momentum-forbidden pathways which are the likely origin of these long lifetimes. Such detailed understanding of long-lived defect states is crucial for quantum and optoelectronic applications.