Edge-Emitting Silicon Nanocrystal Distributed Feedback Laser with Extremely Low Exciton Threshold

The successful integration of a laser into the silicon photonic chip has long been the holy grail of silicon photonics. Among the various methods addressing this challenge, silicon nanocrystal (Si NC) lasers remain a tempting but debated topic due to their complex carrier recombination process. Here we demonstrate an optically pumped edge-emitting first-order distributed feedback Si NC laser by utilizing a versatile nanoimprint lithography method incorporating a composite working stamp. Upon femtosecond pulsed laser pumping, we find that the lasing threshold in exciton number per NC down to 0.021 is unusually low compared with other quantum dot gain materials. To understand this interesting behavior, we have performed systematic transient spectrum experiments on its photoluminescence and transient absorption aimed at revealing the role of self-trapping states in the carrier recombination process. Our results suggest that such states in well passivated Si NCs can be regarded as metastable states that intercept hot electrons and with a time delay, release them back to the conduction band, acting like electron reservoirs that continuously feed the active lasing state as its upper levels. In this perspective, we conclude that the surface states can benefit the buildup of population inversion and lead to inhibition of the Auger process as they temporarily localize the hot electrons outside the NC core and have verified our conclusion by numerical and experimental results, respectively. Our results provide critical information on processes related to Si NC lasing and will aid attempts at Si lasers on-chip.