Enhanced Emission from Defect Levels in Multilayer MoS2

Realizing stimulated emission from defects in 2D-layered semiconductors has the potential to enhance the sensitivity of characterizing their defects. However, stimulated emission from defects in layered materials presents a different set of challenges in carrier lifetime and energy level design and is not achieved so far. Here, photoluminescence (PL) spectroscopy, Raman spectroscopy, and first-principles theory are combined to reveal an anomalous PL intensity-temperature relation and strong polarization effects at a defect emission peak in annealed multilayer MoS2, suggesting defect-based stimulated emission. The emergence of stimulated emission behavior is also controllable (by temperature) and reversible. The observed stimulated emission behavior is supported by a three-level system involving two defect levels from chalcogen vacancies and a pump level from the conduction band edge. First-principles calculations show that the special indirect gap that enables stimulated emission is not native to pristine bulk MoS2 and only emerges under thermal strain.