  Excitonic stimulated emission provides a promising mechanism and route to
achieve low-threshold semiconductor lasers for micro-nano optoelectronic
integrations. However, excitonic stimulated emission from quantum
structure-free semiconductors has rarely been realised at room temperature due
to the phase transition between excitonic and electron-hole plasma states.
Herein, we show that through trap-state and band-edge engineering, bound
exciton states can be stabilised within the hybrid lead bromide perovskite.
Under modest pumping conditions, these states enable stimulated emission
behaviour that exhibits a low threshold carrier density of only 1.6*1017 cm-3,
as well as a high peak gain coefficient of ~1300 cm-1. This is the first time
that bound exciton stimulated emission has been realised at room temperature
from a quantum structure-free semiconductor. Not only does this open up new
research horizons for perovskite materials, but also it has important
implications for semiconductor excitonic physics and the development of
next-generation optoelectronic applications.
