  Monolayer transition metal dichalcogenides (TMDs) provide the most efficient
optical gain materials and have potential for making nanolasers with the
smallest gain media with lowest energy consumption. But lasing demonstrations
based on TMDs have so far been limited to low temperatures. Here, we
demonstrate the first room-temperature laser operation in the infrared
wavelengths from a monolayer of molybdenum ditelluride on a silicon
photonic-crystal nanobeam cavity. Our demonstration is made possible by a
unique choice of TMD material with emission wavelength below silicon
absorption, combined with the high Q-cavity design by silicon nanobeam. Lasing
at 1132 nm is demonstrated at room-temperature pumped by a continuous-wave
laser, with a threshold density at 6.6 W/cm2. The room-temperature linewidth of
0.202 nm is the narrowest with the corresponding Q of 5603, the largest
observed for a TMD laser. This demonstration establishes TMDs as practical
nanolaser materials. The silicon structures provide additional benefits for
silicon-compatible nanophotonic applications in the important infrared
wavelengths.
