Key to the new development is use of materials that can be laid down in single layers and efficiently amplify light (lasing action). Single layer nanolasers have been developed before, but they all had to be cooled to low temperatures using a cryogen like liquid nitrogen or liquid helium. Being able to operate at room temperatures (~77 F) opens up many possibilities for uses of these new lasers,” Ning said.
The joint ASU-Tsinghua research team used a monolayer of molybdenum ditelluride integrated with a silicon nanobeam cavity for their device. By combining molybdenum ditelluride with silicon, which is the bedrock in semiconductor manufacturing and one of the best waveguide materials, the researchers were able to achieve lasing action without cooling, Ning said.
A laser needs two key pieces – a gain medium that produces and amplifies photons, and a cavity that confines or traps photons. While such materials choices are easy for large lasers, they become more difficult at nanometer scales for nanolasers. Nanolasers are smaller than 100th of the thickness of the human hair and are expected to play important roles in future computer chips and a variety of light detection and sensing devices.
Monolayer MoTe2 and silicon photonic crystal nanobeam cavity.
Monolayer transition-metal dichalcogenides (TMDs) have the potential to become efficient optical-gain materials for low-energy-consumption nanolasers with the smallest gain media because of strong excitonic emission. However, until now TMD-based lasing has been realized only at low temperatures. Here we demonstrate for the first time a room-temperature laser operation in the infrared region from a monolayer of molybdenum ditelluride on a silicon photonic-crystal cavity. The observation is enabled by the unique combination of a TMD monolayer with an emission wavelength transparent to silicon, and a high-Q cavity of the silicon nanobeam. The laser is pumped by a continuous-wave excitation, with a threshold density of 6.6 W cm–2. Its linewidth is as narrow as 0.202 nm with a corresponding Q of 5,603, the largest value reported for a TMD laser. This demonstration establishes TMDs as practical materials for integrated TMD–silicon nanolasers suitable for silicon-based nanophotonic applications in silicon-transparent wavelengths.
They have demonstrated the room-temperature operation of a monolayer semiconductor nanolaser for the first time. The impacts of this demonstration can be understood in several ways:
1. room temperature operation of semiconductor lasers of any kind has historically represented important milestones, since such capability is a necessary first step toward any practical applications.
2. monolayers of TMDs allows the fabrication of photonic devices with the smallest possible volume of gain medium and device sizes, but the lack of a room temperature demonstration has generated a general doubt about the feasibility of such smallest optical gain medium overcoming the total loss. This demonstration will thus contribute the establishment of 2D TMDs as a practically viable gain medium and will open a range of novel lasers and photonic devices.
3. since the nanobeam lasers operate on excitonic transitions well below the bandedge of MoTe2, their demonstration indicates the possibility of an excitonic lasing at room temperature, which is still a challenging task in infrared regime and deserves to be further studied. The room temperature realization(37) in UV wavelength shows a threshold that is higher than in our case.
4. a collection of favorable quantitative measures such as small overall device sizes, small modal volume, small active volume, and extremely low threshold power density could lead to exciting applications in high energy efficiency on-chip interconnects. The Si-nanobeam cavity would make such an application more appealing for photonics integration.
5. Their combined MoTe2-nanobeam cavity structure can potentially open a wide range of investigations at room temperature such as electrical injection 2D TMDs-based lasers, valley-spin polarized lasers, or strong cavity-TMD monolayer coupling physics.