LAKE WALES, Fla. — The Nanophotonics Lab at Arizona State University (Tempe), working with Tsinghua University (Beijing), has demonstrated an on-chip CMOS communications laser that the researchers say is the first to lase at room temperature. The team built the proof-of-concept device without III-V compounds by placing a monolayer of molybdenum ditelluride over a nanobeam silicon cavity. Others have achieved monolayer lasing with similar techniques, but only at cryogenic temperatures.
Artist�s rendering of the first CMOS laser achieved with a monolayer of molybdenum ditelluride over a cavity of silicon.
(Source: Arizona State University)
Molybdenum ditelluride (MoTe2) — a compound of molybdenum and tellurium called a transition-metal dichalcogenide — is a semiconductor that can fluoresce with a bandgap in a region enabling infrared lasing at industry-standard communications wavelengths. When crystallized into atomically thin monolayers, it is flexible, crack-resistant, nearly transparent, and CMOS-compatible.
“Our nanobeam cavity is fabricated from a standard CMOS silicon-on-insulator wafer,” Cun-Zheng Ning, the Arizona State electrical-engineering professor who led the team, told EE Times. “We did not use any high-temperature processing, which is often a concern for CMOS. The transfer of the MoTe2 layer is a simple, mechanical process.
Arizona State EE professor Cun-Zheng Ning led the team.
(Source: Arizona State University)
“In other words, we use nothing else but standard processing steps common in CMOS industry.”
As shown in an artist’s rendering of the nanolaser architecture (see figure), the MoTe2 monolayer is placed over a thin silicon beam with holes etched in it. The configuration succeeds in efficiently amplifying light enough to enable lasing in the infrared communications bands.
Ning and Tsinghua researchers Yongzhuo Li, Jianxing Zhang, and Dandan Huang describe the work in detail in “Room-temperature Continuous-wave Lasing from Monolayer Molybdenum Ditelluride Integrated with a Silicon Nanobeam Cavity, published in Nature Nanotechnology. They note that the gain medium amplifies photons, while the cavity confines them. The combination produces excitons in the molybdenum telluride that are 100 times stronger than in conventional semiconductors, enabling room-temperature lasing in the common infrared communications wavelengths. The researchers add that the techniques can be modified to sense the light produced, thus potentially enabling both photonic emitters and photonic receivers to reside on the same CMOS chip.
Top left: Scanning-electron-microscope image shows a silicon-photonic crystal nanobeam that contains an array of etched holes with carefully designed diameters and spacing. Top right: Laser-field intensity profile shows the first three modes along the nanobeam. Bottom: Schematic view of the overall laser structure shows the suspended silicon nanobeam on a silicon substrate with the silicon dioxide layer etched away, leaving an air gap between the bottom silicon substrate and the top silicon nanobeam. The light purple color on top indicates the single molecular layer of molybdenum ditelluride.
(Source: Arizona State University)
As is the usual practice, the proof-of-concept chip used a very low-power conventional laser to pump the molybdenum ditelluride CMOS laser. “Today it is pumped by a continuous-wave helium–neon laser emitting at a 633-nanometer wavelength,” Ning told EE Times, adding that the required threshold for pumping was “much less than that from a red laser pointer.”
The researchers’ next target is to initiate and modulate lasing electrically for on-chip photonics. “Designing an efficient current injection scheme is the key for a successful demonstration of a laser under electrical injection,” Ning told EE Times. “We are currently working on both the design and test fabrication.”
— R. Colin Johnson, Advanced Technology Editor, EE Times 
Related articles:
- IBM Optics Go CMOS
- Nanolaser Enables On-Chip Photonics
- Smart Semi Fiber Does It All
- Graphene Laser to Probe Superconductivity
- Expanding Optical Horizons