Chips that could use light, instead of electricity, to move data would consume much less power—a growing concern as chips’ transistor counts rise. Of the three chief components of optical circuits—light emitters, modulators, and detectors—emitters are the toughest to build. One promising light source for optical chips is molybdenum disulfide (MoS2), which has excellent optical properties when deposited as a single, atom-thick layer, say researchers at Massachusetts Institute of Technology, Cambridge. Other experimental on-chip light emitters have more-complex three-dimensional geometries and use materials that are much more scarce, which would make them more difficult and costly to manufacture.
The researchers from MIT’s departments of Physics and of Electrical Engineering and Computer Science have developed a new technique for building MoS2light emitters tuned to different frequencies, an essential requirement for optoelectronic chips. Since thin films of material can also be patterned onto sheets of plastic, the same work could point toward thin, flexible, bright, color displays.
Most optical communications systems, such as the fiber-optic networks, maximize bandwidth by encoding different data at different optical frequencies. So tunability is crucial to realizing the full potential of optoelectronic chips.
The MIT researchers tuned their emitters by depositing two layers of MoS2 on a silicon substrate. The top layers were rotated relative to the lower layers, and the degree of rotation determined the wavelength of the emitted light. While the researchers knew that rotating the layers should alter the wavelength of the emitted light, they were by no means certain that the light would be intense enough for use in optoelectronics. As it turns out, however, the rotation of the layers relative to each other alters the crystal geometry enough to preserve the band gap.
The emitted light is not quite as intense as that produced by a monolayer of MoS2, but it’s certainly intense enough for practical use, they explained.