Proof of principle—electrically injected plasmonic lasers that run at room temperature—should be possible within a couple of years, and commercial devices could follow quickly.
Researchers have demonstrated the first semiconductor plasmon nanolaser, or “spaser,” that can operate at room temperature.
Photons can’t be confined to areas with dimensions much smaller than half their wavelength, or about 250 nanometers, limiting the extent to which optical devices can be miniaturized. Plasmons, however, can be confined in much smaller spaces and then converted into conventional light waves—making them useful for ultra-high-resolution imaging or miniaturized optical circuits that might, for example, operate 100 times faster than today’s fastest electronic circuits.
Berkeley mechanical-engineering professor Xiang Zhang, postdocs Ren-Min Ma and Rupert Oulton designed and demonstrated the new semiconductor spaser. It uses metals and semiconductors, long recognized to be attractive materials because of their ubiquity and resilience. But previous spasers made of them lost too much energy to sustain lasing unless cooled to extremely low temperatures, below -250 °C.
The team’s device contains a 45-nanometer-thick, 1-micrometer square of cadmium sulfide, a semiconductor used in some solar cells and photoresistors for microchip manufacturing. The square rests on a a 5-nanometer slice of magnesium fluoride, atop a sheet of silver. When light from a commercial laser hits the metal, plasmons are generated on its surface. But the cadmium sulfide square confines the plasmons to the gap, reflecting them back each time they hit an edge. Less than 5 percent of the radiation escapes the structure, allowing sustained surface-plasmon lasing, or “spasing,” at room temperature. The research was published online in Nature Materials on December 19.
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