Researchers Devise New Way to
Make Light Interact with Matter
Reducing the wavelength of light could allow it to be absorbed or emitted by a semiconductor, study suggests.
By David L. Chandler, MIT News Office
Make Light Interact with Matter
Reducing the wavelength of light could allow it to be absorbed or emitted by a semiconductor, study suggests.
By David L. Chandler, MIT News Office
June 4, 2018 -- A new way of enhancing the interactions between
light and matter, developed by researchers at MIT and Israel
The
fundamental principle behind the new approach is a way to get the momentum of
light particles, called photons, to more closely match that of electrons, which
is normally many orders of magnitude greater. Because of the huge disparity in
momentum, these particles usually interact very weakly; bringing their momenta
closer together enables much greater control over their interactions, which
could enable new kinds of basic research on these processes as well as a host
of new applications, the researchers say.
The
new findings, based on a theoretical study, are being published today in the
journal Nature Photonics
in a paper by Yaniv Kurman of Technion (the Israel Institute of Technology, in
Haifa); MIT graduate student Nicholas Rivera; MIT postdoc Thomas Christensen;
John Joannopoulos, the Francis Wright Davis Professor of Physics at MIT; Marin
Soljačić, professor of physics at MIT; Ido Kaminer, a professor of physics at
Technion and former MIT postdoc; and Shai Tsesses and Meir Orenstein at
Technion.
While
silicon is a hugely important substance as the basis for most present-day
electronics, it is not well-suited for applications that involve light, such as
LEDs and solar cells — even though it is currently the principal material used
for solar cells despite its low efficiency, Kaminer says. Improving the
interactions of light with an important electronics material such as silicon
could be an important milestone toward integrating photonics — devices based on
manipulation of light waves — with electronic semiconductor chips.
Most
people looking into this problem have focused on the silicon itself, Kaminer
says, but “this approach is very different — we’re trying to change the light
instead of changing the silicon.” Kurman adds that “people design the matter in
light-matter interactions, but they don’t think about designing the light
side.”
One
way to do that is by slowing down, or shrinking, the light enough to
drastically lower the momentum of its individual photons, to get them closer to
that of the electrons. In their theoretical study, the researchers showed that
light could be slowed by a factor of a thousand by passing it through a kind of
multilayered thin-film material overlaid with a layer of graphene. The layered
material, made of gallium arsenide and indium gallium arsenide layers, alters
the behavior of photons passing through it in a highly controllable way. This
enables the researchers to control the frequency of emissions from the material
by as much as 20 to 30 percent, says Kurman, who is the paper’s lead author.
The
interaction of a photon with a pair of oppositely charged particles — such as
an electron and its corresponding “hole” — produces a quasiparticle called a
plasmon, or a plasmon-polariton, which is a kind of oscillation that takes
place in an exotic material such as the two-dimensional layered devices used in
this research. Such materials “support electromagnetic oscillations on its
surface, really tightly confined” within the material, Rivera says. This
process effectively shrinks the wavelengths of light by orders of magnitude, he
says, bringing it down “almost to the atomic scale.”
Because
of that shrinkage, the light can then be absorbed by the semiconductor, or
emitted by it, he says. In the graphene-based material, these properties can
actually be controlled directly by simply varying a voltage applied to the
graphene layer. In that way, “we can totally control the properties of the
light, not just measure it,” Kurman says.
Although
the work is still at an early and theoretical stage, the researchers say that
in principle this approach could lead to new kinds of solar cells capable of
absorbing a wider range of light wavelengths, which would make the devices more
efficient at converting sunlight to electricity. It could also lead to
light-producing devices, such as lasers and LEDs, that could be tuned
electronically to produce a wide range of colors. “This has a measure of
tunability that’s beyond what is currently available,” Kaminer says.
“The
work is very general,” Kurman says, so the results should apply to many more
cases than the specific ones used in this study. “We could use several other
semiconductor materials, and some other light-matter polaritons.” While this
work was not done with silicon, it should be possible to apply the same
principles to silicon-based devices, the team says. “By closing the momentum
gap, we could introduce silicon into this world” of plasmon-based devices,
Kurman says.
Because
the findings are so new, Rivera says, it “should enable a lot of functionality
we don’t even know about yet.”
Frank
Koppens, a professor of physics at the the Institute
of Photonic Sciences in Barcelona
Koppens
says that “one can envision many applications, such as more efficient light
emitters, solar cells, photodetectors etc. All integrated on a chip! It’s also
a new way to control the color of a light emitter, and I’m sure there will be
applications that we didn’t even think of.”
The
work was supported by MIT’s MISTI Israel program.
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