Bulk silicon made to emit visible lightThe field of photonics has become a major

focus for researchers working on signifi-

cantly improving computing speeds; in

photonic computing, photons replace elec-

trons in representing information, and act

much more quickly. The problem has been

that the components for photonic compu-

ters rely on semiconductors that are able to

emit light; but silicon, the chief semicon-

ducting material in modern electronics and

computing, is not very good at this. It tends

to turn added energy into heat, which pro-

hibits its integration in photonic circuitry.

However, if the optical properties of sili-

con could be augmented, it would be much

easier to integrate it into such circuitry. Now,

a team of nanophotonic specialists from

Penn University’s School of Engineering

and Applied Science, whose work was pub-

lished in the journal Nature Photonics [Cho

et al., Nat. Photon. (2013) doi:10.1038/

nphoton.2013.25], have enabled ‘bulk’ sili-

con to emit broad-spectrum, visible light for

the first time, a breakthrough that could lead

to the use of silicon in devices that contain

both electronic and photonic components.

Building on previous research on plasmo-

nic cavities, they wrapped pure silicon

nanowires in a glass coating before adding

a layer of silver. Taking the shape of the

Greek letter omega, the silver coating lies

underneath the curve of the wire but can-

not move between it and the glass substrate.

The fact that the base is transparent means

the researchers could impart energy to the

semiconductor using a laser before asses-

sing the light the silicon emitted. Despite

the silicon nanowire being excited at only

one energy level, corresponding to the

wavelength of the blue laser, it was able

to produce white light that covers the entire

visible spectrum. As team leader Ritesh

Agarwal points out, this allows ‘‘a broad

bandwidth for possible operation in a

photonic or optoelectronic device. In the

future, it should also be possible to excite

these silicon nanowires electrically.’’

The study is a big step towards the

photonics goal of making silicon emit light

efficiently. Light emission from silicon could

offer the possibility for constructing transis-

tors and other components of a silicon-based

chip with dual functionalities: electronics

and as on-chip light sources. In addition,

as the ultimate goal of silicon photonics is

to achieve an electrically pumped laser

where silicon is the lasing medium, this

research on optically pumped silicon could

be extended through the use of electricity to

induce the emission of light.

Laurie Donaldson

Materials Today � Volume 16, Number 4 �April 2013 NEWS

White light emission from silicon coupled with a

nanocavity under laser excitation.

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