http://phys.org/news/2014-03-quantum-dot-laser-paves-lower-cost.html
With the
explosive growth of bandwidth demand in telecommunications networks, experts
are continually seeking new ways to transmit increasingly large amounts of data
in the quickest and cheapest ways possible. Photonic devices—which convert
light to electricity and vice versa—offer an energy-efficient alternative to
traditional copper network links for information transmission. Unfortunately,
these devices are also almost always prohibitively pricey.
One way to bring those costs down is to make
photonics compatible with the existing silicon microelectronics industry. A
promising way to do that is by growing "quantum dot" lasers directly
on silicon substrates, according to graduate student Alan Y. Liu of the University of California at Santa Barbara (UCSB) and
his colleagues, who include UCSB professors John E. Bowers and Arthur C.
Gossard. Although such quantum dot lasers have been grown on silicon before,
their performance has not equaled that of quantum dot lasers grown on their
native substrates, which are platforms made of similar materials as the quantum
dot lasers themselves.
Now Liu and his collaborators
in Bowers and Gossard's groups have demonstrated a novel quantum dot laser that
not only is grown on silicon but that performs as well as similar lasers grown
on their native substrates. The team will discuss its record-breaking results
achieved using such lasers at this year's OFC Conference and Exposition, being
held March 9-13 in San Francisco, Calif., USA.
The researchers believe the
work is an important step towards large-scale photonic integration in an ultra
low-cost platform.
Currently, so-called
"quantum well" lasers are used for data transmission. They consist of
nanometers-thick layers of light-emitting material, representing the quantum
well, sandwiched between other materials that serve to guide both the injected
electrical current as well as the output light. A quantum dot laser is similar
in design, but the sheets of quantum well materials are replaced with a high
density of smaller dots, each a few nanometers high and tens of nanometers
across. To put it in perspective, 50 billion of them would fit onto one side of
a penny.
"Quantum wells are
continuous in two dimensions, so imperfections in one part of the well can
affect the entire layer. Quantum dots, however, are independent of each other,
and as such they are less sensitive to the crystal imperfections resulting from
the growth of laser material on silicon," Liu said.
"Because of this, we can
grow these lasers on larger and cheaper silicon substrates. And because of
their small size," Liu added, "they require less power to operate
than quantum well lasers while outputting more light, so they would enable
low-cost silicon photonics."
In their new work, the team
grew quantum dots directly on silicon substrates using a technique known as
molecular beam epitaxy, or MBE ("epitaxy" refers to the process of
growing one crystal on top of another, with the orientation of the top layer
determined by that of the bottom).
"The major advantage of
epitaxial growth is that it enables us to exploit the existing economies of
scale for silicon, which would drive down cost," Liu said. He added that
"MBE is the best method for creating high-quality quantum dots that
are suitable for use in lasers" and that "the entire laser can be
grown continuously in a single run, which minimizes potential
contamination."
More information: Presentation W4C.5. titled "High
Performance 1.3μm InAs Quantum Dot Lasers Epitaxially Grown on Silicon"
will take place Wednesday, March 12 at 5:00 p.m. in room 121 of the Moscone Center. (www.ofcconference.org/)
This work was recently
published in Applied
Physics Letters: Liu, A. Y., et al. "High performance
continuous wave 1.3 μm quantum dot lasers on silicon." Applied Physics Letters,
104, 041104 (2014)
