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A*STAR Team Lays Foundations For Hybrid Silicon Lasers

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Researchers develop new technique that paves way for low-cost, mass-produced photonic devices

Producing semiconductor lasers on a silicon wafer is a long-held goal
for the electronics industry, but their fabrication has proved
challenging. Now, researchers at A*STAR (Singapore’s Agency for Science,
Technology and Research) have developed an innovative way to
manufacture them that they say is cheap, simple and scalable.

Hybrid
silicon lasers combine the light-emitting properties of group III–V
semiconductors, like GaAs and InP, with the maturity of silicon
manufacturing techniques. These lasers are attracting considerable
attention as they promise inexpensive, mass-producible optical devices
that can integrate with photonic and microelectronic elements on a
single silicon chip. They have potential in a wide range of
applications, from short-distance data communication to high-speed,
long-distance optical transmission.

In the current production
process, however, lasers are fabricated on separate III–V semiconductor
wafers before being individually aligned to each silicon device - a
time-consuming, costly process that limits the number of lasers that can
be placed on a chip.

To overcome these limitations, Doris
Keh-Ting Ng and her colleagues from the A*STAR Data Storage Institute
have developed an innovative method for producing a hybrid III–V
semiconductor and silicon-on-insulator (SOI) optical microcavity. This
greatly reduces the complexity of the fabrication process and results in
a more compact device.

“It’s very challenging to etch the entire
cavity," says Ng. “Currently, there is no single etch recipe and mask
that allows the whole microcavity to be etched, and so we decided to
develop a new approach."

By first attaching a thin film of III–V
semiconductor to a silicon oxide (SiO2) wafer using a SOI interlayer
thermal bonding process, they produced a strong bond that also removes
the need for strong oxidizing agents, such as Piranha solution or
hydrofluoric acid.

And by using a dual hard-mask technique to
etch the microcavity that confined etching to the intended layer, they
eliminated the requirement to use multiple overlay lithography and
etching cycles — a challenging procedure.

“Our approach cuts down
the number of fabrication steps, reduces the use of hazardous
chemicals, and requires only one lithography step to complete the
process," explains Ng.

The work presents, for the first time, a
new heterocore configuration and integrated fabrication process that
combines low-temperature SiO2 interlayer bonding with dual hard-mask,
single lithography patterning.

“The process not only makes it
possible to produce heterocore devices, it also greatly reduces the
challenges of fabricating them, and could serve as an alternative hybrid
microcavity for use by the research community," says Ng.

The A*STAR-affiliated researchers contributing to this research are from the Data Storage Institute.


'Fabrication
and demonstration of III-V/Si heterocore microcavity lasers via
ultrathin interlayer bonding and dual hard mask techniques',
by Lee, C.-W., Ng, D. K.-T., Tan, A. L. & Wang, Q.; ACS Photonics 3, 2191–2196 (2016).| Article


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