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Technology
What is Quantum Well
Intermixing?
 Quantum
Well Intermixing (QWI) is a post-growth based technique that allows the
energy bandgap of a grown quantum well (QW) to be modified without any use
of epitaxial regrowth.
The ion implantation QWI method makes use of a glass film etched with a 3D
profile as a mask. Neutral impurities, such as phosphorus ions, are
implanted into the semiconductor material through the glass film. The
varying thickness of the film controls the amount of phosphorus ions
implanted in the region above a quantum well. The wafer is sent through an
annealing process. At elevated temperatures, the generated vacancies diffuse
from their high concentration region into low concentration region further
down into the wafer structure. The vacancies movement intermixes the
different atoms in the quantum well structure. The effect of intermixing
creates a graded QW structure thereby increasing its bandgap energy profile
at the intermixed region.
Because bandgaps can be fine tuned at any selected regions of the QW
structure, QWI is able to avoid optical losses at the butt joints of an
active region with a passive region. In effect, seamless wafer-scale light
connects can be created.
DenseLight's advancement to the current art is the use of a glass barrier
film comprising patterns of different profile heights to create different
bandgaps in the corresponding section of the wafer or die. With this wafer
level variable thickness mask, different degrees of intermixing can be
achieved with just a single implantation step.
This innovation is trademarked as DensePICTM and is the subject
of a number of pending international and U.S. patent applications.
This one-step implantation technique simplifies the PIC fabrication process
tremendously, greatly improving the prospect of high yield and low cost PIC
products. Furthermore, since the area of intermixing can be highly precise
up to 2 micron spatial resolutions and the level of bandgap engineering
control can be finely tuned within a cell; this opens up tremendous design
possibilities in photonic integrated circuits. Through this technique, it is
conceivable to manufacture different active and passive regions in various
geometric configurations on a single wafer creating densely function-packed PICs!
For more information about DenseLight's QWI technology please refer to
 WDM Solutions:
Quantum-well intermixing enables multiple functions on a chip Aug2000
Revolutionizing the
Manufacture of PICs with QWI
1. QWI enables Higher Yields and Lower Costs
DenseLight developed its one-step implantation technique which simplifies
the PIC fabrication process tremendously, greatly improving the prospect of
high yield and low cost PIC products. DenseLight's manufacturing center in
Singapore has realized this fabrication technology and aims to supply
customers with its range of advanced PICs products.
Monolithically
integrated 40-channel AWG filter with a 40-photodiode array on i
ndium phosphide substratemeasuring only 6 mm by 8 mm.
This was fabricated using ion implantation QWI process.
2. QWI
enables 2D freedom in Bandgap Engineering
Because bandgaps can be fine tuned at any selected regions of the QW
structure, the QWI technique gives complete 2 dimensional freedom in bandgap
engineering. This opens up tremendous design possibilities in photonic
integrated circuits. QWI fabrications may allow a photonic IC designer to
layout optical functions in a 2 dimensional manner much like an integrated
circuit designer in the electronic domain. Through this technique, it is
conceivable to manufacture different active and passive regions in various
geometric configurations on a single wafer creating densely function-packed
PICs!
By creating different bandgap energies in neighboring cells via QWI, the
different active regions are able to lase at different wavelengths, creating
a multiple wavelength laser array.
Quantum well intermixing was used to engineer the bandgap of the AWG filter
to be transparent, while the broadband photodetector array converts light
energy into electrical energy.
Quantum well intermixing is able to monolithically integrate a DFB laser and
an electro absorption modulator by adjusting the bandgap energies of the 2
regions on the wafer. The DFB section has bandgap energy close to photonic
range, while the EA Modulator section has higher bandgap energy at zero
bias.
3. QWI enables efficient PIC supply chains
DenseLight envisions the day when the the design of photonic integrated
circuits can be composed on a set of common photonic devices such as laser
sources, SOAs (semiconductor optical amplifiers), demultiplexing filters,
electro-absorption modulators, photodetectors, passive waveguides and
couplers. These devices are characterized and standardized as a set of
photonic device design libraries.
A photonic foundry firm should be able to take such a design and manufacture
it in mass volumes. This model ultimately points the way to an outsourced
photonic supply chain where it is feasible for firms to segregate design,
manufacture and distribution activities reducing the need for vertically
integrated firms. With such segregation, outsourcing is possible, yielding
benefits from economies of specialization in design firms and economies of
scale in foundry firms. Hence, better and cheaper photonic components will
eventually empower optical networks.
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