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 indium phosphide substratemeasuring only 6mm 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.