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 DensePIC^TM 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