LANL quantum-dot technology available for licensing

January 11, 2005, Los Alamos, NM--Los Alamos National Laboratory (LANL) is making its semiconductor quantum-dot technology available for commercial licensing. The LANL quantum-dot portfolio includes the use of quantum dots for a broad range of applications including lighting, solar energy, lasers, and coatings.

Specific items in the portfolio include two novel quantum-dot light-emitting-diode (LED) architectures, three sol-gel methods to produce materials with a high loading of quantum dots, a method of dynamic holography, and a method to dramatically raise the efficiencies and to reduce thermal losses in photonic devices such as photovoltaic solar cells.

Many lighting applications--including general lighting, displays, and traffic signals--can benefit from efficient, color-selectable light sources. Quantum dots are chromophores that combine size-controlled emission colors and high emission efficiencies with excellent photostability and chemical flexibility. Applications of nanocrystals in light-emitting technologies have been significantly hindered, however, by difficulties in achieving electrical injection of carriers. The LANL portfolio includes two newly developed architectures that advance the state of the art in this area.

The first LED architecture is a quantum-dot-based light-emitting diode in which semiconductor quantum dots are incorporated into a p-n junction formed from gallium nitride (GaN) injection layers. The critical step in the fabrication of these quantum-dot/GaN hybrid structures is the use of a novel deposition technique--energetic neutral-atom-beam lithography/epitaxy--that allows for the encapsulation of nanocrystals within a GaN matrix without adversely affecting either the quantum-dot integrity or emission efficiency.

The second LED architecture uses a noncontact nonradiative energy transfer from a quantum well to produce light from an adjacent layer of quantum dots. The present embodiment includes an indium gallium nitride quantum well injected with electron-hole pairs with a covering layer of cadmium selenide/zinc sulfide quantum dots. Instead of trying to inject the electron-hole pairs needed for light emission across the insulating organic layer coating the quantum dots, LANL's technology uses a nonradiative transfer process known as Förster energy transfer.

The three new sol-gel methods in the LANL portfolio enable the preparation of solid composites that incorporate colloidal quantum dots as well as colloidal metal nanocrystals. These processes enable production of transparent solid-matrix materials and coatings with beneficial properties that depend on the composition of the encapsulated nanocrystals. The sol-gel-based solutions are highly processable and can be used to form solid composites in the shape of planar films or can be used to mold solid composites of various other shapes and configurations. All three methods have been refined and can be commercialized immediately. Applications include nanocrystal films, photonic devices (for example, LEDs, optical switches, optical amplifiers, and lasers), coatings and UV filters.

The new method of dynamic holography harnesses the absorptive properties of quantum dots to yield holographic gratings that have ultrafast response, high efficiencies, greatly improved photostability, and tunable optical properties. Measurements indicate that the temporal diffraction efficiency (TDE) obtained to date is comparable to the highest results reported for polymeric materials.

The final component of the portfolio is a method to raise efficiencies and reduce thermal losses in photonic devices such as photovoltaic solar cells. Specifically, it is a method of efficient carrier generation via carrier multiplication (producing additional carriers in semiconductor materials from initially generated, high-energy carriers). Although inefficient in bulk semiconductors, carrier multiplication becomes highly efficient in quantum-confined materials. This enhanced carrier multiplication is beneficial to any optical or electronic device application that benefits from the efficient production of carriers. Applications include photovoltaic solar cells, photodiodes with sensitivity from UV to far-IR wavelengths, optical switches, and optical amplifiers.

Information about LANL quantum-dot research is available at quantumdot.lanl.gov. Information on partnering mechanisms can be found at www.lanl.gov/partnerships/.

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