Researchers create multi-colour LEDs

A team of University of California scientists at Los Alamos National Laboratory have developed what it claims is the first inorganic, multi-colour light-emitting diodes based on colloidal quantum dots encapsulated in a gallium nitride semiconductor.

The work represents a 'hybrid' approach to the development of solid-state lighting that offers the advantages of reduced operating expenses, lower energy consumption and more reliable performance.

The team reports on the first successful demonstration of electroluminescence from an all-inorganic, nanocrystal-based architecture where semiconductor nanocrystals are incorporated into a p-n junction formed from semiconducting GaN injection layers.

The LEDs use a novel type of colour-selectable nanoemitters, colloidal quantum dots and make use of emerging GaN manufacturing.

Semiconductor nanocrystals, known also as quantum dots, are attractive nanoscale light emitters that combine size-controlled emission colours and high emission efficiencies with chemical flexibility and excellent photostability.

The use of nanocrystals in light-emitting technologies has always been hindered by the difficulty of making direct electrical connections to the nanocrystals.

By putting the quantum dots between GaN injection layers, the team has overcome this difficulty.

The secret to making the electrical connection to the dots is the use of a technique developed at Los Alamos that use a beam of energetic, neutral nitrogen atoms for growing GaN films.

The technique, called ENABLE (for energetic neutral atom beam lithography/epitaxy), allows the low-temperature encapsulation of nanocrystals in semiconducting GaN without adversely affecting their luminescence.

By encapsulating one nanocrystal layer or two layers of nanocrystals of different sizes, the researchers have demonstrated that their LEDs can emit light of either a single colour or two different colours.

The two-colour-operation regime is an important step towards creating devices that produce white light.