Colour-tuneable inorganic micro-display

Conventional LEDs are monochromatic emitters, that is to say that the colour of light they emit is fixed by the design of the epitaxial material they have been fabricated from. For many applications, such as micro-displays, optical communication, spectroscopy or neurophotonics, it's desirable to have a light source capable of generating light of different colours.

One way of achieving a multi-colour light source is to mechanically pack LEDs, each emitting a different colour, together. By mixing the light from the different LEDs, a range of colours can be emitted. There are disadvantages to this approach, including the difficulty in packaging large arrays of different LEDs together and correctly balancing the emission from each emitter to generate the desired colour. Another approach is to integrate colour-converters, such as phosphors or light-emitting polymers, with LEDs. This also has drawbacks, such as complicating the device fabrication.

As such, we have reported a colour-tuneable micro-LED array, fabricated from a single high-indium content InGaN structure [1], which is capable of tuning the emission colour of individual pixels within the array through direct electronic control. Increasing the injection current to the pixels changes the emission colour. This is illustrated in the image below, where the pixels emit red at low current, with their emission changing to green then yellow at higher currents. The CMOS drivers which control the pixels are pulse-width modulated in order to maintain a constant brightness.

This device represents a novel high-resolution colour-tuneable micro-display, capable of emitting dynamic images suitable for a variety of applications, including micro-displays [2]

References

[1] Z. Gong et al., “Electrical, spectral and optical performance of yellow–green and amber micro-pixelated InGaN light-emitting diodes,” Semiconductor Science and Technology, vol. 27, no. 1, p. 015003, Jan. 2012.

[2] S. Zhang et al., “CMOS-Controlled Color-Tunable Smart Display,” IEEE Photonics Journal, vol. 4, no. 5, pp. 1639–1646, Oct. 2012.