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Gallium nitride based micro-displays comprise LED epi-structures pixelated on a micro-scale (pixels of a few microns to a few 10's of microns in dimension on a similar pitch) such that the pixels can be electronically addressed either individually or in matrix formats. Such displays can be implemented across the full wavelength range covered by gallium nitride alloys, from the deep ultraviolet to the amber/red. Although typically operated on their growth substrates (usually c-plane sapphire) with flip-chip bonding to an electronic backplane, it is possible to transfer the devices to other substrates such as glass via pick-and-place techniques including micro-transfer printing, to facilitate novel formats, array scaling and multi-colour operation. These emissive devices are robust and operate at brightness levels that can exceed other formats of micro-display.
In addition to direct view and projection display applications, the technology also enables a host of other applications. These include optrodes for optogenetics and neuroscience; mask-free photolithography and direct writing; visible light communications; and structured light imaging. For optical communications, the benefits include not only the ability to modulate the individual pixels at data rates that can exceed 1Gb/s (enabled by the high current densities of above 1kA per square cm that the pixels can sustain) but also the capability to implement novel forms of spatial modulation and spatial multiplexing, such as space-shift keying and MIMO [1]. In structured lighting, very high frame rate (kHz to potentially MHz) projection of binary mask pattern sequences is possible, facilitating novel forms of optical navigation, tracking and imaging functions [2].
[1] S. Rajbhandari et al., "A review of gallium nitride LEDS for multi-Gb/s visible light data communications", Semicond. Sci. Technol, , 32, 023001 (2017).
[2] J. Herrnsdorf et al., "Positioning and space-division multiple access enabled by structured illumination with light-emitting diodes", J. Lightwave Technol., 35, 2339 (2017).
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