AlGaN-based UV micro-emitting devices for underwater wireless optical communication – SIRENS

The objective of SIRENS is to develop UV microLEDs for underwater wireless optical communications. The selected material platform, AlGaN based alloys, enables to tune the emission spectral range between 380 and 200 nm, as opposed to conventional UV light technologies. As shorter wavelengths increase light scattering, there is no need for a rigorous alignment between the transmitter and the receiver, enabling non-line of sight underwater wireless optical communications system to be exploited in the real oceanic environment at the expense of slightly more optical power required. In addition, solar radiation noise is highly reduced below 320 nm and water absorption coefficient remains relatively low at 300 nm. Finally, by adjusting the wavelength, potential harm caused by the 230-300 nm spectral window to the DNA’s structure of submarine life can be avoided. Regarding the device, advantages of microLEDs over conventional millimetre LEDs are improved light extraction, current spreading, integration compatibility and better thermal dissipation thus enabling high current density and large output power. Besides the boost in optoelectrical properties, as the microLED diameter becomes smaller, higher modulation bandwidth is reached and thus, higher data transmission rate. However, the top-down etching used to create microLEDs generates surface damage that limit the overall efficiency. The SIRENS project proposes to develop and exploit an original 3D micro-architecture that combines top-down and bottom-up approaches to avoid these detrimental surface effects. Moreover, the architecture will integrate the use and controlled removal of a sacrificial GaN layer to easily transfer the µLEDs on a host substrate, among other advantages. As a result, SIRENS targets to achieve 10 to 60 µm diameter AlGaN-based UV µLED arrays emitting at 300-320 nm with an output power and bandwidth larger than 1 mW and 400 Mhz.