GaN Nanowire Light Emitting Diodes on Metallic Substrates – MetalliGaN

Since general lighting represents about 20% of the electricity consumption worldwide, it is essential to promote energy efficient lighting systems. The wide spread use of Light Emitting Diodes (LEDs) for Solid State Lighting applications represents the best solution for this urgent environmental and economical issue. Although white LEDs based on nitride semiconductors have rapidly progressed over the last years, several issues are still critical and related in particular to cost and efficiency, which requires a rapid breakthrough to reach values compatible with a larger scale industrialization and usage.
The project focuses on these two issues - cost and efficiency – by proposing a radically different approach: the use of very low cost / large area metallic substrates for the deposition of very efficient nitride based core-shell nanowires. This project is of industrial nature. The consortium gathers three companies and two public laboratories.
In this project we propose to use Ni- or Fe-based metallic foils from the French company APERAM / IMPHY and further develop them for specific application to nanowire LEDs. These foils are up to 100 times less expensive per unit surface area than the usual sapphire substrates and can be very highly textured, which allows for vertically oriented growth of the nanowires. They can also sustain the fairly high GaN nanowire OMVPE growth temperatures of about 1000°C. Their high thermal and electrical conductivities, together with their high optical reflectivity will greatly simplify the technological processes and thus reduce the overall cost of the LED further. In order to favour uniform emission on the whole metallic wafer and in order to facilitate the integration processes, the nanowires will be deposited by selective area growth through a deposition mask. The substrate patterning development will be undertaken by SILSEF, a French SME, whose present technology, as developed for silicon wafers, will be extended to metal foils. The nitride core-shell nanowires will be grown by OMVPE at CEA/ LETI which has acquired an extensive expertise in the field of nanowire LEDs. LETI will also be in charge of the nanowire integration process for actually devising the LED and, for this purpose, will benefit from the know-how of LMGP for conformal deposition of very efficient indium-free transparent conducting oxides. Confocal microscopoy will be used to assess the electroluminescent and photoluminescence properties of the integrated nanowires together with cathodoluminescence on single nanowires. Finally, HELIODEL, a spin-off company from CEA/LETI, whose core business is related to GaN nanowire LEDs for lighting, will act as the end user of the project, and, as such, will test the electro-optical properties of such nanowire LEDs on metals.
It is worth noting that this project opens the way to a major and radically new approach towards the realisation of LEDs. Indeed, it proposes a new technological process compatible with roll to roll or continuous flow deposition methods similar to those used or being developed for photovoltaic production processes, allowing an even greater gain in cost and production volume for a new generation of low cost, high efficiency LEDs.