The technique uses a thin layer of titanium metal to provide a crystalline template for the GaN to grow on and a silicon dioxide layer patterned with tiny holes to control the shape and orientation of the growing crystals.
Thin layers of titanium (blue), low temperature GaN (green) and silica (orange) turn a sheet of glass into an ideal substrate to grow GaN LEDs © Nat. Photon.
Nature Photonics - Nearly single-crystalline GaN light-emitting diodes on amorphous glass substrates
The complexity of the manufacturing process could cancel out a lot of the cost-savings of using glass substrates, says Colin Humphreys from the University of Cambridge, UK, who has developed ways to grow GaN LEDs on the large silicon wafers used by the microchip industry. 'It's a lot of separate steps and if you have to take your specimen out of a reactor and put it into another piece of equipment, and then another, and another, that adds enormously to manufacturing costs.'
Choi admits that the performance of the LEDs is not quite as good as those grown on sapphire wafers, but points out that the work is still at proof of concept stage. He adds that the drivers for the project were not only cost and scalability, but also overcoming the scientific stereotype that single crystalline GaN can only be grown on lattice-matched crystalline substrates such as sapphire or silicon.
Single-crystalline GaN-based light-emitting diodes (s-LEDs) on crystalline sapphire wafers can provide point-like light sources with high conversion efficiency and long working lifetimes. Recently, s-LEDs on silicon wafers have been developed in efforts to overcome the size limitations of the sapphire substrate. However, to create larger, cheaper and efficient flat light sources, the fabrication of high-performance s-LEDs on amorphous glass substrates would be required, which remains a scientific challenge. Here, we report the fabrication of nearly single-crystalline GaN on amorphous glass substrates, in the form of pyramid arrays. This is achieved by high-temperature, predominant GaN growth on a site-confined nucleation layer with preferential polycrystalline morphology through local hetero-epitaxy. InGaN/GaN multiple-quantum wells formed on the GaN pyramid arrays exhibit a high internal quantum efficiency of 52%. LED arrays fabricated using these GaN pyramid arrays demonstrate reliable and stable area-type electroluminescent emission with a luminance of 600 cd m^−2.
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