High-efficiency white LED lighting
The wafer size plays an important role in determining how many LED chips can fit on it. Until now, LEDs are being constructed in flat layers. The more light required, the more wafer area has to be produced. However, LED chips now seem to be following the advanced semiconductor industry in going 3D. Within GECCO (3D GaN for high-efficiency solid-state lighting), researchers successfully assembled LEDs in 3D by exploiting the vertical sidewalls of 3D gallium nitride (GaN) structures. Every LED is a tiny lighthouse, emitting light from the entire vertical surface. The prototype chip has a surface five times larger and on the same substrate than current LED chips, thus generating much more light. According to this model, one can make several thousand additional chips from each wafer. As with the majority of white LEDs, a phosphor material covers its surface, transforming the initially blue light into white light. Arrays of sub-micron 3D GaN LED structures were grown with optimised processes on patterned templates fabricated either by employing conventional or nanoimprint lithography. To achieve the 3D chip geometry, researchers applied a particular masking layer to the wafer above the first deposited semiconductor layers. The growth masks, which were required for selective area growth, were optimised not only for homogeneity and reproducibility, but also for the insulating properties inside the LED chip. The team then used a transparent contact material to coat the 3D GaN columns, thereby ensuring that the driving current can spread across the entire surface. Unveiling for the first time a white, phosphor LED chip, GECCO inched closer to high-efficiency solid-state lightning, even though it did not reach the targeted electroluminescence value (200 lm/W).
Keywords
White LED, GaN, solid-state lightning, 3D chip