As the adoption of patterned sapphire substrates (PSS) continues to rise in the LED industry, the time is now to look ahead to new ideas and theories that have the potential to further advance LED lighting. In particular, recent research surrounding nanoscale patterning proves it has promising applications in the LED industry’s future.
But before diving into new patterning processes, how is PSS currently benefiting the industry?
Etching a pattern directly on to a sapphire substrate increases light extraction, allowing LED manufacturers to create the brightest possible LED lights. There are two main ways patterning can increase the light output of an LED:
1) Patterning promotes lateral growth of the epitaxial layers, reducing epitaxial defect density, thereby increasing the amount of light emission of active quantum well layers.
2) Patterns help scatter the photons that are emitted, effectively expanding the light escape cone and increasing total internal reflection, or TIR, and creating a brighter light.
In these ways, patterned substrates contribute to greater light extraction efficiency. Additional manufacturing efficiencies are available with larger diameter substrates in the form of reduced edge loss, less wafer handling, and potentially greater throughput with each reactor cycle, furthering LED chip manufacturers’ objective of increased lumens per dollar.
How are they made?
To create effective PSS, the structures, which can be in the shape of a cone, dome or pyramid, need to be accurately and uniformly etched. Currently, there are two manufacturing processes that are used to fabricate PSS:
1) Dry plasma etching, the process used for the majority of PSS today because of its greater control of precision and uniformity.
2) Wet chemical etching, which is more scalable and faster than dry plasma etching but produces LEDs that are less effective and efficient.
Great precision is required to maintain uniform patterning over a larger surface; therefore dry plasma etching is the processed used for large-diameter PSS.
Research shows that nanopatterning has the potential to be even more efficient than current micro-patterning practices.
Academic researchers have extensively studied nanopatterned substrates to evaluate their potential impact on light extraction efficiency and internal quantum efficiency. The results are extremely promising, as several reports show that LEDs built on nanopatterned substrates produce a significant further increase in luminous efficiency compared with micropatterns.
While it will still be some time before we see nanopatterning used in commercially available LEDs, nanopatterning is an exciting development that shows great promise for the future of LED efficiency.