As a substrate sapphire has two main advantages: first, there is existing industry expertise with the material and production is set up to use sapphire; and second, there is high availability of low-cost sapphire, enabling inexpensive LEDs to be produced.
Of course, there are also a number of disadvantages to sapphire; however, none of them are critical. Disadvantages include lattice mismatch, thermal mismatch, and electrical and thermal conductivity.
Almost all top LED suppliers — including Nichia, Osram Opto, Lumileds, Seoul Semiconductor, Epistar and San’an — use sapphire wafers. Plessey, Lattice Power and Samsung use silicon substrates. Cree is the main supplier for silicon carbide substrate, which will not be adopted by other suppliers because of its cost and lack of availability and expertise. Soraa is known for bulk gallium-nitride (GaN) substrate, which is a good substrate for LEDs, but is more expensive than sapphire and not available on larger wafers.
Sapphire is expected to remain the clear leader, when it comes to substrates used to make LEDs. Silicon has not succeeded as a replacement for sapphire, because of lower yield, lattice mismatch, and the falling price of sapphire wafers. However, it will be interesting to see how much Samsung — which can make use of silicon economies of scale more effectively than other companies — will expand its silicon-based production, which currently comprises only a minority of its production. Other substrates, including silicon, silicon carbide and bulk GaN, are not expected to make substantial gains in the next few years.
- Sapphire was used as the substrate for an estimated 96.3 percent of LEDs produced in 2015, according to the latest research from the IHS LED Intelligence Service, rising to 96.7 percent in 2020
- Sapphire has been boosted by falling prices in 2015, especially for 4-inch wafers comprising 55 percent of the market (by area capacity) in 2015; 6-inch wafers, a growing category, accounted for 9.9 percent in 2015
- Four-inch sapphire wafers are used by Samsung, Seoul Semiconductor, Epistar, San’an and other suppliers, while six-inch wafers are preferred by Osram, Lumileds, LG Innotek and Cree