Replacing epitaxy with bonding could pave the way for 4” substrates.
Gallium nitride (GaN) based blue-white HB-LEDs (High-Brightness LEDs) are now at full production level, posting a CAGR of over 51% and targeting markets in automotives, IT, and general lighting. The market could get a further boost if new engineering technologies such as Smart Cut™ succeed in bringing down substrate prices. Currently, most GaN wafers are grown epitaxially either on a silicon carbide (SiC) or sapphire handle substrate. While GaN and SiC have an acceptable lattice match, SiC is very expensive. The GaN-sapphire lattice mismatch is greater, but as sapphire is cheaper, it currently has the lion’s share of applications. In either case, the substrates used are just 2” in diameter. Growing GaN epitaxially on 4” wafers is not terribly feasible because it tends to bow.
However, if the market is to continue to grow substantially, a way will be needed to manufacture
flat, 4” wafers with a thin active layer of GaN.
Recent GaN announcements from Picogiga and Soitec concerning Smart Cut as an alternative technology are very promising, if layer transfer and bonding can eliminate the bowing problem, as seems possible. •