Epitaxial layers of the LED die in phosphor-converted (PC) LEDs are commonly constructed of gallium-based crystals such indium gallium nitride (InGaN). Because of its straight bandgap, which enables effective optoelectronic applications, InGaN has risen in popularity relative to other semiconductor materials. The most effective white LEDs available today are built of InGaN. InGaN LEDs are capable of producing light with efficacies more than 200 lm/W, external quantum efficiencies of more than 60%, and internal quantum efficiencies of more than 70%.
On sapphire, silicon, silicon carbide, or gallium nitride, inGaN epitaxial growth can occur. Since sapphire is the most economical material to support a relatively high quality GaN epitaxial growth, it is nearly solely used to make LEDs nowadays. However, greater than 13% lattice mismatch is produced by heteroepitaxial development of GaN on sapphire, which leads to a high dislocation density in the epitaxial layers. There are more black areas and reduced luminous efficacy when the dislocation density is large. On the other hand, silicon carbide (SiC) is 4.5 times more compatible with the lattice of gaN than sapphire, allowing for more light extraction. SiC's physical features present considerable processing hurdles, which is one of its drawbacks.
Growing GaN atop GaN is a more advanced method. Fundamentally addressing epitaxial restrictions like lattice mismatch and CTE mismatch is GaN-on-GaN technology. As a result, it is possible to fabricate high breakdown voltage devices with very thick layers of GaN that have a high radiative efficiency.
