Band gaps of semiconductors
The band gaps of III-V compound semiconductors such as gallium arsenide are restricted to 1-2.5 eV, so they can only be used for red- and yellow-emitting devices. For shorter emission wavelengths, the most suitable materials are the III-V nitrides and II-VI selenides. The II-VI materials have similar lattice constants to gallium arsenide, while the bonds for the III-V nitrides are much shorter. Materials with direct band gaps (red) emit light more efficiently that those with indirect band gaps (green).