Substrate 
The semiconductor layer of the semiconductor laser and the LED light emitting portion, is grown on the substrate made of crystallized. Depending on the substrate used in the LED light emission wavelength and selectively used. If the blue LED and white LED, etc. GaN-based semiconductor material of the LED chip, using sapphire, SiC, and Si, etc. as the substrate, if the red LED AlInGaP-based material such as the use of LED chips, such as GaAs is used as the substrate.
 
A reason for the use of LED emission wavelength is different substrates in order to select the LED light emitting part - of the semiconductor crystal lattice constant as close to the lattice constant of the substrate material is inexpensive. This gap between the lattice constant (lattice mismatch) will be reduced, the possibility of disturbing light emission of the crystal defects in the semiconductor layer will be reduced. But also to reduce the unit price of LED chips. Further, the current density and optical output denser blue-violet semiconductor laser element, the use of expensive GaN substrate. GaN substrates are also used part of the blue LED.