What is Band-Gap Engineering?

Direct semiconductors can emit light, the frequency of which depends on the band gap of the semiconductor. Gallium arsenide (GaAs) emits infrared light, while aluminum arsenide (AlAs) emits yellow-green light (visible wavelength range).

During »band-gap engineering«, both semiconductors (here GaAs and AlAs) are mixed so that the new semiconductor has a different bandgap. The more you mix GaAs, the smaller the bandgap of the new semiconductor becomes, and thus, the emitted light shifts to the infrared range.

However, if you add more AlAs, the emitted light shifts into the visible wavelength range. This combination of semiconductors with different band gaps to create new band gaps of the desired size is known as »band-gap engineering«.