Semiconductor quantum dots formed by energy-band engineering have potential applications in the novel optoelectronic devices as an active region materials because of their unique optoelectronic properties.

Applications of semiconductor energy-band engineering into the mid-infrared quantum-cascade lasers with different active region structures such as three wells vertical transition active region,superlattice active region,strain-compensated quantum well active region,bound-to-conti-nuum transition active region and four wells double-phonon resonance active region were introduced.

The characteristics of a heterojunction bipolar transistor (HBT) depends closely on the properties of the material system and can be improved greatly by bandgap engineering.