Quantum dots are unique material structures in which the carriers are three-dimensionally confined and the intrinsic properties altered by the quantum effects to be exploited by controlling their size.Quantum dots have introduced a new form of quantum engineering of fundamental quantum physics and application of quantum devices.In the last 30 years,quantum dots have reallybegun to progress from an interesting theoretical idea to structures of real practical importance for device technology thanks to the development of fabrication technology for precise control of the size,composition and thickness of the material at the atomic and molecular levels.The quantum functions or better performances are highly expected due to the quantum confinements of electrons and holes,since the continuous energyband structures become discrete.