Molecular Beam Epitaxy

9Applications of III–V Semiconductor Quantum Dots in Optoelectronic Devices

Kouichi Akahane and Yoshiaki Nakata

National Institute of Information and Communication Technology, Tokyo, 184‐8795, Japan

9.1 Introduction: Self‐assembled Quantum Dots

Semiconductor quantum dots (QDs) have the potential to improve the properties of optical devices such as semiconductor lasers, semiconductor optical amplifiers (SOAs), and so on. They are of great interest due to their delta‐function‐like density of states, in contrast to conventional bulk semiconductors which have a density of states with a parabolic shape. In particular, if QDs are introduced in semiconductor lasers as gain media, they improve their performance [1–8]. For example, the temperature dependence of the threshold current in a semiconductor laser will disappear because the injected carriers at the QD's discrete energy levels are not allowed to redistribute, even if the temperature increases. However, the fabrication of a QD structure, which can be regarded as a three‐dimensional confinement of carriers with a size of a few tens of nanometers, is more challenging compared to the fabrication of a quantum well (QW). QWs have one‐dimensional confinement of carriers, which can be achieved by growing a layered semiconductor structure using molecular beam epitaxy (MBE). This inspired Goldstein et al. [9] to develop a method for developing a QD structure in the lattice‐mismatched materials system of a III–V semiconductor. They showed a ...