Optical properties and growth of self-assembled quantum dots (SAQDs) for optoelectronic device applications are discussed. After briefly reviewing the history of research on QD lasers, we discuss growth of InAs SQDs including the light emission at the wavelength of 1.52)mum with a narrow linewidth (22 meV) and the area-controlled growth which demonstrates formation of SAQDs in selected local areas on a growth plane using a SiO)-2) mask with MOCVD growth. Then properties of the InGaAs AQDs are investigated by the near- field photoluminescence excitation spectroscopy which reveals gradually increasing continuum absorption connected with the two-dimensional-like (2D-like) wetting layer, resulting in faster relaxation of electrons due to a crossover between OD and 2D character in the density of states. Moreover, we have investigated InGaN self-assembled QDs on a GaN layer achieving the average diameter as small as 8.4nm and a strong light at room temperature. A laser structure with the stacked InGAN QDs embedded in the active layer was fabricated and room temperature operation of blue InGaN QD lasers was achieved under optical excitation. Carrier confinement in QDs was examined using near-field $DAL- photoluminescence measurement: A very sharp spectral line emitted from excitons in individual InGaN QDs was observed. Establishing AlGaN/GaN DBR of high quality, we succeeded in lasing action in InGaN blue light emitting VCSELs. Enhancement of spontaneous emission is demonstrated. Finally, perspective of QD lasers.
"Progress and prospect of quantum dot lasers", Proc. SPIE 4580, Optoelectronics, Materials, and Devices for Communications, (19 October 2001); doi: 10.1117/12.444959; https://doi.org/10.1117/12.444959