Manipulation of confined electrons/excitons and electron-photon interaction in quantum dots is significantly important for establishing nanophotonics defined as photonics related to nanometer-scale structures and optical phenomena as well as device applications. It was 1982 when the concept of quantum dots was first proposed for application to semiconductor lasers, theoretically predicting temperature insensitive threshold current. This unique features results from -function like density of states realized by the quantum dots. After this proposal, in the 1980's, most of significant characteristics of the quantum dot lasers were predicted. These include low threshold current density , enhanced modulation bandwidth and small linewidth enhancement factor. Moreover, the concept of p-doping and tunnel structures for enhancing carrier injection were discussed. Discovery of formation of a three dimensional small structure in lattice mismatched InAs/GaAs in 1985 stimulated the research on fabrication of self-assembled quantum dots leading to demonstration of quantum dot lasers. In particular, recent remarkable progress in the p-doped layers which increase optical gain and differential gain in quantum dot lasers has realized 1.3μm p-doped quantum-dot lasers with temperature-insensitive eye-opening under 10-Gb/s modulation without current adjustments in a temperature range between 20 and 80°C.
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