| The growth of self-assembled quantum dots growth is a strain-driven phenomenon, usually taking place in lattice-mismatched epitixial growth. Electrons and holes confined in these nanoscale man-made objects, give out atomic-like sharp optical transitions. This kind of emission can be used in quantum information processing if the optical extraction efficiency is high enough, which is possible by embedding QDs into a micro-scale optical cavity. This enhancement effect can be estimated as a Purcell effect, which is the largest when the cavity Q is as high as possible and the cavity volume is as small as possible. A microdisk cavity is one of the widely used microcavities in cavity-QED research. In this thesis, we discuss QD lasing in the smallest microdisk (1.8mum) reported. From the cavity mode lines tuning through QD exciton lines, it approaches single QD lasing, usually a Purcell factor of 80 is required to achieve this goal. When the QD is at resonance with a cavity mode, a lasing threshold as low as 10A/cm2, or 300nW for each disk is estimated. Another issue is also important for QD emission to achieve better coupling with the cavity mode, that is, spatial coupling. Therefore, we developed a regrowth technique to place QDs close to the anti-node of the microdisk whispering-gallery modes. Under our preferred growth condition with a long diffusion path for In adatom, the QDs will only appear at the disk edge. We notice an obvious size effect for this regrowth: on larger disk of 30∼m diameter, the QD linear density will saturate at 6/mum; while on smaller disks of 3∼4mum diameter, there are usually only 1∼3 QDs in the whole disk plane. Our micro-PL shows a standard single QD emission signature, as well as a large splitting for the neutral excitons, with opposite linear polarization. This regrowth technique can provide sharp exciton peaks as well as a cavity Q of 4,000 for the small disks of 3∼5 mum diameter. |
