| Research on individual quantum dots (QD) has been of great interest in recent years. QDs are an ideal system for the study of fundamental quantum physics because their atomic-like properties can be engineered. They are also promising in applications such as quantum dot lasers and as building blocks of qubits for quantum computing. The optical properties of the individual QDs are crucial to these applications through the physical processes of coherence, quantum entanglement and carrier dynamics in the highly confined semiconductor nanostructures.; Time-resolved micro-photoluminescence is a powerful tool for the optical study of QDs. A major challenge in these experiments is the ability to probe only a few QDs so that inhomogeneous broadening due to an ensemble measurement doesn't obscure much of the interesting physics. This has traditionally been achieved by near-field optical scanning microscopy and special treatment on the sample to limit the numbers of the QDs under study. However, the throughput of the former method is very low, while the latter alters the sample and isolates the QDs from their environment.; We have developed a high-resolution confocal scanning microscope to address these issues. A subsurface solid immersion technique is utilized to increase the numerical aperture as well as to decrease the effective wavelength, resulting in a spatial resolution of ∼300 nm that is truly capable of probing only a few QDs at a time, concomitant with high throughput that enables time-resolved spectroscopy of single sharp lines of individual QDs.; With this new microscopic techinque, spectral images of individual QDs are obtained to map out distributions, to choose single QDs of interest, and to identify spectral lines from the same QD. Power-dependent photoluminescence spectra manifest the excitonic and multi-excitonic processes, indicating strong and complex interactions of carriers within individual QDs. Time-resolved spectroscopy reveals the fast capture and relaxation processes in the self-assembled InGaAs/GaAs QD system, suggesting the existence of a variety of relaxation channels and cascade evolution of multiexcitons. In addition, the strong quantum confinement results in long lifetime of excitons in the ground state that is a requirement for quantum computing. |
