In recent years, self-assembled quantum dots (SAD) have emerged as a model system for zero-dimensional (0D) behavior in semiconductors. The high quality of the material, the relative ease with which the dots can be fabricated, and the wide variety of material systems in which self-assembly occurs makes these structures highly relevant both for fundamental physics and technology. Since the quantum dots are man-made and all slightly different, inhomogeneous broadening obscures much of the interesting physics in this system when large ensembles of dots are studied, and the resolving power of conventional optics is in general insufficient to distinguish individual or a small number of dots. It is sometimes possible to fabricate samples with somewhat lower dot densities, but in those cases important phenomena such as coupling between neighboring dots becomes unobservable.; Near-field optical scanning microscopy offers a solution to this dilemma. This technique is a form of scanning probe microscopy, similar to atomic force microscopy and scanning tunneling microscopy, and involves the scanning of an aperture small (∼100nm) compared to the wavelength of light, very close (25nm) to the sample under study. When using this aperture to illuminate the sample and/or to collect the optical signal from the sample, spatial resolution is determined solely by the aperture size, allowing the Rayleigh criterion to be violated.; This thesis treats a series of optical spectroscopy experiments performed on SAD's, mostly using a cryogenic near-field microscope operating at 4.2 K. We have focused on the role of the thin quantum well, known as the wetting layer (WL), in which the SAD's are laterally embedded. We show that the influence of the wetting layer on the physics of the systems is much larger than has previously been assumed, giving rise to several distinct phenomena, such as interdot excitation transfer and spectral diffusion in individual quantum dots. We show that these phenomena can be explained by fluctuations in the composition and thickness of the WL, known to exist in SAD samples.
展开▼
