Abstract

A spatial distribution of luminescent centers with sharp (<0.1meV), spectrally distinct emission lines are revealed in a GaAs/AlGaAs quantum wells[1] using low temperature nearfield scanning optical microscopy [2], a technique where a subwavelength source and/or detector of light in close proximity (<40nm) to the sample is used to probe with a resolution beyond the diffraction limit. These centers are the energy eigenstate components that comprise the inhomogeneously broadened line shape observed in standard far-field photoluminescence. Measurements as a function of temperature, magnetic field, and well width establish that these centers arise from excitons localized by quantum well thickness fluctuations. For sufficiently narrow wells, virtually all emission originates from such centers. Quantities such as diffusion (both thermal and tunneling), lateral confinement energies, lifetimes, g-factors from magnetic field induced spin splittings, diamagnetic energy coefficients of the luminescent states can now be measured at a site-by-site individual quantum level rather than averaged over a statistical distribution. This information can be used in turn to provide a direct local picture of the interface fluctuations and how they vary under different MBE growth conditions. Near-field microscopy/spectroscopy provides a means to access energies and homogeneous line widths for the individual eigenstates of these centers, and thus allows the luminescent components to be identified and characterized with the extraordinary detail previously limited to the realm of atomic physics.

© 1995 Optical Society of America