Single quantum dot spectroscopy

Semiconductor quantum dots localize the exciton in all three spatial dimensions and completely quantize the exciton energy spectrum. In the past, experimental studies of quantum dots have been severely hampered by large fluctuations in the dot size which leads to large inhomogeneous broadening in the optical spectra. To avoid this problem, we have developed the capability to measure the photoluminescence (PL) spectra of single quantum dots which are formed naturally from the monolayer-sized interface fluctuations in a thin GaAs/AlGaAs quantum well. This is accomplished by reducing the laser spot size through the use of apertures patterned in an Al mask evaporated directly on the sample surface. By exciting and detecting through a single aperture we obtain PL spectra in which each spectrum is composed of quantum PL lines, the number of which is reduced by going to smaller apertures.