LOW-TEMPERATURE NEAR-FIELD PHOTOLUMINESCENCE SPECTROSCOPY OF INGAAS SINGLE QUANTUM DOTS

We investigate InGaAs single-dot photoluminescence spectra and images using a low-temperature near-field optical microscope. By modifying th e commonly used near-field technique, a high spatial resolution and hi gh detection efficiency are achieved simultaneously. Local collection of the emission signal through a 500 nm (lambda/2) aperture contribute s to the single-dot imaging with a lambda/6 resolution, which is a sig nificant improvement over the conventional spatially resolved spectros copy. Tailoring the tapered structure of the near-field probe enables us to obtain the emission spectra of single dots in the weak excitatio n region, where the carrier injection rate is similar to 10(7) exciton s/s per dot. By employing such a technique, we examine the evolution o f single-dot emission spectra with excitation intensity. In addition t o the ground-state emission, excited-state and biexciton emissions are observed for higher excitation intensities. By a precise investigatio n of the excitation power dependences of individual dots, two-dimensio nal identification of their emission origins is obtained for the first time.