Magneto-optical properties of ring-shaped self-assembled InGaAs quantum dots

We report on measurements of the magneto-optical properties of excitons confined in ring-shaped self-assembled semiconductor quantum dots. The rings are embedded in a field-effect structure that allows the number of confined electrons to be set electrostatically. In addition, electron-hole pairs are generated optically. The resulting photoluminescence spectra of neutral, singly and doubly charged excitons were measured at 4.2 K as a function of the applied magnetic field (0-9 T). The emission energy shows a diamagnetic shift as well as a Zeeman splitting. We measured the emission of different charge states of the exciton in many individual dots, In a few of the measured rings, a new behavior was observed, namely a clear departure from the low field diamagnetic dispersion for fields larger than 6 T. (C) 2002 Elsevier Science B.V. All rights reserved.