Quantum dot intermixing with thermal and laser annealing

Abstract

Photoluminescence (PL) was used to investigate the interdifflision of self-assembled InAs/GaAs quantum dots (QDs) treated by rapid thermal annealing (RTA) and laser annealing. The observation ofintense and sharp shell structures confirmed that the QDs retained their zero-dimensional density of states. In addition, three main effects of alloy intermixing were demonstrated in QDs having different intersublevel spacings. The emission has been strongly blue-shifted, up to -200 meV for RTA samples and 298 meV for the laser annealed ones. The intersublevel spacing was tuned between 6O meV to '-'25 meV in the RTA case, but down to -12 meV in the case of laser-induced intermixing. Finally the inhomogeneous broadening linearly decreased from a FWHM of-46 meV down to smaller than 15 meV for RTA and 8 meV in the most extreme case of laser annealing. For samples annealed at the highest temperatures, the most energetic shells of QDs become unbound. Across varying samples, the result ofthe intermixing was to increase the uniformity of their PL spectra. A onedimensional model of Fickian diffusion for the growth direction was used to model their PL emission. Rapid thermal annealing and laser annealing provide two additional ways of manipulating the energy levels of self-assembled QD ensembles by tuning the intersublevel energy-spacing and the number ofconfined states.