Growth conditions, structural and optical properties of GaN quantum dots (QDs) grown by plasma-assisted molecular beam epitaxy will be examined. It will be shown that, depending on the Ga/N ratio value and on growth temperature, the growth mode of GaN deposited on AlN can be either of the Stranski-Krastanow or of the Frank-Van der Merwe type. It will be shown that vertical correlation results in a red shift and in a narrowing of the photoluminescence spectra.
Growth of Eu-doped GaN quantum dots embedded in AlN will be described. Intense photoluminescence associated with Eu has been measured, with no GaN band-edge emission, as an evidence that carrier recombination mostly occurs through rare earth ion excitation. Persistent photoluminescence of Eu-doped GaN quantum dots as a function of temperature has been put in evidence, as a further confirmation of the recombination of confined carriers through Eu ion excitation.