Study of piezoelectric field in GaN quantum discs embedded in AlGaN nanocolumns

We report on recombination kinetics, by means of time resolved photoluminescence technique, on GaN quantum discs embedded in strain free AlGaN nanocolumn. The emission of the 100 angstrom QD shows a very long time decay (about 20ns), denoting a small radiative rate; in contrast, fast decay time are observed in the case of 20 angstrom disc (similar to 450ps). At the same time a large blue shift of the PL band is found in the 100 angstrom. QD when increasing the power excitation while the PL of the 20 angstrom QD does not show any energy shift. The whole phenomenology can be interpreted in terms of piezoelectric polarization fields inside the strained GaN QDs embedded in relaxed AlGaN nanocolumn.