Subpicosecond thermalization of carriers in polar GaN/AlN quantum dots

We investigate at room temperature the thermalization and recombination dynamics of near-resonantly photogenerated carriers in c-plane GaN/AlN wurtzite quantum dots (QDs) using time-resolved photoluminescence and non-degenerate pump–probe differential transmission. Owing to a continuous gradient in dot height, the QD ensemble exhibits a broad emission range from 3.5 to 4.5 eV. Time-resolved photoluminescence reveals two distinct recombination lifetimes associated with two families of QDs with different morphologies, whose emission energies are governed by the interplay between the quantum-confined Stark effect and lateral confinement. Pump–probe measurements evidence an ultrafast carrier thermalization with subpicosecond rise times on the order of 200 fs, significantly shorter than in other epitaxial III–V QD systems. At longer delays, the relaxation dynamics is non-exponential and strongly dependent on both carrier density and probe energy. It is reproduced by a phenomenological model based on multi-carrier scattering processes, whose efficiency progressively vanishes as the probe energy approaches the luminescence maximum, where interband recombination dominates.