Ultrafast relaxation and optical saturation of intraband absorption of GaN/AlN quantum dots

We report on the measurements of ultrafast relaxation and absorption saturation of the s-pz intraband transition at λ=1.55 μm in GaN/AlN quantum dot superlattice. The recovery time of the intraband absorption is assessed using degenerate pump-probe experiments at room temperature. Measurements reveal a multiexponential decay of the differential transmission with an ultrafast (∼160 fs) and a slower (∼1.5 ps) time constant attributed to the excited state lifetime and to the thermalization time in the ground state, respectively. The saturation intensity of the intraband absorption (<140 MW/cm2) is one order of magnitude smaller than the value measured in nitride quantum wells.