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-p(z) intraband transition at lambda=1.55 mu m 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 (similar to 160 fs) and a slower (similar to 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/cm(2)) is one order of magnitude smaller than the value measured in nitride quantum wells.