Ultrafast intersubband relaxation dynamics at 1.55 μm in GaN/AlN multiple quantum disk nanocolumns

We observed intersubband transition in GaN/AlN multiple quantum disk (MQD) in nanocolumns by absorption spectra. We also investigated ultrafast relaxation dynamics at 1.55 μm by time-resolved saturable absorption. We have found that the temporal response of nanocolumns is almost the same as the multiple-quantum-well (MQW) sample. This indicates that the delay caused by multiple scatterings in MQD nanocolumns is negligible. The saturation intensity for the Brewster configuration in MQD was also estimated.