Phonon sidebands of intersubband absorption in AlGaN/GaN high-electron-mobility transistors

Femtosecond two-color pump-probe experiments in the mid-infrared are performed on intersubband transitions in GaN=Al0:8Ga0:2N heterostructure. In these experiments, we observe around zero time delay distinct phonon sidebands, whic disappear because of spectral diffusion with a time constant of 80 fs. The signal itself decays with a time constant of 380 fs. Th independent boson model agrees very well with all observed results.