Temperature dependence of intersubband scattering in multiple quantum well structures

The temperature dependence of intersubband scattering in n-modulation-doped GaAs/Al_xGa_1-xAs quantum well structures is systematically investigated for the first time by an infrared bleaching technique. In a highly doped sample, where the excited well subband is located above the bottom of the potential minimum of the barrier, a ground state recovery time of several picoseconds is found at T=300 K. At temperatures below 200 K an additional non-exponential component appears extending over approximately 100 ps. In samples where the energy of the excited well subband is lower than the energy of the subbands of the barrier potential minimum, the direct intersubband transition from the excited subband to the lowest subband is observed at T=10 K( tau approximately 2 ps). With rising temperature the measured time constants increase. The results are discussed taking into account the band structures of the samples.