BIEXPONENTIAL INTERSUBBAND RELAXATION IN N-MODULATION-DOPED QUANTUM-WELL STRUCTURES

Intersubband scattering in an n-modulation-doped GaAs/Al0.31Ga0.69As q uantum-well structure is systematically investigated as a function of temperature and pump intensity. For the first time biexponential relax ation is observed during infrared bleaching experiments. The fast comp onent with a time constant of similar to 1 ps, which represents the de population of the first excited well subband, is found to dominate the signal more and more with decreasing temperature and pump intensity. The decay time of the slower component rises with decreasing temperatu re from tau(2) = 8 ps at T = 300 K to tau(2) = 23 ps at T = 10 K. This component is believed to be connected with a carrier transfer to the potential minima in the barrier layers. The intensity dependent excita tion mechanism and the relaxation processes are discussed with the hel p of detailed numerical simulations. (C) 1996 Academic Press Limited