Ultrafast carrier capture in quantum well structures

The authors present an exptl. and theor. study of the carrier capture time into a semiconductor quantum well. The carrier capture time was obtained by measuring both the rise of the quantum well (QW) population using time-resolved luminescence measurements and the decay of the barrier population using pump-probe correlation expts. In the 1st technique, the authors compare the QW rise-times after direct (below the barrier band gap) and indirect (above the barrier band gap) excitation to eliminate the effects of relaxation and exciton formation in the quantum well. The authors report the 1st exptl. observation of oscillations in the carrier capture time between 3 and 20 ps as a function of quantum well thickness, obtained from both techniques. The obsd. capture times are, for the 1st time, in agreement with theor. predictions from an ambipolar capture model