CARRIER CAPTURE INTO A SEMICONDUCTOR QUANTUM-WELL

We experimentally observed an oscillating carrier capture time as a function of quantum well thickness. The capture times were obtained in a separate confinement quantum well structure by subpicosecond rise time measurements of the quantum well luminescence as well as by pump-probe correlation measurements of the population decay in the barrier layer. Both experimental techniques yield an oscillating capture time between 3 and 20 ps, in excellent agreement with the theoretical predictions. In a classical picture, our results correspond to a local capture time oscillating between 0.1 and 1.8 ps. Furthermore, the dependence of the capture time on the excitation energy is analyzed and the time-dependent position of the quasi-Fermi-level in the barrier layer is tracked experimentally. We find that the carrier capture time is very sensitive to the detailed structure parameters as well as to the carrier distribution in the barrier. Carrier capture is found to be an ambipolar process in which the oscillations of the observed capture times are due to the quantum-mechanical oscillation of the electron wave-function overlap above the well. Finally, electron capture is demonstrated to be dominated by LO-phonon emission.