LONG-LIVED INTERMEDIATE STATE IN STRAIN-CONFINED QUANTUM DOTS

We have studied carrier transfer to strain confined dots from a host q uantum well, using selectively excited time-resolved photoluminescence spectroscopy. We find that the photoluminescence decay rate after pic osecond excitation is much slower when excitation is indirect, via tra nsfer from the quantum well, then when it is directly into the dot, ev en though the decay of the quantum well photoluminescence is fast. Thi s result is inconsistent with a simple three level kinetic model of th e transfer process. We propose a tentative model involving an intermed iate nonradiative state, possibly the charge separated state predicted theoretically. (C) 1996 Academic Press Limited