Hole intraband relaxation in strongly confined quantum dots: Revisiting the "phonon bottleneck" problem

We study hole intraband relaxation in strongly confined CdSe quantum dots. We observe a dramatic reduction in the hole energy-loss rate in the final stage of hole relaxation at the bottom of the valence band. This reduction occurs because of a significantly increased inter-level spacing near the band edge, and, in particular, because of a large energy gap separating the lowest ("emitting") hole states from a dense quasi-continuum of higher lying states. A slowed population buildup of the lowest hole state indicates that the "phonon bottle-neck," which is bypassed in the conduction band due to Auger-type electron-hole interactions, still plays a significant role in hole relaxation.