An upper bound to carrier multiplication efficiency in type II colloidal quantum dots.

We experimentally investigate carrier multiplication (CM) in type II CdTe/CdSe quantum dot (QD) heterostructures by the means of a simple and robust subnanosecond transient photoluminescence spectroscopy setup. Experimental conditions were set to minimize the blurring of the CM signature by extraneous effects. The extracted photon energy threshold for CM is consistent with previous studies in CdSe and CdTe QDs (around 2.65 times the type II energy band gap) and we can infer an upper bound to CM yield. This study indicates that, while CM is probably present in type II QD heterostructures below the CM threshold for each constituent separately, it exhibits only a modest yield.