Direct carrier multiplication due to inverse Auger scattering in CdSe quantum dots

Abstract

Many optoelectronic devices could achieve much higher efficiencies if the excess energy of electrons excited well above the conduction band minimum could be used to promote other valence electrons across the gap rather than being lost to phonons. It would then be possible to obtain two electron–hole pairs from one. In bulk materials, this process is inherently inefficient due to the constraint of simultaneous energy and momentum conservation. We calculated the rate of these processes, and of selected competing ones, in CdSe colloidal dots, using our semi-empirical nonlocal pseudopotential approach. We find much higher carrier multiplication rates than in conventional bulk materials for electron excess energies just above the energy gap $E_g.$ We also find that in a neutral dot, the only effective competing mechanism is Auger cooling, whose decay rates can be comparable to those calculated for the carrier multiplication process.