Paper NS+NC-TuA3
Doping PbSe Nanocrystals and Nanowires

Tuesday, October 21, 2008, 2:20 pm, Room 311

We recently proposed that impurity doping in colloidally grown semiconductor nanocrystals is controlled primarily by kinetics, rather than by thermodynamics.^1,2 In this "trapped dopant" model, the diffusion of an impurity through a nanocrystal is negligible at colloidal growth temperatures. Therefore, an impurity can only be incorporated into a growing nanocrystal if it first adsorbs on the surface and is then overgrown. But this simple surface adsorption process is complicated by a competing process: the binding of the impurity by surfactant molecules, which are used in the growth solution to passivate the nanocrystal and control its growth. Here we use density-functional theory to study the interplay and outcome of these two processes for the doping of PbSe nanocrystals and nanowires by a number of candidate impurities (Mn, Cl, In, Cd, Tl, etc) in the presence of several widely used growth surfactants (oleic acid, trioctylphosphine, hexadecylamine). The results suggest that succesful doping requires making a trade-off between surface adsorption (which favors small impurities) and interior trapping (which favors large impurities). Moreover, the widely used surfactant oleic acid binds strongly to almost all impurities, suggesting that standard growth procedures may require modification for successful doping to be realized.

¹ S.C. Erwin, L. Zu, M.I. Haftel, Al.L. Efros, T.A. Kennedy, and D.J. Norris. Nature 436, 91 (2005).
² D.J. Norris, Al.L. Efros, and S.C. Erwin. Science 319, 1776 (2008).