(Invited) Photophysics of QDs Enabled By Gas-Phase PECVD Growth

We have been exploring doping and alloying of semiconductor quantum dots (QDs) and the impact of chemical composition on the QD primary photochemical events including charge generation, separation, and recombination. Dopant incorporation and alloying without phase segregation are significant challenges using conventional colloidal growth methods. Nonthermal plasma-enhanced chemical vapor deposition (PECVD) growth is an attractive approach to overcome these challenges since it is controlled by kinetics rather than thermodynamics. In this presentation, we will describe the PECVD synthesis of silicon quantum dots (Si QDs) that provides the ability to incorporate high concentrations (~1020 cm–3) of either p-type (B:Si) or n-type (P:Si) dopants. We also can use this synthetic technique to prepare co-doped QDs containing both P and B atoms in the same PB:Si QD. Whereas the optical absorption of singly P:Si and B:Si QDs exhibit plasmonic features characteristic of a high concentration of dopants, the co-doped PB:Si QDs instead exhibit photophysics that resemble those of intrinsic Si QDs, for example emission lifetimes of ~100 μs, but with size-dependent optical transitions that are tunable even below the energy of bulk Si (1.12 eV). Finally, we will describe new work on III–V semiconductors, in particular gallium nitride (GaN) QDs, that also exhibit tunable photophysics and serve as useful model systems for photochemically-driven small molecule conversion.