Zinc oxide (ZnO) is a wide-band gap semiconductor with high exciton binding energy and is promising for future optoelectronics. Degenerate doping in ZnO quantum dots (QDs) enables tunable localized surface plasmon resonance (LSPR) in the IR region, but its impact on exciton dynamics remains unexplored. Here, we employ transient absorption spectroscopy to probe exciton dynamics in aluminum-doped ZnO (AZO) QDs. Excitation above the band gap generates hot excitons that relax via thermalization, Auger recombination, and stimulated emission, along with band gap renormalization. The presence of free charge carriers in the conduction band (CB) due to degenerate doping screens Coulomb exciton interactions that leads to suppression of biexciton formation and reduction in Auger recombination lifetime. Despite complete bleaching of ground-state absorption, reminiscent of zero-threshold gain in precharged QDs, no optical gain is achieved in AZO QDs due to doping-induced nonradiative pathways. Our findings highlight how the Burstein–Moss (BM) effect shapes exciton dynamics in degenerately doped wide-band gap QDs.
Singh et al. (Mon,) studied this question.