Ultrafast Intraband Auger Process in Self-Doped Colloidal Quantum Dots

Investigating the separate dynamics of electrons and holes has been challenging although it is critical for fundamental understanding of semiconducting nanomaterials. N-type self-doped colloidal quantum dots (CQDs) with excess electrons occupying the low-lying state in the conduction band (CB) have attracted a great deal of attention because of not only their potential applications to infrared optoelectronics but also their intrinsic system offering a platform for investigating electron dynamics without elusive contributions from holes in the valence band. Here, we show an unprecedented ultrafast intraband Auger process, electron relaxation between spin-orbit coupling states, and exciton-to-ligand vibrational energy transfer process that all occur exclusively in the CB of the self-doped β-HgS CQDs. The electron dynamics obtained by femtosecond mid-IR spectroscopy will pave the way for further understanding of the blinking, disproportionately charging in LEDs, and hot electron dynamics in higher quantum states coupled to surface states of CQDs.