Abstract
Understanding and manipulating hot electron dynamics in semiconductors may enable disruptive energy conversion schemes. Hot electrons in bulk semiconductors usually relax via electron-phonon scattering on a sub-picosecond timescale. Quantum-confined semiconductors such as quantum dots offer a unique platform to prolong hot electron lifetime through their size-tunable electronic structures. Here, we study hot electron relaxation in electron-doped (n-doped) colloidal CdSe quantum dots. For lightly-doped dots we observe a slow 1Pe hot electron relaxation (~10 picosecond) resulting from a Pauli spin blockade of the preoccupying 1Se electron. For heavily-doped dots, a large number of electrons residing in the surface states introduce picosecond Auger recombination which annihilates the valance band hole, allowing us to observe 300-picosecond-long hot electrons as a manifestation of a phonon bottleneck effect. This brings the hot electron energy loss rate to a level of sub-meV per picosecond from a usual level of 1 eV per picosecond. These results offer exciting opportunities of hot electron harvesting by exploiting carrier-carrier, carrier-phonon and spin-spin interactions in doped quantum dots.
Highlights
Understanding and manipulating hot electron dynamics in semiconductors may enable disruptive energy conversion schemes
For heavily-doped quantum dots (QDs), a large number of electrons residing in the surface states induce ps Auger recombination that annihilates the valance band hole
Transmission electron microscope (TEM) images indicate that the diameters are tuned from 4.2 to 5.5 nm (Supplementary Fig. S1)
Summary
Understanding and manipulating hot electron dynamics in semiconductors may enable disruptive energy conversion schemes. For heavily-doped dots, a large number of electrons residing in the surface states introduce picosecond Auger recombination which annihilates the valance band hole, allowing us to observe 300-picosecond-long hot electrons as a manifestation of a phonon bottleneck effect This brings the hot electron energy loss rate to a level of sub-meV per picosecond from a usual level of 1 eV per picosecond. For heavily-doped QDs, a large number of electrons residing in the surface states induce ps Auger recombination that annihilates the valance band hole This allows us to observe 300-ps-long 1Pe hot electrons, which we attribute to the phonon bottleneck effect, representing three orders of magnitude lengthening as compared to neutral QDs. The hot electron energy loss rate is brought to a level of sub-meV/ps from a usual level of ~1 eV/ps
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