Spin blockade and phonon bottleneck for hot electron relaxation observed in n-doped colloidal quantum dots
Junhui Wang, Lifeng Wang, Shuwen Yu, Tao Ding, Dongmei Xiang, Kaifeng Wu
Abstract
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 1P e hot electron relaxation (~10 picosecond) resulting from a Pauli spin blockade of the preoccupying 1S e 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.