Multicarrier Dynamics in Quantum Dots

Abstract

Multicarrier dynamics play an essential role in quantum dot photophysics and photochemistry, and they are primarily governed by nonradiative Auger processes. Auger recombination affects the performance of lasers, light-emitting diodes, and photodetectors, and it has been implicated in fluorescence intermittency phenomena which are relevant in microscopy and biological tagging. Auger cooling is an important mechanism of rapid electron thermalization. Inverse Auger recombination, known as impact ionization, results in carrier multiplication which can enhance the efficiencies of solar cells. This article first reviews the physical picture, theoretical framework and experimental data for Auger processes in bulk crystalline semiconductors. With this context these aspects are then reexamined for nanocrystal quantum dots, and we first consider fundamental features of Auger recombination in these systems. Methods for the chemical control of Auger recombination and Auger cooling are then discussed in the context of how they illuminate the underlying mechanisms, and we also examine the current understanding of carrier multiplication in quantum dots. Manifestations of Auger recombination in quantum dot devices are finally considered, and we conclude the article with a perspective on remaining unknowns in quantum dot multicarrier physics.

Intraband dynamics of mid-infrared HgTe quantum dots

“…6 At the same time, the wave packet nature and close vicinity of car-riers enhance Auger scattering, a good overview of which can be found in a recent review. 7 A larger surface to volume ratio also enhances surface effects and the influence of ligands. [8][9][10][11] Yet, the resulting relaxation pathways are by no means universal for all quantum dot systems.…”

Resolving the Controversy in Biexciton Binding Energy of Cesium Lead Halide Perovskite Nanocrystals through Heralded Single-Particle Spectroscopy

“…Relaxation from the BX to the singly excited (1X) state can occur through the radiative PL process or via nonradiative Auger processes. 3 Hence, the probability of radiative relaxation from the BX state, the BX quantum yield, is indicative of the relative rates of the two processes. A cascaded radiative relaxation from BX to 1X and further to the ground (G) state results in the emission of two photons in rapid succession.…”

Toward Bright Mid-Infrared Emitters: Thick-Shell n-Type HgSe/CdS Nanocrystals

“…In contrast, other applications such as solar energy harvesting utilizing hot-carrier extraction and carrier multiplication are significantly aided when intraband relaxation is slow. 4 − 6 Slow intraband relaxation is also required when intraband transitions, typically between the two lowest quantized conduction levels 1S e and 1P e , are utilized directly for light emission and detection such as in infrared optoelectronics. 7 − 12 It is therefore of broad practical importance to understand and control intraband relaxation rates.…”

“… 13 Electronic phonon bottlenecks are rarely observed in practice, however, because electrons can undergo subpicosecond relaxation by coupling to a valence hole in a process known as Auger cooling. 4 , 14 − 17 Experiments that inhibit Auger cooling, either by hole localization 18 − 20 or by n-doping, 9 , 21 accomplish slower relaxation rates which are often attributed to Forster-like near-field energy transfer involving surface ligand vibrations. 9 , 18 , 19 , 22 , 23 This usually produces intraband lifetimes of tens to hundreds of picoseconds.…”