Phonon-assisted capture and intradot Auger relaxation in quantum dots

Abstract

We report on calculations of capture and relaxation of carriers in quantum dots, specifically, InAs/GaAs self-assembled dots. We point out that the phonon-assisted carrier capture presents strong resonances versus the dot size and that the intradot Auger relaxation is extremely fast in these structures. This shows that energy relaxation in InAs/GaAs self-organized quantum dots is dominated by capture effects.

Photoneutralization and slow capture of carriers in quantum dots probed by resonant excitation spectroscopy

“…While other groups [1,35] have previously used the non-resonant photoluminescence to evaluate the carriers capture rates, we benefit here from the resonant excitation and its optical gating effect to probe the QD ground state, which is determined by the capture of the electrons and holes created by the non-resonant laser. In particular, this method gives access to ultra-slow capture processes in the very low gate power regime where the non-resonant photoluminescence is completely negligible.…”

“…The carriers can be then captured in the QD and the defect in its vicinity, either by the emission of optical phonons, or by Auger processes. The capture of a carrier in the QD by the emission of an optical phonon is a single charge process and is therefore proportional to the number of electrons or holes in the continuum [1,2,39], and in other words to √ P gate . Contrarily to this latter process, the Auger-assisted capture of a carrier involves two charges, where the incident charge in the continuum interacts with a target charge either in the continuum (Auger effect of type (I)), or in the QD (Auger effect of type (II)).…”

“…These calculations are in perfect agreement with timeresolved experiments performed in QDs ensemble [5] and in single QDs [6] where capture times of the order of 100 ps have been measured. On the other hand, irreversible Auger scattering is mainly responsible for the intra-dot relaxation process, and theoretical calculations [1,7] give estimate of the corresponding relaxation times in the 100 fs -10 ps range. In fact, differential transmission measurements [8], pump-probe spectroscopy [9] and time-resolved experiments [10,11] showed that the Auger-assisted processes involved in the intra-dot carriers relaxation occur within characteristic times between 1 ps and 10 ps.…”

“…Then, intra-dot relaxation processes between the different QD discrete states lead to electron and hole population of the ground states from which the QD photoluminescence occurs. Theoretical works show that the capture mechanism relies either on emission of optical phonons [1,2] with typical capture times between 100 fs and 100 ns, or on electron-electron and electron-hole Auger scattering [3,4] with typical capture times between 1 ps and 1 µs. These calculations are in perfect agreement with timeresolved experiments performed in QDs ensemble [5] and in single QDs [6] where capture times of the order of 100 ps have been measured.…”

InAs QDs on InP: polarization insensitive SOA and non-radiative Auger processes

“…In that case, the Auger process has a positive impact on the device performance (Veselinov et al 2007, Miska et al 2008 . Most theoretical models published up to now consider the relaxation into the conduction band of the QD or neglect the influence of strain or VB coupling (Ferreira and Bastard 1999, Magnusdottir et al 2003, Nielsen et al 2005). In bulk materials or QW systems, Auger processes usually refer to nonradiative processes affecting interband optical transitions (Beattie and Landsberg 1958).…”