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

Abstract

We investigate experimentally and theoretically the resonant emission of single InAs/GaAs quantum dots in a planar microcavity. Due to the presence of at least one residual charge in the quantum dots, the resonant excitation of the neutral exciton is blocked. The influence of the residual doping on the initial quantum dots charge state is analyzed, and the resonant emission quenching is interpreted as a Coulomb blockade effect. The use of an additional non-resonant laser in a specific low power regime leads to the carrier draining in quantum dots and allows an efficient optical gating of the exciton resonant emission. A detailed population evolution model, developed to describe the carrier draining and the optical gate effect, perfectly fits the experimental results in the steady state and dynamical regimes of the optical gate with a single set of parameters. We deduce that ultra-slow Auger-and phonon-assisted capture processes govern the carrier draining in quantum dots with relaxation times in the 1 -100 µs range. We conclude that the optical gate acts as a very sensitive probe of the quantum dots population relaxation in an unprecedented slow-capture regime.

Effects of photo-neutralization on the emission properties of quantum dots

“…While in our samples we do not observe such a high level of emission quenching as shown in Refs. [4,1], we do observe blinking. This blinking manifests itself in an exponential decay in the autocorrelation measurements (in red in Fig.…”

“…Recently, Nguyen et al performed studies [4,1] of emission quenching in quantum dots under cw resonant excitation. They showed that the origin of this phenomenon lies in the Coulomb blockade caused by a residual hole.…”

“…Trion emission indicates the presence of a residual charge in the quantum dot. A defect in the vicinity of the quantum dot acts as a hole or electron reservoir [4,1], from where it can be captured by the quantum dot. Another possible explanation for the blinking effect could be an energy shift of the biexciton state caused by the electric field of the trapped charges in the vicinity of the quantum dot, through the quantum confined Stark effect [10].…”

“…Photo-neutralization is the name given to a technique that stabilizes a quantum dot environment using an off-resonant light source [1]. Since it is not possible to grow semiconductors without defects or impurities, a possibility to stabilize the environment is desirable.…”

Generating indistinguishable photons from a quantum dot in a noisy environment

“…Charge noise is present under both incoherent [3,37,38] and coherent [32,33,[39][40][41][42] excitation. The origins of the charge traps that host the fluctuations can vary depending on the sample; potential sources include nearby surface states in processed photonic structures [43][44][45], traps created at heterostructure interfaces [41], impurities from intentional dopants [39], and residual background dopant impurities [42,46]. Charge noise is often identified as an origin of increased ensemble dephasing and decreased two-photon interference visibility [3,5,7,31,47].…”