Real-Time Detection of Single Auger Recombination Events in a Self-Assembled Quantum Dot

Abstract

Auger recombination is a non-radiative process, where the recombination energy of an electron-hole pair is transferred to a third charge carrier. It is a common effect in colloidal quantum dots that quenches the radiative emission with an Auger recombination time below nanoseconds. In self-assembled QDs, the Auger recombination has been observed with a much longer recombination time in the order of microseconds.Here, we use two-color laser excitation on the exciton and trion transition in resonance fluorescence on a single self-assembled quantum dot to monitor in real-time every quantum event of the Auger process. Full counting statistics on the random telegraph signal give access to the cumulants and demonstrate the tunability of the Fano factor from a 1 arXiv:1911.04789v2 [cond-mat.mes-hall] 13 Nov 2019Poissonian to a sub-Poissonian distribution by Auger-mediated electron emission from the dot. Therefore, the Auger process can be used to tune optically the charge carrier occupation of the dot by the incident laser intensity; independently from the electron tunneling from the reservoir by the gate voltage. Our findings are not only highly relevant for the understanding of the Auger process, it also demonstrates the perspective of the Auger effect for controlling precisely the charge state in a quantum system by optical means.The excitonic transitions in self-assembled quantum dots (QDs) 1,2 realize perfectly a twolevel system in a solid-state environment. These transitions can be used to generate single photon sources 3,4 with high photon indistinguishability, 5,6 an important prerequisite to use quantum dots as building blocks in (optical) quantum information and communication technologies. 7,8 Moreover, self-assembled QDs are still one of the best model systems to study in an artificial atom the carrier dynamics, 9,10 the spin-and angular-momentum properties 11,12 and charge carrier interactions. 13 One important effect of carrier interactions is the Auger process: An electron-hole pair recombines and instead of emitting a photon, the recombination energy is transferred to a third charge carrier, which is then energetically ejected from the QD. 14-17 This is a common effect, mostly studied in colloidal QDs, where it quenches the radiative emission with recombination times in the order of picoseconds to nanoseconds. [18][19][20] This limits the efficiency of optical devices containing QDs like LEDs 21,22 or single photon sources. [23][24][25] In self-assembled QDs, Auger recombination was speculated to be absent, and only recently, it was directly observed in optical measurements on a single self-assembled QD coupled to a charge reservoir with recombination times in the order of microseconds. 26As a single Auger process is a quantum event, it is unpredictable and only the statistical evaluation of many processes gives access to the physical information of the recombination

Auger and spin dynamics in a self-assembled quantum dot

“…The QD layer is embedded in a p-i-n diode structure with a highly n-doped GaAs layer as a charge reservoir and a highly p-doped GaAs layer as an epitaxial gate 34 . Between the charge reservoir and the QD, 45 nm (AlGa)As are implemented as tunneling barrier to achieve electron tunneling times in the order of milliseconds (see Lochner et al 28 for details about the sample structure). An applied voltage between charge reservoir and gate can control the charge state of the QD.…”

“…This scattering process is well known from colloidal QDs [22][23][24] and has been directly observed just recently in resonance fluorescence measurements 25 with Auger recombination rates in the order of microseconds. [26][27][28][29] In this paper, we show time-resolved resonance fluorescence (RF) measurements on the trion transitions of a a) Electronic mail: hendrik.mannel@uni-due.de negatively-charged InAs QD, embedded in an electrically controllable diode structure and charged by electron tunneling from a nearby charge reservoir. An applied magnetic field B of up to 10 T in Faraday geometry (here, parallel to the growth axis) splits the trion into a lower ("red") and a higher ("blue") energy transition.…”

Post-processing of real-time quantum event measurements for an optimal bandwidth

“…bedded in a p-i-n diode structure (see Fig. 1(a), (b) and [16] for more details). The n + -doped back contact serves as an electron reservoir, separated from the QD by a tunnel barrier of 30 nm GaAs, 10 nm Al 0.33 Ga 0.67 As and 5 nm GaAs.…”

“…For example, timeresolved photoluminescence can be used to study charge * jens.kerski@uni-due.de fluctuations in colloidal nanocrystals at room temperature [13,14]. Also, resonant fluorescence at compared to the mK scale high temperatures (4.2 K) can be used to study tunneling [15] and Auger processes [16] in selfassembled quantum dots (QDs) as well as spin dynamics [17] in quantum dot molecules. The optical excitation of the single quantum emitter by resonant fluorescence offers a high energetic resolution, and the detection of the single photons with avalanche photodiodes or superconducting nanowire detectors promises a high bandwidth.…”

Ultrafast separation of multiexcitons within core/shell quantum dot hybrid systems

“…Auger recombination is a non-radiative process in which the energy released during electron and hole recombination is transferred to a third charge carrier (either electron or hole) which is then excited to a higher energy state. [23][24][25] Alternatively, it has been shown that multiple electrons can be transferred from photoexcited QDs to different molecular acceptors, e.g. methylene blue (MB).…”