Effect of random field fluctuations on excitonic transitions of individual CdSe quantum dots

Abstract

The quantum confined Stark effect is observed for quantum dots (QD's) exposed to randomly fluctuating electric fields in epitaxial structures. These fields, attributed to charges localized at defects in the vicinity of the QD's, lead to a jitter in the emission energies of individual QD's. This jitter has typical frequencies of below about 1 Hz and is characteristic for each QD thus providing a unique means to unambiguously identify the emission spectra of single QD's. Up to eight lines are identified for individual QD's and attributed to excitonic, biexcitonic, and LO-phonon-assisted transitions. The intensity of the LO-phonon replica is surprisingly large corresponding to Huang-Rhys factors of about one

Temperature dependence of the zero-phonon linewidth in quantum dots: An effect of the fluctuating environment

“…In the former case, the experimental results show marked differences depending on the spectroscopic techniques. In photoluminescence (PL) measurements, the experimental evidence of light-induced spectral diffusion in single QDs has revealed the existence of randomly fluctuating electric fields due to the presence of localized charges in the vicinity of the QD [1][2][3][4]. This phenomenon with spectral jitters ranging from few tens of µeV to several meV breaks down the simple picture of a two-level system where the linewidth is given by the radiative limit in the µeV range.…”

“…Impurities, defects or localized charges in the vicinity of a QD induce micro-electric fields that shift the QD emission line through the quantum confined Stark effect [1][2][3][4]. The fluctuations of the QD environment thus randomize the emission energy over a spectral range Σ on a characteristic correlation time τ c .…”

Fluorescence Intermittency in Self-Assembled InP Quantum Dots

“…One of the most interesting findings so far reported in quantum dot (QD) systems is the fluctuation of the PL peak energy and intensity with time, which would be unobservable in macroscopic studies. The former phenomenon, called as the spectral diffusion, is observed in CdSe [1][2][3][4] and InAlAs [5] QDs, where the PL peak energies from confined excitons and their LO sidebands fluctuate during the time of measurement. The latter phenomenon is referred to as the fluorescence intermittency or random telegraph signal, where the PL intensity switches between two or more discrete levels as the time goes by [1,[5][6][7][8][9].…”

Optical Properties of III–V Quantum Dots

“…Two sets of lines obviously exhibit the same spectral diffusion pattern in time. The spectral diffusion results from randomly charging and discharging of defects and interface states around the QDs, resulting in a synchronously changing electric field [50]. Since each QD experiences a different electric field in time, all its emission lines show the same, characteristic emission pattern -allowing for a discrimination of single dot spectra, even if they overlap.…”