Dephasing of excitons and multiexcitons in undoped andp-doped InAs/GaAs quantum dots-in-a-well

Abstract

We report an experimental investigation of the dephasing of excitons and multiexcitons in technologically relevant undoped and p-doped InAs/GaAs dot-in-a-well structures emitting near 1.3 m wavelength. Using a transient four-wave mixing technique in heterodyne detection, we measured the excitonic dephasing due to phonon coupling in the temperature range from 5 to 300 K, and the multiexcitonic dephasing at low temperature by electrically injecting carriers through a p-i-n diode structure. While the temperature-dependent excitonic dephasing is found to be similar to previous studies, the contribution from electrically injected carriers is weaker in these dot-in-a-well systems due to a reduced pure dephasing from Coulomb interaction with carriers in the barrier material. Moreover, multiexcitonic transitions contribute with a subpicosecond dephasing, corresponding to a homogeneous broadening in the meV range. In the p-doped structure, positively charged multiexcitons are formed due to the built-in hole reservoir, which show a dominating dephasing component in the subpicosecond range. However, a weaker component in the 10 ps range is observed and attributed to final states with spin-forbidden relaxation.

Electronic Enhancement of the Exciton Coherence Time in Charged Quantum Dots

“…The zero-power limit of the fit (solid blue line in Fig. 2(c)) is used to determine a linewidth of γ 0 = 0.45 ± 0.05 µeV ( T 2 = 1.46 ± 0.07 ns), which is consistent with population-lifetime limited transition linewidths previously measured for trions in QDs and indicates that additional pure dephasing mechanisms such as electron-phonon coupling are absent from the measurements [8, 9]. From the same fit we also extract the absorption saturation power P 0 = 53 ± 5 pW.…”

Homogeneous linewidth narrowing of the charged exciton via nuclear spin screening in an InAs/GaAs quantum dot ensemble

“…These limitations can be avoided by investigating QD ensembles using spin noise spectroscopy [15,16] or nonlinear optical spectroscopy techniques, such as spectral hole burning [17][18][19], four-wave mixing [20], or coherent multidimensional spectroscopy [21,22]. An ultralong coherence time up to ∼1.5 ns, corresponding to a sub-μeV dephasing rate, has been measured for the positively charged exciton in InAs QDs at cryogenic temperature [23]. Such a long coherence time indicates almost complete absence of pure dephasing effects arising from exciton-exciton and * kevin.silverman@nist.gov exciton-phonon interactions.…”

Fifth-order nonlinear optical response of excitonic states in an InAs quantum dot ensemble measured with two-dimensional spectroscopy

“…Additional insight into dephasing mechanisms and coherent interactions between excitons can be gained by using nonlinear techniques, in which many-body interactions give rise to distinct features in the nonlinear signals 14 . Transient four-wave mixing (FWM) has been particularly suitable for revealing the effects of phonon and inter-exciton scattering on the dephasing rate of excitons, biexcitons and trions even in the presence of strong inhomogeneity [15][16][17][18] . More recently, optical two-dimensional Fouriertransform spectroscopy 19 (2DFTS) -an extension of three-pulse FWM -has been demonstrated as an extremely sensitive tool for investigating coherent excitonic interactions [20][21][22] and incoherent relaxation dynamics 23 in interfacial GaAs QDs.…”