Dephasing of excited‐state excitons in InGaAs quantum dots

Physical Review Letters, 2001

We measure a dephasing time of several hundred picoseconds at low temperature in the groundstate transition of strongly confined InGaAs quantum dots, using a highly sensitive four-wave mixing technique. Between 7 and 100 K the polarization decay has two distinct components resulting in a non-Lorentzian line shape with a lifetime-limited zero-phonon line and a broadband from elastic excitonacoustic phonon interactions.

Physical Review B, 2005

We report systematic measurements of the dephasing of the excitonic ground-state transition in a series of InGaAs/ GaAs quantum dots having different quantum confinement potentials. Using a highly sensitive fourwave mixing technique, we measure the polarization decay in the temperature range from 5 to 120 K on nine samples having the energy distance from the dot ground-state transition to the wetting layer continuum ͑confinement energy͒ tuned from 332 to 69 meV by thermal annealing. The width and the weight of the zerophonon line in the homogeneous line shape are inferred from the measured polarization decay and are discussed within the framework of recent theoretical models of the exciton-acoustic phonon interaction in quantum dots. The weight of the zero-phonon line is found to decrease with increasing lattice temperature and confinement energy, consistently with theoretical predictions by the independent Boson model. The temperature-dependent width of the zero-phonon line is well reproduced by a thermally activated behavior having two constant activation energies of 6 and 28 meV, independent of confinement energy. Only the coefficient to the 6-meV activation energy shows a systematic increase with increasing confinement energy. These findings rule out that the process of one-phonon absorption from the excitonic ground state into higher energy states is the underlying dephasing mechanism.

Physical Review Letters, 2003

We have measured the exciton dephasing time in InAs=GaAs quantum dot molecules having different interdot barrier thicknesses in the temperature range from 5 to 60 K, using a highly sensitive four-wave mixing heterodyne technique. At 5 K dephasing times of several hundred picoseconds are found. Moreover, a systematic dependence of the dephasing dynamics on the barrier thickness is observed. These results show how the quantum-mechanical coupling of the electronic wave functions in the molecules affects both the exciton radiative lifetime and the exciton-acoustic phonon interaction.

Physical Review B, 2008

Polaron dephasing processes are investigated in InAs/ GaAs dots using far-infrared transient four wave mixing ͑FWM͒ spectroscopy. We observe an oscillatory behavior in the FWM signal shortly ͑Ͻ5 ps͒ after resonant excitation of the lowest energy conduction band transition due to coherent acoustic phonon generation. The subsequent single exponential decay yields long intraband dephasing times of 90 ps. We find good agreement between our measured and calculated FWM dynamics, and show that both real and virtual acoustic phonon processes are necessary to explain the temperature dependence of the polarization decay.

Physical Review Letters, 2002

We measure the dephasing time of ground-state excitonic transitions in InGaAs quantum dots under electrical injection in the temperature range from 10 to 70 K. Electrical injection into the barrier region results in a pure dephasing of the excitonic transitions. Once the injected carriers fill the electronic ground state, the biexciton to exciton transition is probed and a correlation of the exciton and biexciton phonon scattering mechanisms is found. Additional filling of the excited states creates multiexcitons that show a fast dephasing due to population relaxation.

physica status solidi (a), 2002

Time-resolved four-wave mixing in strongly confined and electrically pumped InGaAs quantum dots is measured at different temperatures. Without electrical injection, the dephasing time of the dot ground state transition is lifetime-limited and of several hundred picoseconds at low temperature. Under electrical injection, the sum of the contributions from empty and populated dots with a relative phase shift of p is evidenced near transparency.

Physical Review B, 2010

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-in 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.

Journal of Applied Physics, 2011

Recently, longitudinal acoustic phonons have been identified as the main source of the intensity damping observed in Rabi rotation measurements of the ground-state exciton of a single InAs/GaAs quantum dot. Here we report experiments of intensity damped Rabi rotations in the case of detuned laser pulses. The results have implications for the coherent optical control of both excitons and spins using detuned laser pulses.

Physical Review B, 2004

We measure the dephasing time of the exciton ground-state transition in In 1-x Ga x As quantum dots using a sensitive four-wave mixing technique. We find experimental evidence that the dephasing time is given only by the radiative lifetime at low temperatures. We demonstrate the tunability of the radiatively limited dephasing time from 400 ps up to 2 ns in a series of annealed In 1-x Ga x As quantum dots with increasing quantumconfinement energy from 69 meV to 330 meV.

IEEE Journal of Selected Topics in Quantum Electronics, 2002

We present an extensive experimental study of the exciton relaxation and dephasing in InGaAs quantum dots (QDs) in the temperature range from 10 K to 295 K. The QDs are embedded in the active region of an electrically pumped semiconductor optical amplifier. Ultrafast four-wave mixing and differential transmission spectroscopy on the dot ground-state transition are performed with a sensitive heterodyne detection technique. The importance of the population relaxation dynamics to the dephasing is determined as a function of injection current and temperature. Above 150 K dephasing processes much faster than the population relaxation are present, due to both carrier-phonon scattering and Coulomb interaction with the injected carriers. Only at low temperatures (30 K) does population relaxation of multiexcitons in the gain regime fully determine the dephasing.