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

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 1.3μm 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.