Excitonic field screening and bleaching in InGaN/GaN multiple quantum wells

Photoinduced carrier dynamics in a sequence of InGaN/GaN multiple quantum wells (MQWs) are studied by employing steady state and ultrafast spectroscopy at room temperature. Time-resolved photoluminescence (PL) measured short carrier lifetimes of ∼140 ps at room temperature. Steady state differential transmission was used to measure the in-well field screening due to the photoinjected carriers. The observed offset in emission energy from excitonic screening energies is consistent with the emission of carriers through localized states slightly below the excitonic resonance energy. Furthermore, time-resolved differential transmission with amplified pulses, where significant carrier densities can be optically generated, provides evidence of both excitonic bleaching and field screening in these InGaN quantum wells (QWs). The comparison of the time-resolved differential absorption spectra at various carrier densities allows us to identify different carrier recombination dynamics in the InGaN well and to separate the field screening from the bleaching effects. Finally, the extreme prolongation of the carrier recombination lifetime up to ∼4 μs suggests the spatial separation between electrons and holes under the large in-well fields.