Ultrafast differential transmission spectroscopy of excitonic transitions in InGaN/GaN multiple quantum wells

Abstract

Room-temperature carrier dynamics in InGaN/GaN multiple quantum wells are studied by employing ultrafast pump–probe spectroscopy. Specifically, the observed differential spectral signatures are characteristic of changes in the absorption coefficient through both a reduction of the quantum-confined Stark shift due to the photoinduced in-well field screening (low carrier densities) and excitonic absorption quenching (high carrier densities). The comparison of the differential absorption spectra at different injected carrier densities allows us to separate field screening from excitonic bleaching. The estimated in-well field at the transition point between field screening and excitonic bleaching is consistent with the theoretical value of the piezoelectric field in the strained InGaN well.