Stokes shift in quantum wells: Trapping versus thermalization

Low temperature photoluminescence and photoluminescence excitation measurements have been performed in a set of Inₓ{Ga}_{1{{-}}x}$As/GaAs samples with a different indium molar fraction, well width, growth conditions, and post-growth treatment. This has allowed to change in a controlled way the degree and source of disorder in the samples, thus resulting in an excitonic absorption linewidth varying between 1 and 18 meV, and an ensuing Stokes shift changing between zero and 8 meV. The conditions of validity of two different models relating the Stokes shift to the linewidth broadening have been established in terms of different regimes of disorder and temperature. A continuous transition between those regimes has been demonstrated. {} 1996 The American Physical Society.