  Low temperature photoluminescence and photoluminescence excitation
measurements have been performed in a set of InGaAs/GaAs samples with 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 ensueing 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.
