  Considering effects of electric field on the low temperature absorption line
of quantum well excitons, we show that, for moderate strength of the electric
field, the main contribution to the field dependence of the line-width results
from field induced modifications of inhomogeneous broadening of excitons. We
find that the strength of the random potential acting on quantum well excitons
due to alloy disorder and interface roughness can either decrease or increase
with field depending upon the thickness of the well. This means that under
certain conditions one can observe counterintuitive narrowing of exciton
spectral lines in electric field.
