  A re-ordered valence band in GaN/AlGaN quantum wells with respect to GaN
epilayers has been found as a result of the observation of an enhanced g-factor
in magneto-luminescence spectra in fields up to 55 T. This has been caused by a
reversal of the states in the strained AlGaN barriers thus giving different
barrier heights for the different quantum well hole states. From k.p
calculations in the quasi-cubic approximation, a change in the valence-band
ordering will account for the observed values for the g-factors.
  We have also observed the well-width dependence of the in-plane extent of the
excitonic wavefunction from which we infer an increase in the exciton binding
energy with the reduction of the well width in general agreement with
theoretical calculations of Bigenwald et al (phys. stat. sol. (b) 216, 371
(1999)) that uses a variational approach in the envelope function formalism
that includes the effect of the electric field in the wells.
