PHOTOLUMINESCENCE DISCONTINUITIES CLOSE TO THE FILLING FACTOR V=1

We report the measurement of magnetophotoluminescence spectra in high- mobility GaAs/GaAlAs heterojunctions as a function of density and temp erature. For densities below 1 x 10(11) cm(-2) the PL is excitonic in nature, but at higher densities a transition occurs at Landau occupanc ies below v = 1 to a ''free-hole'' luminescence, accompanied by a red shift of the FL. The transition is strongly temperature dependent. We also describe the observation of a FIR modulation of the PL signal, wh ich is found to modulate only the excitonic PL. (C) 1998 Elsevier Scie nce B.V. All rights reserved.