  The magnetophotoluminescence (MPL) behavior of a GaAs/Al(0.3)Ga(0.7)As single
heterojunction has been investigated to 60T. We observed negatively charged
singlet and triplet exciton states that are formed at high magnetic fields
beyond the nu=1 quantum Hall state. The variation of the charged exciton
binding energies are in good agreement with theoretical predictions. The MPL
transition intensities for these states showed intensity variations (maxima and
minima) at the nu=1/3 and 1/5 fractional quantum Hall (FQH) state as a
consequence of a large reduction of electron-hole screening at these filling
factors.
