MAGNETOOPTICAL STUDY ON EXCITON SCREENING IN P-TYPE ALXGA1-XAS INYGA1-YAS QUANTUM-WELLS/

We have studied exciton unbinding in empty and p-doped quantum wells, using magnetophotoluminescence excitation measurements. The use of p-t ype quantum wells allows us to discriminate unambiguously between exci ton bleaching by Coulomb screening and by the Pauli exclusion principl e. We found that the ground-state heavy-hole exciton, which experience s both effects, is unbound at hole densities in the range (6-9) x 10(1 5) m(-2). In contrast, the ground-state light-hole and first excited h eavy-hole excitons, which are only screened by the Coulomb interaction , still have a finite binding energy at these densities. However, for both bands, its Value is far below what is found in an undoped well. F urthermore, we found a strong indication that, in p-doped wells, the e xcitons of excited subbands are less efficiently screened than those o f the Light-hole ground state, due to the lesser overlap of the screen ing ground-state heavy holes with the excited subbands than with the g round-state light holes.