STRONG EFFECTS OF CARRIER CONCENTRATION ON THE FERMI-EDGE SINGULARITYIN MODULATION-DOPED INP INXGA1-XAS HETEROSTRUCTURES/

The presence of the Fermi-edge singularity (FES) in photoluminescence spectra of n-type modulation-doped InP/InxGa1-xAs quantum structures i s found to be strongly dependent on the concentration of a two-dimensi onal electron gas (2DEG). The FES is observed in samples with a high c oncentration of the 2DEG, whereas it is not so in low-doped samples wi th a concentration of the 2DEG close to approximate to 4.0 x 10(11) cm (-2). The suppression of the FES in the latter case occurs even under optimal conditions for the FES observation, i.e., in quantum structure s where (i) a hole localization is realized by the alloy fluctuation p otential and (ii) an enhanced interaction between the 2DEG and photocr eated holes is ensured by a close distance between the Fermi level and the empty upper electron subband. An analysis of the results obtained based on the self-consistent calculations of the band-bending, subban d structure, and spatial distribution of carrier density suggests that the observed dependence of the FES on the 2DEG density presumably ref lects intrinsic properties of the 2D system and is not related to a re duction of overlap between electron and hole wave functions with decre asing concentration of the 2DEG. This conclusion is also confirmed by a comparison with previously reported data. A detailed understanding o f the observed dependence requires further theoretical studies.