FERMI ENHANCEMENT AND BAND-GAP RENORMALIZATION OF ALXGA1-XAS/GAAS MODULATION-DOPED QUANTUM-WELLS

A comparative study of photoluminescence and photoluminescence-excitation spectra of thin n- and p-type modulation-doped Al(x)Ga1-xAs/GaAs quantum wells is presented for sheet carrier densities up to 10(12) cm.2. Photoluminescence-excitation spectra reveal a rather weak enhancement of the oscillator strength at the Fermi edge which is not observable in the emission spectra. The renormalization of the quasi-two-dimensional band gap is obtained by comparison with undoped quantum wells of the same width. The experimental data compare favorably with our calculations of the band-gap renormalization within the local-density approximation as well as with the self-energy shifts of electron and hole subbands calculated within the random-phase approximation. The importance of a detailed line-shape analysis for the separation of intrinsic and extrinsic components in the photoluminescence spectra is emphasized.