We studied the carrier-spin polarization in an n-type modulation-doped single quantum well. The sample shows a high electron concentration and the second electron subband is marginally occupied. Photoluminescence and photoluminescence excitation were performed in the continuous-wave regime. The results reveal a polarization profile determined by the hole relaxation. A higher degree of polarization was observed for the luminescence related to the recombination of electrons in the second conduction subband. This suggests that the photo-created electrons localized close to the Fermi level maintain their polarization. (C) 1999 Academic Press.253551554