INVESTIGATION OF THE PHOTOLUMINESCENCE LINEWIDTH BROADENING IN SYMMETRICAL AND ASYMMETRIC INGAAS GAAS N-TYPE DELTA-DOPED QUANTUM-WELLS/

We have performed a systematic study of photoluminescence (PL) line sh ape in n-type delta-doped In0.15Ga0.85As/GaAs quantum wells (delta QWs ). Samples grown by molecular beam epitaxy with well widths of 60, 100 , 300 Angstrom, with sheet doping concentration ranging from 10(11) to 10(13) cm(-2), were analysed. Two positions were considered for the d oping planes, at the centre (symmetric) and at the edge (asymmetric) o f the QW. The luminescence spectrum from the symmetric 60 Angstrom del ta QW exhibits a dominating broad structure that at low excitation con dition and low temperature has an almost rectangular form. The square shape of this spectrum is explained by the collective recombination of electrons from the conduction band with thermalized photogenerated ho les. For the symmetric L(w) = 300 Angstrom samples, the PL spectra dis play an almost symmetric peak followed by a small shoulder on the high er or lower energy side depending on the carrier concentrations. For t he asymmetric 300 Angstrom delta QW sample two distinct peaks were obs erved. They were correlated to transitions involving the fundamental a nd first excited electronic subbands.