Investigation of the photoluminescence linewidth broadening in symmetric and asymmetric InGaAsGaAs n-type δ-doped quantum wells

We have performed a systematic study of photoluminescence (PL) line shape in n-type δ-doped In0.15Ga0.85AsGaAs quantum wells (δ QWs). Samples grown by molecular beam epitaxy with well widths of 60, 100, 300 Å, with sheet doping concentration ranging from 1011 to 1013 cm−2, were analysed. Two positions were considered for the doping planes, at the centre (symmetric) and at the edge (asymmetric) of the QW. The luminescence spectrum from the symmetric 60 Å δ QW exhibits a dominating broad structure that at low excitation condition 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 holes. For the symmetric LW = 300 Å samples, the PL spectra display an almost symmetric peak followed by a small shoulder on the higher or lower energy side depending on the carrier concentrations. For the asymmetric 300 Å δ QW sample two distinct peaks were observed. They were correlated to transitions involving the fundamental and first excited electronic subbands.