Electron-hole plasma in pulse photoexcited single quantum wells

We report photoluminescence studies of MOCVD grown, GaAsAl_xGa_1?xAs single quantum wells which were intensly excited with a pulse dye laser at T=2K. For a well width of d～40Å, the spectra are interpreted as due to the radiative recombination of a hot electron-hole plasma confined to the well. The density of charge carriers and their temperature depend upon the excitation intensity, and vary in the range of 10¹¹–10¹³ cm^?2 and 100–500K for an absorbed photon flux of 10¹³–10¹⁶ photons-cm^?2 per pulse, respectively. The observed spectral features are identified as the e1-hh1 and e1-lh1 transitions and two additional bands which are tentatively assigned to transitions involving virtual bound states of either the electron or the hole. The electron-hole plasma spectra of the d～40Å sample are strongly polarized perpendicular to the well quantization axis. For wider wells (d～80 and 150Å) smaller photoexcited carrier densities were observed for the same absorbed photon flux. It is thus concluded that the capture efficiency of the well is small.