ENHANCEMENT OF THE FREE-TO-BOUND TRANSITION IN NARROW GAAS/AL0.3GA0.7AS QUANTUM WELLS VIA A POSSIBLE EXCITONIC AUGER MECHANISM

The recombination of an n=1 quantized electron with a hole bound at an acceptor in a so-called free-to-bound (FB) transition has been observed in GaAs/Al0.3Ga0.7As quantum wells with a rather low p-type doping level (<1×1017 cm-3) in selective photoluminescence (SPL) upon excitation in the vicinity of the free exciton (FE). This is in contrast to the photoluminescence (PL) measurements with above-band-gap excitation, where the FB band is not seen. This FB transition is strikingly enhanced at excitation resonant with the heavy-hole (hh) or light-hole (lh) state of the FE. The peak intensity of the FB reaches about 8% of the corresponding FE intensity at resonant excitation in the investigated sample. The intensity correlation between the FE and FB is also observed in the PL-excitation measurements and in the temperature dependence of the SPL spectra. The observed results are tentatively explained in terms of a multistep excitonic Auger mechanism where the hole of the FE is attracted and captured by an ionized acceptor. The excess energy is transferred to the electron, which is then excited into the continuum. In the final step a free electron recombines with a hole from the neutral acceptor in a FB transition. The free carriers created by this process have also been detected by photoconductivity measurements upon excitation resonant with the exciton states, which is consistent with the proposed excitonic Auger recombination model. © 1990 The American Physical Society.