Photoluminescence excitation (PLE) measurements have been performed in several GaAs-based structures by monitoring the electron-carbon acceptor and the exciton bound to carbon recombinations. In both cases we show that the separate capture of free carriers makes the main contribution to the electron-carbon transition and to the formation of the bound exciton. A dip is indeed observed in the PLE spectra at the energy of the free exciton. The contribution of the bound exciton relaxation to the two-hole transition is pointed out.

• Received 20 January 1997

DOI:https://doi.org/10.1103/PhysRevB.56.3834