Sharp line donor-acceptor recombination in Mn-implanted GaAs

More than 40 sharp low temperature photoluminescent (PL) lines were observed in the energy range 1.44 - 1.48 eV in Mn implanted VPE GaAs. These are due to a donor-acceptor pair (DAP) recombination where the individual lines arise from a transition at pairs with different lattice separation and a corresponding Coulomb interaction. This is the first observation of a discrete DAP luminescence in GaAs that exists in spite of the large Bohr radii of donors. S_As or Si_Ga are most likely involved in DAP recombination being usual residual donors in VPE GaAs. The line energy positions are in a good agreement with the Coulomb interaction on the discrete lattice site distances. It is necessary to take into account that two distinct types of DAP spectra are seen in this material: with pairs in one sublattice and in the different sublattices. The observation of the sharp line decay after the laser excitation pulse shows that the lines with higher energy exhibit the lower lifetime. Over 90% sharp line PL intensity decays during the first 100 ns confirming DAP nature of the recombination process observed.