Carrier recombination processes in GaAsN: from the dilute limit to alloying

Low-temperature time-resolved photoluminescence (TR-PL) experiments were used to study the dependence on nitrogen composition of the nature, the energy and the dynamics of radiative carrier recombinations in GaAs_1-xN_x alloys. Epitaxial layers were grown on [001] GaAs substrates by molecular beam epitaxy using solid sources for group-III and As elements, and a radiofrequency plasma source for N. The nitrogen content, measured by secondary ion mass spectroscopy, was in the range 5 × 10^-5 - 7 × 10^-2. PL spectra are dominated by the emission from the discrete states of nitrogen-based excitonic complexes for the very low x regime (around 5 × 10^-5), showing exponential time decays. For x larger than 5 × 10^-4, PL spectra are rather dominated by emission from a continuum of states originating from nitrogen clusters. In this case, nonexponential time decays are obtained. It is shown that these PL decays involve complex carrier transfers between the various available states. Changing the nitrogen content changes the recombination mechanism by changing the distance between the clusters.