Low-temperature emission in dilute GaAsN alloys grown by metalorganic vapor phase epitaxy

We have investigated the optical emission from $GaAs1−xNx$ epilayers with $4.3×10−4<x<0.012$⁠. The samples were grown on GaAs(001) substrates by metal-organic vapor phase epitaxy using dimethylhydrazine as the nitrogen precursor. We find that the incorporation of nitrogen in GaAs generates deep radiative centers at around $250meV$ below the GaAsN band gap. The defects associated with these centers can be eliminated through an optimization of the growth temperature and reactor pressure, and by postgrowth annealing at $700°C$⁠. We also find that, contrary to what was suggested by Makimoto et al. [Appl. Phys. Lett. 70, 2984 (1997)], the near-gap emission located close to $25meV$ below the gap is not related to a free-to-bound transition even in the samples with the lowest nitrogen content. Rather, we associate this emission to excitons bound to overlapping nitrogen clusters.