Effect of rapid thermal annealing on the properties of GaNAs thin films grown by molecular beam epitaxy

High-resolution X-ray diffraction (HRXRD) and micro-Raman scattering probe have been used to study the effect of post-growth thermal annealing on GaNAs thin films grown on (0 0 1) GaAs substrates by solid-source molecular beam epitaxy assisted with a nitrogen radio-frequency plasma source. X-ray reciprocal space mapping shows slightly in-plane strain relaxation after annealing, however, the vertical lattice constant measured by HRXRD from the (0 0 4) atoms planes shows a shrinkage, which is contrary to both the relaxation of tensile strain and the decreasing of nitrogen due to out-diffusion. The ratio of Raman intensity between the nitrogen-localized vibration mode and the GaAs-like LO is found to increase as a function of annealing temperature, which provides evidence for the increase of substitutional NAs atoms at elevated temperatures. The anneal-induced vertical lattice shrinkage can be explained in term of the redistribution of nitrogen bonding configurations among the substitutional NAs, interstitial N-N, and the N-As complex.