Enhancement of the direct optical transition in nanocrystallized GaAsN alloys

Using x-ray diffraction, cross-sectional transmission electron microscopy (XTEM), and infrared absorption techniques, we have investigated the effects of nanocrystallization on the structural and optical properties of GaAs_0.99N_0.01 grown by plasma-enhanced molecular-beam epitaxy. The x-ray diffraction results of postgrowth annealed samples with a protective Si₃N₄ cap exhibit significant lattice relaxation, structural inhomogeneity, and apparent nitrogen "loss," indicating the occurrence of phase separation after thermal treatment. High-resolution XTEM confirms the formation of N-enriched GaAsN nanocrystals embedded at the GaAsN/Si₃N₄ interface. Infrared absorption study demonstrates that the annealed sample has a strongly enhanced direct optical transition.