Growth of GaAsN: surface study by AFM and optical properties

We report on the growth of GaAs1-xNx thin films On GaAs subatrates (2 degrees off) by metalorganic vapor-phase epitaxy, in the temperature range 500-600 degreesC. A mixture of N-2 and H-2 was used as the carrier gas. Using dimethylhydrazine as nitrogen source, we incorporated up to 3.5% of nitrogen, at 530 degreesC. The growth condition dependence of nitrogen content was studied, and it reveals a distribution coefficient 350 times lower for nitrogen than for arsine at 530 degreesC. Nitrogen incorporation is controlled by surface kinetics. The evolution of surface morphology has been investigated by atomic force microscopy as a function of the nitrogen composition and of growth temperature. For nitrogen content up to similar to2%, the GaAsN vicinal surface is characterized by a step-terrace structure with bunched steps: and the step edges straighten when increasing the growth temperature. For higher nitrogen content terraces are no longer observed and, above, similar to3% widely-spaced cross-hatch lines, characteristic of a partial relaxation of strain in the epilayers, appear. Optical properties were studied by low (7 K) and room-temperature photoluminescence and photoreflectance. As usual for this material, a degradation of optical characteristics is observed with increasing N content along with the evolution of surface morphology. (C) 2001 Elsevier Science Ltd. All rights reserved.