Growth of GaAsN: surface study by AFM and optical properties

We report on the growth of GaAs1-xNx thin films On GaAs subatrates (2 degre es off) by metalorganic vapor-phase epitaxy, in the temperature range 500-6 00 degreesC. A mixture of N-2 and H-2 was used as the carrier gas. Using di methylhydrazine as nitrogen source, we incorporated up to 3.5% of nitrogen, at 530 degreesC. The growth condition dependence of nitrogen content was s tudied, and it reveals a distribution coefficient 350 times lower for nitro gen than for arsine at 530 degreesC. Nitrogen incorporation is controlled b y surface kinetics. The evolution of surface morphology has been investigat ed 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 s teps: and the step edges straighten when increasing the growth temperature. For higher nitrogen content terraces are no longer observed and, above, si milar to3% widely-spaced cross-hatch lines, characteristic of a partial rel axation 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 obs erved with increasing N content along with the evolution of surface morphol ogy. (C) 2001 Elsevier Science Ltd. All rights reserved.