Structure of GaAsN alloy within miscibility gap

We report on the structural and electronic properties of a series of GaAs
_1-x
N
_x
with wide x range. The alloys were grown on (001) GaAs substrate using plasma-assisted molecular beam epitaxy. Transmission electron microscopy and selective area electron diffraction (SAD) were used to probe the crystalline of GaAs
_0.496
N
_0.504
sample. The results indicate that the alloy is polycrystalline and amorphous. In the polycrystalline observed zinc-blende (ZB) and hexagonal structure. In this result, we suggest generation of miscibility and phase separation from two kind of structure. Calculation the vertical and horizontal lattice constant with x in the range from 0.106-0.848. Observed the az is dramatic drop with increase N content and a
_xy
slow decrease, we suggest this result relation of nitrogen cluster alone [001] and residual horizontal substrate strain. Photo-modulated reflectance spectroscopy was used to determine the energy gap of the GaAs
_1-x
N
_x
alloys, which ranges from 0.7-2.0 eV, covering a large part of the solar spectrum. The energy gap is in agreement with BAC model.