Undoped and heavily Mg-doped polycrystalline GaN (poly-GaN) films grown on fused silica substrate at 310 °C are investigated by transmission electron microscopy, reflected high-energy electron diffraction and X-ray diffraction measurements. Undoped poly-GaN films were composed of nano-columns roughly with surface-normal c-axis orientations (c-orientations). Similar structures were found in 2.0 at% Mg-doped poly-GaN, while no appreciable c-orientations were observed in 5.2 at% Mg-doped films. The observed difference can be explained by a reduction in the growth anisotropy due to an increase in the growth rate along the direction perpendicular to the [0 0 0 1] of each crystallite.
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