In situ reflection high-energy electron diffraction (RHEED) and atomic force microscopy (AFM) observations were performed to monitor and characterize the growth processes and surface morphology of GaN on AlxGa1-xN surface in gas-source molecular beam epitaxy. It was found that the growth mode can be changed by introducing Si before GaN growth, where the Si is believed to play an important role in the change of the AlxGa1-xN surface free energy. Without introducing Si, the GaN growth mode was two-dimensional and (1 × 3) reconstruction was observed. The growth mode of GaN was changed from two-dimensional to three-dimensional by introducing Si on the AlxGa1-xN surface. Nanoscale GaN dots were successfully formed on AlxGa1-xN/6H-SiC(0 0 0 1) surfaces. Furthermore, the density of the GaN dots was found to be dependent on the amount of Si dose and the growth temperature.
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