Nanoscale GaN dots were successfully formed onAlxGa1−xN/6H-SiC(0001)surfaces by 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 theAlxGa1−xNsurface 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 theAlxGa1−xNsurface.In situreflection high-energy electron diffraction and atomic force microscopy observations were used to monitor and characterize the growth processes and surface morphology. ©1998 American Institute of Physics.