Effect of the polar surface on GaN nanostructure morphology and growth orientation

Wurtzite gallium nitride nanostructures were grown by thermal reaction of gallium oxide and ammonia. The resulting morphology varied depending on ammonia flow rate. At 75sccm only nanowires were obtained, while polyhedral crystals and nanobelts were observed at 175sccm. Scanning electron microscopy and transmission electron microscopy revealed both thin smooth and thick corrugated nanowires. The growth orientations of most of the smooth ones, as well as the nanobelts, were perpendicular to the c axis (⟨0001⟩), while the corrugated nanowires and the large polyhedra grew parallel to ⟨0001⟩. We propose a model to explain these variations of morphology and growth orientation in terms of the Ga∕N ratio and the different characteristic length of {0001} polar surface in the different nanostructures.