Formation of AlN and GaN nanocolumns on Si(111) using molecular beam epitaxy with ammonia as a nitrogen source

We have demonstrated growth of AlN and GaN nanocolumns using molecular beam epitaxy with ammonia as a nitrogen source. The appearance of the columnar structure is correlated with the use of a low-temperature AlN buffer layer, grown at about 650 degrees C. Field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM) indicate that the column diameters range from 12 to 30 nm. Layers were grown on Si(111) substrates with a variety of AlN buffer layer growth conditions. The AlN columns are distinct though tightly packed, and the tips of the columns are separated. Large, platelet-like protrusions are observed for low growth temperatures. Results from X-ray diffraction (XRD) and low-temperature photoluminescence (PL) are also discussed.