Roughness analysis of GaN surfaces at different annealing temperatures for an AlN buffer layer

The surface morphologies of AlN and GaN on Si(111) and Si(100) were studied using atomic force microscopy. The AlN buffer layer was deposited using RF sputtering for 30 minutes on Si(111) and Si(100) substrates, and then the specimens were annealed at 850 degrees C, 950 degrees C and 1050 degrees C for 60 minutes in an NH3 atmosphere. It was found that the grains of AlN became larger by increasing the annealing temperature. GaN was grown on AlN/Si(111) and AlN/Si(100) substrates by using a hydride vapor phase epitaxy technique. The surface of GaN grown on the AlN/Si substrate showed thick- thread and fine-thread patterns. The microstructure of GaN grown on the buffer-GaN/Al2O3 had a step-flow pattern. These phenomena could be explained by a lattice mismatch and the growth temperature. A power spectral density analysis was performed on the GaN surfaces and the results were compared with the experimental data.