Nucleation of A1N on SiC substrates by seeded sublimation growth

摘要

The nucleation of aluminum nitride (AlN) on silicon carbide (SiC) seed by sublimation growth was investigated. Silicon-face, 8° off-axis 4H-SiC (0001) and on-axis 6H-SiC (0001) were employed as seeds. Initial growth for 15 min and extended growth for 2 h suggested that 1850 ℃ was the optimum temperature of AlN crystal growth: on an 8° off-axis substrate, AlN grew laterally forming a continuous layer with regular "step" features; on the on-axis substrate, AlN grew vertically as well as laterally, generating an epilayer with hexagonal sub-grains of different sizes. The layer's c-lattice constant was larger than pure AlN, which was caused by the compression of the AlN film and impurities (Si, C) incorporation. Polarity sensitive and defect selective etchings were performed to examine the surface polarity and dislocation density. All the samples had an Al-polar surface and no N-polar inversion domains were observed. Threading dislocations were present regardless of the substrate misorientation. Basal plane dislocations (BPDs) were revealed only on the AlN films on the 8° off-axis substrates. The total dislocation density was in the order of 10~8cm~(-2) when the film was 20-30 μm thick.