Influence of nitridation time on growth of AlN layers on different sapphire substrate off-cut angles

This work describes the role of nitridation time and off-cut angles of sapphire in improving growth of AlN layers. It was found that the nitridation formed AlON layer, of which this layer can be useful for improving the atomic arrangement of overgrown AlN layers. Based on FHWMs of XRD-rocking curve (XRC-FWHMs), the TDD decreases with increasing nitridation time up to 20 min, especially for the AlN layer grown on 0.5° off-cut sapphire. Meanwhile, as revealed by N1s XPS spectra, prolonged nitridation tends to destroy the AlON layer, thereby increasing the TDD. In general, the impact of the sapphire off-cut angles on the TDD reduction is insignificant, especially with longer nitridation. Moreover, the surface roughness of the AlN layers can be reduced by increasing nitridation time, including the ones grown on 3.0° off-cut sapphire. It is worth noting that macro-steps typically observed on the surface of AlN on higher off-cut angles of sapphire are less evident in this work. This indicates that the initiation of macro-steps or step-bunching can be suppressed by nitridation. However, this limits the TDs inclination which is also an essential in reducing the TDD.