A study on growth characteristics of GaN layers grown by MOCVD on Si (111) substrate

The difference in lattice parameters and thermal expansion coefficient between GaN and Si which results in many defects in the grown GaN is larger than that between GaN and sapphire. In order to obtain high-quality GaN films on Si substrate, it is essential to understand growth characteristics of GaN. In this study, GaN layers were grown on Si(111) substrates by MOCVD for two different GaN growth durations, using AlN and LT-GaN buffer layers. Using TEM and XRD, we carried out the comparative investigation of growth characteristics of GaN by characterizing lattice coherency, crystallinity, orientation relationship and defects formed. The localized region with high defect density was formed by lattice mismatch between AlN buffer layer and GaN. The TEM and FFT analyses revealed that the high quality and defect-free GaN formed above the transition region is attributed to the fact that local stress induced by lattice mismatch and incoherency is released in the transition region by generating a number of dislocations of opposite sign. As the growth thickness of GaN increases, the defect density of GaN decreased and its crystallinity is enhanced.