Growth of GaN film on Si (1Â 1Â 1) substrate using AlN sandwich structure as buffer

A single high temperature AlN (HT-AlN) buffer has been used to relieve the stress in the growth of GaN epilayers on Si (1 1 1) substrates, but the growth of crack-free GaN on Si is still difficult due to the large mismatch of the lattice and coefficient of thermal-expansion (CTE) between GaN and Si. In this paper, we report the growth of 1.2 μm thick crack-free GaN epilayers on 2 in. Si (1 1 1) substrates using the AlN sandwich structure as a buffer. The surface morphologies of the samples were observed using a microscope and AFM. Further analysis shows that the crack-free sample is closely correlated to the introduction of the AlN sandwich structure as the buffer. To better understand the relationship between the cracks and the stress, Raman scattering has been used to study the stress in the samples. The results indicate that the sandwich structure with top AlN and bottom AlN can more effectively accommodate the strain energy caused by CTE mismatch stress.