Silicon is a promising substrate for GaN growth due to its low cost, large size and potential applications in the
integration of optoelectronic and microelectronic devices. However, a high lattice (~17%) and thermal (~56%) mismatch
between Si substrate and GaN epilayer causes large tensile stress and leads to the formation of cracks when the GaN
layer thickness is above 1.0 μm during the cooling down to room temperature. Therefore, the growth of high quality and
crack-free GaN layers on silicon substrates is still a challenging issue. It has been widely reported that cracking problem
can be mitigated by using techniques like low-temperature (LT) AlN interlayers, AlxGa1-xN transition layer, thin SixNy
interlayers, AlN/GaN superlattices, etc. In this work, we used the LT-AlN interlayers for strain engineering during the
growth of GaN layers by low-pressure metal-organic chemical vapor deposition (LP-MOCVD) on Si(111) substrates.
And we investigated the fluence of the thickness of LT-AlN interlayers, which is considered as one of the most important
factors in reducing tensile stress and controlling density of micro-cracks in GaN layer. Optical microscopy, atomic force
microscopy, X-ray diffraction and Raman spectrum were employed to characterize these samples of GaN epilayers. The
results demonstrate that the crystal quality of GaN depends strongly on the thickness of the epilayers, and crack-free
GaN layers with thickness exceeding 1.5 μm can be achieved by using LT-AlN interlayers with an optimized thickness.