Interlayer Investigations of GaN Heterostructures Integrated into Silicon Substrates by Surface Activated Bonding

Thinning the buffer layer thickness between the GaN epilayer and Si substrate without introducing large residual stress is persistently desired for GaN-on-Si devices to promote their thermal budgets and low-cost, multifunctional applications. In this work, the GaN-on-Si heterostructures were directly bonded at room temperature by surface activated bonding (SAB) and the therein residual stress states were investigated by confocal micro-Raman. The effects of thermal annealing process on the residual stress and interfacial microstructure in SAB fabricated GaN-on-Si heterostructures were also systematically investigated by in situ micro-Raman and transmission electron microscopy. It was found that a significant relaxation and a more uniform stress distribution was obtained in SAB bonded GaN-on-Si heterostructure in comparison with that of MOCVD grown sample; however, with increasing annealing temperature, the residual stresses at the SAB bonded GaN layer and Si layer evolute monotonically in different trends. The main reason can be ascribed to the amorphous layer formed at the bonding interface, which played a critical stress relaxation role and transformed into a much thinner crystallized interlayer without any observable structural defects after 1000 °C annealing.