Stress evolution in AlN growth on nano-patterned sapphire substrates

The stress evolution behavior of AlN grown on nano-patterned substrates (NPSSs) has been investigated. It is found that there are two sources of the tensile stress for AlN grown on NPSSs. One originates from the coalescence of grain islands of the AlN nucleation layer, and then the voids provide a channel for the gradual release of the tensile stress to nearly stress-free state accompanied by the lateral growth process of the AlN columns on the mesas. The other originates from the contacting of adjacent columns to complete the coalescence process, which is responsible for the residual tensile stress in the top AlN epilayer after completing the coalescence. This understanding of the stress evolution is certainly of great significance in AlN-based material and devices.