Surface morphology evolution of C-plane sapphire during multi-step thermal annealing

Abstract

The surface morphology evolution of the C-plane (0001) sapphire surface with the 4° miscut angle towards A-plane is thermally annealed at temperatures of 1100 °C and 1200 °C for different dwell times varying between 3-12 hours in multiple steps, resulting in a total of 30 hours. Atomic Force Microscopy (AFM) observations are used to systematically study the effects of the thermal annealing process, temperature, and time on the evolution of the periodicity and step height of structures. The step-terrace structures with straight step-edges along the direction were observed over the entire surface after 3 hours of annealing at 1100 °C. The step-terrace structure morphology evolves through the step-bunching and facet coarsening mechanisms during the multi-step thermal annealing process. Step-bunching begins with the formation of contact points between the adjacent steps by diffusion of atoms. Its onset is associated with a threshold value of the periodicity of step-terrace structures. By varying the annealing temperature during the multi-step thermal annealing process, the evolution of step-terrace structures can be manipulated by delaying the process of step-bunching.