Step unbunching phenomenon on 4H-SiC (0001) surface during hydrogen etching

We here report a step unbunching phenomenon, which is the inverse of the phenomenon of step bunching. When a 4H-SiC (0001) surface is annealed at a high temperature, step bunching arises due to the different velocities of the step motion in adjacent steps, resulting in steps with a height of more than several nanometers. We found that the bunched steps, thus, obtained by hydrogen etching in an Ar/H-2 atmosphere were unbunched into lower height steps when annealed subsequently at lower temperatures. This unbunching phenomenon can be well explained by the consequence of the competition between energetics and kinetics. Our findings provide another approach for the surface smoothing of SiC by hydrogen etching and may give significant insight into the application of SiC power devices and two-dimensional materials growth techniques in general.

Automated summary

We have discovered a step unbunching phenomenon that is the opposite of the step bunching phenomenon. When a 4H-SiC (0001) surface is annealed at a high temperature, steps bunch up due to different velocities of step motion, resulting in steps taller than several nanometers. However, we found that these bunched steps can be unbunched into lower height steps when subsequently annealed at lower temperatures. This competition between energetics and kinetics can explain the underlying mechanism. This finding provides a new method for surface smoothing of SiC using hydrogen etching and has potential implications for SiC power devices and two-dimensional material growth techniques.