Effect of repetition nanoindentation of GaN epilayers on a-axis sapphire substrates

In this work, gallium nitride (GaN) epilayers were deposited on a‐axis sapphire substrate by means of metal organic chemical vapor deposition (MOCVD). Berkovich nanoindentation was used to explore the repetition pressure‐induced impairment of the GaN film. The observation of load‐displacement vs stress‐strain curves concludes that basal slip is implicated in the deformation on the A plane GaN. The increase in the hardness (H) and elastic modulus (E) was determined from cyclic nanoindentation, and resulted in a crack due to the formation of incipient slip bands and/or the to‐and‐fro motion of mobile dislocation. It is indicated that the generation of individual dislocation and residual deformation of the GaN films are showed by CL mapping analysis. From the morphological studies, it is revealed that the crack was found by means of atomic force microscope (AFM) technique at nine loading/reloading cycles even after the indentation beyond the critical depth on the residual indentation impression. Copyright © 2010 John Wiley & Sons, Ltd.