Comparative study on the nanomechanical behavior and physical properties influenced by the epitaxial growth mechanisms of GaN thin films

Abstract

The effect of carrier gas on nanomechanical properties of GaN thin films grown on (0001) sapphire substrates by metal–organic chemical vapor deposition (MOCVD) process, was studied by Berkovich nanoindentation. GaN/H2 and GaN/N2 films were deposited using hydrogen and nitrogen, as carrier gases, respectively. New method was developed to compute the contact stiffness versus the penetration depth using a single load–displacement curve. It was found that the hardness and Young’s modulus of GaN/H2 are lower than those of GaN/N2. Moreover, pop-in events were revealed for GaN/H2, in contrast for GaN/N2. Fracture was only manifested in the imprint of GaN/N2 due to its low fracture toughness. Besides, it was disclosed the high sensitivity of loading rate only for GaN/H2. The GaN/N2 sample experiences plastic strain relaxation, while GaN/H2 is a highly stressed sample; hence, it has less dislocation density compared to GaN/N2 sample. We demonstrated that the used carrier gas influences on GaN epitaxial growth process, which in return deeply affects the resulting dislocation density and dislocation plasticity mechanisms. These latter, tailor the nanomechanical properties of GaN samples and the indentation-induced deformation behavior.