Recrystallization of epitaxial GaN under indentation

TL;DR

This study demonstrates that epitaxial GaN films can undergo recrystallization under mechanical indentation, with Raman spectroscopy confirming the formation of stress-free crystalline regions due to dislocation nucleation and lattice reorganization.

Contribution

It provides the first detailed analysis of GaN recrystallization induced by indentation, combining hardness measurements and Raman mapping to identify the process.

Findings

Recrystallization occurs at ~10 GPa hardness under indentation.

Dislocation nucleation triggers lattice plasticity and recrystallization.

Raman spectroscopy confirms stress relaxation and crystal quality improvement.

Abstract

We report recrystallization of epitaxial (epi-) GaN(0001) film under indentation.Hardness value is measured close to 10 GPa, using a Berkovich indenter. Pop-in burst in the loading line indicates nucleation of dislocations setting in plastic motion of lattice atoms under stress field for the recrystallization process. Micro-Raman studies are used to identify the recrystallization process. Raman area mapping indicates the crystallized region. Phonon mode corresponding to E2(high) close to 570 cm-1 in the as-grown epi-GaN is redshifted to stress free value close to 567 cm-1 in the indented region. Evolution of A1(TO) and E1(TO) phonon modes are also reported to signify the recrystallization process.