Elastic and plastic properties of GaN determined by nano-indentation of bulk crystal

The major obstacle to the production of a blue laser is posed by difficulties with the preparation of defect-free GaN layers. A considerable amount of empirical work is presently being undertaken to achieve this goal. However, there is a lack of basic research on the reduction of residual stress and defects in these epilayers since the mechanical characteristics of GaN have not been measured yet. This is due to difficulties with experimental examination of thin films. This work addresses the mechanical properties of bulk GaN obtained by a high-pressure method. Young's modulus (295 GPa), hardness (20 GPa), yield strength (15 GPa), and the stress-strain curve of GaN have been evaluated using nano-indentation. The cause of the sudden depth excursions during indentation of GaN epilayers has been clarified. (C) 1999 American Institute of Physics. [S0003-6951(99)00140-0].