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 difficulti es 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 hav e not been measured yet. This is due to difficulties with experimental exam ination of thin films. This work addresses the mechanical properties of bul k GaN obtained by a high-pressure method. Young's modulus (295 GPa), hardne ss (20 GPa), yield strength (15 GPa), and the stress-strain curve of GaN ha ve been evaluated using nano-indentation. The cause of the sudden depth exc ursions during indentation of GaN epilayers has been clarified. (C) 1999 Am erican Institute of Physics. [S0003-6951(99)00140-0].