Raman Measurements and Stress Analysis in Gallium Ion Implanted Gallium   Nitride Epitaxial Layers on Sapphire
  In this article, we estimate hydrostatic stress developed in gallium ion implanted gallium nitride epitaxial layers using Raman measurements. We have calculated deformation potential constants for $E_2$(high) mode in these epi-layers. The presence of a polar phonon-plasmon coupling in these systems has also been demonstrated. In as-implanted samples, with an increase in implantation fluence, we have observed disorder-activated Raman scattering. 
S. Mal, A. Singha, S. Dhara, A. Roy