Micro-Raman imaging of GaN hexagonal island structures

We use Raman scattering to obtain a stress map of lateral epitaxy overgrown GaN. Isolated hexagonal islands are grown by selective area overgrowth wit hout a seed layer. Stress mapping is obtained from shifts in the E-2 phonon . GaN in the aperture area has the greatest biaxial compressive stress, app roximate to 0.18 GPa. The overgrowth region is under slightly smaller stres s, about 0.15 GPa. We attribute marked variations in the A(1)(LO) phonon in tensity to spatial variations in the free carrier concentration. This is fo und to be small in the aperture region and high in the lateral overgrowth. The position-dependent presence of the lower coupled plasmon-phonon band is consistent with this interpretation. (C) 1999 American Institute of Physic s. [S0003-6951(99)03338-0].