Raman microscopy of lateral epitaxial overgrowth of GaN on sapphire

We have used confocal Raman microscopy to investigate lateral epitaxially o vergrown (LEO) GaN on sapphire substrates. The one-phonon Raman spectra are consistent with pyramidal growth of the GaN before coalescence has occurre d. The position and asymmetric line shape of the A(1) longitudinal optical (LO) phonon demonstrate that the LEO GaN is doped. The dopant is most likel y Si from the SiN mask used to produce the LEO GaN. The carrier concentrati on is estimated to be 1 x 10(17) cm(-3). We have also used Raman microscopy to spatially resolve the yellow emission from different regions of the LEO GaN. (C) 1999 American Institute of Physics. [S0003-6951(99)02123-3].